# Chapter 3. Linux Commands

#### Contents:

Alphabetical Summary of Commands

This chapter presents the Linux user, programmer, and system administration commands. Each entry is labeled with the command name on the outer edge of the page. The syntax line is followed by a brief description and a list of available options. Many commands come with examples at the end of the entry. If you need only a quick reminder or suggestion about a command, you can skip directly to the examples.

Typographic conventions for describing command syntax are listed in the Preface. For help in locating commands, see the index at the back of this book.

We've tried to be as thorough as possible in listing options. The basic command information and most options should be correct; however, there are many Linux distributions and many versions of commands. New options are added and sometimes old options are dropped. You may, therefore, find some differences between the options you find described here and the ones on your system. When there seems to be a discrepancy, check the manpage. For most commands you can also use the option --help to get a brief usage message. (Even when it isn't a valid option, it will usually result in an "invalid option" error along with the usage message.)

Traditionally, commands take single-letter options preceded by a single hyphen, like -d. A more recent convention allows long options preceded by two hyphens, like --debug. Often, a feature can be invoked through either the old style or the new style of options.

## 3.1. Alphabetical Summary of Commands

agetty | agetty [options] port baudrate [term] System administration command. The Linux version of getty. Set terminal type, modes, speed, and line discipline. agetty is invoked by init. It is the second process in the series init-getty-login-shell, which ultimately connects a user with the Linux system. agetty reads the user's login name and invokes the login command with the user's name as an argument. While reading the name, agetty attempts to adapt the system to the speed and type of device being used. You must specify a port, which agetty will search for in the /dev directory. You may use -, in which case agetty reads from standard input. You must also specify baudrate, which may be a comma-separated list of rates, through which agetty will step. Optionally, you may specify the term, which is used to override the TERM environment variable. #### Options -h Specify hardware, not software, flow control. -i Suppress printing of /etc/issue before printing the login prompt. -l program Specify the use of program instead of /bin/login. -m Attempt to guess the appropriate baud rate. -t timeout Specify that agetty should exit if the open on the line succeeds and there is no response to the login prompt in timeout seconds. -L Do not require carrier detect; operate locally only. Use this when connecting terminals.
apmd | apmd [options] System administration command. apmd handles events reported by the Advanced Power Management BIOS driver. The driver reports on battery level and requests to enter sleep or suspend mode. apmd will log any reports it gets via syslogd and take steps to make sure that basic sleep and suspend requests are handled gracefully. You can fine-tune the behavior of apmd by specifying an apmd_proxy command to run when it receives an event. #### Options -c n, --check n Set the number of seconds to wait for an event before rechecking the power level. Default is to wait indefinitely. Setting this causes the battery levels to be checked more frequently. -P command, --apmd_prxy command Specify the apmd_proxy command to run when APM driver events are reported. This is generally a shell script. The command will be invoked with parameters indicating what kind of event was received. The parameters are in the next list. -p n, --percentage n Log information whenever the power changes by n percent. The default is 5. Values greater than 100 will disable logging of power changes. -V, --version Print version and exit. -v, --version Verbose mode; all events are logged. -W, --wall Use wall to alert all users of a low battery status. -w n, --warn n Log a warning at ALERT level when the battery charge drops below n percent. The default is 10. Negative values disable low battery level warnings. -q, --quiet Disable low battery level warnings. -?, --help Print help summary and exit. #### Parameters The apmd proxy script will be invoked with the following parameters: start Invoked when the daemon starts. stop Invoked when the daemon stops. suspend [ system | user ] Invoked when a suspend request has been made. The second parameter indicates whether the request was made by the system or by the user. standby [ system | user ] Invoked when a standby request has been made. The second parameter indicates whether the request was made by the system or by the user. resume [ suspend | standby | critical ] Invoked when the system resumes normal operation. The second parameter indicates the mode the system was in before resuming. (critical suspends indicate an emergency shutdown. After a critical suspend the system may be unstable and you can use the resume command to help you recover from the suspension. change power Invoked when system power is changed from AC to battery or from battery to AC. change battery Invoked when the APM BIOS driver reports that the battery is low. change capability Invoked when the APM BIOS driver reports some hardware that affects its capability has been added or removed.
apropos | apropos string ... Search the short manual page descriptions in the whatis database for occurrences of each string and display the result on the standard output. Like whatis, except that it searches for strings instead of words. Equivalent to man -k.
> ar | ar [-V] key [args] [posname] archive [files] Maintain a group of files that are combined into a file archive. Used most commonly to create and update library files as used by the link editor (ld). Only one key letter may be used, but each can be combined with additional args (with no separations between). posname is the name of a file in archive. When moving or replacing files, you can specify that they be placed before or after posname. -V prints the version number of ar on standard error. #### Key d Delete files from archive. m Move files to end of archive. p Print files in archive. q Append files to archive. r Replace files in archive. t List the contents of archive or list the named files. x Extract contents from archive or only the named files. #### Arguments a Use with r or m key to place files in the archive after posname. b Same as a but before posname. c Create archive silently. f Truncate long filenames. i Same as b. l For backward compatibility; meaningless in Linux. o Preserve original timestamps. s Force regeneration of archive symbol table (useful after running strip). S Do not regenerate symbol table. u Use with r to replace only files that have changed since being put in archive. v Verbose; print a description of actions taken. #### Example Replace mylib.a with object files from the current directory:
>     ar r mylib.a `ls *.o
arch | arch Print machine architecture type to standard output. Equivalent to uname -m.
arp | arp [options] TCP/IP command. Clear, add to, or dump the kernel's ARP cache (/proc/net/arp). #### Options -v Verbose mode. -t type Search for type entries when examining the ARP cache. type must be ether (Ethernet) or ax25 (AX.25 packet radio); ether is the default. -a [hosts] Display hosts' entries or, if none are specified, all entries. -d host Remove host's entry. -s host hardware-address Add the entry host hardware-address, where ether class addresses are 6 hexadecimal bytes, colon-separated. -f file Read entries from file and add them.
as | as [options] files Generate an object file from each specified assembly language source file. Object files have the same root name as source files but replace the .s suffix with .o. There may be some additional system-specific options. #### Options -- [ | files] Read input files from standard input, or from files if the pipe is used. -a[dhlns][=file] With only the -a option, list source code, assembler listing, and symbol table. The other options specify additional things to list or omit: -ad Omit debugging directives. -ah Include the high-level source code, if available. -al Include an assembly listing. -an Suppress forms processing. -as Include a symbol listing. =file Set the listing filename to file. -defsym symbol=value Define the symbol to have the value value, which must be an integer. -f Skip preprocessing. --gstabs Generate stabs debugging information. -o objfile Place output in object file objfile (default is file.o). -v Display the version number of the assembler. -I path Include path when searching for .include directives. -K Warn before altering difference tables. -L Do not remove local symbols, which begin with L. -R Combine both data and text in text section. -W Quiet mode.
> at | at [options] time Execute commands at a specified time and optional date. The commands are read from standard input or from a file. (See also batch.) End input with EOF. time can be formed either as a numeric hour (with optional minutes and modifiers) or as a keyword. It can contain an optional date, formed as a month and date, a day of the week, or a special keyword (today or tomorrow). An increment can also be specified. The at command can always be issued by a privileged user. Other users must be listed in the file /etc/at.allow if it exists; otherwise, they must not be listed in /etc/at.deny. If neither file exists, only a privileged user can issue the command. #### Options -c job [job...] Display the specified jobs on the standard output. This option does not take a time specification. -d job [job...] Delete the specified jobs. Same as atrm. -f file Read job from file, not standard input. -l Report all jobs that are scheduled for the invoking user. Same as atq. -m Mail user when job has completed, regardless of whether output was created. -q letter Place job in queue denoted by letter, where letter is any single letter from a-z or A-Z. Default queue is a. (The batch queue defaults to b.) Higher-lettered queues run at a lower priority. -V Display the version number. #### Time hh:mm [modifiers] Hours can have one digit or two (a 24-hour clock is assumed by default); optional minutes can be given as one or two digits; the colon can be omitted if the format is h, hh, or hhmm; (e.g., valid times are 5, 5:30, 0530, 19:45). If modifier am or pm is added, time is based on a 12-hour clock. If the keyword zulu is added, times correspond to Greenwich Mean Time. midnight | noon | teatime | now Use any one of these keywords in place of a numeric time. teatime translates to 4:00 p.m.; now must be followed by an increment. #### Date month num[, year] month is one of the 12 months, spelled out or abbreviated to its first three letters; num is the calendar date of the month; year is the four-digit year. If the given month occurs before the current month, at schedules that month next year. day One of the seven days of the week, spelled out or abbreviated to its first three letters. today | tomorrow Indicate the current day or the next day. If date is omitted, at schedules today when the specified time occurs later than the current time; otherwise, at schedules tomorrow. #### Increment Supply a numeric increment if you want to specify an execution time or day relative to the current time. The number should precede any of the keywords minute, hour, day, week, month, or year (or their plural forms). The keyword next can be used as a synonym of + 1. #### Examples Note that the first two commands are equivalent:
>     at 1945 pm December 9
>     at 7:45pm Dec 9
>     at 3 am Saturday
>     at now + 5 hours
>     at noon next day
atq | atq [options] List the user's pending jobs, unless the user is a privileged user; in that case, everybody's jobs are listed. Same as at -l. #### Options -q queue Query only the specified queue and ignore all other queues. -v Show jobs that have completed but not yet been deleted. -V Print the version number.
atrm | atrm [options] job [job...] Delete jobs that have been queued for future execution. Same as at -d. #### Options -q queue Remove job from the specified queue. -V Print the version number and then exit.
badblocks | badblocks [options] device block-count System administration command. Search device for bad blocks. You must specify the number of blocks on the device (block-count). #### Options -b blocksize Expect blocksize-byte blocks. -o file Direct output to file. -v Verbose mode. -w Test by writing to each block and then reading back from it.
> banner | banner [option] [characters] Print characters as a poster. If no characters are supplied, banner prompts for them and reads an input line from standard input. By default, the results go to standard output, but they are intended to be sent to a printer. #### Option -w width Set width to width characters. Note that if your banner is in all lowercase, it will be narrower than width characters. If -w is not specified, the default width is 132. If -w is specified but width is not provided, the default is 80. #### Example
>     /usr/games/banner -w50 Happy Birthday! |lpr
> basename | basename name [suffix] basename option Remove leading directory components from a path. If suffix is given, remove that also. The result is printed to standard output. #### Options --help Print help message and then exit. --version Print the version number and then exit. #### Examples
>     % basename /usr/lib/libm.a
>     libm.a

>     % basename /usr/lib/libm.a .a
>     libm
batch | batch [options] [time] Execute commands entered on standard input. If time is omitted, execute them when the system load permits (when the load average falls below 0.8). Very similar to at, but does not insist that the execution time be entered on the command line. See at for details. #### Options -f file Read job from file, not standard input. -m Mail user when job has completed, regardless of whether output was created. -q letter Place job in queue denoted by letter, where letter is one letter from a-z or A-Z. The default queue is a. (The batch queue defaults to b.) Higher-lettered queues run at a lower priority. -V Print the version number and then exit. -v Display the time a job will be executed.
bash | bash [options] [file [arguments;]] sh [options] [file [arguments]] Standard Linux shell, a command interpreter into which all other commands are entered. For more information, see Chapter 7, "bash: The Bourne-Again Shell".
> bc | bc [options] [files] bc is a language (and compiler) whose syntax resembles that of C, but with unlimited-precision arithmetic. bc consists of identifiers, keywords, and symbols, which are briefly described in the following entries. Examples are given at the end. Interactively perform arbitrary-precision arithmetic or convert numbers from one base to another. Input can be taken from files or read from the standard input. To exit, type quit or EOF. #### Options -l, --mathlib Make functions from the math library available. -s, --standard Ignore all extensions, and process exactly as in POSIX. -w, --warn When extensions to POSIX bc are used, print a warning. -q, --quiet Do not display welcome message. -v, --version Print version number. #### Identifiers An identifier is a series of one or more characters. It must begin with a lowercase letter but may also contain digits and underscores. No uppercase letters are allowed. Identifiers are used as names for variables, arrays, and functions. Variables normally store arbitrary-precision numbers. Within the same program you may name a variable, an array, and a function using the same letter. The following identifiers would not conflict: x Variable x. x[i] Element i of array x. i can range from 0 to 2047 and can also be an expression. x(y,z) Call function x with parameters y and z. #### Input-output keywords ibase, obase, scale, and last store a value. Typing them on a line by themselves displays their current value. You can also change their values through assignment. The letters A-F are treated as digits whose values are 10-15. ibase = n Numbers that are input (e.g., typed) are read as base n (default is 10). obase = n Numbers that are displayed are in base n (default is 10). Note: Once ibase has been changed from 10, use A to restore ibase or obase to decimal. scale = n Display computations using n decimal places (default is 0, meaning that results are truncated to integers). scale is normally used only for base-10 computations. last Value of last printed number. #### Statement keywords A semicolon or a newline separates one statement from another. Curly braces are needed when grouping multiple statements. if (rel-expr) {statements} [else {statements}] Do one or more statements if relational expression rel-expr is true. Otherwise, do nothing, or if else (an extension) is specified, do alternative statements. For example:
>          if(x==y) {i = i + 1} else {i = i - 1}
> while (rel-expr) {statements} Repeat one or more statements while rel-expr is true; for example:
>          while(i>0) {p = p*n; q = a/b; i = i-1}
> for (expr1;rel-expr;expr2) {statements} Similar to while; for example, to print the first 10 multiples of 5, you could type:
>          for(i=1; i<=10; i++) i*5
> GNU bf does not require three arguments to for. A missing argument 1 or 3 means that those expressions will never be evaluated. A missing argument 2 evaluates to the value 1. break Terminate a while or for statement. print list GNU extension. It provides an alternate means of output. list consists of a series of comma-separated strings and expressions; print displays these entities in the order of the list. It does not print a newline when it terminates. Expressions are evaluated, printed, and assigned to the special variable last. Strings (which may contain special characters, i.e., characters beginning with \) are simply printed. Special characters can be: a Alert or bell b Backspace f Form feed n Newline r Carriage return q Double quote t Tab \ Backslash continue GNU extension. When within a for statement, jump to the next iteration. halt GNU extension. Cause the bc processor to quit. limits GNU extension. Print the limits enforced by the local version of bc. #### Function keywords define f(args) { Begin the definition of function f having the arguments args. The arguments are separated by commas. Statements follow on successive lines. End with a }. auto x, y Set up x and y as variables local to a function definition, initialized to 0 and meaningless outside the function. Must appear first. return(expr) Pass the value of expression expr back to the program. Return 0 if (expr) is left off. Used in function definitions. sqrt(expr) Compute the square root of expression expr. length(expr) Compute how many significant digits are in expr. scale(expr) Same as length, but count only digits to the right of the decimal point. read( ) GNU extension. Read a number from standard input. Return value is the number read, converted via the value of ibase. #### Math library functions These are available when bc is invoked with -l. Library functions set scale to 20. s(angle) Compute the sine of angle, a constant or expression in radians. c(angle) Compute the cosine of angle, a constant or expression in radians. a(n) Compute the arctangent of n, returning an angle in radians. e(expr) Compute e to the power of expr. l(expr) Compute the natural log of expr. j(n, x) Compute the Bessel function of integer order n. #### Operators These consist of operators and other symbols. Operators can be arithmetic, unary, assignment, or relational: arithmetic + - * / % ^ unary - ++ -- assignment =+ =- =* =/ =% =^ = relational < <= > >= == != #### Other symbols /* */ Enclose comments. () Control the evaluation of expressions (change precedence). Can also be used around assignment statements to force the result to print. {} Use to group statements. [] Indicate array index. "text" Use as a statement to print text. #### Examples Note in these examples that when you type some quantity (a number or expression), it is evaluated and printed, but assignment statements produce no display.
>     ibase = 8       Octal input
>     20              Evaluate this octal number
>     16              Terminal displays decimal value
>     obase = 2       Display output in base 2 instead of base 10
>     20              Octal input
>     10000           Terminal now displays binary value
>     ibase = A       Restore base-10 input
>     scale = 3       Truncate results to 3 decimal places
>     8/7             Evaluate a division
>     1.001001000     Oops!  Forgot to reset output base to 10
>     obase=10        Input is decimal now, so A isn't needed
>     8/7
>     1.142           Terminal displays result (truncated)
> The following lines show the use of functions:
>     define p(r,n){  Function p uses two arguments
>     auto v          v is a local variable
>     v = r^n         r raised to the n power
>     return(v)}      Value returned

>     scale=5
>     x=p(2.5,2)      x = 2.5 ^ 2
>     x               Print value of x
>     6.25
>     length(x)       Number of digits
>     3
>     scale(x)        Number of places right of decimal point
>     2
biff | biff [arguments] Notify user of mail arrival and sender's name. biff operates asynchronously. Mail notification works only if your system is running the comsat(8) server. The command biff y enables notification, and the command biff n disables notification. With no arguments, biff reports biff's current status.
bison | bison [options] file Given a file containing context-free grammar, convert into tables for subsequent parsing while sending output to file.c. This utility is both to a large extent compatible with yacc and named for it. All input files should use the suffix .y; output files will use the original prefix. All long options (those preceded by --) may instead be preceded by +. #### Options -b prefix, --file-prefix=prefix Use prefix for all output files. -d, --defines Generate file.h, producing #define statements that relate bison's token codes to the token names declared by the user. -r, --raw Use bison token numbers, not yacc-compatible translations, in file.h. -k, --token-table Include token names and values of YYNTOKENS, YYNNTS, YYNRULES, and YYNSTATES in file.c. -l, --no-lines Exclude #line constructs from code produced in file.c. (Use after debugging is complete.) -n, --no-parser Suppress parser code in output, allowing only declarations. Assemble all translations into a switch statement body and print it to file.act. -o file, --output-file=file Output to file. -p prefix, --name-prefix=prefix Substitute prefix for yy in all external symbols. -t, --debug Compile runtime debugging code. -v, --verbose Verbose mode. Print diagnostics and notes about parsing tables to file.output. -V, --version Display version number. -y, --yacc, --fixed-output-files Duplicate yacc's conventions for naming output files.
> bootpd | bootpd [options] [configfile [dumpfile] ] TCP/IP command. Internet Boot Protocol server. bootpd normally is run by /etc/inetd by including the following line in the file /etc/inetd.conf:
>     bootps dgram udp wait root /etc/bootpd bootpd
> This causes bootpd to be started only when a boot request arrives. It may also be started in standalone mode, from the command line. Upon startup, bootpd first reads its configuration file, /etc/bootptab (or the configfile listed on the command line), then begins listening for BOOTREQUEST packets. bootpd looks in /etc/services to find the port numbers it should use. Two entries are extracted: bootps -- the bootp server listening port -- and bootpc -- the destination port used to reply to clients. If bootpd is compiled with the -DDEBUG option, receipt of a SIGUSR1 signal causes it to dump its memory-resident database to the file /etc/bootpd.dump or the command-line specified dumpfile. #### Options -c directory Force bootpd to work in directory. -d level Specify the debugging level. Omitting level will increment the level by 1. -t timeout Specify a timeout value in minutes. A timeout value of 0 means wait forever. #### Configuration file The bootpd configuration file has a format in which two-character, case-sensitive tag symbols are used to represent host parameters. These parameter declarations are separated by colons. The general format is:
>     hostname:tg=value:tg=value:tg=value
where hostname is the name of a bootp client and tg is a tag symbol. The currently recognized tags are listed next. #### Tags
Tag | Meaning
--- | ---
bf | Bootfile
bs | Bootfile size in 512-octet blocks
cs | Cookie server address list
ds | Domain name server address list
gw | Gateway address list
ha | Host hardware address
hd | Bootfile home directory
hn | Send hostname
ht | Host hardware type (see Assigned Numbers RFC)
im | Impress server address list
ip | Host IP address
lg | Log server address list
lp | lpr server address list
ns | IEN-116 name server address list
rl | Resource location protocol server address list
sm | Host subnet mask
tc | Table continuation
to | Time offset in seconds from UTC
ts | Time server address list
vm | Vendor magic cookie selector
There is also a generic tag, T n, where n is an RFC 1048 vendor field tag number. Generic data may be represented as either a stream of hexadecimal numbers or as a quoted string of ASCII characters.
> bootpgw | bootpgw [options] server Internet Boot Protocol Gateway. Maintain a gateway that forwards bootpd requests to server. In addition to dealing with BOOTREPLY packets, also deal with BOOTREQUEST packets. bootpgw is normally run by /etc/inetd by including the following line in the file /etc/inetd.conf:
>     bootps dgram udp wait root /etc/bootpgw bootpgw
This causes bootpgw to be started only when a boot request arrives. bootpgw takes all the same options as bootpd, except -c.
bootptest | bootptest [options] server [template] TCP/IP command. Test server's bootpd daemon by sending requests every second for 10 seconds or until the server responds. Read options from the template file, if provided. #### Options -f file Read the boot filename from file. -h Identify client by hardware, not IP, address. -m magic-number Provide magic-number as the first word of the vendor options field.
bzip2 | bzip2 [options] filenames bunzip2 [options] filenames bzcat [option] filenames bzip2recover filenames File compression and decompression utility similar to gzip, but uses a different algorithm and encoding method to get better compression. bzip2 replaces each file in filenames with a compressed version of the file and with a .bz2 extension appended. bunzip2 decompresses each file compressed by bzip2 (ignoring other files, except to print a warning). bzcat decompresses all specified files to standard output, and bzip2recover is used to try to recover data from damaged files. #### Options -- End of options; treat all subsequent arguments as filenames. -dig Set block size to dig × 100KB when compressing, where dig is a single digit from 1 to 9. -c, --stdout Compress or decompress to standard output. -d, --decompress Force decompression. -f, --force Force overwrite of output files. Default is not to overwrite. Also forces breaking of hard links to files. -k, --keep Keep input files; don't delete them. -L, --license, -V, --version Print license and version information and exit. -q, --quiet Quiet. Print only critical messages. -s, --small Use less memory, at the expense of speed. -t, --test Check the integrity of the files, but don't actually compress them. -v, --verbose Verbose. Show the compression ratio for each file processed. Add more -v's to increase the verbosity. -z, --compress Forces compression, even if invoked as bunzip2 or bzcat. --repetitive-fast, --repetitive-best Sometimes useful in versions earlier than 0.9.5 (which has an improved sorting algorithm) for providing some control over the algorithm.
c++ | c++ [options] files See g++.
> cal | cal [-jy] [[month] year] Print a 12-month calendar (beginning with January) for the given year or a one-month calendar of the given month and year. month ranges from 1 to 12. year ranges from 1 to 9999. With no arguments, print a calendar for the current month. #### Options -j Display Julian dates (days numbered 1 to 365, starting from January 1). -m Display Monday as the first day of the week. -y Display entire year. #### Examples
>     cal 12 1995
>     cal 1994 > year_file
cardctl | cardctl [options] command System administration command. Control PCMCIA sockets or select the current scheme. The current scheme is sent along with the address of any inserted cards to configuration scripts (by default located in /etc/pcmcia). The scheme command displays or changes the scheme. The other commands operate on a named card socket number or, if no number is given, all sockets. #### Commands config [socket] Display current socket configuration. eject [socket] Prepare the system for the card(s) to be ejected. ident [socket] Display card identification information. insert [socket] Notify system that a card has been inserted. reset [socket] Send reset signal to card. resume [socket] Restore power to socket and reconfigure for use. scheme [name] Display current scheme or change to specified scheme name. status [socket] Display current socket status. suspend [socket] Shut down device and cut power to socket. #### Options -c directory Look for card configuration information in directory instead of /etc/pcmcia. -f file Use file to keep track of the current scheme instead of /var/run/pcmcia-scheme. -s file Look for current socket information in file instead of /var/run/stab.
cardmgr | cardmgr [options] System administration command. The PCMCIA card daemon. cardmgr monitors PCMCIA sockets for devices that have been added or removed. When a card is detected, it attempts to get the card's ID and configure it according to the card configuration database (usually stored in /etc/pcmcia/config). By default, cardmgr both creates a system log entry when it detects cards and beeps. Two high beeps mean it successfully identified and configured a device. One high beep followed by one low beep means it identified the device, but was unable to configure it successfully. One low beep means it could not identify the inserted card. Information on the currently configured cards can be found in /var/run/stab. #### Options -c directory Look in directory for the card configuration database instead of /etc/pcmcia. -d use modprobe instead of insmod to load the PCMCIA device driver. -f Run in the foreground to process the current cards, then run as a daemon. -m directory Look in directory for card device modules instead of /lib/modules/ ```uname -r```. -o Configure the cards present in one pass, then exit. -p file Write cardmgr's process ID to file instead of /var/run/cardmgr.pid. -q Run in quiet mode. No beeps. -s file Write current socket information to file instead of /var/run/stab. -v Verbose mode. -V Print version number and exit.
> cat | cat [options] [files] Read (concatenates) one or more files and print them on standard output. Read standard input if no files are specified or if - is specified as one of the files; input ends with EOF. You can use the > operator to combine several files into a new file or >> to append files to an existing file. #### Options -A, --show-all Same as -vET. -b, --number-nonblank Number all nonblank output lines, starting with 1. -e Same as -vE. -E, --show-ends Print $ at the end of each line. -n, --number Number all output lines, starting with 1. -s, --squeeze-blank Squeeze down multiple blank lines to one blank line. -t Same as -vT. -T, --show-tabs Print TAB characters as ^I. -u Ignored; retained for Unix compatibility. -v, --show-nonprinting Display control and nonprinting characters, with the exception of LINEFEED and TAB. #### Examples
>     cat ch1               Display a file
>     cat ch1 ch2 ch3 > all Combine files
>     cat note5 >> notes    Append to a file
>     cat > temp1           Create file at terminal; end with EOF
>     cat > temp2 << STOP   Create file at terminal; end with STOP
cc | cc [options] files See gcc.
cpp | cpp [options] [ ifile [ ofile ] ] GNU C language preprocessor. cpp is invoked as the first pass of any C compilation by the gcc command. The output of cpp is a form acceptable as input to the next pass of the C compiler, and cpp normally invokes gcc after it finishes processing. ifile and ofile are, respectively, the input and output for the preprocessor; they default to standard input and standard output. #### Options -$ Do not allow $ in identifiers. -dM Suppress normal output. Print series of #defines that create the macros used in the source file. -dD Similar to -dM but exclude predefined macros and include results of preprocessing. -idirafter dir Search dir for header files when a header file is not found in any of the included directories. -imacros file Process macros in file before processing main files. -include file Process file before main file. -iprefix prefix When adding directories with -iwithprefix, prepend prefix to the directory's name. -iwithprefix dir Append dir to the list of directories to be searched when a header file cannot be found in the main include path. If -iprefix has been set, prepend that prefix to the directory's name. -lang-c, -lang-c++, -lang-objc, -lang-objc++ Expect the source to be in C, C++, Objective C, or Objective C++, respectively. -lint Display all lint commands in comments as #pragma lint command. -nostdinc Search only specified, not standard, directories for header files. -nostdinc++ Suppress searching of directories believed to contain C++-specific header files. -pedantic Warn verbosely. -pedantic-errors Produce a fatal error in every case in which -pedantic would have produced a warning. -traditional Behave like traditional C, not ANSI. -undef Suppress definition of all nonstandard macros. -A name[=def] Assert name with value def as if defined by a #assert. -C Pass along all comments (except those found on cpp directive lines). By default, cpp strips C-style comments. -D name[=def] Define name with value def as if by a #define. If no =def is given, name is defined with value 1. -D has lower precedence than -U. -H Print pathnames of included files, one per line, on standard error. -I dir Search in directory dir for #include files whose names do not begin with / before looking in directories on standard list. #include files whose names are enclosed in double quotes and do not begin with / will be searched for first in the current directory, then in directories named on -I options, and last in directories on the standard list. -M [-MG] Suppress normal output. Print a rule for make that describes the main source file's dependencies. If -MG is specified, assume that missing header files are actually generated files, and look for them in the source file's directory. -MD file Similar to -M, but output to file; also compile the source. -MM Similar to -M. Describe only those files included as a result of #include "file". -MMD file Similar to -MD, but describe only the user's header files. -P Preprocess input without producing line-control information used by next pass of C compiler. -U name Remove any initial definition of name, where name is a reserved symbol predefined by the preprocessor or a name defined on a -D option. Names predefined by cpp are unix and i386 (for Intel systems). -Wcomment, -Wcomments Warn when encountering the beginning of a nested comment. -Wtraditional Warn when encountering constructs that are interpreted differently in ANSI from traditional C. #### Special names cpp understands various special names, some of which are: __DATE__ Current date (e.g., Oct 10 1999) __FILE__ Current filename (as a C string) __LINE__ Current source line number (as a decimal integer) __TIME__ Current time (e.g., 12:00:00) These special names can be used anywhere, including macros, just like any other defined names. cpp's understanding of the line number and filename may be changed using a #line directive. #### Directives All cpp directive lines start with # in column 1. Any number of blanks and tabs is allowed between the # and the directive. The directives are: #assert name (string) Define a question called name, with an answer of string. Assertions can be tested with #if directives. The predefined assertions for #system, #cpu, and #machine can be used for architecture-dependent changes. #unassert name Remove assertion for question name. #define name token-string Define a macro called name, with a value of token-string. Subsequent instances of name are replaced with token-string. #define name( arg, ... , arg ) token-string This allows substitution of a macro with arguments. token-string will be substituted for name in the input file. Each call to name in the source file includes arguments that are plugged into the corresponding args in token-string. #undef name Remove definition of the macro name. No additional tokens are permitted on the directive line after name. #ident string Put string into the comment section of an object file. #include "filename", #include<filename> Include contents of filename at this point in the program. No additional tokens are permitted on the directive line after the final " or >. #line integer-constant "filename" Cause cpp to generate line-control information for the next pass of the C compiler. The compiler behaves as if integer-constant is the line number of the next line of source code and filename (if present) is the name of the input file. No additional tokens are permitted on the directive line after the optional filename. #endif End a section of lines begun by a test directive (#if, #ifdef, or #ifndef). No additional tokens are permitted on the directive line. #ifdef name Lines following this directive and up to matching #endif or next #else or #elif will appear in the output if name is currently defined. No additional tokens are permitted on the directive line after name. #ifndef name Lines following this directive and up to matching #endif or next #else or #elif will appear in the output if name is not currently defined. No additional tokens are permitted on the directive line after name. #if constant-expression Lines following this directive and up to matching #endif or next #else or #elif will appear in the output if constant-expression evaluates to nonzero. #elif constant-expression An arbitrary number of #elif directives are allowed between an #if, #ifdef, or #ifndef directive and an #else or #endif directive. The lines following the #elif and up to the next #else, #elif, or #endif directive will appear in the output if the preceding test directive and all intervening #elif directives evaluate to zero, and the constant-expression evaluates to nonzero. If constant-expression evaluates to nonzero, all succeeding #elif and #else directives will be ignored. #else Lines following this directive and up to the matching #endif will appear in the output if the preceding test directive evaluates to 0, and all intervening #elif directives evaluate to 0. No additional tokens are permitted on the directive line. #error Report fatal errors. #warning Report warnings, but then continue processing.
cfdisk | cfdisk [options] [device] System administration command. Partition a hard disk. device may be /dev/hda (default), /dev/hdb, /dev/sda, /dev/sdb, /dev/sdc, or /dev/sdd. See also fdisk. #### Options -a Highlight the current partition with a cursor, not reverse video. -c cylinders Specify the number of cylinders. -h heads Specify the number of heads. -s sectors Specify the number of sectors per track. -z Do not read the partition table; partition from scratch. -P format Display the partition table in format, which must be r (raw data), s (sector order), or t (raw format). #### Commands up arrow, down arrow Move among partitions. b Toggle partition's bootable flag. d Delete partition (allow other partitions to use its space). g Alter the disk's geometry. Prompt for what to change: cylinders, heads, or sectors (c, h, or s, respectively). h Help. m Attempt to ensure maximum usage of disk space in the partition. n Create a new partition. Prompt for more information. p Display the partition table. q Quit without saving information. t Prompt for a new filesystem type, and change to that type. u Change the partition size units, rotating from megabytes to sectors to cylinders and back. W Save information. Note that this letter must be uppercase.
> chattr | chattr [options] mode files Modify file attributes. Specific to Linux Second Extended Filesystem. Behaves similarly to symbolic chmod, using +, -, and =. mode is in the form opcode attribute. See also lsattr. #### Options -R Modify directories and their contents recursively. -V Print modes of attributes after changing them. -v version Set the file's version. #### Opcodes + Add attribute. - Remove attribute. = Assign attributes (removing unspecified attributes). #### Attributes A Don't update access time on modify. a Append only for writing. Can be set or cleared only by a privileged user. c Compressed. d No dump. i Immutable. Can be set or cleared only by a privileged user. s Secure deletion; the contents are zeroed on deletion. u Undeletable. S Synchronous updates. #### Examples
>     chattr +a myfile     As superuser
> chfn | chfn [options] [username] Change the information that is stored in /etc/passwd and displayed when a user is fingered. Without options, chfn enters interactive mode and prompts for changes. To make a field blank, enter the keyword none. Only a privileged user can change information for another user. For regular users, chfn prompts for the user's password before making the change. #### Options -f, --full-name Specify new full name. -h, --home-phone Specify new home phone number. -o, --office Specify new office number. -p, --office-phone Specify new office phone number. -u, --help Print help message and then exit. -v, --version Print version information and then exit. #### Example
>     chfn -f "Ellen Siever" ellen
chgrp | chgrp [options] newgroup files chgrp [options] Change the group of one or more files to newgroup. newgroup is either a group ID number or a group name located in /etc/group. Only the owner of a file or a privileged user may change its group. #### Options -c, --changes Print information about those files that are changed. -f, --silent, --quiet Do not print error messages about files that cannot be changed. --help Print help message and then exit. -R, --recursive Traverse subdirectories recursively, applying changes. --reference=filename Change the group to that associated with filename. In this case, newgroup is not specified. -v, --verbose Verbosely describe ownership changes. --version Print version information and then exit.
> chmod | chmod [options] mode files chmod [options] --reference=filename files Change the access mode (permissions) of one or more files. Only the owner of a file or a privileged user may change its mode. mode can be numeric or an expression in the form of who opcode permission. who is optional (if omitted, default is a); choose only one opcode. Multiple modes may be specified, separated by commas. #### Options -c, --changes Print information about files that are changed. -f, --silent, --quiet Do not notify user of files that chmod cannot change. --help Print help message and then exit. -R, --recursive Traverse subdirectories recursively, applying changes. --reference=filename Change permissions to those associated with filename. -v, --verbose Print information about each file, whether changed or not. --version Print version information and then exit. #### Who u User g Group o Other a All (default) #### Opcode + Add permission. - Remove permission. = Assign permission (and remove permission of the unspecified fields). #### Permissions r Read. w Write. x Execute. s Set user (or group) ID. t Sticky bit; save text (file) mode or prevent removal of files by nonowners (directory). u User's present permission. g Group's present permission. o Other's present permission. Alternatively, specify permissions by a three-digit octal number. The first digit designates owner permission; the second, group permission; and the third, other's permission. Permissions are calculated by adding the following octal values: 4 Read. 2 Write. 1 Execute. Note: A fourth digit may precede this sequence. This digit assigns the following modes: 4 Set user ID on execution to grant permissions to process based on file's owner, not on permissions of user who created the process. 2 Set group ID on execution to grant permissions to process based on the file's group, not on permissions of user who created the process. 1 Set sticky bit. #### Examples Add execute-by-user permission to file:
>     chmod u+x file
> Either of the following will assign read/write/execute permission by owner (7), read/execute permission by group (5), and execute-only permission by others (1) to file:
>     chmod 751 file
>     chmod u=rwx,g=rx,o=x file
> Any one of the following will assign read-only permission to file for everyone:
>     chmod =r file
>     chmod 444 file
>     chmod a-wx,a+r file
> Set the user ID, assign read/write/execute permission by owner, and assign read/execute permission by group and others:
>     chmod 4755 file
chown | chown [options] newowner files chown [options] --reference=filename files Change the ownership of one or more files to newowner. newowner is either a user ID number or a login name located in /etc/passwd. chown also accepts users in the form newowner:newgroup or newowner.newgroup. The last two forms change the group ownership as well. If no owner is specified, the owner is unchanged. With a period or colon but no group, the group is changed to that of the new owner. Only the current owner of a file or a privileged user may change its owner. #### Options -c, --changes Print information about those files that are changed. --dereference Follow symbolic links. -f, --silent, --quiet Do not print error messages about files that cannot be changed. -h, --no-dereference Change the ownership of each symbolic link (on systems that allow it), rather than the referenced file. -v, --verbose Print information about all files that chown attempts to change, whether or not they are actually changed. -R, --recursive Traverse subdirectories recursively, applying changes. --reference=filename Change owner to the owner of filename instead of specifying a new owner explicitly. --help Print help message and then exit. --version Print version information and then exit.
chpasswd | chpasswd [option] System administration command. Change user passwords in a batch. chpasswd accepts input in the form of one username:password pair per line. If the -e option is not specified, password will be encrypted before being stored. #### Option -e Passwords given are already encrypted.
chroot | chroot newroot [command] System administration command. Change root directory for command or, if none is specified, for a new copy of the user's shell. This command or shell is executed relative to the new root. The meaning of any initial / in pathnames is changed to newroot for a command and any of its children. In addition, the initial working directory is newroot. This command is restricted to privileged users.
> chsh | chsh [options] [username] Change your login shell, interactively or on the command line. Warn if shell does not exist in /etc/shells. Specify the full path to the shell. chsh prompts for your password. Only a privileged user can change another user's shell. #### Options -l, --list-shells Print valid shells, as listed in /etc/shells, and then exit. -s shell, --shell shell Specify new login shell. -u, --help Print help message and then exit. -v, --version Print version information and then exit. #### Example
>     chsh -s /bin/tcsh
cksum | cksum [files] Compute a cyclic redundancy check (CRC) checksum for all files; used to ensure that a file was not corrupted during transfer. Read from standard input if the character - or no files are given. Display the resulting checksum, the number of bytes in the file, and (unless reading from standard input) the filename.
clear | clear Clear the terminal display.
> cmp | cmp [options] file1 file2 [skip1 [skip2]] Compare file1 with file2. Use standard input if file1 is - or missing. See also comm and diff. Files can be of any type. skip1 and skip2 are optional offsets in the files at which the comparison is to start. #### Options -c, --print-chars Print differing bytes as characters. -i num, --ignore-initial=num Ignore the first num bytes of input. -l, --verbose Print offsets and codes of all differing bytes. -s, --quiet, --silent Work silently; print nothing, but return exit codes: 0 Files are identical. 1 Files are different. 2 Files are inaccessible. #### Example Print a message if two files are the same (exit code is 0):
>     cmp -s old new && echo 'no changes'
> col | col [options] A postprocessing filter that handles reverse linefeeds and escape characters, allowing output from tbl or nroff to appear in reasonable form on a terminal. #### Options -b Ignore backspace characters; helpful when printing manpages. -f Process half-line vertical motions, but not reverse line motion. (Normally, half-line input motion is displayed on the next full line.) -l n Buffer at least n lines in memory. The default buffer size is 128 lines. -x Normally, col saves printing time by converting sequences of spaces to tabs. Use -x to suppress this conversion. #### Examples Run myfile through tbl and nroff, then capture output on screen by filtering through col and more:
>     tbl myfile | nroff | col | more
> Save manpage output for the ls command in out.print, stripping out backspaces (which would otherwise appear as ^H):
>     man ls | col -b > out.print
colcrt | colcrt [options] [files] A postprocessing filter that handles reverse linefeeds and escape characters, allowing output from tbl or nroff to appear in reasonable form on a terminal. Put half-line characters (e.g., subscripts or superscripts) and underlining (changed to dashes) on a new line between output lines. #### Options - Do not underline. -2 Double space by printing all half-lines.
> colrm | colrm [start [stop]] Remove specified columns from a file, where a column is a single character in a line. Read from standard input and write to standard output. Columns are numbered starting with 1; begin deleting columns at (including) the start column, and stop at (including) the stop column. Entering a tab increments the column count to the next multiple of either the start or stop column; entering a backspace decrements it by 1. #### Example
>     colrm 3 5 < test1 > test2
column | column [options] [files] Format input from one or more files into columns, filling rows first. Read from standard input if no files are specified. #### Options -c num Format output into num columns. -s char Delimit table columns with char. Meaningful only with -t. -t Format input into a table. Delimit with whitespace, unless an alternate delimiter has been provided with -s. -x Fill columns before filling rows.
> comm | comm [options] file1 file2 Compare lines common to the sorted files file1 and file2. Three-column output is produced: lines unique to file1, lines unique to file2, and lines common to both files. comm is similar to diff in that both commands compare two files. But comm can also be used like uniq; that is, comm selects duplicate or unique lines between two sorted files, whereas uniq selects duplicate or unique lines within the same sorted file. #### Options - Read the standard input. -num Suppress printing of column num. Multiple columns may be specified and should not be space-separated. --help Print help message and exit. --version Print version information and exit. #### Example Compare two lists of top-10 movies, and display items that appear in both lists:
>     comm -12 siskel_top10 ebert_top10
compress | compress [options] files Compress one or more files, replacing each with the compressed file of the same name with .Z appended. If no file is specified, compress standard input. Each file specified is compressed separately. compress ignores files that are symbolic links. See also gzip. #### Options -b maxbits Limit the maximum number of bits. -c Write output to standard output, not to a .Z file. -d Decompress instead of compressing. Same as uncompress. -f Force generation of an output file even if one already exists. -r If any of the specified files is a directory, compress recursively. -v Print compression statistics. -V Print version and compilation information and then exit.
  > cp | cp [options] file1 file2 cp [options] files directory Copy file1 to file2, or copy one or more files to the same names under directory. If the destination is an existing file, the file is overwritten; if the destination is an existing directory, the file is copied into the directory (the directory is not overwritten). #### Options -a, --archive Preserve attributes of original files where possible. Same as -dpR. -b, --backup Back up files that would otherwise be overwritten. -d, --no-dereference Do not dereference symbolic links; preserve hard link relationships between source and copy. -f, --force Remove existing files in the destination. -i, --interactive Prompt before overwriting destination files. -l, --link Make hard links, not copies, of nondirectories. -p, --preserve Preserve all information, including owner, group, permissions, and timestamps. -P, --parents Preserve intermediate directories in source. The last argument must be the name of an existing directory. For example, the command:
  >     cp --parents jphekman/book/ch1 newdir
copies the file jphekman/book/ch1 to the file newdir/jphekman/book/ch1, creating intermediate directories as necessary. -r, -R, --recursive Copy directories recursively. -S backup-suffix, --suffix=backup-suffix Set suffix to be appended to backup files. This may also be set with the SIMPLE_BACKUP_SUFFIX environment variable. The default is ~. You need to explicitly include a period if you want one before the suffix (e.g., specify .bak, not bak). -s, --symbolic-link Make symbolic links instead of copying. Source filenames must be absolute. -u, --update Do not copy a file to an existing destination with the same or newer modification time. -v, --verbose Before copying, print the name of each file. -V type, --version-control=type Set the type of backups made. You may also use the VERSION_CONTROL environment variable. The default is existing. Valid arguments are: t, numbered Always make numbered backups. nil, existing Make numbered backups of files that already have them; otherwise, make simple backups. never, simple Always make simple backups. -x, --one-file-system Ignore subdirectories on other filesystems.
> cpio | cpio flags [options] Copy file archives in from or out to tape or disk, or to another location on the local machine. Each of the three flags -i, -o, or -p accepts different options. #### Flags -i, --extract [options] [patterns] Copy in (extract) from an archive files whose names match selected patterns. Each pattern can include Bourne shell filename metacharacters. (Patterns should be quoted or escaped so they are interpreted by cpio, not by the shell.) If pattern is omitted, all files are copied in. Existing files are not overwritten by older versions from the archive unless -u is specified. -o, --create [options] Copy out to an archive a list of files whose names are given on the standard input. -p, --pass-through [options] directory Copy (pass) files to another directory on the same system. Destination pathnames are interpreted relative to the named directory. #### Comparison of valid options Options available to the -i, -o, and -p flags are shown here. (The - is omitted for clarity):
>     i:   bcdf mnrtsuv B SVCEHMR IF
>     o: 0a c         vABL VC HM O F
>     p: 0a  d lm    uv  L V    R
> #### Options -0, --null Expect list of filenames to be terminated with null, not newline. This allows files with a newline in their names to be included. -a, --reset-access-time Reset access times of input files after reading them. -A, --append Append files to an existing archive, which must be a disk file. Specify this archive with -O or -F. -b, --swap Swap bytes and half-words to convert between big-endian and little-endian 32-bit integers. -B Block input or output using 5120 bytes per record (default is 512 bytes per record). --blocksize=size Set input or output blocksize to size × 512 bytes. -c Read or write header information as ASCII characters; useful when source and destination machines are different types. -C n, --io-size=n Like -B, but blocksize can be any positive integer n. -d, --make-directories Create directories as needed. -E file, --pattern-file=file Extract filenames from the archives that match patterns in file. -f, --nonmatching Reverse the sense of copying; copy all files except those that match patterns. -F file, --file=file Use file as the archive, not stdin or stdout. file can reside on another machine, if given in the form user@hostname:file (where user@ is optional). --force-local Assume that file (provided by -F, -I, or -O) is a local file, even if it contains a colon (:) indicating a remote file. -H type, --format=type Use type format. Default for copy-out is bin; for copy-in the default is autodetection of the format. Valid formats (all caps also accepted) are: bin Binary odc Old (POSIX.1) portable format newc New (SVR4) portable format crc New (SVR4) portable format with checksum added tar Tar ustar POSIX.1 tar (also recognizes GNU tar archives) hpbin HP-UX's binary (obsolete) hpodc HP-UX's portable format -I file Read file as an input archive. May be on a remote machine (see -F). -k Ignored. For backward compatibility. -l, --link Link files instead of copying. -L, --dereference Follow symbolic links. -m, --preserve-modification-time Retain previous file modification time. -M msg, --message=msg Print msg when switching media, as a prompt before switching to new media. Use variable %d in the message as a numeric ID for the next medium. -M is valid only with -I or -O. -n, --numeric-uid-gid When verbosely listing contents, show user ID and group ID numerically. --no-absolute-filenames Create all copied-in files relative to the current directory. --no-preserve-owner Make all copied files owned by yourself, instead of the owner of the original. Useful only if you are a privileged user. -O file Archive the output to file, which may be a file on another machine (see -F). --only-verify-crc For a CRC-format archive, verify the CRC of each file; don't actually copy the files in. --quiet Don't print the number of blocks copied. -r Rename files interactively. -R [user][:group], --owner [user][:group] Reassign file ownership and group information to the user's login ID (privileged users only). -s, --swap-bytes Swap bytes of each two-byte half-word. -S, --swap-half-words Swap half-words of each four-byte word. --sparse For copy-out and copy-pass, write files that have large blocks of zeros as sparse files. -t, --list Print a table of contents of the input (create no files). When used with the -v option, resembles output of ls -l. -u, --unconditional Unconditional copy; old files can overwrite new ones. -v, --verbose Print a list of filenames processed. -V, --dot Print a dot for each file read or written (this shows cpio at work without cluttering the screen). --version Print version number and then exit. #### Examples Generate a list of files whose names end in .old using find; use list as input to cpio:
>     find . -name "*.old" -print | cpio -ocBv > /dev/rst8
> Restore from a tape drive all files whose names contain save (subdirectories are created if needed):
>     cpio -icdv "*save*" < /dev/rst8
> Move a directory tree:
>     find . -depth -print | cpio -padm /mydir
cron | cron System administration command. Normally started in a system startup file. Execute commands at scheduled times, as specified in users' files in /var/cron/tabs. Each file shares its name with the user who owns it. The files are controlled via the command crontab.
> crontab | crontab [options] [file] View, install, or uninstall your current crontab file. A privileged user can run crontab for another user by supplying -u user. A crontab file is a list of commands, one per line, that will execute automatically at a given time. Numbers are supplied before each command to specify the execution time. The numbers appear in five fields, as follows:
>     Minute       0-59

>     Hour         0-23

>     Day of month 1-31

>     Month        1-12
>                   Jan, Feb, Mar, ...

>     Day of week   0-6, with 0 = Sunday
>                  Sun, Mon, Tue, ...
> Use a comma between multiple values, a hyphen to indicate a range, and an asterisk to indicate all possible values. For example, assuming these crontab entries:
>     59 3 * * 5     find / -print | backup_program
>     0 0 1,15 * *   echo "Timesheets due" | mail user
The first command backs up the system files every Friday at 3:59 a.m., and the second command mails a reminder on the 1st and 15th of each month. The superuser can always issue the crontab command. Other users must be listed in the file /etc/cron.allow if it exists; otherwise, they must not be listed in /etc/cron.deny. If neither file exists, only the superuser can issue the command. #### Options The -e, -l, and -r options are not valid if any files are specified. -e Edit the user's current crontab file (or create one). -l Display the user's crontab file on standard output. -r Delete the user's crontab file. -u user Indicates which user's crontab file will be acted upon.
csh | csh [options] [file [arguments]] C shell, a command interpreter into which all other commands are entered. For more information, see Chapter 8, "csh and tcsh".
> csplit | csplit [options] file arguments Separate file into context-based sections and place sections in files named xx00 through xxn (n < 100), breaking file at each pattern specified in arguments. See also split. #### Options - Read from standard input. -b suffix, --suffix-format=suffix Append suffix to output filename. This option causes -n to be ignored. suffix must specify how to convert the binary integer to readable form by including exactly one of the following: %d, %i, %u, %o, %x, or %X. The value of suffix determines the format for numbers as follows: %d Signed decimal %i Same as %d %u Unsigned decimal %o Octal %x Hexadecimal %X Same as %x. -f prefix, --prefix=prefix Name new files prefix 00 through prefixn (default is xx00 through xx n). -k, --keep-files Keep newly created files, even when an error occurs (which would normally remove these files). This is useful when you need to specify an arbitrarily large repeat argument, {n}, and you don't want an out-of-range error to cause removal of the new files. -n num, --digits=num Use output filenames with numbers num digits long. The default is 2. -s, -q, --silent, --quiet Suppress all character counts. -z, --elide-empty-files Do not create empty output files. However, number as if those files had been created. #### Arguments Any one or a combination of the following expressions may be specified as arguments. Arguments containing blanks or other special characters should be surrounded by single quotes. /expr/[offset] Create file from the current line up to the line containing the regular expression expr. offset should be of the form +n or -n, where n is the number of lines below or above expr. %expr%[offset] Same as /expr/ except no file is created for lines previous to line containing expr. num Create file from current line up to (but not including) line number num. When followed by a repeat count (number inside {}), put the next num lines of input into another output file. {n} Repeat argument n times. May follow any of the preceding arguments. Files will split at instances of expr or in blocks of num lines. If * is given instead of n, repeat argument until input is exhausted. #### Examples Create up to 20 chapter files from the file novel:
>     csplit -k -f chap. novel '/CHAPTER/' '{20}'
> Create up to 100 address files (xx00 through xx99), each four lines long, from a database named address_list:
>     csplit -k address_list 4 {99}
> ctags | ctags [options] files Create a list of function and macro names that are defined in the specified C, C++, FORTRAN, Java, Perl, yacc, or other source files. The output list (named tags by default) contains lines of the form:
>     name     file     context
> where name is the function or macro name, file is the source file in which name is defined, and context is a search pattern that shows the line of code containing name. After the list of tags is created, you can invoke vi on any file and type:
>     :set tags=tagsfile
>     :tag name
This switches the vi editor to the source file associated with the name listed in tagsfile (which you specify with -t). etags produces an equivalent file for tags to be used with Emacs. #### Options -a, --append Append tag output to existing list of tags. -d, --defines Include tag entries for C preprocessor definitions. -i file, --include=file Add a note to the tags file that file should be consulted in addition to the normal input file. -l language, --language=language Consider the files that follow this option to be written in language. Use the -h option for a list of languages and their default filename extensions. -o file, --output=file Write to file. -r regexp, --regex=regexp Include a tag for each line that matches regexp in the files following this option. -R, --no-regex Don't include tags based on regular-expression matching for the files that follow this option. -t, --typedefs Include tag entries for typedefs. -u, --update Update tags file to reflect new locations of functions (e.g., when functions are moved to a different source file). Old tags are deleted; new tags are appended. -v, --vgrind Print to standard output a listing (index) of each function, source file, and page number (1 page = 64 lines). -w, --no-warn Suppress warning messages. -x, --cxref Produce a listing of each function, and its line number, source file, and context. -B, --backward-search Search for tags backward through files. -C, --c++ Expect .c and .h files to contain C++, not C, code. -H, -h, --help Print usage information and exit. -S, --ignore-indentation Normally ctags uses indentation to parse the tag file; this option tells it to rely on it less. -T, --typedefs-and-c++ Include tag entries for typedefs, structs, enums, unions, and C++ member functions. -V, --version Print the version number and exit.
> cut | cut options [files] Cut out selected columns or fields from one or more files. In the following options, list is a sequence of integers. Use a comma between separate values and a hyphen to specify a range (e.g., 1-10,15,20 or 50-). See also paste and join. #### Options -b list, --bytes list Specify list of positions; only bytes in these positions will be printed. -c list, --characters list Cut the column positions identified in list. -d c, --delimiter c Use with -f to specify field delimiter as character c (default is tab); special characters (e.g., a space) must be quoted. -f list, --fields list Cut the fields identified in list. -n Don't split multibyte characters. -s, --only-delimited Use with -f to suppress lines without delimiters. --output-delimiter=string Use string as the output delimiter. By default, the output delimiter is the same as the input delimiter. --help Print help message and then exit. --version Print version information and then exit. #### Examples Extract usernames and real names from /etc/passwd:
>     cut -d: -f1,5 /etc/passwd
> Find out who is logged on, but list only login names:
>     who | cut -d"" -f1
> Cut characters in the fourth column of file, and paste them back as the first column in the same file:
>     cut -c4 file | paste - file
  > date | date [options] [+format] [date] Print the current date and time. You may specify a display format. format can consist of literal text strings (blanks must be quoted) as well as field descriptors, whose values will appear as described in the following entries (the listing shows some logical groupings). A privileged user can change the system's date and time. #### Options +format Display current date in a nonstandard format. For example:
  >     % date +"%A %j %n%k %p"
  >     Tuesday 248
  >     15 PM
> The default is %a %b %e %T %Z %Y -- e.g., Tue Sep 5 14:59:37 EDT 2000. -d date, --date date Display date, which should be in quotes and may be in the format d days or m months d days to print a date in the future. Specify ago to print a date in the past. You may include formatting (see the "Format" section that follows). -f datefile, --file=datefile Like -d but printed once for each line of datefile. -I [timespec], --iso-8601[=timespec] Display in ISO-8601 format. If specified, timespec can have one of the values date (for date only), hours, minutes, or seconds to get the indicated precision. -r file, --reference=file Display the time file was last modified. -R, --rfc-822 Display the date in RFC 822 format. --help Print help message and exit. --version Print version information and exit. -s date, --set date Set the date. -u, --universal Set the date to Greenwich Mean Time, not local time. #### Format % Literal %. - Do not pad fields (default: pad fields with zeros). _ Pad fields with space (default: zeros). %a Abbreviated weekday. %b Abbreviated month name. %c Country-specific date and time format. %d Day of month (01-31). %h Same as %b. %j Julian day of year (001-366). %k Hour in 24-hour format, without leading zeros (0-23). %l Hour in 12-hour format, without leading zeros (1-12). %m Month of year (01-12). %n Insert a new line. %p String to indicate AM or PM. %r Time in %I:%M:%S %p (12-hour) format. %s Seconds since "The Epoch," 1970-01-01 00:00:00 UTC (a nonstandard extension). %t Insert a tab. %w Day of week (Sunday = 0). %x Country-specific date format. %y Last two digits of year (00-99). %z RFC 822-style numeric time zone. %A Full weekday. %B Full month name. %D Date in %m/%d/%y format. %H Hour in 24-hour format (00-23). %I Hour in 12-hour format (01-12). %M Minutes (00-59). %S Seconds (00-59). %T Time in %H:%M:%S format. %U Week number in year (00-53); start week on Sunday. %V Week number in year (01-52); start week on Monday. %W Week number in year (00-53); start week on Monday. %X Country-specific time format. %Y Four-digit year (e.g., 1996). %Z Time zone name. #### Strings for setting date Strings for setting the date may be numeric or nonnumeric. Numeric strings consist of time, day, and year in the format MMDDhhmm[[CC]YY][.ss]. Nonnumeric strings may include month strings, time zones, a.m., and p.m. time A two-digit hour and two-digit minute (hhmm); hh uses 24-hour format. day A two-digit month and two-digit day of month (MMDD); default is current day and month. year The year specified as either the full four-digit century and year or just the two-digit year; the default is the current year. #### Examples Set the date to July 1 (0701), 4 a.m. (0400), 1995 (95):
>     date 0701040095
> The command:
>     date +"Hello%t Date is %D %n%t Time is %T"
> produces a formatted date as follows:
>     Hello     Date is 05/09/93
>          Time is 17:53:39
> dd | dd options Make a copy of an input file (if) using the specified conditions, and send the results to the output file (or standard output if of is not specified). Any number of options can be supplied, although if and of are the most common and are usually specified first. Because dd can handle arbitrary blocksizes, it is useful when converting between raw physical devices. #### Options bs=n Set input and output blocksize to n bytes; this option overrides ibs and obs. cbs=n Set the size of the conversion buffer (logical record length) to n bytes. Use only if the conversion flag is ascii, ebcdic, ibm, block, or unblock. conv=flags Convert the input according to one or more (comma-separated) flags listed next. The first five flags are mutually exclusive. ascii EBCDIC to ASCII. ebcdic ASCII to EBCDIC. ibm ASCII to EBCDIC with IBM conventions. block Variable-length records (i.e., those terminated by a newline) to fixed-length records. unblock Fixed-length records to variable-length. lcase Uppercase to lowercase. ucase Lowercase to uppercase. noerror Continue processing after read errors. notrunc Don't truncate output file. swab Swap each pair of input bytes. sync Pad input blocks to ibs with trailing zeros. count=n Copy only n input blocks. ibs=n Set input blocksize to n bytes (default is 512). if=file Read input from file (default is standard input). obs=n Set output blocksize to n bytes (default is 512). of=file Write output to file (default is standard output). seek=n Skip n output-sized blocks from start of output file. skip=n Skip n input-sized blocks from start of input file. --help Print help message and then exit. --version Print the version number and then exit. You can multiply size values (n) by a factor of 1024, 512, or 2 by appending the letter k, b, or w, respectively. You can use the letter x as a multiplication operator between two numbers. #### Examples Convert an input file to all lowercase:
>     dd if=caps_file of=small_file conv=lcase
> Retrieve variable-length data; write it as fixed-length to out:
>     data_retrieval_cmd | dd of=out conv=sync,block
debugfs | debugfs [[option] device] System administration command. Debug an ext2 filesystem. device is the special file corresponding to the device containing the ext2 filesystem (e.g., /dev/hda3). #### Option -w Open the filesystem read-write. #### Commands cat file Dump the contents of an inode to standard output. cd directory Change the current working directory to directory. chroot directory Change the root directory to be the specified inode. close Close the currently open filesystem. clri file Clear the contents of the inode corresponding to file. dump file out_file Dump the contents of an inode to out_file. expand_dir directory Expand directory. find_free_block [goal] Find first free block starting from goal (if specified) and allocate it. find_free_inode [dir [mode]] Find a free inode and allocate it. freeb block Mark block as not allocated. freei file Free the inode corresponding to file. help Print a list of commands understood by debugfs. icheck block Do block-to-inode translation. initialize device blocksize Create an ext2 filesystem on device. kill_file file Remove file and deallocate its blocks. ln source_file dest_file Create a link. ls [pathname] Emulate the ls command. modify_inode file Modify the contents of the inode corresponding to file. mkdir directory Make directory. mknod file [p|[[c|b] major minor]] Create a special device file. ncheck inode Do inode-to-name translation. open [-w] device Open a filesystem. pwd Print the current working directory. quit Quit debugfs. rm file Remove file. rmdir directory Remove directory. setb block Mark block as allocated. seti file Mark in use the inode corresponding to file. show_super_stats List the contents of the super block. stat file Dump the contents of the inode corresponding to file. testb block Test whether block is marked as allocated. testi file Test whether the inode corresponding to file is marked as allocated. unlink file Remove a link. write source_file file Create a file in the filesystem named file, and copy the contents of source_file into the destination file.
depmod | depmod [options] modules System administration command. Create a dependency file for the modules given on the command line. This dependency file can be used by modprobe to automatically load the relevant modules. The normal use of depmod is to include the line /sbin/depmod -a in one of the files in /etc/rc.d so the correct module dependencies will be available after booting the system. #### Options -a Create dependencies for all modules listed in /etc/conf.modules. -d Debug mode. Show all commands being issued. -e Print a list of all unresolved symbols. -v Print a list of all processed modules. #### Files /etc/conf.modules Information about modules: which ones depend on others, and which directories correspond to particular types of modules. /sbin/insmod, /sbin/rmmod Programs that depmod relies on.
df | df [options] [name] Report the amount of free disk space available on all mounted filesystems or on the given name. (df cannot report on unmounted filesystems.) Disk space is shown in 1KB blocks (default) or 512-byte blocks (if the environment variable POSIXLY_CORRECT is set). name can be a device name (e.g., /dev/hd*), the directory name of a mounting point (e.g., /usr), or a directory name (in which case df reports on the entire filesystem in which that directory is mounted). #### Options -a, --all Include empty filesystems (those with 0 blocks). --block-size=n Show space as n-byte blocks. -h, --human-readable Print sizes in a format friendly to human readers (e.g., 1.9G instead of 1967156). -H, --si Like -h, but show as power of 1000 rather than 1024. -i, --inodes Report free, used, and percent-used inodes. -k, --kilobytes Print sizes in kilobytes. -l, --local Show local filesystems only. -m, --megabytes Print sizes in megabytes. --no-sync Show results without invoking sync first (i.e., without flushing the buffers). This is the default. -P, --portability Use POSIX output format (i.e., print information about each filesystem on exactly one line). --sync Invoke sync (flush buffers) before getting and showing sizes. -t type, --type=type Show only type filesystems. -T, --print-type Print the type of each filesystem in addition to the sizes. -x type, --exclude-type=type Show only filesystems that are not of type type. --help Print help message and then exit. --version Print the version and then exit.
diff | diff [options] [diroptions] file1 file2 Compare two text files. diff reports lines that differ between file1 and file2. Output consists of lines of context from each file, with file1 text flagged by a < symbol and file2 text by a > symbol. Context lines are preceded by the ed command (a, c, or d) that would be used to convert file1 to file2. If one of the files is -, standard input is read. If one of the files is a directory, diff locates the filename in that directory corresponding to the other argument (e.g., diff my_dir junk is the same as diff my_dir/junk junk). If both arguments are directories, diff reports lines that differ between all pairs of files having equivalent names (e.g., olddir/program and newdir/program); in addition, diff lists filenames unique to one directory, as well as subdirectories common to both. See also cmp. #### Options -a, --text Treat all files as text files. Useful for checking to see if binary files are identical. -b, --ignore-space-change Ignore repeating blanks and end-of-line blanks; treat successive blanks as one. -B, --ignore-blank-lines Ignore blank lines in files. -c Context diff: print 3 lines surrounding each changed line. -C n, --context[=n] Context diff: print n lines surrounding each changed line. The default context is 3 lines. -d, --minimal To speed up comparison, ignore segments of numerous changes and output a smaller set of changes. -D symbol, --ifdef=symbol When handling C files, create an output file that contains all the contents of both input files, including #ifdef and #ifndef directives that reflect the directives in both files. -e, --ed Produce a script of commands (a, c, d) to re-create file2 from file1 using the ed editor. -F regexp, --show-function-line[=regexp] For context and unified diff, show the most recent line containing regexp before each block of changed lines. -H Speed output of large files by scanning for scattered small changes; long stretches with many changes may not show up. --help Print brief usage message. --horizon-lines=n In an attempt to find a more compact listing, keep n lines on both sides of the changed lines when performing the comparison. -i, --ignore-case Ignore case in text comparison. Uppercase and lowercase are considered the same. -I regexp, --ignore-matching-lines=regexp Ignore lines in files that match the regular expression regexp. -l, --paginate Paginate output by passing it to pr. -L label, --label label, --label=label For context and unified diff, print label in place of the filename being compared. The first such option applies to the first filename and the second option to the second filename. --left-column For two-column output (-y), show only left column of common lines. -n, --rcs Produce output in RCS diff format. -N, --new-file Treat nonexistent files as empty. -p, --show-c-function When handling files in C or C-like languages such as Java, show the function containing each block of changed lines. Assumes -c but can also be used with a unified diff. -P, --unidirectional-new-file If two directories are being compared and the first lacks a file that is in the second, pretend that an empty file of that name exists in the first directory. -q, --brief Output only whether files differ. -r, --recursive Compare subdirectories recursively. -s, --report-identical-files Indicate when files do not differ. -S filename, --starting-file=filename For directory comparisons, begin with the file filename, skipping files that come earlier in the standard list order. --suppress-common-lines For two-column output (-y), do not show common lines. -t, --expand-tabs Produce output with tabs expanded to spaces. -T, --initial-tab Insert initial tabs into output to line up tabs properly. -u Unified diff: print old and new versions of lines in a single block, with 3 lines surrounding each block of changed lines. -U n, --unified[=n] Unified diff: print old and new versions of lines in a single block, with n lines surrounding each block of changed lines. The default context is 3 lines. -v, --version Print version number of this version of diff. -w, --ignore-all-space Ignore all whitespace in files for comparisons. -W n, --width=n For two-column output (-y), produce columns with a maximum width of n characters. Default is 130. -x regexp, --exclude=regexp Do not compare files in a directory whose names match regexp. -X filename, --exclude-from=filename Do not compare files in a directory whose names match patterns described in the file filename. -y, --side-by-side Produce two-column output. -n For context and unified diff, print n lines of context. Same as specifying a number with -C or -U.
diff3 | diff3 [options] file1 file2 file3 Compare 3 files and report the differences. No more than one of the files may be given as - (indicating that it is to be read from standard input). The output is displayed with the following codes: ==== All three files differ. ====1 file1 is different. ====2 file2 is different. ====3 file3 is different. diff3 is also designed to merge changes in two differing files based on a common ancestor file (i.e., when two people have made their own set of changes to the same file). diff3 can find changes between the ancestor and one of the newer files and generate output that adds those differences to the other new file. Unmerged changes are places where both of the newer files differ from each other and at least one of them from the ancestor. Changes from the ancestor that are the same in both of the newer files are called merged changes. If all three files differ in the same place, it is called an overlapping change. This scheme is used on the command line with the ancestor being file2, the second filename. Comparison is made between file2 and file3, with those differences then applied to file1. #### Options -3, --easy-only Create an ed script to incorporate into file1 unmerged, nonoverlapping differences between file1 and file3. -a, --text Treat files as text. -A, --show-all Create an ed script to incorporate all changes, showing conflicts in bracketed format. -e, --ed Create an ed script to incorporate into file1 all unmerged differences between file2 and file3. -E, --show-overlap Create an ed script to incorporate unmerged changes, showing conflicts in bracketed format. -x, --overlap-only Create an ed script to incorporate into file1 all differences where all three files differ (overlapping changes). -X Same as -x, but show only overlapping changes, in bracketed format. -m, --merge Create file with changes merged (not an ed script). -L label, --label=label Use label to replace filename in output. -i Append the w (save) and q (quit) commands to ed script output. -T, --initial-tab Begin lines with a tab instead of two spaces in output to line tabs up properly. -v, --version Print version information and then exit.
dip | dip [options] [chat scriptfile] System administration command. Set up or initiate dial-up Internet connections. dip can be used to establish connections for users dialing out or dialing in. Commands can be used in interactive mode or placed in a script file for use in dial-out connections. To establish dial-in connections, dip is often is used as a shell and may be executed using the commands diplogin or diplogini. #### Options -a In dial-in mode, prompt for username and password. Same as the diplogini command. -i Initiate a login shell for a dial-in connection. Same as the diplogin command. -k Kill the most recent dip process or the process running on the device specified by the -l option. -l device Used with the -k option. Specifies a tty device. -m mtu Maximum Transfer Unit. The default is 296. -p protocol The protocol to use: SLIP, CSLIP, PPP, or TERM. -t Command mode. This is usually done for testing. -v Verbose mode. #### Commands Most of these commands can be used either in interactive mode or in a script file. beep times Beep the terminal the specified number of times. bootp Retrieve local and remote IP addresses using the BOOTP protocol. break Send a BREAK. chatkey keyword code Map a modem response keyword to a numeric code. config [interface|routing] [pre|up|down|post] arguments Modify interface characteristics or the routing table, before the link comes up, when it is up, when it goes down, or after it is down. The syntax for arguments is the same as arguments for the ifconfig or route commands. databits 7|8 Set the number of data bits. dec $variable [value] Decrement $variable by value. The default is 1. default Set default route to the IP address of the host connected to. dial phonenumber [timeout] Dial phonenumber. Abort if remote modem doesn't answer within timeout seconds. Set $errlvl according to the modem response. echo on|off Enable or disable the display of modem commands. exit [n] Exit the script. Optionally return the number n as the exit status. flush Clear the input buffer. get $variable [ask|remote [timeout]] value Set $variable to value. If ask is specified, prompt the user for a value. If remote is specified, retrieve the value from the remote system. Abort after timeout seconds. goto label Jump to the section identified by label. help List available commands. if expr goto label Jump to the section identified by label if the expression evaluates to true. An expression compares a variable to a constant using one of these operators: =, !=, <, >, <=, or >=. inc $variable [value] Increment $variable by value. The default is 1. init string Set the string used to initialize the modem. The default is ATE0 Q0 V1 X1. mode protocol Set the connection protocol. Valid values are SLIP, CSLIP, PPP, and TERM. The default is SLIP. netmask mask Set the subnet mask. parity E|O|N Set the line parity to even, odd, or none. password Prompt user for password. proxyarp Install a proxy ARP entry in the local ARP table. print $variable Display the content of $variable. psend command Execute command in a shell, and send output to the serial device. Commands are executed using the user's real UID. port device Specify the serial device the modem is attached to. quit Exit with a nonzero exit status. Abort the connection. reset Reset the modem. securid Prompt user for the variable part of an ACE System SecureID password and send it together with the stored prefix to the remote system. securidf prefix Store the fixed part of an ACE System SecureID password. send string Send string to the serial device. shell command Execute command in a shell using the user's real UID. skey [timeout] Wait for an S/Key challenge, then prompt user for the secret key. Generate and send the response. Abort if challenge is not received within timeout seconds. S/Key support must be compiled into dip. sleep time Wait time seconds. speed bits-per-second Set the port speed. Default is 38400. stopbits 1|2 Set the number of stop bits. term Enable terminal mode. Pass keyboard input directly to the serial device. timeout time Set the number of seconds the line can be inactive before the link is closed. wait text [timeout] Wait timeout seconds for text to arrive from the remote system. If timeout is not specified, wait forever.
dirname | dirname pathname Print pathname excluding the last level. Useful for stripping the actual filename from a pathname. If there are no slashes (no directory levels) in pathname, dirname prints `.` to indicate the current directory. See also basename.
dmesg | dmesg [options] System administration command. Display the system control messages from the kernel ring buffer. This buffer stores all messages since the last system boot or the most recent ones, if the buffer has been filled. #### Options -c Clear buffer after printing messages. -n level Set the level of system message that will display on console.
dnsdomainname | dnsdomainname TCP/IP command. Print the system's DNS domain name. See also hostname.
domainname | domainname [name] NFS/NIS command. Set or display name of current NIS domain. With no argument, domainname displays the name of the current NIS domain. Only a privileged user can set the domain name by giving an argument; this is usually done in a startup script.
dosfsck | dosfsck [options] device fsck.ext2 [options] device System administration command. Similar to fsck, but specifically intended for MS-DOS filesystems. When checking an MS-DOS filesystem, fsck calls this command. Normally dosfsck stores all changes in memory, then writes them when checks are complete. #### Options -a Automatically repair the system; do not prompt the user. -A Use the Atari version of the MS-DOS filesystem. -d file Drop the named file from the file allocation table. Force checking, even if kernel has already marked the filesystem as valid. dosfsck will normally exit without checking if the system appears to be clean. -l file Consult file for a list of bad blocks, in addition to checking for others. -n Ensure that no changes are made to the filesystem. When queried, answer "no." -p "Preen." Repair all bad blocks noninteractively. -t Display timing statistics. -v Verbose. -y When queried, answer "yes." -B size Expect to find the superblock at size; if it's not there, exit. -F Flush buffer caches before checking. -L file Consult file for list of bad blocks instead of checking filesystem for them.
du | du [options] [directories] Print disk usage (as the number of 1KB blocks used by each named directory and its subdirectories; default is current directory). #### Options -a, --all Print usage for all files, not just subdirectories. -b, --bytes Print sizes in bytes. -c, --total In addition to normal output, print grand total of all arguments. -D, --dereference-args Follow symbolic links, but only if they are command-line arguments. -h, --human-readable Print sizes in human-reader-friendly format. -H, --si Like -h, but show as power of 1000 rather than 1024. -k, --kilobytes Print sizes in kilobytes (this is the default). -l, --count-links Count the size of all files, whether or not they have already appeared (i.e., via a hard link). -L, --dereference Follow symbolic links. --exclude=pattern Exclude files that match pattern. --max-depth=num Report sizes for directories only down to num levels below the starting point (which is level 0). -m, --megabytes Print sizes in megabytes. -s, --summarize Print only the grand total for each named directory. -S, --separate-dirs Do not include the sizes of subdirectories when totaling the size of parent directories. -x, --one-file-system Display usage of files in current filesystem only. -X, --exclude-from=file Exclude files that match any pattern in file. --help Print help message and then exit. --version Print the version and then exit.
dumpe2fs | dumpe2fs device System administration command. Print information about device's superblock and blocks group.
dumpkeys | dumpkeys [options] Print information about the keyboard driver's translation tables to standard output. Further information is available in the manual pages under keytables. #### Options -1, --separate-lines Print one line for each modifier/keycode pair and prefix plain to each unmodified keycode. -c charset, --charset=charset Specify character set with which to interpret character code values. The default character set is iso-8859-1. The full list of valid character sets is available with the --help option. --compose-only Print compose key combinations only. Requires compose key support in the kernel. -f, --full-table Output in canonical, not short, form: for each key, print a row with modifier combinations divided into columns. --funcs-only Print function key string definitions only; do not print key bindings or string definitions. -h, --help Print help message and the version. -i, --short-info Print in short-info format, including information about acceptable keycode keywords in the keytable files; the number of actions that can be bound to a key; a list of the ranges of action codes (the values to the right of a key definition); and the number of function keys that the kernel supports. --keys-only Print key bindings only; do not print string definitions. -l, --long-info Print the same information as in --short-info, plus a list of the supported action symbols and their numeric values. -n, --numeric Print action code values in hexadecimal notation; do not attempt to convert them to symbolic notation. -S num, --shape=num Print using num to determine table shape. Values of num are: 0 Default 1 Same as --full-table 2 Same as --separate-lines 3 One line for each keycode up to the first hole, then one line per modifier/keycode pair
e2fsck | e2fsck [options] device fsck.ext2 [options] device System administration command. Similar to fsck, but specifically intended for Linux Second Extended Filesystems. When checking a second extended filesystem, fsck calls this command. #### Options -b superblock Use superblock instead of default superblock. -d Debugging mode. -f Force checking, even if kernel has already marked the filesystem as valid. e2fsck will normally exit without checking if the system appears to be clean. -l file Consult file for a list of bad blocks, in addition to checking for others. -n Ensure that no changes are made to the filesystem. When queried, answer "no." -p "Preen." Repair all bad blocks noninteractively. -t Display timing statistics. -v Verbose. -y When queried, answer "yes." -B size Expect to find the superblock at size; if it's not there, exit. -F Flush buffer caches before checking. -L file Consult file for list of bad blocks instead of checking filesystem for them.
> echo | echo [-n] [string] This is the /bin/echo command. echo also exists as a command built into the C shell and bash. The following character sequences have special meanings: \a Alert (bell) \b Backspace \c Suppress trailing newline \f Form feed \n Newline \r Carriage return \t Horizontal tab \v Vertical tab \\ Literal backslash \nnn The octal character whose ASCII code is nnn. #### Options -e Enable character sequences with special meaning. (In some versions, this option is not required in order to make the sequences work.) -E Disable character sequences with special meaning. -n Suppress printing of newline after text. --help Print help message and then exit. --version Print version information and then exit. #### Examples
>     /bin/echo "testing printer" | lp
>     /bin/echo "TITLE\nTITLE" > file ; cat doc1 doc2 >> file
>     /bin/echo "Warning: ringing bell \a"
> egrep | egrep [options] [regexp] [files] Search one or more files for lines that match an extended regular expression regexp. egrep doesn't support the regular expressions \(, \), \n, \<, \>, \{, or \} but does support the other expressions, as well as the extended set +, ?, |, and ( ). Remember to enclose these characters in quotes. Regular expressions are described in Chapter 9, "Pattern Matching". Exit status is 0 if any lines match, 1 if none match, and 2 for errors. See grep for the list of available options. Also see fgrep. egrep typically runs faster than those commands. #### Examples Search for occurrences of Victor or Victoria in file:
>     egrep 'Victor(ia)*' file
>     egrep '(Victor|Victoria)' file
> Find and print strings such as old.doc1 or new.doc2 in files, and include their line numbers:
>     egrep -n '(old|new)\.doc?' files
emacs | emacs [options] [files] A text editor and all-purpose work environment. For more information, see Chapter 10, "The Emacs Editor".
env | env [option] [variable=value ... ] [command] Display the current environment or, if an environment variable is specified, set it to a new value and display the modified environment. If command is specified, execute it under the modified environment. #### Options -, -i, --ignore-environment Ignore current environment entirely. -u name, --unset name Unset the specified variable. --help Print help message and then exit. --version Print version information and then exit.
> etags | etags [options] files Create a list of function and macro names that are defined in the specified C, Pascal, FORTRAN, yacc, or flex source files. The output list (named tags by default) contains lines of the form:
>     name     file     context
> where name is the function or macro name, file is the source file in which name is defined, and context is a search pattern that shows the line of code containing name. After the list of tags is created, you can invoke Emacs on any file and type:
>     ESC-x visit-tags-table
> You will be prompted for the name of the tag table; the default is TAGS. To switch to the source file associated with the name listed in tagsfile, type:
>     ESC-x find-tag
You will be prompted for the tag you would like Emacs to search for. ctags produces an equivalent tags file for use with vi. #### Options -a, --append Append tag output to existing list of tags. -d, --defines Include tag entries for C preprocessor definitions. -i file, --include=file Add a note to the tags file that file should be consulted in addition to the normal input file. -l language, --language=language Consider the files that follow this option to be written in language. Use the -h option for a list of languages and their default filename extensions. -o file, --output=file Write to file. -r regexp, --regex=regexp Include a tag for each line that matches regexp in the files following this option. -C, --c++ Expect .c and .h files to contain C++, not C, code. -D, --no-defines Do not include tag entries for C preprocessor definitions. -H, -h, --help Print usage information. -R, --noregex Don't include tags based on regular-expression matching for the files that follow this option. -S, --ignore-indentation Normally etags uses indentation to parse the tag file; this option tells it to rely on it less. -V, --version Print the version number.
ex | ex [options] file An interactive command-based editor. For more information, see Chapter 11, "The vi Editor".
expand | expand [options] files Convert tabs in given files (or standard input, if the file is named -) to appropriate number of spaces; write results to standard output. #### Options -tabs, -t, --tabs tabs tabs is a comma-separated list of integers that specify the placement of tab stops. If exactly one integer is provided, the tab stops are set to every integer spaces. By default, tab stops are 8 spaces apart. With -t and --tabs, the list may be separated by whitespace instead of commas. -i, --initial Convert tabs only at the beginning of lines. --help Print help message and then exit. --version Print version information and then exit.
> expr | expr arg1 operator arg2 [ operator arg3 ... ] Evaluate arguments as expressions and print the result. Arguments and operators must be separated by spaces. In most cases, an argument is an integer, typed literally or represented by a shell variable. There are three types of operators: arithmetic, relational, and logical, as well as keyword expressions. Exit status for expr is 0 (expression is nonzero and nonnull), 1 (expression is 0 or null), or 2 (expression is invalid). #### Arithmetic operators Use these to produce mathematical expressions whose results are printed: + Add arg2 to arg1. - Subtract arg2 from arg1. * Multiply the arguments. / Divide arg1 by arg2. % Take the remainder when arg1 is divided by arg2. Addition and subtraction are evaluated last, unless they are grouped inside parentheses. The symbols *, (, and ) have meaning to the shell, so they must be escaped (preceded by a backslash or enclosed in single quotes). #### Relational operators Use these to compare two arguments. Arguments can also be words, in which case comparisons are defined by the locale. If the comparison statement is true, the result is 1; if false, the result is 0. Symbols > and < must be escaped. =, == Are the arguments equal? != Are the arguments different? > Is arg1 greater than arg2? >= Is arg1 greater than or equal to arg2? < Is arg1 less than arg2? <= Is arg1 less than or equal to arg2? #### Logical operators Use these to compare two arguments. Depending on the values, the result can be arg1 (or some portion of it), arg2, or 0. Symbols | and & must be escaped. | Logical OR; if arg1 has a nonzero (and nonnull) value, the result is arg1; otherwise, the result is arg2. & Logical AND; if both arg1 and arg2 have a nonzero (and nonnull) value, the result is arg1; otherwise, the result is 0. `:` Like grep; arg2 is a pattern to search for in arg1. arg2 must be a regular expression. If part of the arg2 pattern is enclosed in \( \), the result is the portion of arg1 that matches; otherwise, the result is simply the number of characters that match. By default, a pattern match always applies to the beginning of the first argument (the search string implicitly begins with a ^). Start the search string with .* to match other parts of the string. #### Keywords index string character-list Return the first position in string that matches the first possible character in character-list. Continue through character-list until a match is found, or return 0. length string Return the length of string. match string regex Same as string : regex. quote token Treat token as a string, even if it would normally be a keyword or an operator. substr string start length Return a section of string, beginning with start, with a maximum length of length characters. Return null when given a negative or nonnumeric start or length. #### Examples Division happens first; result is 10:
>     expr 5 + 10 / 2
> Addition happens first; result is 7 (truncated from 7.5):
>     expr \( 5 + 10 \) / 2
> Add 1 to variable i. This is how variables are incremented in shell scripts:
>     i=`expr $i + 1
> Print 1 (true) if variable a is the string "hello":
>     expr $a = hello
> Print 1 (true) if b plus 5 equals 10 or more:
>     expr $b + 5 \>= 10
> Find the 5th, 6th, and 7th letters of the word character:
>     expr substr character 5 3
> In the examples that follow, variable p is the string "version.100". This command prints the number of characters in p:
>     expr $p : '.*'           Result is 11
> Match all characters and print them:
>     expr $p : '\(.*\)'       Result is "version.100"
> Print the number of lowercase letters at the beginning of p:
>     expr $p : '[a-z]*'       Result is 7
> Match the lowercase letters at the beginning of p:
>     expr $p : '\([a-z]*\)'   Result is "version"
> Truncate $x if it contains five or more characters; if not, just print $x. (Logical OR uses the second argument when the first one is 0 or null; i.e., when the match fails.)
>     expr $x : '\(.....\)' \| $x
> In a shell script, rename files to their first five letters:
>     mv $x `expr $x : '\(.....\)' \| $x
(To avoid overwriting files with similar names, use mv -i.)
false | false A null command that returns an unsuccessful (nonzero) exit status. Normally used in bash scripts. See also true.
fdformat | fdformat [options] device Low-level format of a floppy disk. The device for a standard format is usually /dev/fd0 or /dev/fd1. #### Option -n Do not verify format after completion.
fdisk | fdisk [options] [device] System administration command. Maintain disk partitions via a menu. fdisk displays information about disk partitions, creates and deletes disk partitions, and changes the active partition. It is possible to assign a different operating system to each of the four partitions, though only one partition is active at any given time. You can also divide a physical partition into several logical partitions. The minimum recommended size for a Linux system partition is 40MB. Normally, device will be /dev/hda, /dev/hdb, /dev/sda, /dev/sdb, /dev/hdc, /dev/hdd, and so on. See also cfdisk. #### Options -l List partition tables and exit. -s partition Display the size of partition, unless it is a DOS partition. #### Commands a Toggle a bootable flag on current partition. d Delete current partition. l List all partition types. m Main menu. n Create a new partition; prompt for more information. p Print a list of all partitions and information about each. q Quit; do not save. t Replace the type of the current partition. u Modify the display/entry units, which must be cylinders or sectors. v Verify: check for errors; display a summary of the number of unallocated sectors. w Save changes; exit.
fetchmail | fetchmail [options] [servers...] System administration command. Retrieve mail from mail servers and forward it to the local mail delivery system. fetchmail retrieves mail from servers that support the common mail protocols POP2, POP3, IMAP2bis, and IMAP4. Messages are delivered via SMTP through port 25 on the local host and through your system's mail delivery agent (such as sendmail), where they can be read through the user's mail client. fetchmail settings are stored in the ~/.fetchmailrc file. Parameters and servers can also be set on the command line, which will override settings in the .fetchmailrc file. fetchmail is compatible with the popclient program, and users can use both without having to adjust file settings. #### Options -a, --all Retrieve all messages from server, even ones that have already been seen but left on the server. The default is to only retrieve new messages. -A type, --auth type Specify the type of authentication. type may be: password, kerberos_v5, or kerberos. Authentication type is usually established by fetchmail by default, so this option isn't very useful. -B n, --fetchlimit n Set the maximum number of messages (n) accepted from a server per query. -b n, --batchlimit n Set the maximum number of messages sent to an SMTP listener per connection. When this limit is reached, the connection will be broken and reestablished. The default of 0 means no limit. -c, --check Check for mail on a single server without retrieving or deleting messages. Works with IMAP but not well with other protocols, if at all. -D [domain], --smtpaddress [domain] Specify the domain name placed in RCPT TO lines sent to SMTP. The default is the local host. -E header, --envelope header Change the header assumed to contain the mail's envelope address (usually "X-Envelope-to:") to header. -e n, --expunge n Tell an IMAP server to EXPUNGE (i.e., purge messages marked for deletion) after n deletes. A setting of 0 indicates expunging only at the end of the session. Normally, an expunge occurs after each delete. -F, --flush For POP3 and IMAP servers, remove previously retrieved messages from the server before retrieving new ones. -f file, --fetchmailrc file Specify a nondefault name for the fetchmail configuration file. -I specification, --interface specification Require that the mail server machine is up and running at a specified IP address (or range) before polling. The specification is given as interface/ipaddress/mask. The first part indicates the type of TCP connection expected (sl0, ppp0, etc.), the second is the IP address, and the third is the bit mask for the IP, assumed to be 255.255.255.255. -K, --nokeep Delete all retrieved messages from the mail server. -k, --keep Keep copies of all retrieved messages on the mail server. -l size, --limit size Set the maximum message size that will be retrieved from a server. Messages larger than this size will be left on the server and marked unread. -M interface, --monitor interface In daemon mode, monitor the specified TCP/IP interface for any activity besides itself, and skip the poll if there is no other activity. Useful for PPP connections that automatically time out with no activity. -m command, --mda command Pass mail directly to mail delivery agent, rather than send to port 25. The command is the path and options for the mailer, such as /usr/lib/sendmail -oem. A %T in the command will be replaced with the local delivery address, and an %F will be replaced with the message's From address. -n, --norewrite Do not expand local mail IDs to full addresses. This option will disable expected addressing and should only be used to find problems. -P n, --port n Specify a port to connect to on the mail server. The default port numbers for supported protocols are usually sufficient. -p proto, --protocol proto Specify the protocol to use when polling a mail server. proto can be: POP2 Post Office Protocol 2. POP3 Post Office Protocol 3. APOP POP3 with MD5 authentication. RPOP POP3 with RPOP authentication. KPOP POP3 with Kerberos v4 authentication on port 1109. IMAP IMAP2bis, IMAP4, or IMAP4rev1. fetchmail autodetects their capabilities. IMAP-K4 IMAP4 or IMAP4rev1 with Kerberos v4 authentication. IMAP-GSS IMAP4 or IMAP4rev1 with GSSAPI authentication. ETRN ESMTP. -Q string, --qvirtual string Remove the prefix string, which is the local user's hostid, from the address in the envelope header (such as "Delivered-To:"). -r folder, --folder folder Retrieve the specified mail folder from the mail server. -s, --silent Suppress status messages during a fetch. -U, --uidl For POP3, track the age of kept messages via unique ID listing. -u name, --username name Specify the user name to use when logging into the mail server. -V, --version Print the version information for fetchmail and display the options set for each mail server. Performs no fetch. -v, --verbose Display all status messages during a fetch. -Z nnn, --antispam nnn Specify the SMTP error nnn to signal a spam block from the client. If nnn is -1, this option is disabled.
> fgrep | fgrep [options] pattern [files] Search one or more files for lines that match a literal text string pattern. Exit status is 0 if any lines match, 1 if not, and 2 for errors. See grep for the list of available options. Also see egrep. #### Examples Print lines in file that don't contain any spaces:
>     fgrep -v '' file
> Print lines in file that contain the words in spell_list:
>     fgrep -f spell_list file
> file | file [options] files Classify the named files according to the type of data they contain. file checks the magic file (usually /usr/share/magic) to identify some file types. #### Options -b Brief mode; do not prepend filenames to output lines. -c Check the format of the magic file (files argument is invalid with -c). Usually used with -m. -f file Read the names of files to be checked from file. -L Follow symbolic links. By default, symbolic links are not followed. -m file Search for file types in file instead of /usr/share/magic. -n Flush standard output after checking a file. -s Check files that are block or character special files in addition to checking ordinary files. -v Print the version. -z Attempt checking of compressed files. Many file types are understood. Output lists each filename, followed by a brief classification such as:
>     ascii text
>     c program text
>     c-shell commands
>     data
>     empty
>     iAPX 386 executable
>     directory
>     [nt]roff, tbl, or eqn input text
>     shell commands
>     symbolic link to ../usr/etc/arp
> #### Example List all files that are deemed to be troff/nroff input:
>     file * | grep roff
> find | find [pathnames] [conditions] An extremely useful command for finding particular groups of files (numerous examples follow this description). find descends the directory tree beginning at each pathname and locates files that meet the specified conditions. The default pathname is the current directory. The most useful conditions include -print (which is the default if no other expression is given), -name and -type (for general use), -exec and -size (for advanced users), and -mtime and -user (for administrators). Conditions may be grouped by enclosing them in \( \) (escaped parentheses), negated with ! (use \! in the C shell), given as alternatives by separating them with -o, or repeated (adding restrictions to the match; usually only for -name, -type, -perm). Modification refers to editing of a file's contents. Change refers to modification, permission or ownership changes, and so on; therefore, for example, -ctime is more inclusive than -atime or -mtime. #### Conditions and actions -atime +n | -n | n Find files that were last accessed more than n (+n), less than n (-n), or exactly n days ago. Note that find changes the access time of directories supplied as pathnames. -ctime +n | -n | n Find files that were changed more than n (+n), less than n (-n), or exactly n days ago. A change is anything that changes the directory entry for the file, such as a chmod. -depth Descend the directory tree, skipping directories and working on actual files first (and then the parent directories). Useful when files reside in unwritable directories (e.g., when using find with cpio). -exec command { } \; Run the Linux command, from the starting directory on each file matched by find (provided command executes successfully on that file; i.e., returns a 0 exit status). When command runs, the argument { } substitutes the current file. Follow the entire sequence with an escaped semicolon (\;). -follow Follow symbolic links and track the directories visited (don't use this with -type l). -group gname Find files belonging to group gname. gname can be a group name or a group ID number. -inum n Find files whose inode number is n. -links n Find files having n links. -mount, -xdev Search for files that reside only on the same filesystem as pathname. -mtime +n | -n | n Find files that were last modified more than n (+n), less than n (-n), or exactly n days ago. A modification is a change to a file's data. -name pattern Find files whose names match pattern. Filename metacharacters may be used but should be escaped or quoted. -newer file Find files that have been modified more recently than file; similar to -mtime. Affected by -follow only if it occurs after -follow on the command line. -ok command { }\; Same as -exec but prompts user to respond with y before command is executed. -perm nnn Find files whose permission flags (e.g., rwx) match octal number nnn exactly (e.g., 664 matches -rw-rw-r--). Use a minus sign before nnn to make a "wildcard" match of any unspecified octal digit (e.g., -perm -600 matches -rw-******, where * can be any mode). -print Print the matching files and directories, using their full pathnames. Return true. -regex pattern Like -path but uses grep-style regular expressions instead of the shell-like globbing used in -name and -path. -size n[c] Find files containing n blocks, or if c is specified, n characters long. -type c Find files whose type is c. c can be b (block special file), c (character special file), d (directory), p (fifo or named pipe), l (symbolic link), s (socket), or f (plain file). -user user Find files belonging to user (name or ID). -daystart Calculate times from the start of the day today, not 24 hours ago. -maxdepth num Do not descend more than num levels of directories. -mindepth num Begin applying tests and actions only at levels deeper than num levels. -noleaf Normally, find assumes that each directory has at least two hard links that should be ignored (a hard link for its name and one for "."; i.e., two fewer "real" directories than its hard link count indicates). -noleaf turns off this assumption, a useful practice when find runs on non-Unix-style filesystems. This forces find to examine all entries, assuming that some might prove to be directories into which it must descend (a time-waster on Unix). -amin +n | -n | n Find files last accessed more than n (+n), less than n (-n), or exactly n minutes ago. -anewer file Find files that were accessed after file was last modified. Affected by -follow when after -follow on the command line. -cmin +n | -n | n Find files last changed more than n (+n), less than n (-n), or exactly n minutes ago. -cnewer file Find files that were changed after they were last modified. Affected by -follow when after -follow on the command line. -empty Continue if file is empty. Applies to regular files and directories. -false Return false value for each file encountered. -fstype type Match files only on type filesystems. Acceptable types include minix, ext, ext2, xia, msdos, umsdos, vfat, proc, nfs, iso9660, hpfs, sysv, smb, and ncpfs. -gid num Find files with numeric group ID of num. -ilname pattern A case-insensitive version of -lname. -iname pattern A case-insensitive version of -name. -ipath pattern A case-insensitive version of -path. -iregex pattern A case-insensitive version of -regex. -lname pattern Search for files that are symbolic links, pointing to files named pattern. pattern can include shell metacharacters and does not treat / or . specially. The match is case-insensitive. -mmin +n | -n | n Find files last modified more than n (+n), less than n (-n), or exactly n minutes ago. -nouser The file's user ID does not correspond to any user. -nogroup The file's group ID does not correspond to any group. -path pattern Find files whose names match pattern. Expect full pathnames relative to the starting pathname (i.e., do not treat / or . specially). #### Examples List all files (and subdirectories) in your home directory:
>     find $HOME -print
> List all files named chapter1 in the /work directory:
>     find /work -name chapter1 -print
> List all files beginning with memo owned by ann:
>     find /work -name 'memo*' -user ann -print
> Search the filesystem (begin at root) for manpage directories:
>     find / -type d -name 'man*' -print
> Search the current directory, look for filenames that don't begin with a capital letter, and send them to the printer:
>     find . \! -name '[A-Z]*' -exec lpr {}\;
> Find and compress files whose names don't end with .gz:
>     gzip `find . \! -name '*.gz' -print
> Remove all empty files on the system (prompting first):
>     find / -size 0 -ok rm {} \;
> Search the system for files that were modified within the last two days (good candidates for backing up):
>     find / -mtime -2 -print
> Recursively grep for a pattern down a directory tree:
>     find /book -print | xargs grep '[Nn]utshell'
> If the files kt1 and kt2 exist in the current directory, their names can be printed with the command:
>     $ find . -name 'kt[0-9]'
>     ./kt1
>     ./kt2
> Since the command prints these names with an initial ./ path, you need to specify the ./ when using the -path option:
>     $ find . -path './kt[0-9]'
>     ./kt1
>     ./kt2
> The -regex option uses a complete pathname, like -path, but treats the following argument as a regular expression rather than a glob pattern (although in this case the result is the same):
>     $ find . -regex './kt[0-9]'
>     ./kt1
>     ./kt2
finger | finger [options] users Display data about one or more users, including information listed in the files .plan and .project in each user's home directory. You can specify each user either as a login name (exact match) or as a first or last name (display information on all matching names). Networked environments recognize arguments of the form user@host and @host. #### Options -l Force long format (default): everything included by the -s option and home directory, home phone, login shell, mail status, .plan, .project, and .forward. -m Suppress matching of users' "real" names. -p Omit .plan and .project files from display. -s Show short format: login name, real name, terminal name, write status, idle time, office location, and office phone number.
fingerd | in.fingerd [option] TCP/IP command. Remote user information server. fingerd provides a network interface to the finger program. It listens for TCP connections on the finger port and, for each connection, reads a single input line, passes the line to finger, and copies the output of finger to the user on the client machine. fingerd is started by inetd and must have an entry in inetd's configuration file, /etc/inetd.conf. #### Option -w Include additional information, such as uptime and the name of the operating system.
flex | flex [options] [file] flex (Fast Lexical Analyzer Generator) is a faster variant of lex. It generates a lexical analysis program (named lex.yy.c) based on the regular expressions and C statements contained in one or more input files. See also bison, yacc, and the O'Reilly book lex & yacc by John Levine, Tony Mason, and Doug Brown. #### Options -b Generate backup information to lex.backup. -d Debug mode. -f Use faster compilation (limited to small programs). -h Help summary. -i Scan case-insensitively. -l Maximum lex compatibility. -o file Write output to file instead of lex.yy.c. -p Print performance report. -s Exit if the scanner encounters input that does not match any of its rules. -t Print to standard out. (By default, flex prints to lex.yy.c.) -v Print a summary of statistics. -w Suppress warning messages. -B Generate batch (noninteractive) scanner. -F Use the fast scanner table representation. -I Generate an interactive scanner (default). -L Suppress #line directives in lex.yy.c. -P prefix Change default yy prefix to prefix for all globally visible variable and function names. -V Print version number. -7 Generate a 7-bit scanner. -8 Generate an 8-bit scanner (default). -+ Generate a C++ scanner class. -C Compress scanner tables but do not use equivalence classes. -Ca Align tables for memory access and computation. This creates larger tables but gives faster performance. -Ce Construct equivalence classes. This creates smaller tables and sacrifices little performance (default). -Cf Generate full scanner tables, not compressed. -CF Generate faster scanner tables, like -F. -Cm Construct metaequivalence classes (default). -Cr Bypass use of the standard I/O library. Instead use read() system calls.
fmt | fmt [options] [files] Convert text to specified width by filling lines and removing newlines. Concatenate files on the command line, or read text from standard input if - (or no file) is specified. By default, preserve blank lines, spacing, and indentation. fmt attempts to break lines at the end of sentences and to avoid breaking lines after a sentence's first word or before its last. #### Options -c, --crown-margin Crown margin mode. Do not change each paragraph's first two lines' indentation. Use the second line's indentation as the default for subsequent lines. -p prefix, --prefix=prefix Format only lines beginning with prefix. -s, --split-only Suppress line-joining. -t, --tagged-paragraph Tagged paragraph mode. Same as crown mode when the indentation of the first and second lines differs. If the indentation is the same, treat the first line as its own separate paragraph. -u, --uniform-spacing Print exactly one space between words and two between sentences. -w width, --width=width Set output width to width. The default is 75. --help Print help message and then exit. --version Print version information and then exit.
fold | fold [option] [files] Break the lines of the named files so that they are no wider than the specified width (default is 80). fold breaks lines exactly at the specified width, even in the middle of a word. Reads from standard input when given - as a file. #### Options -b, --bytes Count bytes, not columns (i.e., consider tabs, backspaces, and carriage returns to be one column). -s, --spaces Break at spaces only, if possible. -w, --width width Set the maximum line width to width. Default is 80.
formail | formail [options] Filter standard input into mailbox format. If no sender is apparent, provide the sender foo@bar. By default, escape bogus From lines with >. #### Options +skip Do not split first skip messages. -total Stop after splitting total messages. -a headerfield Append headerfield to header, unless it already exists. If headerfield is Message-ID or Resent-Message-ID with no contents, generate a unique message ID. -b Do not escape bogus From lines. -c When header fields are more than one line long, concatenate the lines. -d Do not assume that input must be in strict mailbox format. -e Allow messages to begin one immediately after the other; do not require empty space between them. -f Do not edit non-mailbox-format lines. By default, formail prepends From to such lines. -i headerfield Append headerfield whether or not it already exists. Rename each existing headerfield to Old-headerfield, unless they are empty. -k For use only with -r. Keep the body as well as the fields specified by -r. -m minfields Require at least minfields before recognizing the beginning of a new message. Default is 2. -n Allow simultaneous formail processes to run. -p prefix Escape lines with prefix instead of >. -q Do not display write errors, duplicate messages, and mismatched Content-Length fields. This is the default; use -q- to turn it off. -r Throw away all existing fields, retaining only X-Loop, and generate autoreply header instead. You can preserve particular fields with the -i option. -s Must be the last option; everything following it will be assumed to be its arguments. Divide input to separate mail messages, and pipe them to the program specified or concatenate them to standard output (by default). -t Assume sender's return address to be valid. (By default, formail favors machine-generated addresses.) -u headerfield Delete all but the first occurrence of headerfield. -x headerfield Display the contents of headerfield on a single line. -z When necessary, add a space between field names and contents. Remove ("zap") empty fields. -A headerfield Append headerfield whether or not it already exists. -B Assume that input is in BABYL rmail format. -D maxlen idcache Remember old message IDs (in idcache, which will grow no larger than approximately maxlen). When splitting, refuse to output duplicate messages. Otherwise, return true on discovering a duplicate. With -r, look at the sender's mail address instead of the message ID. -I headerfield Append headerfield whether or not it already exists. Remove existing fields. -R oldfield newfield Change all fields named oldfield to newfield. -U headerfield Delete all but the last occurrence of headerfield. -Y Format in traditional Berkeley style (i.e., ignore Content-Length fields). -X headerfield Display the field name and contents of headerfield on a single line.
free | free [options] Display statistics about memory usage: total free, used, physical, swap, shared, and buffers used by the kernel. #### Options -b Calculate memory in bytes. -k Default. Calculate memory in kilobytes. -m Calculate memory in megabytes. -o Do not display "buffer adjusted" line. The -o switch disables the display "-/+ buffers" line. -s time Check memory usage every time seconds. -t Display all totals on one line at the bottom of output. -V Display version information.
fsck | fsck [options] [filesystem] ... System administration command. Call the filesystem checker for the appropriate system type, to check and repair filesystems. If a filesystem is consistent, the number of files, number of blocks used, and number of blocks free are reported. If a filesystem is inconsistent, fsck prompts before each correction is attempted. fsck's exit code can be interpreted as the sum of all of those conditions that apply: 1 Errors were found and corrected. 2 Reboot suggested. 4 Errors were found but not corrected. 8 fsck encountered an operational error. 16 fsck was called incorrectly. 128 A shared library error was detected. #### Options -- Pass all subsequent options to filesystem-specific checker. All options that fsck doesn't recognize will also be passed. -r Interactive mode; prompt before making any repairs. -s Serial mode. -t fstype Specify the filesystem type. Do not check filesystems of any other type. -A Check all filesystems listed in /etc/fstab. -N Suppress normal execution; just display what would be done. -R Meaningful only with -A: check all filesystems listed in /etc/fstab except the root filesystem. -T Suppress printing of title. -V Verbose mode.
fsck.minix | fsck.minix [options] device System administration command. Similar to fsck, but specifically intended for Linux MINIX filesystems. #### Options -a Automatic mode; repair without prompting. -f Force checking, even if kernel has already marked the filesystem. fsck.minix will normally exit without checking if the system appears to be clean. -l List filesystems. -m Enable MINIX-like "mode not cleared" warnings. -r Interactive mode; prompt before making any repairs. -s Display information about superblocks. -v Verbose mode.
ftp | ftp [options] [hostname] Transfer files to and from remote network site hostname. ftp prompts the user for a command. The commands are listed after the options. Some of the commands are toggles, meaning they turn on a feature when it is off and vice versa. #### Options -d Enable debugging. -g Disable filename globbing. -i Turn off interactive prompting. -n No autologin upon initial connection. -v Verbose. Show all responses from remote server. #### Commands ![command [args]] Invoke an interactive shell on the local machine. If arguments are given, the first is taken as a command to execute directly, with the rest of the arguments as that command's arguments. $ macro-name [args] Execute the macro macro-name that was defined with the macdef command. Arguments are passed to the macro unglobbed. account [passwd] Supply a supplemental password that will be required by a remote system for access to resources once a login has been successfully completed. If no argument is given, the user will be prompted for an account password in a nonechoing mode. append local-file [remote-file] Append a local file to a file on the remote machine. If remote-file is not given, the local filename is used after being altered by any ntrans or nmap setting. File transfer uses the current settings for type, format, mode, and structure. ascii Set the file transfer type to network ASCII (default). bell Sound a bell after each file transfer command is completed. binary Set file transfer type to support binary image transfer. bye Terminate FTP session and then exit ftp. case Toggle remote computer filename case mapping during mget. The default is off. When case is on, files on the remote machine with all-uppercase names will be copied to the local machine with all-lowercase names. cd remote-directory Change working directory on remote machine to remote-directory. cdup Change working directory of remote machine to its parent directory. chmod [mode] [remote-file] Change file permissions of remote-file. If options are omitted, the command prompts for them. close Terminate FTP session and return to command interpreter. cr Toggle carriage return stripping during ASCII-type file retrieval. delete remote-file Delete file remote-file on remote machine. debug [debug-value] Toggle debugging mode. If debug-value is specified, it is used to set the debugging level. dir [remote-directory] [local-file] Print a listing of the contents in the directory remote-directory, and, optionally, place the output in local-file. If no directory is specified, the current working directory on the remote machine is used. If no local file is specified or - is given instead of the filename, output comes to the terminal. disconnect Synonym for close. form format Set the file transfer form to format. Default format is file. get remote-file [local-file] Retrieve the remote-file and store it on the local machine. If the local filename is not specified, it is given the same name it has on the remote machine, subject to alteration by the current case, ntrans, and nmap settings. If local file is -, output comes to the terminal. glob Toggle filename expansion for mdelete, mget, and mput. If globbing is turned off, the filename arguments are taken literally and not expanded. hash Toggle hash-sign (#) printing for each data block transferred. help [command] Print help information for command. With no argument, ftp prints a list of commands. idle [seconds] Get/set idle timer on remote machine. seconds specifies the length of the idle timer; if omitted, the current idle timer is displayed. image Same as binary. lcd [directory] Change working directory on local machine. If directory is not specified, the user's home directory is used. ls [remote-directory] [local-file] Print listing of contents of directory on remote machine, in a format chosen by the remote machine. If remote-directory is not specified, current working directory is used. macdef macro-name Define a macro. Subsequent lines are stored as the macro macro-name; a null line terminates macro input mode. When $i is included in the macro, loop through arguments, substituting the current argument for $i on each pass. Escape $ with \. mdelete remote-files Delete the remote-files on the remote machine. mdir remote-files local-file Like dir, except multiple remote files may be specified. mget remote-files Expand the wildcard expression remote-files on the remote machine and do a get for each filename thus produced. mkdir directory-name Make a directory on the remote machine. mls remote-files local-file Like nlist, except multiple remote files may be specified, and the local file must be specified. mode [mode-name] Set file transfer mode to mode-name. Default mode is stream mode. modtime [file-name] Show last modification time of the file on the remote machine. mput [local-files] Expand wildcards in local-files given as arguments and do a put for each file in the resulting list. newer remote-file [local-file] Get file if remote file is newer than local file. nlist [remote-directory] [local-file] Print list of files of a directory on the remote machine to local-file (or the screen if local-file is not specified). If remote-directory is unspecified, the current working directory is used. nmap [inpattern outpattern] Set or unset the filename mapping mechanism. The mapping follows the pattern set by inpattern, a template for incoming filenames, and outpattern, which determines the resulting mapped filename. The sequences $1 through $9 are treated as variables, for example, the inpattern $1.$2, along with the input file readme.txt, would set $1 to readme and $2 to txt. An outpattern of $1.data would result in an output file of readme.data. $0 corresponds to the complete filename. [string1, string2] is replaced by string1, unless that string is null, in which case it's replaced by string2. ntrans [inchars [outchars ]] Set or unset the filename character translation mechanism. Characters in a filename matching a character in inchars are replaced with the corresponding character in outchars. If no arguments are specified, the filename mapping mechanism is unset. If arguments are specified: Characters in remote filenames are translated during mput and put commands issued without a specified remote target filename. Characters in local filenames are translated during mget and get commands issued without a specified local target filename. open host [port] Establish a connection to the specified host FTP server. An optional port number may be supplied, in which case ftp will attempt to contact an FTP server at that port. prompt Toggle interactive prompting. proxy ftp-command Execute an FTP command on a secondary control connection (i.e., send commands to two separate remote hosts simultaneously). put local-file [remote-file] Store a local file on the remote machine. If remote-file is left unspecified, the local filename is used after processing according to any ntrans or nmap settings in naming the remote file. File transfer uses the current settings for type, file, structure, and transfer mode. pwd Print name of the current working directory on the remote machine. quit Synonym for bye. quote arg1 arg2... Send the arguments specified, verbatim, to the remote FTP server. recv remote-file [local-file] Synonym for get. reget remote-file [local-file] Retrieve a file (like get), but restart at the end of local-file. Useful for restarting a dropped transfer. remotehelp [command-name] Request help from the remote FTP server. If command-name is specified, remote help for that command is returned. remotestatus [filename] Show status of the remote machine, or, if filename is specified, filename on remote machine. rename [from] [to] Rename file from on remote machine to to. reset Clear reply queue. restart marker Restart the transfer of a file from a particular byte count. rmdir [directory-name] Delete a directory on the remote machine. runique Toggle storing of files on the local system with unique filenames. When this option is on, rename files as .1 or .2, and soon, as appropriate, to preserve unique filenames, and report each such action. Default value is off. send local-file [remote-file] Synonym for put. sendport Toggle the use of PORT commands. site [command] Get/set site-specific information from/on remote machine. size filename Return size of filename on remote machine. status Show current status of ftp. struct [struct-name] Set the file transfer structure to struct-name. By default, stream structure is used. sunique Toggle storing of files on remote machine under unique filenames. system Show type of operating system running on remote machine. tenex Set file transfer type to that needed to talk to TENEX machines. trace Toggle packet tracing. type [type-name] Set file transfer type to type-name. If no type is specified, the current type is printed. The default type is network ASCII. umask [mask] Set user file-creation mode mask on the remote site. If mask is omitted, the current value of the mask is printed. user username [password] [account] Identify yourself to the remote FTP server. ftp will prompt the user for the password, if not specified and the server requires it, and the account field. verbose Toggle verbose mode. ? [command] Same as help.
ftpd | in.ftpd [options] TCP/IP command. Internet File Transfer Protocol server. The server uses the TCP protocol and listens at the port specified in the ftp service specification. ftpd is started by inetd and must have an entry in inetd's configuration file, /etc/inetd.conf. #### Options -d Write debugging information to the syslog. -l Log each FTP session in the syslog. -T maxtimeout Set maximum timeout period in seconds. Default limit is 15 minutes. -t timeout Set timeout period to timeout seconds.
fuser | fuser [options] [files | filesystems] Identify processes that are using a file or filesystem. fuser outputs the process IDs of the processes that are using the files or local filesystems. Each process ID is followed by a letter code: c if process is using file as current directory, e if executable, f if an open file, m if a shared library, and r if the root directory. Any user with permission to read /dev/kmem and /dev/mem can use fuser, but only a privileged user can terminate another user's process. fuser does not work on remote (NFS) files. If more than one group of files is specified, the options may be respecified for each additional group of files. A lone dash (-) cancels the options currently in force, and the new set of options applies to the next group of files. #### Options - Return all options to defaults. -signal Send signal instead of SIGKILL. -a Display information on all specified files, even if they are not being accessed by any processes. -i Request user confirmation to kill a process. Ignored if -k is not also specified. -k Send SIGKILL signal to each process. -l List signal names. -m Expect files to exist on a mounted filesystem; include all files accessing that filesystem. -s Silent. -u User login name, in parentheses, also follows process ID. -v Verbose. -V Display version information.
g++ | g++ [options] files Invoke gcc with the options necessary to make it recognize C++. g++ recognizes all the file extensions gcc does, in addition to C++ source files (.C, .cc, or .cxx files) and C++ preprocessed files (.ii files). See also gcc.
gated | gated [options] TCP/IP command. Gateway routing daemon. gated handles multiple routing protocols and replaces routed and any routing daemons that speak the Hello, EGP, or BGP routing protocols. gated currently handles the RIP, BGP, EGP, Hello, and OSPF routing protocols and can be configured to perform all or any combination of the five. #### Options -c Parse configuration file for syntax errors, then exit gated, leaving a dump file in /usr/tmp/gated_dump. -f config_file Use alternate configuration file, config_file. Default is /etc/gated.conf. -n Do not modify kernel's routing table. -t [trace_options] Start gated with the specified tracing options enabled. If no flags are specified, assume general. The trace flags are: adv Management of policy blocks. all Includes normal, policy, route, state, task, and timer. general Includes normal and route. iflist The kernel interface list. normal Normal protocols instances. parse Lexical analyzer and parser. policy Instances in which policy is applied to imported and exported routes. route Any changes to routing table. state State machine transitions. symbols Symbols read from kernel -- note that they are read before the configuration file is parsed, so this option must be specified on the command line. task System tasks and interfaces. timer Timer usage. -C Parse configuration file for errors and set exit code to indicate if there were any (1) or not (0), then exit. -N Do not daemonize.
gawk | gawk [options] `script' [var=value...] [files] gawk [options] -f scriptfile [var=value...] [files] The GNU version of awk, a program that does pattern matching, record processing, and other forms of text manipulation. For more information, see Chapter 13, "The gawk Scripting Language".
gcc | gcc [options] files Compile one or more C source files (file.c), assembler source files (file.s), or preprocessed C source files (file.i). If the file suffix is not recognizable, assume that the file is an object file or library. gcc automatically invokes the link editor ld (unless -c, -S, or -E is supplied). In some cases, gcc generates an object file having a .o suffix and a corresponding root name. By default, output is placed in a.out. gcc accepts many system-specific options not covered here. Note: gcc is the GNU form of cc; on most Linux systems, the command cc will invoke gcc. The command g++ will invoke gcc with the appropriate options for interpreting C++. #### Options -a Provide profile information for basic blocks. -ansi Enforce full ANSI conformance. -b machine Compile for use on machine type. -c Create linkable object file for each source file, but do not call linker. -dD Print #defines. -dM Suppress normal output. Print series of #defines that are in effect at the end of preprocessing. -dN Print #defines with macro names only, not arguments or values. -fno-asm Do not recognize asm, inline, or typeof as keywords. Implied by -ansi. -fno-builtin Do not recognize built-in functions unless they begin with two underscores. -fno-gnu-keywords Do not recognize classof, headof, signature, sigof, or typeof as keywords. -fno-ident Do not respond to #ident commands. -fsigned-bitfields -funsigned-bitfields -fno-signed-bitfields -fno-unsigned-bitfields Set default control of bitfields to signed or unsigned if not explicitly declared. -fsigned-char Cause the type char to be signed. -fsyntax-only Check for syntax errors. Do not attempt to actually compile. -funsigned-char Cause the type char to be unsigned. -g Include debugging information for use with gdb. -g level Provide level amount of debugging information. level must be 1, 2, or 3, with 1 providing the least amount of information. The default is 2. -idirafter dir Include dir in the list of directories to search when an include file is not found in the normal include path. -include file Process file before proceeding to the normal input file. -imacros file Process the macros in file before proceeding to the normal input file. -iprefix prefix When adding directories with -iwithprefix, prepend prefix to the directory's name. -isystem dir Add dir to the list of directories to be searched when a system file cannot be found in the main include path. -iwithprefix dir Append dir to the list of directories to be searched when a header file cannot be found in the main include path. If -iprefix has been set, prepend that prefix to the directory's name. -l lib Link to lib. -nostartfiles Force linker to ignore standard system startup files. -nostdinc Search only specified, not standard, directories for header files. -nostdinc++ Suppress searching of directories believed to contain C++-specific header files. -nostdlib Suppress linking to standard library files. -o file Specify output file as file. Default is a.out. -p Provide profile information for use with prof. -pedantic Warn verbosely. -pedantic-errors Err in every case in which -pedantic would have produced a warning. -pg Provide profile information for use with gprof. -pipe Transfer information between stages of compiler by pipes instead of temporary files. -s Remove all symbol table and relocation information from the executable. -save-temps Save temporary files in the current directory when compiling. -static Suppress linking to shared libraries. -traditional Attempt to behave like a traditional C compiler. -traditional-cpp Cause the preprocessor to attempt to behave like a traditional C preprocessor. -trigraphs Include trigraph support. -u symbol Force the linker to search libraries for a definition of symbol and to link to them, if found. -undef Define only those constants required by the language standard, not system-specific constants like unix. -v Verbose mode. Display commands as they are executed, gcc version number, and preprocessor version number. -w Suppress warnings. -x language Expect input file to be written in language, which may be c, objective-c, c-header, c++, cpp-output, assembler, or assembler-with-cpp. If none is specified as language, guess the language by filename extension. -A question(answer) If the preprocessor encounters a conditional such as #if question, assert answer in response. To turn off standard assertions, use -A-. -B path Specify the path directory in which the compiler files are located. -C Retain comments during preprocessing. Meaningful only with -E. -D name[=def] Define name with value def as if by a #define. If no =def is given, name is defined with value 1. -D has lower precedence than -U. -E Preprocess the source files, but do not compile. Print result to standard output. -I dir Include dir in list of directories to search for include files. If dir is -, search those directories that were specified by -I before the -I- only when #include "file" is specified, not #include <file>. -L dir Search dir in addition to standard directories. -M Instead of compiling, print a rule suitable for inclusion in a makefile that describes dependencies of the source file based on its #include directives. Implies -E. -MD Similar to -M, but sends dependency information to files ending in .d in addition to ordinary compilation. -MG Used with -M or -MM. Suppress error messages if an included file does not exist; useful if the included file is automatically generated by a build. -MMD Similar to -MD, but record only user header file information, not system header file information. -MM Similar to -M, but limit the rule to non-standard #include files; that is, only files declared through #include "file" and not those declared through #include <file>. -H Print pathnames of included files, one per line, on standard error. -O[level] Optimize. level should be 1, 2, 3, or 0. The default is 1. 0 turns off optimization; 3 optimizes the most. -P Preprocess input without producing line-control information used by next pass of C compiler. Meaningful only with -E. -S Compile source files into assembler code, but do not assemble. -U name Remove any initial definition of name, where name is a reserved symbol predefined by the preprocessor or a name defined on a -D option. Names predefined by cpp are unix and i386. -V version Attempt to run gcc version version. -W Warn more verbosely than normal. -Wl,option Invoke linker with option, which may be a comma-separated list. -Wa,option Call assembler with option, which may be a comma-separated list. -Waggregate-return Warn if any functions return structures or unions are defined or called. -Wall Enable -W, -Wchar-subscripts, -Wcomment, -Wformat, -Wimplicit, -Wparentheses, -Wreturn-type, -Wswitch, -Wtemplate-debugging, -Wtrigraphs, -Wuninitialized, and -Wunused. -Wcast-align Warn when encountering instances in which pointers are cast to types that increase the required alignment of the target from its original definition. -Wcast-qual Warn when encountering instances in which pointers are cast to types that lack the type qualifier with which the pointer was originally defined. -Wchar-subscripts Warn when encountering arrays with subscripts of type char. -Wcomment Warn when encountering the beginning of a nested comment. -Wconversion Warn in particular cases of type conversions. -Werror Exit at the first error. -Wformat Warn about inappropriately formatted printfs and scanfs. -Wimplicit Warn when encountering implicit function or parameter declarations. -Winline Warn about illegal inline functions. -Wmissing-declarations Warn if a global function is defined without a previous declaration. -Wmissing-prototypes Warn when encountering global function definitions without previous prototype declarations. -Wnested-externs Warn if an extern declaration is encountered within a function. -Wno-import Don't warn about use of #import. -Wp,options Pass options to the preprocessor. Multiple options are separated by commas. Not a warning parameter. -Wparentheses Enable more verbose warnings about omitted parentheses. -Wpointer-arith Warn when encountering code that attempts to determine the size of a function or void. -Wredundant-decls Warn if anything is declared more than once in the same scope. -Wreturn-type Warn about functions defined without return types or with improper return types. -Wshadow Warn when a local variable shadows another local variable. -Wstrict-prototypes Insist that argument types be specified in function declarations and definitions. -Wswitch Warn about switches that skip the index for one of their enumerated types. -Wtemplate-debugging Warn if debugging is not available for C++ templates. -Wtraditional Warn when encountering code that produces different results in ANSI C and traditional C. -Wtrigraphs Warn when encountering trigraphs. -Wuninitialized Warn when encountering uninitialized automatic variables. -Wunused Warn about unused variables and functions. -Xlinker option Pass an option to the linker. A linker option with an argument requires two -Xs, the first specifying the option and the second specifying the argument. #### Pragma directives #pragma interface [header-file] Used in header files to force object files to provide definition information via references, instead of including it locally in each file. C++-specific. #pragma implementation [header-file] Used in main input files to force generation of full output from header-file (or, if it is not specified, from the header file with the same base name as the file containing the pragma directive). This information will be globally visible. Normally the specified header file contains a #pragma interface directive.
gdb | gdb [options] [program [core|pid]] GDB (GNU DeBugger) allows you to step through C, C++, and Modula-2 programs in order to find the point at which they break. The program to be debugged is normally specified on the command line; you can also specify a core or, if you want to investigate a running program, a process ID. #### Options -s file, -symbols=file Consult file for symbol table. With -e, also uses file as the executable. -e file, -exec=file Use file as executable, to be read in conjunction with source code. May be used in conjunction with -s to read symbol table from the executable. -c file, -core=file Consult file for information provided by a core dump. -x file, -command=file Read gdb commands from file. -d directory, -directory=directory Include directory in path that is searched for source files. -n, -nx Ignore .gdbinit file. -q, -quiet Suppress introductory and copyright messages. -batch Exit after executing all the commands specified in .gdbinit and -x files. Print no startup messages. -cd=directory Use directory as gdb's working directory. -f, -fullname Show full filename and line number for each stack frame. -b bps Set line speed of serial device used by GDB to bps. -tty=device Set standard in and standard out to device. #### Common commands These are just some of the more common gdb commands; there are too many commands to list all of them here: bt Print the current location within the program and a stack trace showing how the current location was reached. (where does the same thing.) break Set a breakpoint in the program. cd Change the current working directory. clear Delete the breakpoint where you just stopped. commands List commands to be executed when breakpoint is hit. c Continue execution from a breakpoint. delete Delete a breakpoint or a watchpoint; also used in conjunction with other commands. display Cause variables or expressions to be displayed when program stops. down Move down one stack frame to make another function the current one. frame Select a frame for the next continue command. info Show a variety of information about the program. For instance, info breakpoints shows all outstanding breakpoints and watchpoints. jump Start execution at another point in the source file. kill Abort the process running under gdb's control. list List the contents of the source file corresponding to the program being executed. next Execute the next source line, executing a function in its entirety. print Print the value of a variable or expression. pwd Show the current working directory. ptype Show the contents of a datatype, such as a structure or C++ class. quit Exit gdb. reverse-search Search backward for a regular expression in the source file. run Execute the program. search Search for a regular expression in the source file. set variable Assign a value to a variable. signal Send a signal to the running process. step Execute the next source line, stepping into a function if necessary. undisplay Reverse the effect of the display command; keep expressions from being displayed. until Finish the current loop. up Move up one stack frame to make another function the current one. watch Set a watchpoint (i.e., a data breakpoint) in the program. whatis Print the type of a variable or function.
gdc | gdc [options] command TCP/IP command. Administer gated. Various commands start and stop the daemon, send signals to it, maintain the configuration files, and manage state and core dumps. #### Options -c size Specify maximum core dump size. -f size Specify maximum file dump size. -m size Specify maximum data segment size. -n Suppress editing of the kernel forwarding table. -q Quiet mode: suppress warnings and log errors to syslogd instead of standard error. -s size Specify maximum stack size. -t seconds Wait seconds seconds (default is 10) for gated to complete specified operations at start and stop time. #### Commands BACKOUT Restore /etc/gated.conf from /etc/gated.conf-, whether or not the latter exists. backout Restore /etc/gated.conf from /etc/gated.conf-, assuming the latter exists. checkconf Report any syntax errors in /etc/gated.conf. checknew Report any syntax errors in /etc/gated.conf+. COREDUMP Force gated to core dump and exit. createconf Create an empty /etc/gated.conf+ if one does not already exist, and set it to mode 664, owner root, group gdmaint. dump Force gated to dump to /usr/tmp/gated_dump and then continue normal operation. interface Reload interface configuration. KILL Terminate immediately (ungracefully). modeconf Set all configuration files to mode 664, owner root, group gdmaint. newconf Make sure that /etc/gated.conf+ exists and move it to /etc/gated.conf. Save the old /etc/gated.conf as /etc/gated.conf-. reconfig Reload configuration file. restart Stop and restart gated. rmcore Remove any gated core files. rmdmp Remove any gated state dump files. rmparse Remove any gated files that report on parse errors. These are generated by the checkconf and checknew commands. running Exit with zero status if gated is running and nonzero if it is not. start Start gated, unless it is already running, in which case return an error. stop Stop gated as gracefully as possible. term Terminate gracefully. toggletrace Toggle tracing. #### Files /etc/gcd.conf+ The test configuration file. Once you're satisfied that it works, you should run gated newconf to install it as /etc/gated.conf. /etc/gated.conf- A backup of the old configuration file. /etc/gated.conf-- A backup of the backup of the old configuration file. /etc/gated.conf The actual configuration file. /etc/gated.pid gated's process ID. /usr/tmp/gated_dump The state dump file. /usr/tmp/gated_parse A list of the parse errors generated by reading the configuration file.
getkeycodes | getkeycodes Print the kernel's scancode-to-keycode mapping table.
getty | getty [options] port [speed [term [lined]]] System administration command. Set terminal type, modes, speed, and line discipline. Linux systems may use agetty instead, which uses a different syntax. getty is invoked by init. It is the second process in the series init-getty-login-shell, which ultimately connects a user with the Linux system. getty reads the user's login name and invokes the login command with the user's name as an argument. While reading the name, getty attempts to adapt the system to the speed and type of device being used. You must specify a port argument, which getty will use to attach itself to the device /dev/port. getty will then scan the defaults file, usually /etc/default/getty, for runtime values and parameters. These may also be specified, for the most part, on the command line, but the values in the defaults file take precedence. The speed argument is used to point to an entry in the file /etc/gettydefs, which contains the initial baud rate, tty settings, and login prompt and final speed and settings for the connection. The first entry is the default in /etc/gettydefs. term specifies the type of terminal, with lined the optional line discipline to use. #### Options -c file Check the gettydefs file. file is the name of the gettydefs file. Produces the files' values and reports parsing errors to standard output. -d file Use a different default file. -h Do not force a hangup on the port when initializing. -r delay Wait for single character from port, then wait delay seconds before proceeding. -t timeout If no username is accepted within timeout seconds, close connection. -w string Wait for string characters from port before proceeding.
gprof | gprof [options] [object_file] Display the profile data for an object file. The file's symbol table is compared with the call graph profile file gmon.out (previously created by compiling with gcc -pg). #### Options -a Do not display statically declared functions. Since their information might still be relevant, append it to the information about the functions loaded immediately before. -b Do not display information about each field in the profile. -c Consult the object file's text area to attempt to determine the program's static call graph. Display static-only parents and children with call counts of 0. -e routine Do not display entries for routine and its descendants. -f routine Print only routine, but include time spent in all routines. -k from to Remove arcs between the routines from and to. -s Summarize profile information in the file gmon.sum. -v Print version and exit. -z Include zero-usage calls. -E routine Do not display entries for routine and its descendants or include time spent on them in calculations for total time. -F routine Print only information about routine. Do not include time spent in other routines.
> grep | grep [options] pattern [files] Search one or more files for lines that match a regular expression pattern. Regular expressions are described in Chapter 9, "Pattern Matching". Exit status is 0 if any lines match, 1 if none match, and 2 for errors. See also egrep and fgrep. #### Options -a, --text Don't suppress output lines with binary data; treat as text. -b, --byte-offset Print the byte offset within the input file before each line of output. -b, --byte-offset Print the byte offset within the input file before each line of output. -c, --count Print only a count of matched lines. With -v or --revert-match option, count nonmatching lines. -d action, --directories=action Define an action for processing directories. Possible actions are: read Read directories like ordinary files (default). skip Skip directories. recurse Recursively read all files under each directory. Same as -r. -e pattern, --regexp=pattern Search for pattern. Same as specifying a pattern as an argument, but useful in protecting patterns beginning with -. -f file, --file=file Take a list of patterns from file, one per line. -h, --no-filename Print matched lines but not filenames (inverse of -l). -i, --ignore-case Ignore uppercase and lowercase distinctions. -l, --files-with-matches List the names of files with matches but not individual matched lines; scanning per file stops on the first match. -n, --line-number Print lines and their line numbers. -q, --quiet, --silent Suppress normal output in favor of quiet mode; the scanning stops on the first match. -r, --recursive Recursively read all files under each directory. Same as -d recurse. -s, --no-messages Suppress error messages about nonexistent or unreadable files. -v, --revert-match Print all lines that don't match pattern. -w, --word-regexp Match on whole words only. Words are divided by characters that are not letters, digits, or underscores. -x, --line-regexp Print lines only if pattern matches the entire line. -A num, --after-context=num Print num lines of text that occur after the matching line. -B num, --before-context=num Print num lines of text that occur before the matching line. -C[num], --context=[num], -num Print num lines of leading and trailing context. Default context is 2 lines. -L, --files-without-match List files that contain no matching lines. -V, --version Print the version number and then exit. #### Examples List the number of users who use tcsh:
>     grep -c /bin/tcsh /etc/passwd
> List header files that have at least one #include directive:
>     grep -l '^#include' /usr/include/*
> List files that don't contain pattern:
>     grep -c pattern files | grep :0
groff | groff [options] [files] troff [options] [files] Frontend to the groff document-formatting system, which normally runs troff along with a postprocessor appropriate for the selected output device. Options without arguments can be grouped after a single dash (-). A filename of - denotes standard input. #### Options -a Generate an ASCII approximation of the typeset output. -b Print a backtrace. -C Enable compatibility mode. -d cs, -d name=s Define the character c or string name to be the string s. -e Preprocess with eqn. -E Don't print any error messages. -f fam Use fam as the default font family. -F dir Search dir for subdirectories with DESC and font files before the default /usr/lib/groff/font. -h Print a help message. -i Read standard input after all files have been processed. -l Send the output to a printer (as specified by the print command in the device description file). -L arg Pass arg to the spooler. Each argument should be passed with a separate -L option. -m name Read the macro file tmac.name. -M dir Search directory dir for macro files before the default directory /usr/lib/groff/tmac. -n num Set the first page number to num. -N Don't allow newlines with eqn delimiters; equivalent to eqn's -N option. -o list Output only pages specified in list, which is a comma-separated list of page ranges. -p Preprocess with pic. -P arg Pass arg to the postprocessor. Each argument should be passed with a separate -P option. -r cn, -name=n Set the number register c or name to n. c is a single character and n is any troff numeric expression. -R Preprocess with refer. -s Preprocess with soelim. -S Use safer mode (i.e., pass the -S option to pic and use the -msafer macros with troff). -t Preprocess with tbl. -T dev Prepare output for device dev; the default is ps. -v Make programs run by groff print out their version number. -V Print the pipeline on stdout instead of executing it. -w name Enable warning name. You can specify multiple -w options. See the troff manpage for a list of warnings. -W name Disable warning name. You can specify multiple -W options. See the troff manpage for a list of warnings. -z Suppress troff output (except error messages). -Z Do not postprocess troff output. Normally groff automatically runs the appropriate postprocessor. #### Devices ascii Typewriter-like device dvi TeX dvi format latin1 Typewriter-like devices using the ISO Latin-1 character set ps PostScript X75 75-dpi X11 previewer X100 100-dpi X11 previewer lj4 HP LaserJet4-compatible (or other PCL5-compatible) printer #### Environment variables GROFF_COMMAND_PREFIX If set to be X, groff will run Xtroff instead of troff. GROFF_FONT_PATH Colon-separated list of directories in which to search for the devname directory. GROFF_TMAC_PATH Colon-separated list of directories in which to search for the macro files. GROFF_TMPDIR If set, temporary files will be created in this directory; otherwise, they will be created in TMPDIR (if set) or /tmp (if TMPDIR is not set). GROFF_TYPESETTER Default device. PATH Search path for commands that groff executes.
groupadd | groupadd [options] group System administration command. Create new group account group. #### Options -g gid Assign numerical group ID. (By default, the first available number above 500 is used.) The value must be unique unless the -o option is used. -o Accept a nonunique gid with the -g option.
groupdel | groupdel group System administration command. Remove group from system account files. You may still need to find and change permissions on files that belong to the removed group.
groupmod | groupmod [options] group System administration command. Modify group information for group. #### Options -g gid Change the numerical value of the group ID. Any files that have the old gid will have to be changed manually. The new gid must be unique unless the -o option is used. -n name Change the group name to name. -o Override. Accept a nonunique gid.
groups | groups [options] [users] Show the groups that each user belongs to (default user is the owner of the current group). Groups are listed in /etc/passwd and /etc/group. #### Options --help Print help message. --version Print version information.
grpck | grpck [option] [files] System administration command. Remove corrupt or duplicate entries in the /etc/group and /etc/gshadow files. Generate warnings for other errors found. grpck will prompt for a "yes" or "no" before deleting entries. If the user replies "no," the program will exit. If run in a noninteractive mode, the reply to all prompts is "no." Alternate group and gshadow files can be checked. If other errors are found, the user will be encouraged to run the groupmod command. #### Option -n Noninteractive mode. #### Exit codes 0 Success. 1 Syntax error. 2 One or more bad group entries found. 3 Could not open group files. 4 Could not lock group files. 5 Could not write group files.
grpconv | grpconv grpunconv System administration command. Like pwconv, the grpconv command creates a shadowed group file to keep your encrypted group passwords safe from password cracking programs. grpconv creates the /etc/gshadow file based on your existing /etc/groups file and replaces your encrypted password entries with x. If you add new entries to the /etc/groups file, you can run grpconv again to transfer the new information to /etc/gshadow. It will ignore entries that already have a password of x and convert those that do not. grpunconv restores the encrypted passwords to your /etc/groups file and removes the /etc/gshadow file.
gs | gs [options] [files] An interpreter for Adobe Systems' PostScript and PDF (Portable Document Format) languages; used for document processing. With - in place of files, standard input is used. #### Options -- filename arg1 ... Take the next argument as a filename, but use all remaining arguments to define ARGUMENTS in userdict (not systemdict) as an array of those strings, before running the file. -g number1 x number2 Specify width and height of device; intended for systems like the X Window System. -q Quiet startup. -r number, -r number1 x number2 Specify X and Y resolutions (for the benefit of devices, such as printers, that support multiple X and Y resolutions). If only one number is given, it is used for both X and Y resolutions. -D name=token, -d name=token Define a name in systemdict with the given definition. The token must be exactly one token (as defined by the token operator) and must not contain any whitespace. -D name, -d name Define a name in systemdict with a null value. -I directories Adds the designated list of directories at the head of the search path for library files. -S name=string, -s name=string Define a name in systemdict with a given string as value. #### Special names -dDISKFONTS Causes individual character outlines to be loaded from the disk the first time they are encountered. -dNOBIND Disables the bind operator. Useful only for debugging. -dNOCACHE Disables character caching. Useful only for debugging. -dNODISPLAY Suppresses the normal initialization of the output device. May be useful when debugging. -dNOPAUSE Disables the prompt and pause at the end of each page. -dNOPLATFONTS Disables the use of fonts supplied by the underlying platform (e.g., the X Window System). -dSAFER Disables the deletefile and renamefile operators and the ability to open files in any mode other than read-only. -dWRITESYSTEMDICT Leaves systemdict writable. -sDEVICE=device Selects an alternate initial output device. -sOUTPUTFILE=filename Selects an alternate output file (or pipe) for the initial output device.
gunzip | gunzip [options] [files] Uncompress files compressed by gzip. See gzip for a list of options.
gzexe | gzexe [option] [files] Compress executables. When run, these files automatically uncompress, thus trading time for space. gzexe creates backup files (filename~), which should be removed after testing the original. #### Option -d Decompress files.
gzip | gzip [options] [files] gunzip [options] [files] zcat [options] [files] Compress specified files (or read from standard input) with Lempel-Ziv coding (LZ77). Rename compressed file to filename.gz; keep ownership modes and access/modification times. Ignore symbolic links. Uncompress with gunzip, which takes all of gzip's options, except those specified. zcat is identical to gunzip -c and takes the options -fhLV, described here. Files compressed with the compress command can be decompressed using these commands. #### Options -n, --fast, --best Regulate the speed of compression using the specified digit n, where -1 or --fast indicates the fastest compression method (less compression) and -9 or --best indicates the slowest compression method (most compression). The default compression level is -6. -a, --ascii ASCII text mode: convert end-of-lines using local conventions. This option is supported only on some non-Unix systems. -c, --stdout, --to-stdout Print output to standard output, and do not change input files. -d, --decompress, --uncompress Same as gunzip. -f, --force Force compression. gzip would normally prompt for permission to continue when the file has multiple links, its .gz version already exists, or it is reading compressed data to or from a terminal. -h --help Display a help screen and then exit. -l, --list Expects to be given compressed files as arguments. Files may be compressed by any of the following methods: gzip, deflate, compress, lzh, and pack. For each file, list uncompressed and compressed sizes (the latter being always -1 for files compressed by programs other than gzip), compression ratio, and uncompressed name. With -v, also print compression method, the 32-bit CRC of the uncompressed data, and the timestamp. With -N, look inside the file for the uncompressed name and timestamp. -L, --license Display the gzip license and quit. -n, --no-name When compressing, do not save the original filename and timestamp by default. When decompressing, do not restore the original filename if present, and do not restore the original timestamp if present. This option is the default when decompressing. -N, --name Default. Save original name and timestamp. When decompressing, restore original name and timestamp. -q, --quiet Print no warnings. -r, --recursive When given a directory as an argument, recursively compress or decompress files within it. -S suffix, --suffix suffix Append .suffix. Default is gz. A null suffix while decompressing causes gunzip to attempt to decompress all specified files, regardless of suffix. -t, --test Test compressed file integrity. -v, --verbose Print name and percent size reduction for each file. -V, --version Display the version number and compilation options.
halt | halt [options] System administration command. Insert a note in the file /var/log/wtmp; if the system is in runlevel 0 or 6, stop all processes; otherwise, call shutdown -nf. #### Options -d Suppress writing to /var/log/wtmp. -f Call halt even when shutdown -nf would normally be called (i.e., force a call to halt, even when not in runlevel 0 or 6). -n Suppress normal call to sync. -w Suppress normal execution; simply write to /var/log/wtmp.
> head | head [options] [files] Print the first few lines (default is 10) of one or more files. If files is missing or -, read from standard input. With more than one file, print a header for each file. #### Options -c num[bkm], --bytes num Print first num bytes or, if num is followed by b, k, or m, first num 512-byte blocks, 1-kilobyte blocks, or 1-megabyte blocks. --help Display help and then exit. -n num, --lines num, -num Print first num lines. Default is 10. -q, --quiet, --silent Quiet mode; never print headers giving filenames. -v, --verbose Print filename headers, even for only one file. --version Output version information and then exit. #### Examples Display the first 20 lines of phone_list:
>     head -20 phone_list
> Display the first 10 phone numbers having a 202 area code:
>     grep '(202)' phone_list | head
host | host [options] host [server] host [options] zone [server] System administration command. Print information about specified hosts or zones in DNS. Hosts may be IP addresses or hostnames; host converts IP addresses to hostnames by default and appends the local domain to hosts without a trailing dot. Default servers are determined in /etc/resolv.conf. For more information about hosts and zones, try Chapters 1 and 2 of DNS and BIND by Paul Albitz and Cricket Liu, published by O'Reilly & Associates. #### Options -a Same as -t ANY. -c class Search for specified resource record class (IN, INTERNET, CS, CSNET, CH, CHAOS, HS, HESIOD, ANY, or *). Default is IN. -d Debugging mode. -dd is a more verbose version. -e Do not print information about domains outside of specified zone. For hostname queries, do not print "additional information" or "authoritative nameserver." -f file Output to file as well as standard out. -i Given an IP address, return the corresponding in-addr.arpa address, class (always PTR), and hostname. -l zone List all machines in zone. -m Print only MR, MG, and MB records; recursively expand MR (renamed mail box) and MG (mail group) records to MB (mail box) records. -o Do not print output to standard out. -p [server] For use with -l. Query only the zone's primary nameserver (or server) for zone transfers, instead of those authoritative servers that respond. Useful for testing unregistered zones. -q Quiet. Suppress warning, but not error, messages. -r Do not ask contacted server to query other servers, but require only the information that it has cached. -t type Look for type entries in the resource record. type may be A, NS, PTR, ANY, or * (all). -u Use TCP, not UDP. -v Verbose. Include all fields from resource record, even time-to-live and class, as well as "additional information" and "authoritative nameservers" (provided by the remote nameserver). -vv Very verbose. Include information about host's defaults. -w Never give up on queried server. -x Allow multiple hosts or zones to be specified. If a server is also specified, the argument must be preceded by -X. -A For hostnames, look up the associated IP address, and then reverse look up the hostname, to see if a match occurs. For IP addresses, look up the associated hostname, and determine whether the host recognizes that address as its own. For zones, check IP addresses for all hosts. Exit silently if no incongruities are discovered. -C Similar to -l, but also check to see if the zone's name servers are really authoritative. The zone's SOA (start of authority) records specify authoritative name servers (in NS fields). Those servers are queried; if they do not have SOA records, host reports a lame delegation. Other checks are made as well. -D Similar to -H but include the names of hosts with more than one address per defined name. -E Similar to -H but do not treat extra-zone hosts as errors. Extra-zone hosts are hosts in an undefined subdomain. -F file Redirect standard out to file, and print extra resource record output only on standard out. -G zone Similar to -H but include the names of gateway hosts. -H zone Print the number of unique hosts within zone. Do not include aliases. Also list all errors found (extra-zone names, duplicate hosts). -I chars Do not print warnings about domain names containing illegal characters chars, such as _. -L level For use with -l. List all delegated zones within this zone, up to level deep, recursively. -P servers For use with -l. servers should be a comma-separated list. Specify preferred hosts for secondary servers to use when copying over zone data. Highest priority is given to those servers that match the most domain components in a given part of servers. -R Treat non-fully-qualified hostnames as BIND does, searching each component of the local domain. -S For use with -l. Print all hosts within the zone to standard out. Do not print hosts within subzones. Include class and IP address. Print warning messages (illegal names, lame delegations, missing records, etc.) to standard error. -T Print time-to-live values (how long information about each host will remain cached before the nameserver refreshes it). -X server Specify a server to query, and allow multiple hosts or zones to be specified. -Z When printing recource records, include trailing dot in domain names, and print time-to-live value and class name.
hostid | hostid Print the ID number in hexadecimal of the current host.
hostname | hostname [option] [nameofhost] Set or print name of current host system. A privileged user can set the hostname with the nameofhost argument. #### Option -a, --alias Display the alias name of the host (if used). -d, --domain Print DNS domain name. -f, --fqdn, --long Print fully qualified domain name. -F file, --file file Consult file for hostname. -h, --help Print a help message and then exit. -i, --ip-address Display the IP address(es) of the host. -s, --short Trim domain information from the printed name. -v, --verbose Verbose mode. -V, --version Print version information and then exit. -y, --yp, --nis Display the NIS domain name. A privileged user can set a new NIS domain name with nameofhost.
hwclock | hwclock [options] System administration command. Read or set the hardware clock. This command maintains change information in /etc/adjtime, which can be used to adjust the clock based on how much it drifts over time. hwclock replaces the clock command. The single-letter options are included for compatibility with the older command. #### Options You may specify only one of the following options: -a Adjust the hardware clock based on information in /etc/adjtime and set the system clock to the new time. --adjust Adjust the hardware clock based on information in /etc/adjtime. --date date Meaningful only with the --set option. date is a string appropriate for use with the date command. --debug Print information about what hwclock is doing. -r, --show Print the current time stored in the hardware clock. -s, --hctosys Set the system time in accordance with the hardware clock. --set Set the hardware clock according to the time given in the --date parameter. --test Do not actually change anything. This is good for checking syntax. -u, --utc The hardware clock is stored in Universal Coordinated Time. --version Print version and exit. -w, --systohc Set the hardware clock in accordance with the system time.
icmpinfo | icmpinfo [options] TCP/IP command. Intercept and interpret ICMP packets. Print the address and name of the message's sender, the source port, the destination port, the sequence, and the packet size. By default, provide information only about packets that are behaving oddly. #### Options -k Kill the syslogd process begun by -l. -l Record via syslogd. Only a privileged user may use this option. -n Use IP addresses instead of hostnames. -p Suppress decoding of port number: do not attempt to guess the name of the service that is listening at that port. -s Include IP address of interface that received the packet, in case there are several interfaces on the host machine. -v Verbose. Include information about normal ICMP packets. You may also specify -vv and -vvv for extra verbosity.
id | id [options] [username] Display information about yourself or another user: user ID, group ID, effective user ID and group ID if relevant, and additional group IDs. #### Options -g, --group Print group ID only. -G, --groups Print supplementary groups only. -n, --name With -u, -g, or -G, print user or group name, not number. -r, --real With -u, -g, or -G, print real, not effective, user ID or group ID. -u, --user Print user ID only. --help Print help message and then exit. --version Print version information.
identd | in.identd [options] [kernelfile [kmemfile]] TCP/IP command. Provide the name of the user whose process is running a specified TCP/IP connection. You may specify the kernel and its memory space. #### Options -a ip_address Bind to ip_address. Useful only with -b. By default, bind to the INADDR_ANY address. -b Run standalone; not for use with inetd. -d Allow debugging requests. -g gid Attempt to run in the group gid. Useful only with -b. -i Run as a daemon, one process per request. -l Log via syslogd. -m Allow multiple requests per session. -n Return user IDs instead of usernames. -N Do not provide a user's name or user ID if the file .noident exists in the user's home directory. -o When queried for the type of operating system, always return OTHER. -p port Listen at port instead of the default, port 113. -t seconds Exit if no new requests have been received before seconds seconds have passed. Note that, with -i or -w, the next new request will result in identd being restarted. Default is infinity (never exit). -u uid Attempt to run as uid. Useful only with -b. -V Print version and exit. -w Run as a daemon, one process for all requests.
ifconfig | ifconfig [interface] ifconfig [interface address_family parameters addresses] TCP/IP command. Assign an address to a network interface and/or configure network interface parameters. ifconfig is typically used at boot time to define the network address of each interface on a machine. It may be used at a later time to redefine an interface's address or other parameters. Without arguments, ifconfig displays the current configuration for a network interface. Used with a single interface argument, ifconfig displays that particular interface's current configuration. #### Arguments interface String of the form name unit, for example, en0. address_family Since an interface may receive transmissions in differing protocols, each of which may require separate naming schemes, you can specify the address_family to change the interpretation of the remaining parameters. You may specify inet (the default; for TCP/IP), ax25 (AX.25 Packet Radio), ddp (Appletalk Phase 2), or ipx (Novell). Parameters The following parameters may be set with ifconfig: allmulti/-allmulti Enable/disable sending of incoming frames to the kernel's network layer. arp/-arp Enable/disable use of the Address Resolution Protocol in mapping between network-level addresses and link-level addresses. broadcast (inet only.) Specify address to use to represent broadcasts to the network. Default is the address with a host part of all 1s (i.e., x.y.z.255 for a class C network). debug/-debug Enable/disable driver-dependent debugging code. dest_address Specify the address of the correspondent on the other end of a point-to-point link. down Mark an interface "down" (unresponsive). hw class address Set the interface's hardware class and address. class may be ether (Ethernet), ax25 (AX.25 Packet Radio), or ARCnet. irq addr Set the device's interrupt line. metric n Set routing metric of the interface to n. Default is 0. mtu num Set the interface's Maximum Transfer Unit (MTU). multicast Set the multicast flag. netmask mask (inet only.) Specify how much of the address to reserve for subdividing networks into subnetworks. mask can be specified as a single hexadecimal number with a leading 0x, with a dot notation Internet address, or with a pseudonetwork name listed in the network table /etc/networks. pointopoint/-pointopoint [address] Enable/disable point-to-point interfacing, so that the connection between the two machines is dedicated. up Mark an interface "up" (ready to send and receive). trailers/-trailers Request/disable use of a "trailer" link-level encapsulation when sending. address Either a hostname present in the hostname database (/etc/hosts), or an Internet address expressed in the Internet standard dot notation.
> imake | imake options C preprocessor (cpp) interface to the make utility. imake (for include make) solves the portability problem of make by allowing machine dependencies to be kept in a central set of configuration files, separate from the descriptions of the various items to be built. The targets are contained in the Imakefile, a machine-independent description of the targets to be built, written as cpp macros. imake uses cpp to process the configuration files and the Imakefile, and to generate machine-specific Makefiles, which can then be used by make. One of the configuration files is a template file, a master file for imake. This template file (default is Imake.tmpl) #includes the other configuration files that contain machine dependencies such as variable assignments, site definitions, and cpp macros, and directs the order in which the files are processed. Each file affects the interpretation of later files and sections of Imake.tmpl. Comments may be included in imake configuration files, but the initial # needs to be preceded with an empty C comment:
>     /**/#
> For more information, see cpp and make. Also check out the Nutshell Handbook Software Portability with imake, by Paul DuBois. #### Options -D define Set directory-specific variables. This option is passed directly to cpp. -e Execute the generated Makefile. Default is to leave this to the user. -f filename Name of per-directory input file. Default is Imakefile. -I directory Directory in which imake template and configuration files may be found. This option is passed directly to cpp. -s filename Name of make description file to be generated. If filename is a -- , the output is written to stdout. The default is to generate, but not execute, a Makefile. -T template Name of master template file used by cpp. This file is usually located in the directory specified with the -I option. The default file is Imake.tmpl. -v Print the cpp command line used to generate the Makefile. #### Tools Following is a list of tools used with imake: makedepend [options] files Create header file dependencies in Makefiles. make- depend reads the named input source files in sequence and parses them to process #include, #define, #undef, #ifdef, #ifndef, #endif, #if, and #else directives so it can tell which #include directives would be used in a compilation. makedepend determines the dependencies and writes them to the Makefile. make then knows which object files must be recompiled when a dependency has changed. makedepend has the following options: -- options -- Ignore any unrecognized options following a double hyphen. A second double hyphen terminates this action. Recognized options between the hyphens are processed normally. -a Append dependencies to any existing ones instead of replacing existing ones. -f filename Write dependencies to filename instead of to Makefile. -m Print a warning when encountering a multiple inclusion. -s string Use string as delimiter in file, instead of # DO NOT DELETE THIS LINE -- make depend depends on it. -v Verbose. List all files included by main source file. -D name Define name with the given value (first form) or with value 1 (second form). -I dir Add directory dir to the list of directories searched. -Y dir Search only dir for include files. Ignore standard include directories. mkdirhier dir... Create directory dir and all missing parent directories during file installation operations. xmkmf [option] [topdir] [curdir] Bootstrap a Makefile from an Imakefile. topdir specifies the location of the project root directory. curdir (usually omitted) is specified as a relative pathname from the top of the build tree to the current directory. The -a option is equivalent to the following command sequence:
>          % xmkmf
>          % make Makefiles
>          % make includes
>          % make depend
#### Configuration files Following is a list of the imake configuration files: Imake.tmpl Master template for imake. Imake.tmpl includes all the other configuration files, plus the Imakefile in the current directory. Imake.params Contains definitions that apply across sites and vendors. Imake.rules Contains cpp macro definitions that are configured for the current platform. The macro definitions are fed into imake, which runs cpp to process the macros. Newlines (line continuations) are indicated by the string @@\ (double at sign, backslash). site.def Contains site-specific (as opposed to vendor-specific) information, such as installation directories, what set of programs to build, and any special versions of programs to use during the build. The site.def file changes from machine to machine. Project.tmpl File containing X-specific variables. Library.tmpl File containing library rules. Server.tmpl File containing server-specific rules. .cf The .cf files are the vendor-specific VendorFiles that live in Imake.vb. A .cf file contains platform-specific definitions, such as version numbers of the operating system and the compiler and workarounds for missing commands. The definitions in .cf files override the defaults, defined in Imake.params. #### The Imakefile The Imakefile is a per-directory file that indicates targets to be built and installed and rules to be applied. imake reads the Imakefile and expands the rules into Makefile target entries. An Imakefile may also include definitions of make variables and list the dependencies of the targets. The dependencies are expressed as cpp macros, defined in Imake.rules. Whenever you change an Imakefile, you need to rebuild the Makefile and regenerate header file dependencies. For more information on imake, see Software Portability with imake by Paul DuBois.
imapd | imapd TCP/IP command. The Interactive Mail Access Protocol (IMAP) server daemon. imapd is invoked by inetd and listens on port 143 for requests from IMAP clients. IMAP allows mail programs to access remote mailboxes as if they were local. IMAP is a richer protocol than POP because it allows a client to retrieve message-level information from a server mailbox instead of the entire mailbox. IMAP can be used for online and offline reading. The popular Pine mail client contains support for IMAP.
inetd | inetd [option] [configuration_file] TCP/IP command. Internet services daemon. inetd listens on multiple ports for incoming connection requests. When it receives one, it spawns the appropriate server. When started, inetd reads its configuration information from either configuration_file, or from the default configuration file /etc/inetd.conf. It then issues a call to getservbyname, creates a socket for each server, and binds each socket to the port for that server. It does a listen on all connection-based sockets, then waits, using select for a connection or datagram. When a connection request is received on a listening socket, inetd does an accept, creating a new socket. It then forks, dups, and execs the appropriate server. The invoked server has I/O to stdin, stdout, and stderr done to the new socket, connecting the server to the client process. When there is data waiting on a datagram socket, inetd forks, dups, and execs the appropriate server, passing it any server program arguments. A datagram server has I/O to stdin, stdout, and stderr done to the original socket. If the datagram socket is marked as wait, the invoked server must process the message before inetd considers the socket available for new connections. If the socket is marked nowait, inetd continues to process incoming messages on that port. The following servers may be started by inetd: bootpd, bootpgw, fingerd, ftpd, imapd, popd, rexecd, rlogind, rshd, talkd, telnetd, and tftpd. Do not arrange for inetd to start named, routed, rwhod, sendmail, listen, or any NFS server. inetd rereads its configuration file when it receives a hangup signal, SIGHUP. Services may be added, deleted, or modified when the configuration file is reread. #### Option -d Turn on socket-level debugging and print debugging information to stdout. #### Files /etc/inetd.conf Default configuration file. /var/run/inetd.pid inetd's process ID.
info | info [options] [topics] GNU hypertext reader: display online documentation previously built from Texinfo input. Info files are arranged in a hierarchy and can contain menus for subtopics. When entered without options, the command displays the top-level info file (usually /usr/local/info/dir). When topics are specified, find a subtopic by choosing the first topic from the menu in the top-level info file, the next topic from the new menu specified by the first topic, and so on. The initial display can also be controlled by the -f and -n options. #### Options -d directories, --directory directories Search directories, a colon-separated list, for info files. If this option is not specified, use the INFOPATH environment variable or the default directory (usually /usr/local/info). --dribble file Store each keystroke in file, which can be used in a future session with the --restore option to return to this place in info. -f file, --file file Display specified info file. -n node, --node node Display specified node in the info file. -o file, --output file Copy output to file instead of displaying it at the screen. --help Display brief help. --restore file When starting, execute keystrokes in file. --subnodes Display subtopics. --version Display version. --vi-keys Use vi-like key bindings.
init | init [option] [runlevel] System administration command. #### Option -t seconds When changing runlevels, send SIGKILL seconds after SIGTERM. Default is 20. #### Files init is the first process run by any Unix machine at boot time. It verifies the integrity of all filesystems and then creates other processes, using fork and exec, as specified by /etc/inittab. Which processes may be run are controlled by runlevel. All process terminations are recorded in /var/run/utmp and /var/log/wtmp. When the runlevel changes, init sends SIGTERM and then, after 20 seconds, SIGKILL to all processes that cannot be run in the new runlevel. #### Runlevels The current runlevel may be changed by telinit, which is often just a link to init. The default runlevels vary from distribution to distribution, but these are standard: 0 Halt the system. 1, s, S Single-user mode. 6 Reboot the system. q, Q Reread /etc/inittab. Check the /etc/inittab file for runlevels on your system.
insmod | insmod [options] file [symbol=value ...] System administration command. Load the module file into the kernel, changing any symbols that are defined on the command line. If the module file is named file.o or file.mod, the module will be named file. #### Options -f Force loading of module, even if some problems are encountered. -m Output a load map. -o name Name module name instead of attempting to name it from the object file's name. -x Do not export: do not add any external symbols from the module to the kernel's symbol table.
install | install [options] [file] directories System administration command. Used primarily in makefiles to update files. install copies files into user-specified directories. It will not overwrite a file. Similar to cp but attempts to set permission modes, owner, and group. #### Options -d, --directory Create any missing directories. -g group, --group group Set group ID of new file to group (privileged users only). -m mode, --mode mode Set permissions of new file to mode (octal or symbolic). By default, the mode is 0755. -o [owner], --owner [owner] Set ownership to owner or, if unspecified, to root (privileged users only). -s, --strip Strip symbol tables.
ipchains | ipchains command [options] System administration command. Edit IP firewall rules in the 2.2 Linux kernel. A 2.2 Linux kernel compiled with firewall support will examine the headers of all network packets and compare them to matching rules to see what it should do with the packet. A firewall rule consists of some matching criteria and a target, a result to be applied if the packet matches the criteria. The rules are organized into chains. You can use these rules to build a firewall or just reject certain kinds of network connections. Firewall rules are organized into chains, an ordered checklist that the kernel works through looking for matches. There are three built-in chains input, output, and forward. Packets entering the system are tested against the input chain. Those exiting the system are checked against the output chain. If an incoming packet is destined for some other system, it is checked against the forward chain. Each of these chains has a default target, a policy, in case no match is found. User-defined chains can be created and used as targets for packets, but they have no default policies. If no match can be found in a user-defined chain, the packet is returned to the chain from which it was called and tested against the next rule in that chain. ipchains only changes the rules in the running kernel. When the system is powered off, all those changes are lost. You can use the ipchains-save command to make a script you can later run with ipchains-restore to restore your firewall settings. Such a script is often called at boot up and many distributions have an ipchains initialization script that uses the output from ipchains-save. #### Commands ipchains is always invoked with one of the following commands: -A chain rules, --append chain rules Append new rules to chain. -I chain number rules, --insert <chain number rules Insert rules into chain at the ordinal position given by number. -D chain rules, --delete chain rules Delete rules from chain. Rules can be specified by their ordinal number in the chain as well as by a general rule description. -R chain number rule, --replace chain number rule Replace a rule in chain. The rule to be replaced is specified by its ordinal number. -C chain rule, --check chain rules Construct a network packet that matches the given rule and check how chain will handle it. The rule must describe the source, destination, protocol, and interface of the packet to be constructed. -L [chain], --list $PARAMETER List the rules in chain. If no chain is specified, list the rules in all chains. -ML, --masquerading --list List masquerading connections. -MS tcp tcpfin udp, --masquerading --set tcp tcpfin udp Set timeout value in seconds for masquerading connections. -MS always takes three parameters specifying the timeout values for TCP sessions, TCP sessions that have received a FIN packet, and UDP packets. -F chain, --flush chain Remove all rules from chain. -Z [chain], --zero [chain] Reset the packet and byte counters in chain. If no chain is specified, all chains will be reset. When used without specifying a chain and combined with the -L command, it lists the current counter values before they are reset. -N chain, --new-chain chain Create a new chain. The chain's name must be unique. -X [chain], --delete-chain chain Delete chain. Only user-defined chains can be deleted, and there can be no references to the chain to be deleted. If no argument is given, all user-defined chains will be deleted. -P chain target, --policy chain target Set the policy for a built-in chain; the target itself cannot be a chain. -h [icmp] Print a brief help message. If the option icmp is given, print a list of valid ICMP types. #### Targets A target can be the name of a chain or one of the following special values: ACCEPT Let the packet through. DENY Drop the packet. MASQ Masquerade the packet so it appears that it originated from the current system. Reverse packets from masqueraded connections are unmasqueraded automatically. This is a legal target for only the forward chain, or user-defined chains used in forwarding packets. To use this target, the kernel must be compiled with support for IP masquerading. REDIRECT [port] Redirect incoming packets to a local port on which you are running a transparent proxy program. If the specified port is 0 or is not given, the destination port of the packet is used as the redirection port. REDIRECT is only a legal target for the input chain or user-defined chains used in handling incoming packets. The kernel must be compiled with support for transparent proxies. REJECT Drop the packet and send an ICMP message back to the sender indicating the packet was dropped. RETURN Return to the chain from which this chain was called and check the next rule. If RETURN is the target of a rule in a built-in chain, then the built-in chain's default policy is applied. #### Rule specification parameters These options are used to create rules for use with the preceding commands. Rules consist of some matching criteria and usually a target to jump to (-j) if the match is made. Many of the parameters for these matching rules can be expressed as a negative with an exclamation point (!) meaning "not." Those rules will match everything except the given parameter. -p [!] name, --protocol [!]$PARAMETER Match packets of protocol name. The value of name can be given as a name or number as found in the file /etc/protocols. The most common values are tcp, udp, icmp, or the special value all. The number 0 is equivalent to all, and this is the default value when this option is not used. -s [!] address[/mask] [!] [port], --source [!] address[/mask] [!] [port] Specifies the source address and port of the packet that will match this rule. The address may be supplied as a hostname, a network name, or an IP address. The optional mask is the netmask to use and may be supplied either in the traditional form (e.g., /255.255.255.0) or in the modern form (e.g., /24). The optional port specifies the TCP, UDP, or ICMP type that will match. You may supply a port specification only if you've supplied the -p parameter with one of the tcp, udp or icmp protocols. A colon can be used to indicate an inclusive range of ports or ICMP values to be used. (e.g., 20:25 for ports 20 through 25). If the first port parameter is missing, the default value is 0. If the second is omitted, the default value is 65535. -d [!] address[/mask] [!] [port], --destination [!] address[/mask] [port] Match packets with the destination address. The syntax for this command's parameters is the same as for the -s option. -j target, --jump target Jump to a special target or a user-defined chain. If this option is not specified for a rule, matching the rule only increases the rule's counters and the packet is tested against the next rule. -i [!] name, --interface name Match packets from interface name[+]. name is the network interface used by your system (e.g., eth0 or ppp0). A + can be used as a wildcard, so ppp+ would match any interface name beginning with ppp. [!] -f, [!]--fragment $PARAMETER The rule applies to everything but the first fragment of a fragmented packet. --source-port [!] port Match packets from the source port. The syntax for specifying ports can be found in the preceding description of the -s option. --destination-port [!] port Match packets with the destination port. The syntax for specifying ports can be found in the preceding description of the -s option. --icmp-type [!] type Match packets with ICMP type name or number of type. #### Options -b, --bidirectional Put rule in both the input and output chain so packets will be matched in both directions. -v, --verbose Verbose mode. -n, --numeric Print all IP address and port numbers in numeric form. By default, names are displayed when possible. -l, --log Log information for the matching packet to the system log. -t andmask xormask, --TOS andmask xormask Change the Type of Service field in the packet's header. The TOS field is first ANDed with the 8-bit hexadecimal mask andmask, then XORed with the 8-bit hexadecimal mask xormask. Rules that would affect the least significant bit (LSB) portion of the TOS field are rejected. -x, --exact Expand all numbers in a listing (-L). Display the exact value of the packet and byte counters instead of rounded figures. [!] -y, --syn Match only incoming TCP connection requests, those with the SYN bit set and the ACK and FIN bits cleared. This blocks incoming TCP connections but leaves outgoing connections unaffected. --line-numbers Used with the -L command. Add the line number to the beginning of each rule in a listing indicating its position in the chain. --no-warnings Disable all warnings
ipchains-restore | ipchains-restore [options] System administration command. Restore firewall rules. ipchains-restore takes commands generated by ipchains-save and uses them to restore the firewall rules for each chain. Often used by initialization scripts to restore firewall settings on boot. #### Options -f Force updates of existing chains without asking. -v Print rules as they are being restored. -p If a nonexisting chain is targeted by a rule, create it.
ipchains-save | ipchains-save [chain] [option] System administration command. Print the IP firewall rules currently stored in the kernel to stdout. If no chain is given, all chains will be printed. Output is usually redirected to a file, which can later be used by ipchains-restore to restore the firewall. #### Option - v Print out rules to stderr as well as stdout, making them easier to see when redirecting output.
> ipfwadm | ipfwadm category command parameters [options] ipfwadm -M [ -l | -s ] [options] Administer a firewall and its rules, firewall accounting, and IP masquerading in the 2.0 Linux kernel. This command is replaced with ipchains in the 2.2 kernel, and ipchains is replaced by iptables in the 2.4 kernel. There are four categories of rules: IP packet accounting, IP input firewall, IP output firewall, and IP forwarding firewall. The rules are maintained in lists, with a separate list for each category. See the manpage for ipfw(4) for a more detailed description of how the lists work. Each ipfwadm command specifies only one category and one rule. To create a secure firewall, you issue multiple ipfwadm commands; the combination of their rules work together to ensure that your firewall operates as you intend it to. The second form of the command is for masquerading. The commands -l and -s described in the later list are the only ones that can be used with the masquerading category, -M. #### Categories One of the following flags is required to indicate the category of rules to which the command that follows the category applies. -A [direction] IP accounting rules. Optionally, a direction can be specified: in Count only incoming packets. out Count only outgoing packets. both Count both incoming and outgoing packets; this is the default. -F IP forwarding firewall rules. -I IP input firewall rules. -M IP masquerading administration. Can be used only with the -l or -s command. -O IP output firewall rules. #### Commands The category is followed by a command indicating the specific action to be taken. Unless otherwise specified, only one action can be given on a command line. For the commands that can include a policy, the valid policies are: accept Allow matching packets to be received, sent, or forwarded. deny Block matching packets from being received, sent, or forwarded. reject Block matching packets from being received, sent, or forwarded and also return an ICMP error message to the sending host. The commands are: -a [policy] Append one or more rules to the end of the rules for the category. No policy is specified for accounting rules. For firewall rules, a policy is required. When the source and/or destination names resolve to more than one address, a rule is added for each possible address combination. -c Check whether this IP packet would be accepted, denied, or rejected by the type of firewall represented by this category. Valid only when the category is -I, -O, or -F. Requires the -V parameter to be specified (see "Parameters," later). -d [policy] Delete one or more entries from the list of rules for the category. No policy is specified for accounting rules. The parameters specified with this command must exactly match the parameters from an append or insert command, or no match will be found and the rule will not be removed. Only the first matching rule in the list of rules is deleted. -f Remove (flush) all rules for the category. -h Display a help message with a brief description of the command syntax. Specified with no category:
>          % ipfwadm -h
  > -i [policy] Insert a new rule at the beginning of the selected list for the category. No policy is specified for accounting rules. For firewall rules, a policy is required. When the source and/or destination names resolve to more than one address, a rule is added for each possible address combination. -l List all rules for the category. This option may be combined with the -z option to reset the packet and byte counters after listing their current values. Unless the -x option is also specified, the packet and byte counters are shown as number K or number M, rounded to the nearest integer. See also the -e option described under "Options" later. -p policy Change the default policy for the selected type of firewall to policy. The default policy is used when no matching rule is found. Valid only with -I, -O, or -F. -s tcp tcpfin udp Set the masquerading timeout values; valid only with -M. The three parameters are required and represent the timeout value in seconds for TCP sessions, TCP sessions after receiving a FIN packet, and UDP packets, respectively. A timeout value of 0 preserves the current timeout value of the corresponding entry. -z Reset the packet and byte counters for all rules in the category. This command may be combined with the -l command. #### Parameters The following parameters can be specified with the -a, -i, -d, or -c commands, except as noted. Multiple parameters can be specified on a single ipfwadm command line. -D address[/mask] [port ...] The destination specification (optional). See the description of -S for the syntax, default values, and other requirements. ICMP types cannot be specified with -D. -P protocol The protocol of the rule or packet; possible values are tcp, udp, icmp, or all. Defaults to all, which matches all protocols. -P cannot be specified with the -c command. -S address[/mask] [port ...] The source IP address, specified as a hostname, a network name, or an IP address. The source address and mask default to 0.0.0.0/0. If -S is specified, -P must also be specified. The optional mask is specified as a network mask or as the number of 1s on the left of the network mask (e.g., a mask of 24 is equivalent to 255.255.255.0). The mask defaults to 32. One or more values of port may optionally be specified, indicating what ports or ICMP types the rule applies to. The default is all. Ports may be specified by their /etc/ services entry. The syntax for indicating a range of ports is:
  >     lowport:highport
  > For example:
  >     -S 172.29.16.1/24 ftp:ftp-data
> -V address The address of the network interface the packet is received from (if category is -I) or is being sent to (if category is -O). address can be a hostname or an IP address, and defaults to 0.0.0.0, which matches any interface address. -V is required with the -c command:
>          -V 172.29.16.1
> -W name Identical to -V but takes a device name instead of its address:
>          -W ppp0
#### Options -b Bidirectional mode. The rule matches IP packets in both directions. This option is valid only with the -a, -i, and -d commands. -e Extended output. Used with the -l command to also show the interface address and any rule options. When listing firewall rules, also shows the packet and byte counters and the TOS (Type of Service) masks. When used with -M, also shows information related to delta sequence numbers. -k Match TCP acknowledgment packets (i.e., only TCP packets with the ACK bit set). This option is ignored for all other protocols and is valid only with the -a, -i, and -d commands. -m Accept masquerade packets for forwarding, making them appear to have originated from the local host. Recognizes reverse packets and automatically demasquerades them, bypassing the forwarding firewall. This option is valid only in forwarding firewall rules with policy accept. The kernel must have been compiled with CONFIG_IP_MASQUERADE defined. -n Numeric output. Print IP addresses and port numbers in numeric format. -o Log packets that match this rule to the kernel log. This option is valid only with the -a, -i, and -d commands. The kernel must have been compiled with CONFIG_IP_FIREWALL_VERBOSE defined. -r [port] Redirect packets to a local socket, even if they were sent to a remote host. If port is 0 (the default), the packet's destination port is used. This option is valid only in input firewall rules with policy accept. The kernel must have been compiled with CONFIG_IP_TRANSPARENT_ PROXY defined. -t andmask xormask Specify masks used for modifying the TOS field in the IP header. When a packet is accepted (with or without masquerading) by a firewall rule, its TOS field is bitwise ANDed with andmask, and the result is bitwise XORed with xormask. The masks are specified as 8-bit hexadecimal values. This option is valid only with the -a, -i, and -d commands and has no effect when used with accounting rules or with firewall rules for rejecting or denying a packet. -v Verbose output. Print detailed information about the rule or packet to be added, deleted, or checked. This option is valid only with the -a, -i, -d, and -c commands. -x Expand numbers. Display the exact value of the packet and byte counters, instead of a rounded value. This option is valid only when the counters are being listed anyway (see also the -e option). -y Match TCP packets with the SYN bit set and the ACK bit cleared. This option is ignored for packets of other protocols and is valid only with the -a, -i, and -d commands.
iptables | iptables command [options] System administration command. Configure netfilter filtering rules. In the 2.4 kernel, the ipchains firewall capabilities are replaced with the netfilter kernel module. netfilter can be configured to work just like ipchains, but it also comes with the module iptables, which is similar to ipchains but extensible. iptables rules consist of some matching criteria and a target, a result to be applied if the packet matches the criteria. The rules are organized into chains. You can use these rules to build a firewall, masquerade your local area network, or just reject certain kinds of network connections. There are three built-in tables for iptables, one for network filtering (filter), one for Network Address Translation (nat), and the last for specialized packet alterations (mangle). Firewall rules are organized into chains, ordered check lists of rules that the kernel works through looking for matches. The filter table has three built-in chains: INPUT, OUTPUT, and FORWARD. The INPUT and OUTPUT chains handle packets originating from or destined for the host system. The FORWARD chain handles mail just passing through the host system. The nat table also has three built-in chains: PREROUTING, POSTROUTING, and OUTPUT. mangle has only two chains: PREROUTING and OUTPUT. netfilter checks packets entering the system. After applying any PREROUTING rules it passes them to the INPUT chain or to the FORWARD chain if the packet is just passing through. Upon leaving, the system packets are passed to the OUTPUT chain and then on to any POSTROUTING rules. Each of these chains has a default target, a policy, in case no match is found. User-defined chains can also be created and used as targets for packets but do not have default policies. If no match can be found in a user-defined chain, the packet is returned to the chain from which it was called and tested against the next rule in that chain. iptables only changes the rules in the running kernel. When the system is powered off, all changes are lost. You can use the iptables-save command to make a script you can run with iptables-restore to restore your firewall settings. Such a script is often called at bootup. Many distributions will have an iptables initialization script that uses the output from iptables-save. #### Commands iptables is always invoked with one of the following commands: -A chain rules, --append chain rules Append new rules to chain. -I chain number rules, --insert chain number rules Insert rules into chain at the ordinal position given by number. -D chain rules, --delete chain rules Delete rules from chain. Rules can be specified by their ordinal number in the chain as well as by a general rule description. -R chain number rule, --replace chain number rule Replace a rule in chain. The rule to be replaced is specified by its ordinal number. -C chain rule, --check chain rules Check how chain will handle a network packet that matches the given rule. The rule must describe the source, destination, protocol, and interface of the packet to be constructed. -L [chain], --list $PARAMETER List the rules in chain or all chains if chain is not specified. -F [chain], --flush chain Remove all rules from chain or from all chains if chain is not specified. -Z [chain], --zero chain Zero the packet and byte counters in chain. If no chain is specified, all chains will be reset. When used without specifying a chain and combined with the -L command, it lists the current counter values before they are reset chain. -N chain, --new-chain chain Create a new chain. The chain's name must be unique. This is how user-defined chains are created. -X [chain], --delete-chain chain Delete the specified user-defined chain or all user-defined chains if no chain is specified. -P chain target, --policy chain target Set the default policy for a built-in chain; the target itself cannot be a chain. -E old-chain new-chain, --rename-chain old-chain new-chain Rename old-chain to new-chain. -h [icmp] Print a brief help message. If the option icmp is given, print a list of valid ICMP types. #### Targets A target may be the name of a chain or one of the following special values. ACCEPT Let the packet through. DROP Drop the packet. QUEUE Send packets to the user space for processing. RETURN Stop traversing the current chain and return to the point in the previous chain from which this one was called. If RETURN is the target of a rule in a built-in chain, the built-in chain's default policy is applied. #### Rule specification parameters These options are used to create rules for use with the preceding commands. Rules consist of some matching criteria and usually a target to jump to (-j) if the match is made. Many of the parameters for these matching rules can be expressed as a negative with an exclamation point (!) meaning "not." Those rules will match everything except the given parameter. -p [!] name, --protocol [!]$PARAMETER Match packets of protocol name. The value of name can be given as a name or number as found in the file /etc/protocols. The most common values are tcp, udp, icmp, or the special value all. The number 0 is equivalent to all and this is the default value when this option is not used. If there are extended matching rules associated with the specified protocol, they will be loaded automatically. You need not use the -m option to load them. -s [!] address[/mask] [!] [port], --source [!] address[/mask] [!] [port] Match packets with the source address. The address may be supplied as a hostname, a network name, or an IP address. The optional mask is the netmask to use and may be supplied either in the traditional form (e.g., /255.255.255.0) or in the modern form (e.g., /24). -d [!] address[/mask] [!] [port], --destination [!] address[/mask] [port] Match packets from the destination address. See the description of -s for the syntax of this option. -j target, --jump target Jump to a special target or a user-defined chain. If this option is not specified for a rule, matching the rule only increases the rule's counters, and the packet is tested against the next rule. -i [!] name[+], --in-interface name[+] Match packets being received from interface name. name is the network interface used by your system (e.g., eth0 or ppp0). A + can be used as a wildcard, so ppp+ would match any interface name beginning with ppp -o [!] name[+], --out-interface name[+] Match packets being sent from interface name. See the description of -i for the syntax for name. [!] -f, [!]--fragment $PARAMETER The rule applies only to the second or further fragments of a fragmented packet. #### Options -v, --verbose Verbose mode. -n, --numeric Print all IP address and port numbers in numeric form. By default, text names are displayed when possible. -x, --exact Expand all numbers in a listing (-L). Display the exact value of the packet and byte counters instead of rounded figures. -m module, --match Explicitly load matching rule extensions associated with module. See the following section, "Match Extensions." -h [icmp], --help [icmp] Print help message. If icmp is specified, a list of valid ICMP type names will be printed. -h can also be used with the -m option to get help on an extension module. --line-numbers Used with the -L command. Add the line number to the beginning of each rule in a listing, indicating its position in the chain. #### Match extensions Several kernel modules come with netfilter to extend matching capabilities of rules. Those associated with particular protocols are loaded automatically when the -p option is used to specify the protocol. Others need to be loaded explicitly with the -m option. tcp Loaded when -p tcp is the only protocol specified. --source-port [!] [port][:port], --sport [!] [port][:port] Match the specified source ports. Using the colon specifies an inclusive range of services to match. If the first port is omitted, 0 is the default. If the second port is omitted, 65535 is the default. You can also use a dash instead of a colon to specify the range. --destination-port [!] [port][:port], --dport [!] [port][:port] Match the specified destination ports. The syntax is the same as for --source-port. --tcp-flags [!] mask comp Match the packets with the TCP flags specified by mask and comp. mask is a comma-separated list of flags that should be examined. comp is a comma-separated list of flags that must be set for the rule to match. Valid flags are SYN, ACK, FIN, RST, URG, PSH, ALL, and NONE. [!] --syn Match packets with the SYN bit set and the ACK and FIN bits cleared. These are packets that request TCP connections; blocking them prevents incoming connections. Shorthand for --tcp-flags SYN,RST,ACK SYN. udp Loaded when -p udp is the only protocol specified. --source-port [!] [port][:port], --sport [!] [port][:port] Match the specified source ports. The syntax is the same as for the --source-port option of the TCP extension. --destination-port [!] [port][:port], --dport [!] [port][:port] Match the specified destination ports. The syntax is the same as for --source-port option of the TCP extension. icmp Loaded when -p icmp is the only protocol specified. --icmp-type [!] type Match the specified icmp type. type may be a numeric ICMP type or one of the ICMP type names shown by the command iptables -p icmp -h. mac Loaded explicitly with the -m option. --mac-source [!] address Match the source address that transmitted the packet. address must be given in colon-separated hexbyte notation (for example, --mac-source 00:60:08:91:CC:B7. limit Loaded explicitly with the -m option. The limit extensions are used to limit the number of packets matched. This is useful when combined with the LOG target. Rules using this extension match until the specified limit is reached. --limit rate Match addresses at the given rate. rate is specified as a number with an optional /second, /minute, hour, or /day suffix. When this option is not set, the default is `'`3/hour`'`. --limit-burst [number] Set the maximum number of packets to match in a burst. Once the number has been reached, no more packets are matched for this rule until the number has recharged. It recharges at the rate set by the --limit option. When not specified, the default is 5. multiport Loaded explicitly with the -m option. The multiport extensions match sets of source or destination ports. These rules can be used only in conjunction with -p tcp and -p udp. Up to 15 ports can be specified in a comma-separated list. --source-port [ports] Match the given source ports. --destination-port [ports] Match the given destination ports. --port [ports] Match if the packet has the same source and destination port and that port is one of the given ports. mark Loaded explicitly with the -m option. This module works with the MARK extension target: --mark value[/mask] Match the given unsigned mark value. If a mask is specified, it is logically ANDed with the mark before comparison. owner Loaded explicitly with the -m option. The owner extensions match a local packet's creator's user, group process, and session IDs. This makes sense only as a part of the OUTPUT chain. --uid-owner userid Match packets created by a process owned by userid. --gid-owner groupid Match packets created by a process owned by groupid. --pid-owner processid Match packets created by process ID processid. --sid-owner sessionid Match packets created by a process in the session sessionid. state Loaded explicitly with the -m option. This module matches the connection state of a packet. --state states Match the packet if it has one of the states in the comma-separated list states. Valid states are INVALID, ESTABLISHED, NEW, and RELATED. tos Loaded explicitly with the -m option. This module matches the Type of Service field in a packet's header. --tos value Match the packet if it has a TOS of value. value can be a numeric value or a Type of Service name. iptables -m tos -h will give you a list of valid TOS values. #### Target extensions Extension targets are optional additional targets supported by separate kernel modules. They have their own associated options. LOG Log the packet's information in the system log. --log-level level Set the syslog level by name or number (as defined by syslog.conf). --log-prefix prefix Begin each log entry with the string prefix. The prefix string may be up to 30 characters long. --log-tcp-sequence Log the TCP sequence numbers. This is a security risk if your log is readable by users. --log-tcp-options Log options from the TCP packet header. --log-ip-options Log options from the IP packet header. MARK Used to mark packets with an unsigned integer value you can use later with the mark matching extension. Valid only with the mangle table. --set-mark value Mark the packet with value. REJECT Drop the packet and, if appropriate, send an ICMP message back to the sender indicating the packet was dropped. If the packet was an ICMP error message, an unknown ICMP type, or a nonhead fragment, or if too many ICMP messages have already been sent to this address, no message is sent. --reject-with type Send the specified ICMP message type. Valid values are icmp-net-unreachable, icmp-host- unreachable, icmp-port-unreachable, or icmp-proto-unreachable. If the packet was an ICMP ping packet, type may also be echo-reply. TOS Set the Type of Service field in the IP header. TOS is a valid target only for rules in the mangle table. --set-tos value Set the TOS field to value. You can specify this as an 8-bit value or as a TOS name. You can get a list of valid names using iptables -j TOS -h. SNAT Modify the source address of the packet and all future packets in the current connection. SNAT is valid only as a part of the POSTROUTING chain in the nat table. --to-source address[-address][port-port] Specify the new source address or range of addresses. If a tcp or udp protocol has been specified with the -p option, source ports may also be specified. If none is specified, map the new source to the same port if possible. If not, map ports below 512 to other ports below 512, those between 512 and 1024 to other ports below 1024, and ports above 1024 to other ports above 1024. DNAT Modify the destination address of the packet and all future packets in the current connection. DNAT is valid only as a part of the POSTROUTING chain in the nat table. --to-destination address[-address][port-port] Specify the new destination address or range of addresses. The arguments for this option are the same as the --to-source argument for the SNAT extension target. MASQUERADE Masquerade the packet so it appears that it originated from the current system. Reverse packets from masqueraded connections are unmasqueraded automatically. This is a legal target only for chains in the nat table that handle incoming packets and should be used only with dynamic IP addresses (like dial-up.) For static addresses use DNAT. --to-ports port[-port] Specify the port or range of ports to use when masquerading. This option is only valid if a tcp or udp protocol has been specified with the -p option. If this option is not used, the masqueraded packet's port will not be changed. REDIRECT [--to-port port] Redirect the packet to a local port. This is useful for creating transparent proxies. --to-ports port[-port] Specify the port or range of ports on the local system to which the packet should be redirected. This option is valid only if a tcp or udp protocol has been specified with the -p option. If this option is not used, the redirected packet's port will not be changed.
iptables-restore | iptables-restore [file] System administration command. Restore firewall rules. iptables-restore takes commands generated by iptables-save and uses them to restore the firewall rules for each chain. Often used by initialization scripts to restore firewall settings on boot. file is the name of a file whose contents were generated by iptables-save. If not specified, the command takes its input from stdin. This command was not completed at the time this book went to print. There may be options not listed here.
iptables-save | iptables-save [chain] System administration command. Print the IP firewall rules currently stored in the kernel to stdout. If no chain is given, all chains will be printed. Output may be redirected to a file that can later be used by iptables-restore to restore the firewall. This command was not completed at the time this book went to print. There may be options not listed here.
ispell | ispell [options] [files] Compare the words of one or more named files with the system dictionary. Display unrecognized words on the top of the screen, accompanied by possible correct spellings, and allow editing, via a series of commands. #### Options -b Back up original file in filename.bak. -d file Search file instead of standard dictionary file. -m Suggest different root/affix combinations. -n Expect nroff or troff input file. -p file Search file instead of personal dictionary file. -t Expect TeX or LaTeX input file. -w chars Consider chars to be legal, in addition to a-z and A-Z. -x Do not back up original file. -B Search for missing blanks (resulting in concatenated words) in addition to ordinary misspellings. -C Do not produce error messages in response to concatenated words. -L number Show number lines of context. -M List interactive commands at bottom of screen. -N Suppress printing of interactive commands. -P Do not attempt to suggest more root/affix combinations. -S Sort suggested replacements by likelihood that each is correct. -T type Expect all files to be formatted by type. -W n Never consider words that are n characters or less to be misspelled. -V Use hat notation (^L) to display control characters and M- to display characters with the high bit set. #### Interactive Commands ? Display help screen. space character Accept the word in this instance. number Replace with suggested word that corresponds to number. !command Invoke shell and execute command in it. Prompt before exiting. a Accept word as correctly spelled, but do not add it to personal dictionary. i Accept word and add it (capitalized, if so in file) to personal dictionary. l Search system dictionary for words. q Exit without saving. r Replace word. u Accept word and add lowercase version of it to personal dictionary. x Skip to the next file, saving changes. ^L Redraw screen. ^Z Suspend ispell.
join | join [options] file1 file2 Join lines of two sorted files by matching on a common field. If either file1 or file2 is -, read from standard input. #### Options -a filenum Print a line for each unpairable line in file filenum, in addition to the normal output. -e string Replace missing input fields with string. -i, --ignore-case Ignore case differences when comparing keys. -1 fieldnum1 Join field in file1 is fieldnum1. Default is the first field. -2 fieldnum2 Join field in file2 is fieldnum2. Default is the first field. -o fieldlist Order the output fields according to fieldlist, where each entry in the list is in the form filenum.fieldnum. Entries are separated by commas or blanks. -t char Specifies the field-separator character (default is whitespace ). -v filenum Print only unpairable lines from file filenum. --help Print help message and then exit. --version Print the version number and then exit.
kbd_mode | kbd_mode [option] Print or set the current keyboard mode, which may be RAW, MEDIUMRAW, or XLATE. #### Options -a Set mode to XLATE (ASCII mode). -k Set mode to MEDIUMRAW (keycode mode). -s Set mode to RAW (scancode mode). -u Set mode to UNICODE (UTF-8 mode).
kbdrate | kbdrate [options] System administration command. Control the rate at which the keyboard repeats characters, as well as its delay time. Using this command without options sets a repeat rate of 10.9 characters per second; the default delay is 250 milliseconds. When Linux boots, however, it sets the keyboard rate to 30 characters per second. #### Options -s Suppress printing of messages. -r rate Specify the repeat rate, which must be one of the following numbers (all in characters per second): 2.0, 2.1, 2.3, 2.5, 2.7, 3.0, 3.3, 3.7, 4.0, 4.3, 4.6, 5.0, 5.5, 6.0, 6.7, 7.5, 8.0, 8.6, 9.2, 10.0, 10.9, 12.0, 13.3, 15.0, 16.0, 17.1, 18.5, 20.0, 21.8, 24.0, 26.7, or 30.0. -d delay Specify the delay, which must be one of the following (in milliseconds): 250, 500, 750, or 1000.
kerneld | kerneld System administration command. kerneld automatically loads kernel modules when they are needed, thereby reducing kernel memory usage from unused loaded modules and replacing manual loading of modules with modprobe or insmod. If a module has not been used for more than one minute, kerneld automatically removes it. kerneld comes with the modules-utilities package and is set up during kernel configuration; its functionality is provided by interactions between that package and the kernel. kerneld is aware of most common types of modules. When more than one possible module can be used for a device (such as a network driver), kerneld uses the configuration file /etc/conf.modules, which contains path information and aliases for all loadable modules, to determine the correct module choice. kerneld can also be used to implement dial-on-demand networking, such as SLIP or PPP connections. The network connection request can be processed by kerneld to load the proper modules and set up the connection to the server.
kill | kill [option] IDs This is the /bin/kill command; there is also a shell command of the same name. Send a signal to terminate one or more process IDs. You must own the process or be a privileged user. If no signal is specified, TERM is sent. #### Options -l List all signals. -p Print the process ID of the named process, but don't send it a signal. To use this option, specify the full path (e.g., /bin/kill -p). -signal The signal number (from /usr/include/sys/signal.h) or name (from kill -l). With a signal number of 9 (HUP), the kill cannot be caught by the process; use this to kill a process that a plain kill doesn't terminate. The default is TERM.
killall | killall [options] names Kill processes by command name. If more than one process is running the specified command, kill all of them. Treat command names that contain a / as files; kill all processes that are executing that file. #### Options -signal Send signal to process (default is TERM). signal may be a name or number. -e Require an exact match to kill very long names (i.e., longer than 15 characters). Normally, killall kills everything that matches within the first 15 characters. With -e, such entries are skipped. (Use -v to print a message for each skipped entry.) -g Kill the process group to which the process belongs. -i Prompt for confirmation before killing processes. -l List known signal names. -q Quiet; do not complain of processes not killed. -v Verbose: after killing process, report success and process ID. -V Print version information. -w Wait for all killed processes to die. Note that killall may wait forever if the signal was ignored or had no effect, or if the process stays in zombie state.
killall5 | killall5 The System V equivalent of killall, this command kills all processes except those on which it depends.
klogd | klogd [options] System administration command. Control which kernel messages are displayed on the console; prioritize all messages, and log them through syslogd. On many operating systems, syslogd performs all the work of klogd, but on Linux the features are separated. Kernel messages are gleaned from the /proc filesystem and from system calls to syslogd. By default, no messages appear on the console. Messages are sorted into 8 levels, 0-7, and the level number is prepended to each message. #### Priority levels 0 Emergency situation (KERN_EMERG). 1 A crucial error has occurred (KERN_ALERT). 2 A serious error has occurred (KERN_CRIT). 3 An error has occurred (KERN_ERR). 4 A warning message (KERN_WARNING). 5 The situation is normal but should be checked (KERN_NOTICE). 6 Information only (KERN_INFO). 7 Debugging messages (KERN_DEBUG). #### Options -c level Print all messages of a higher priority (lower number) than level to the console. -d Debugging mode. -f file Print all messages to file; suppress normal logging. -k file Use file as source of kernel symbols. -n Avoid autobackgrounding. This is needed when klogd is started from init. -o One-shot mode. Prioritize and log all current messages, then immediately exit. -s Suppress reading of messages from the /proc filesystem. #### Files /usr/include/linux/kernel.h, /usr/include/sys/syslog.h Sources for definitions of each logging level /proc/kmsg A file examined by klogd for messages /var/run/klogd.pid klogd's process ID
ksyms | ksyms [options] System administration command. Print a list of all exported kernel symbols (name, address, and defining module, if applicable). #### Options -a Include symbols from unloaded modules. -h Suppress header message. -m Include starting address and size. Useful only for symbols in loaded modules. #### File /proc/ksyms Another source of the same information
lastlog | lastlog [options] System administration command. Print the last login times for system accounts. Login information is read from the file /var/log/lastlog. #### Options -t n Print only logins more recent than n days ago. -u name Print only login information for user name.
ld | ld [options] objfiles Combine several objfiles, in the specified order, into a single executable object module (a.out by default). ld is the link editor and is often invoked automatically by compiler commands. #### Options -c file Consult file for commands. -d, -dc, -dp Force the assignment of space to common symbols. -defsym symbol=expression Create the global symbol with the value expression. -e symbol Set symbol as the address of the output file's entry point. -i Produce a linkable output file; attempt to set its magic number to OMAGIC. -l arch Include the archive file arch in the list of files to link. -m linker Emulate linker. -n Make text read-only; attempt to set NMAGIC. -noinhibit-exec Produce output file even if errors are encountered. -o output Place output in output, instead of a.out. -oformat format Specify output format. -r Produce a linkable output file; attempt to set its magic number to OMAGIC. -s Do not include any symbol information in output. -shared Create a shared library. -sort-common Do not sort global common symbols by size. -t Announce each input file's name as it is processed. -u symbol Force symbol to be undefined. -v, --version Show version number. --verbose Print information about ld; print the names of input files while attempting to open them. -warn-common Warn when encountering common symbols combined with other constructs. -warn-once Provide only one warning per undefined symbol. -x With -s or -S, delete all local symbols that begin with L. -L dir Search directory dir before standard search directories (this option must precede the -l option that searches that directory). -M Display a link map on standard out. -Map file Print a link map to file. -N Allow reading of and writing to both data and text; mark ouput if it supports Unix magic numbers; do not page-align data. -R file Obtain symbol names and addresses from file, but suppress relocation of file and its inclusion in output. -S Do not include debugger symbol information in output. -Tbss address Begin bss segment of output at address. -Tdata address Begin data segment of output at address. -Ttext address Begin text segment of output at address. -Ur Synonymous with -r except when linking C++ programs, where it resolves constructor references. -X With -s or -S, delete local symbols beginning with L. -V Show version number and emulation linkers for -m option.
ldconfig | ldconfig [options] directories System administration command. Examine the libraries in the given directories, /etc/ld.so.conf, /usr/lib, and /lib; update links and cache where necessary. Usually run in startup files or after the installation of new shared libraries. #### Options -D Debug. Suppress all normal operations. -l Library mode. Expect libraries as arguments, not directories. Manually link specified libraries. -n Suppress examination of /usr/lib and /lib and reading of /etc/ld.so.conf; do not cache. -N Do not cache; only link. -p Print all directories and candidate libraries in the cache. Expects no arguments. -v Verbose. Include version number, and announce each directory as it is scanned and links as they are created. -X Do not link; only rebuild cache. #### Files /lib/ld.so Linker and loader. /etc/ld.so.conf List of directories that contain libraries. /etc/ld.so.cache List of the libraries found in those libraries mentioned in /etc/ld.so.conf.
ldd | ldd [options] programs Display a list of the shared libraries each program requires. #### Options -v Display ldd's version. -V Display the linker's version.
less | less [options] [filename] less is a program for paging through files or other output. It was written in reaction to the perceived primitiveness of more (hence its name). Some commands may be preceded by a number. #### Options -[z]num Set number of lines to scroll to num. Default is one screenful. A negative num sets the number to num lines less than the current number. +[+]command Run command on startup. If command is a number, jump to that line. The option ++ applies this command to each file in the command-line list. -? Print help screen. Ignore all other options; do not page through file. -a When searching, begin after last line displayed. (Default is to search from second line displayed.) -b buffers Use buffers buffers for each file (default is 10). Buffers are 1 kilobyte in size. -c Redraw screen from top, not bottom. -d Suppress dumb-terminal error messages. -e Automatically exit after reaching EOF twice. -f Force opening of directories and devices; do not print warning when opening binaries. -g Highlight only string found by past search command, not all matching strings. -h num Never scroll backward more than num lines at once. -i Make searches case-insensitive, unless the search string contains uppercase letters. -j num Position target line on line num of screen. Target line can be the result of a search or a jump. Count lines beginning from 1 (top line). A negative num is counted back from bottom of screen. -k file Read file to define special key bindings. -m Display more-like prompt, including percent of file read. -n Do not calculate line numbers. Affects -m and -M options and = and v commands (disables passing of line number to editor). -o file When input is from a pipe, copy output to file as well as to screen. (Prompt for overwrite authority if file exists.) -p pattern At startup, search for first occurrence of pattern. m Set medium prompt (specified by -m). M Set long prompt (specified by -M). = Set message printed by = command. -q Disable ringing of bell on attempts to scroll past EOF or before beginning of file. Attempt to use visual bell instead. -r Display "raw" control characters, instead of using ^x notation. Sometimes leads to display problems. -s Print successive blank lines as one line. -t tag Edit file containing tag. Consult ./tags (constructed by ctags). -u Treat backspaces and carriage returns as printable input. -w Print lines after EOF as blanks instead of tildes (~). -x n Set tab stops to every n characters. Default is 8. -y n Never scroll forward more than n lines at once. -B Do not automatically allocate buffers for data read from a pipe. If -b specifies a number of buffers, allocate that many. If necessary, allow information from previous screens to be lost. -C Redraw screen by clearing it and then redrawing from top. -E Automatically exit after reaching EOF once. -G Never highlight matching search strings. -I Make searches case-insensitive, even when the search string contains uppercase letters. -M Prompt more verbosely than with -m, including percentage, line number, and total lines. -N Print line number before each line. -O file Similar to -o but does not prompt when overwriting file. -P[m,M,=]prompt Set prompt (as defined by -m, -M, or =). Default is short prompt (-m). -Q Never ring terminal bell. -S Cut, do not fold, long lines. -T file With the -t option or :t command, read file instead of ./tags. -U Treat backspaces and carriage returns as control characters. -X Do not send initialization and deinitialization strings from termcap to terminal. #### Commands Many commands can be preceded by a numeric argument, referred to as number in the command descriptions. SPACE, ^V, f, ^F Scroll forward the default number of lines (usually one windowful). z Similar to SPACE but allows the number of lines to be specified, in which case it resets the default to that number. RETURN, ^N, e, ^E, j, ^J Scroll forward. Default is one line. Display all lines, even if the default is more lines than the screen size. d, ^D Scroll forward. Default is one-half the screen size. The number of lines may be specified, in which case the default is reset. b, ^B, ESC-v Scroll backward. Default is one windowful. w Like b but allows the number of lines to be specified, in which case it resets the default to that number. y, ^Y, ^P, k, ^K Scroll backward. Default is one line. Display all lines, even if the default is more lines than the screen size. u, ^U Scroll backward. Default is one-half the screen size. The number of lines may be specified, in which case the default is reset. r, ^R, ^L Redraw screen. R Like r but discard buffered input. F Scroll forward. When an EOF is reached, continue trying to find more output, behaving similarly to tail -f. g, <, ESC-< Skip to a line. Default is 1. G, >, ESC-> Skip to a line. Default is the last one. p, % Skip to a position number percent of the way into the file. { If the top line on the screen includes a {, find its matching }. If the top line contains multiple {s, use number to determine which one to use in finding a match. } If the bottom line on the screen includes a }, find its matching {. If the bottom line contains multiple }s, use number to determine which one to use in finding a match. ( If the top line on the screen includes a (, find its matching ). If the top line contains multiple (s, use number to determine which one to use in finding a match. ) If the bottom line on the screen includes a ), find its matching (. If the bottom line contains multiple )s, use number to determine which one to use in finding a match. [ If the top line on the screen includes a [, find its matching ]. If the top line contains multiple [s, use number to determine which one to use in finding a match. ] If the bottom line on the screen includes a ], find its matching [. If the bottom line contains multiple ]s, use number to determine which one to use in finding a match. ESC-^F Behave like { but prompt for two characters, which it substitutes for { and } in its search. ESC-^B Behave like } but prompt for two characters, which it substitutes for { and } in its search. m Prompt for a lowercase letter and then use that letter to mark the current position. ' Prompt for a lowercase letter and then go to the position marked by that letter. There are some special characters: ' Return to position before last "large movement." ^ Beginning of file. $ End of file. ^X^X Same as '. /pattern Find next occurrence of pattern, starting at second line displayed. Some special characters can be entered before pattern: ! Find lines that do not contain pattern. * If current file does not contain pattern, continue through the rest of the files in the command line list. @ Search from the first line in the first file specified on the command line, no matter what the screen currently displays. ?pattern Search backward, beginning at the line before the top line. Treats !, *, and @ as special characters when they begin pattern, as / does. ESC-/pattern Same as /*. ESC-?pattern Same as ?*. n Repeat last pattern search. N Repeat last pattern search, in the reverse direction. ESC-n Repeat previous search command but as though it were prefaced by *. ESC-N Repeat previous search command but as though it were prefaced by * and in the opposite direction. ESC-u Toggle search highlighting. :e [filename] Read in filename and insert it into the command-line list of filenames. Without filename, reread the current file. filename may contain special characters: % Name of current file # Name of previous file ^X^V, E Same as :e. :n Read in next file in command-line list. :p Read in previous file in command-line list. :x Read in first file in command-line list. :f, =, ^G Print filename, position in command-line list, line number on top of window, total lines, byte number, and total bytes. - Expects to be followed by a command-line option letter. Toggles the value of that option or, if appropriate, prompts for its new value. -+ Expects to be followed by a command-line option letter. Resets that option to its default. -- Expects to be followed by a command-line option letter. Resets that option to the opposite of its default, where the opposite can be determined. _ Expects to be followed by a command-line option letter. Display that option's current setting. +command Execute command each time a new file is read in. q, :q, :Q, ZZ Exit. v Not valid for all versions. Invoke editor specified by $VISUAL or $EDITOR, or vi if neither is set. ! [command] Not valid for all versions. Invoke $SHELL or sh. If command is given, run it and then exit. Special characters: % Name of current file # Name of previous file !! Last shell command | mark-letter command Not valid for all versions. Pipe fragment of file (from first line on screen to mark-letter) to command. mark-letter may also be: ^ Beginning of file. $ End of file. ., newline Current screen is piped. #### Prompts The prompt interprets certain sequences specially. Those beginning with % are always evaluated. Those beginning with ? are evaluated if certain conditions are true. Some prompts determine the position of particular lines on the screen. These sequences require that a method of determining that line be specified. See the -P option and the manpage for more information.
ln | ln [options] sourcename [destname] ln [options] sourcenames destdirectory Create pseudonyms (links) for files, allowing them to be accessed by different names. In the first form, link sourcename to destname, where destname is usually a new filename, or (by default) the current directory. If destname is an existing file, it is overwritten; if destname is an existing directory, a link named sourcename is created in that directory. In the second form, create links in destdirectory, each link having the same name as the file specified. #### Options -b, --backup Back up files before removing the originals. -d, -F, --directory Allow hard links to directories. Available to privileged users. -f, --force Force the link (don't prompt for overwrite permission). --help Print a help message and then exit. -i, --interactive Prompt for permission before removing files. -n, --no-dereference Replace symbolic links to directories instead of dereferencing them. --force is useful with this option. -s, --symbolic Create a symbolic link. This lets you link across filesystems and also see the name of the link when you run ls -l (otherwise, there's no way to know the name that a file is linked to). -S suffix, --suffix suffix Append suffix to files when making backups, instead of the default ~. -v, --verbose Verbose mode. --version Print version information and then exit. -V, --version-control value Control the types of backups made. The acceptable values for version-control are: t, numbered Numbered. nil,existing Simple (~) unless a numbered backup exists; then make a numbered backup. never, simple Simple.
locate | locate [options] pattern Search database(s) of filenames and print matches. *, ?, [, and ] are treated specially; / and . are not. Matches include all files that contain pattern, unless pattern includes metacharacters, in which case locate requires an exact match. #### Options -d path, --database=path Search databases in path. path must be a colon- separated list. -h, --help Print a help message and then exit. --version Print version information and then exit.
lockfile | lockfile [options] filenames Create semaphore file(s), used to limit access to a file. When lockfile fails to create some of the specified files, it pauses for 8 seconds and retries the last one on which it failed. The command processes flags as they are encountered (i.e., a flag that is specified after a file will not affect that file). #### Options -sleeptime Time lockfile waits before retrying after a failed creation attempt. Default is 8 seconds. -! Invert return value. Useful in shell scripts. -l lockout_time Time (in seconds) after a lockfile was last modified at which it will be removed by force. See also -s. -ml, -mu If the permissions on the system mail spool directory allow it or if lockfile is suitably setgid, it can lock and unlock your system mailbox with the options -ml and -mu, respectively. -r retries Stop trying to create files after retries retries. The default is -1 (never stop trying). When giving up, remove all created files. -s suspend_time After a lockfile has been removed by force (see -l), a suspension of 16 seconds takes place by default. (This is intended to prevent the inadvertent immediate removal of any lockfile newly created by another program.) Use -s to change the default 16 seconds.
logger | logger [options] [message...] TCP/IP command. Add entries to the system log (via syslogd). A message can be given on the command line, or standard input is logged. #### Options -f file Read message from file. -i Include the process ID of the logger process. -p pri Enter message with the specified priority pri. Default is user.notice. -t tag Mark every line in the log with the specified tag.
login | login [name | option] Log in to the system. login asks for a username (name can be supplied on the command line) and password (if appropriate). If successful, login updates accounting files, sets various environment variables, notifies users if they have mail, and executes startup shell files. Only the root user can log in when /etc/nologin exists. That file is displayed before the connection is terminated. Furthermore, root may connect only on a tty that is listed in /etc/securetty. If ~/.hushlogin exists, execute a quiet login. If /var/adm/lastlog exists, print the time of the last login. #### Options -f Suppress second login authentication. -h host Specify name of remote host. Normally used by servers, not humans; may be used only by root. -p Preserve previous environment.
logname | logname [option] Consult /var/run/utmp for user's login name. If found, print it; otherwise, exit with an error message. #### Options --help Print a help message and then exit. --version Print version information and then exit.
logrotate | logrotate [options] config_files System administration command. Manipulate log files according to commands given in config_files. #### Options -d Debug mode. No changes will be made to log files. -s, --state file Save state information in file. The default is /var/lib/logrotate.status. --usage Usage version and copyright information. #### Commands compress Compress old versions of log files with gzip. copytruncate Copy log file, then truncate it in place. For use with programs whose logging cannot be temporarily halted. create [permissions] [owner] [group] After rotation, re-create log file with the specified permissions, owner, and group. permissions must be in octal. If any of these parameters is missing, the log file's original attributes will be used. daily Rotate log files every day. delaycompress Don't compress log file until the next rotation. errors address Mail any errors to the given address. endscript End a postrotate or prerotate script. ifempty Rotate log file even if it is empty. Overrides the default notifempty option. include file Read the file into current file. If file is a directory, read all files in that directory into the current file. mail address Mail any deleted logs to address. monthly Rotate log files only the first time logrotate is run in a month. nocompress Override compress. nocopytruncate Override copytruncate. nocreate Override create. nodelaycompress Override delaycompress. noolddir Override olddir. notifempty Override ifempty. olddir directory Move logs into directory for rotation. directory must be on the same physical device as the original log files. postrotate Begin a script of directives to apply after the log file is rotated. The script ends when the endscript directive is read. prerotate Begin a script of directives to apply before a log file is rotated. The script ends when the endscript directive is read. rotate number The number of times to rotate a log file before removing it. size n[k|M] Rotate log file when it is greater than n bytes. n can optionally be followed by k for kilobytes or M for megabytes.
look | look [options] string [file] Search for lines in file (/usr/dict/words by default) that begin with string. #### Options -a Use alternate dictionary /usr/dict/web2. -d Compare only alphanumeric characters. -f Search is not case-sensitive. -t character Stop checking after the first occurrence of character.
lpc | lpc [command] System administration command. Control line printer. If executed without a command, lpc will accept commands from standard input. #### Commands ?, help [commands] Get a list of commands or help on specific commands. abort all|printer Terminate current printer daemon and disable printing for the specified printer. clean all|printer Remove files that cannot be printed from the specified printer queues. disable all|printer Disable specified printer queues. down all|printer message Disable specified printer queues and put message in the printer status file. enable all|printer Enable the specified printer queues. exit, quit Exit lpc. restart all|printer Try to restart printer daemons for the specified printers. start all|printer Enable the printer queues and start printing daemons for the specified printers. status all|printer Return the status of the specified printers. stop all|printer Disable the specified printer daemons after any current jobs are completed. topq printer [jobnumbers] [users] Put the specifed jobs at the top of the printer's queue in the order the jobs are listed. up all|printer Enable print queues and restart daemons for the specified printers.
lpd | lpd [option] [port] TCP/IP command. Line printer daemon. lpd is usually invoked at boot time from the rc2 file. It makes a single pass through the printer configuration file (traditionally /etc/printcap) to find out about the existing printers and prints any files left after a crash. It then accepts requests to print files in a queue, transfer files to a spooling area, display a queue's status, or remove jobs from a queue. In each case, it forks a child process for each request, then continues to listen for subsequent requests. If port is specified, lpd listens on that port; otherwise, it uses the getservbyname call to ascertain the correct port. The file lock in each spool directory prevents multiple daemons from becoming active simultaneously. After the daemon has set the lock, it scans the directory for files beginning wth cf. Lines in each cf file specify files to be printed or nonprinting actions to be performed. Each line begins with a key character, which specifies information about the print job or what to do with the remainder of the line. Key characters are: C Classification -- string to be used for the classification line on the burst page. c cifplot file. f Formatted file -- name of a file to print that is already formatted. g Graph file. H Hostname -- name of machine where lpd was invoked. J Job name -- string to be used for the jobname on the burst page. L Literal -- this line contains identification information from the password file and causes the banner page to be printed. l Formatted file, but suppress page breaks and printing of control characters. M Mail -- send mail to the specified user when the current print job completes. n ditroff file. P Person -- login name of person who invoked lpd. r DVI file. T Title -- string to be used as the title for pr. t troff file. U Unlink -- name of file to remove upon completion of printing. #### Option -l Enable logging of all valid requests. #### Files /etc/printcap Printer description file /var/spool/* Spool directories /var/spool/*/minfree Minimum free space to leave /dev/lp* Printer devices /etc/hosts.equiv Machine names allowed printer access /etc/hosts.lpd Machine names allowed printer access, but not under same administrative control
lpq | lpq [options] [user] Check the print spool queue for status of print jobs. For each job, display username, rank in the queue, filenames, job number, and total file size (in bytes). If user is specified, display information only for that user. #### Options -l Print information about each file comprising a job. -P printer Specify which printer to query. Without this option, lpq uses the printer set in the PRINTER environment variable or the default system printer. num Check status for job number num.
lpr | lpr [options] files Send files to the printer spool queue. #### Options -c Expect data produced by cifplot. -d Expect data produced by TeX in the DVI (device- independent) format. -f Use a filter that interprets the first character of each line as a standard carriage control character. -g Expect standard plot data as produced by the plot routines. -l Use a filter that allows control characters to be printed and suppresses page breaks. -n Expect data from ditroff (device-independent troff). -p Use pr to format the files. -t Expect data from troff (phototypesetter commands). -v Expect a raster image for devices like the Benson Varian. -P printer Output to printer instead of the printer specified in the PRINTER environment variable or the system default. -h Do not print the burst page. -m Send mail to notify of completion. -r Remove the file upon completion of spooling. Cannot be used with the -s option. -s Use symbolic links instead of copying files to the spool directory. This can save time and disk space for large files. Files should not be modified or removed until they have been printed. -`#`num Print num copies of each listed file. -C string Replace system name on the burst page with string. -J name Replace the job name on the burst page with name. If omitted, uses the first file's name. -T title Use title as the title when using pr. -i [cols] Indent the output. Default is 8 columns. Specify number of columns to indent with the cols argument. -w num Set num characters as the page width for pr.
lprm | lprm [options] [jobnum] [user] Remove a print job from the print spool queue. You must specify a job number or numbers, which can be obtained from lpq. A privileged user may use the user parameter to remove all files belonging to a particular user or users. #### Options -P printer Specify printer name. Normally, the default printer or printer specified in the PRINTER environment variable is used. - Remove all jobs in the spool owned by user.
lpstat | lpstat [options] Show the status of the print queue. With options that take a list argument, omitting the list produces all information for that option. list can be separated by commas or, if enclosed in double quotes, by spaces. #### Options -a [list] Show whether the list of printer or class names is accepting requests. -c [list] Show information about printer classes named in list. -d Show the default printer destination. -f [list] Verify that the list of forms is known to lp. -l Use after -f to describe available forms, after -p to show printer configurations, or after -s to describe printers appropriate for the specified character set or print wheel. -o [list] Show the status of output requests. list contains printer names, class names, or request IDs. -p [list] Show the status of printers named in list. -r Show whether the print scheduler is on or off. -R Show the job's position in the print queue. -s Summarize the print status (shows almost everything). -t Show all status information (reports everything). -u [list] Show request status for users on list. list can be all to show information on all users. -v [list] Show device associated with each printer named in list.
lptest | lptest [length] [count] Generate a lineprinter test pattern on standard output. Prints a standard ripple pattern of all printable ASCII characters, offset by one position on each succeeding line. #### Parameters length Specify the output line length (default is 79). count Specify the number of lines to print (default is 200).
> ls | ls [options] [names] List contents of directories. If no names are given, list the files in the current directory. With one or more names, list files contained in a directory name or that match a file name. names can include filename metacharacters. The options let you display a variety of information in different formats. The most useful options include -F, -R, -l, and -s. Some options don't make sense together (e.g., -u and -c). #### Options -1, --format=single-column Print one entry per line of output. -a List all files, including the normally hidden files whose names begin with a period. -b, --escape Display nonprinting characters in octal and alphabetic format. -c, --time-ctime, --time=status List files by status change time (not creation/modification time). --color, --colour, --color=yes, --colour=yes Colorize the names of files depending on the type of file. --color=no, --colour=no Disables colorization. This is the default. Provided to override a previous color option. --color=tty, --colour=tty Same as --color, but only if standard output is a terminal. Very useful for shell scripts and command aliases, especially if your favorite pager does not support color control codes. -d, --directory Report only on the directory, not its contents. -f Print directory contents in exactly the order in which they are stored, without attempting to sort them. --full-time List times in full, rather than use the standard abbreviations. --help Print a help message and then exit. -i, --inode List the inode for each file. -k, --kilobytes If file sizes are being listed, print them in kilobytes. This option overrides the environment variable POSIXLY_CORRECT. -l, --format=long, --format=verbose Long format listing (includes permissions, owner, size, modification time, etc.). -m, --format=commas Merge the list into a comma-separated series of names. -n, --numeric-uid-gid Like -l, but use group-ID and user-ID numbers instead of owner and group names. -p Mark directories by appending `/` to them. -q, --hide-control-chars Show nonprinting characters as `?`. -r, --reverse List files in reverse order (by name or by time). -s, --size Print size of the files in blocks. -t, --sort=time Sort files according to modification time (newest first). -u, --time=atime, --time=access, --time=use Sort files according to the file access time. --version Print version information on standard output, then exit. -x, --format=across, --format=horizontal List files in rows going across the screen. -A, --almost-all List all files, including the normally hidden files whose names begin with a period. Does not include the . and . directories. -B, --ignore-backups Do not list files ending in ~, unless given as arguments. -C, --format=vertical List files in columns (the default format). -F, --classify Flag filenames by appending `/` to directories, `*` to executable files, `@` to symbolic links, `|` to FIFOs, and `=` to sockets. -G, --no-group In long format, do not display group name. -I, --ignore pattern Do not list files whose names match the shell pattern pattern, unless they are given on the command line. -L, --dereference List the file or directory referenced by a symbolic link rather than the link itself. -N, --literal Do not list filenames. -Q, --quote-name Quote filenames with `"`; quote nongraphic characters with alphabetic and octal backslash sequences. -R, --recursive Recursively list subdirectories as well as the specified (or current) directory. -S, --sort=size Sort by file size, largest to smallest. -T, --tabsize n_cols Assume that each tabstop is n_cols columns wide. The default is 8. -U, --sort=none Do not sort files. Similar to -f but display in long format. -X, --sort=extension Sort by file extension. #### Examples List all files in the current directory and their sizes; use multiple columns and mark special files:
>     ls -asCF
> List the status of directories /bin and /etc:
>     ls -ld /bin /etc
> List C source files in the current directory, the oldest first:
>     ls -rt *.c
> Count the nonhidden files in the current directory:
>     ls | wc -l
lsattr | lsattr [options] [files] Print attributes of files on a Linux Second Extended File System. See also chattr. #### Options -a List all files in specified directories. -d List directories' attributes, not the attributes of the contents. -R List directories and their contents recursively. -v List version of files. -V List version and then exit.
lsmod | lsmod System administration command. List all loaded modules: their name, size (in 4KB units) and, if appropriate, a list of referring modules. #### File /proc/modules Source of the same information.
m4 | m4 [options] [macros] [files] Macro processor for C and other files. #### Options -e, --interactive Operate interactively, ignoring interrupts. -d flags, --debug=flags Specify flag-level debugging. -l n, --arglength=n Specify the length of debugging output. -o file, --error-output=file Place output in file. Despite the name, print error messages on standard error. -p, --prefix-built-ins Prepend m4_ to all built-in macro names. -s, --synclines Insert #line directives for the C preprocessor. -B n Set the size of the push-back and argument collection buffers to n (default is 4096). -D name[=value], --define=name[=value] Define name as value or, if value is not specified, define name as null. -E, --fatal-warnings Consider all warnings to be fatal, and exit after the first of them. -F file, --freeze-state file Record m4's frozen state in file, for later reloading. -G, --traditional Behave like traditional m4, ignoring GNU extensions. -H n, --hashsize=n Set symbol-table hash array to n (default is 509). -I directory, --include=directory Search directory for include files. -Q, --quiet, --silent Suppress warning messages. -R file, --reload-state file Load state from file before starting execution. -U name, --undefine=name Undefine name.
> mail | mail [options] [users] Read mail or send mail to other users. The mail utility allows you to compose, send, receive, forward, and reply to mail. mail has two main modes: compose mode, in which you create a message, and command mode, in which you manage your mail. While mail is a powerful utility, it can be tricky for a novice user. Most Linux distributions include pine and elm, which are much easier to use. This section presents mail commands, options, and files. To get you started, here are two of the most basic commands. To enter interactive mail-reading mode, type:
>     mail
> To begin writing a message to user, type:
>     mail user
Enter the text of the message, one line at a time, pressing Enter at the end of each line. To end the message, enter a single period (`.`) in the first column of a new line, and press Enter. #### Command-line options -b list Set blind carbon copy field to comma-separated list. -c list Set carbon copy field to comma-separated list. -d Print debugging information. -f [file] Process contents of file, instead of /var/spool/mail/$user. If file is omitted, process mbox in the user's home directory. -i Do not respond to tty interrupt signals. -n Do not consult /etc/mail.rc when starting up. -p Read mail in POP mode. -s subject Set subject to subject. -u Process contents of /var/spool/mail/$user. Default. -v Verbose. Print information about mail delivery to standard out. -I Interactive -- even when standard input has been redirected from the terminal. -N When printing a mail message or entering a mail folder, do not display message headers. -P Disable POP mode. #### Compose-mode commands ~! Execute a shell escape from compose mode. ~? List compose mode escapes. ~b names Add names to or edit the Bcc: header. ~c names Add names to or edit the Cc: header. ~d Read in the dead.letter file. ~e Invoke text editor. ~f messages Insert messages into message being composed. ~F messages Similar to ~f, but include message headers. ~h Add to or change all the headers interactively. ~m messages Similar to ~f, but indent with a tab. ~M messages Similar to ~m, but include message headers. ~p Print message header fields and message being sent. ~q Abort current message composition. ~r filename Append file to current message. ~s string Change Subject: header to string. ~t names Add names to or edit the To list. ~v Invoke editor specified with the VISUAL environment variable. ~| command Pipe message through command. ~: mail-command Execute mail-command. ~~string Insert string in text of message, prefaced by a single tilde (~). If string contains a ~, it must be escaped with a \. #### Command-mode commands
? | List summary of commands (help screen).
! | Execute a shell command.
- num | Print numth previous message; defaults to immediately previous.
alias (a) | Print or create alias lists.
alternates (alt) | Specify remote accounts on remote machines that are yours. Tell mail not to reply to them.
chdir (c) | cd to home or specified directory.
copy (co) | Similar to save, but do not mark message for deletion.
delete (d) | Delete message.
dp | Delete current message and display next one.
edit (e) | Edit message.
exit (ex, x) | Exit mail without updating folder.
file (fi) | Switch folders.
folder (fold) | Read messages saved in a file. Files can be:
| # Previous
| % System mailbox
| %user user's system mailbox
| & mbox
| +folder File in folder directory.
folders | List folders.
headers (h) | List message headers at current prompt.
headers+ (h+) | Move forward one window of headers.
headers- (h-) | Move back one window of headers.
help | Same as ?.
hold (ho) | Hold messages in system mailbox.
ignore | Append list of fields to ignored fields.
mail user (m) | Compose message to user.
mbox | Default. Move specified messages to mbox on exiting.
next (n) | Type next message or next message that matches argument.
preserve (pr) | Synonym for hold.
print [list] (p) | Display each message in list.
Print [list] (P) | Similar to print, but include header fields.
quit (q) | Exit mail and update folder.
reply (r) | Send mail to all on distribution list.
Reply (R) | Send mail to author only.
respond | Same as reply.
retain | Always include this list of header fields when printing messages. With no arguments, list retained fields.
save (s) | Save message to folder.
saveignore | Remove ignored fields when saving.
saveretain | Override saveignore to retain specified fields.
set (se) | Set or print mail options.
shell (sh) | Enter a new shell.
size | Print size of each specified message.
source | Read commands from specified file.
top | Print first few lines of each specified message.
type (t) | Same as print.
Type (T) | Same as Print.
unalias | Discard previously defined aliases.
undelete (u) | Restore deleted message.
unread (U) | Mark specified messages as unread.
unset (uns) | Unset mail options.
visual (v) | Edit message with editor specified by the VISUAL environment variable.
write (w) | Write message, without header, to file.
xit (x) | Same as exit.
z | Move mail's attention to next windowful of text. Use z- to move it back.
#### mail options These options are used inside of the .mailrc file. The syntax is set option or unset option.
append | Append (do not prepend) messages to mbox.
ask | Prompt for subject.
askbcc | Prompt for blind carbon copy recipients.
askcc | Prompt for carbon copy recipients.
asksub | Prompt for Subject line.
autoprint | Print next message after a delete.
chron | Display messages in chronological order, most recent last.
debug | Same as -d on command line.
dot | Interpret a solitary . as an EOF.
folder | Define directory to hold mail folders.
hold | Keep message in system mailbox upon quitting.
ignore | Ignore interrupt signals from terminal. Print them as @.
ignoreeof | Do not treat ^D as an EOF.
metoo | Do not remove sender from groups when mailing to them.
noheader | Same as -N on command line.
nokerberos | Retrieve POP mail via POP3, not KPOP, protocol.
nosave | Do not save aborted letters to dead.letter.
pop-mail | Retrieve mail with POP3 protocol, and save it in mbox.pop.
prompt | Set prompt to a different string.
Replyall | Switch roles of Reply and reply.
quiet | Do not print version at startup.
searchheaders | When given the specifier /x:y, expand all messages that contain the string y in the x header field.
verbose | Same as -v on command line.
verbose-pop | Display status while retrieving POP mail.
#### Special files
calendar | Contains reminders that the operating system mails to you.
.maildelivery | Mail delivery configuration file.
.mailrc | Mail configuration file.
triplog | Keeps track of your automatic response recipients.
tripnote | Contains automatic message.
mailq | mailq [option] System administration command. List all messages in the sendmail mail queue. Equivalent to sendmail -bp. #### Option -v Verbose mode.
mailstats | mailstats [options] System administration command. Display a formatted report of the current sendmail mail statistics. #### Options -C file Use sendmail configuration file file instead of the default sendmail.cf file. -f file Use sendmail statistics file file instead of the file specified in the sendmail configuration file. -o Don't show the name of the mailer in the report.
> make | make [options] [targets] [macro definitions] Update one or more targets according to dependency instructions in a description file in the current directory. By default, this file is called makefile or Makefile. Options, targets, and macro definitions can be in any order. Macros definitions are typed as:
>     name=string
  > For more information on make, see Managing Projects with make by Andrew Oram and Steve Talbott. #### Options -d, --debug Print detailed debugging information. -e, --environment-overrides Override makefile macro definitions with environment variables. -f makefile, --file=makefile, --makefile=makefile Use makefile as the description file; a filename of `-` denotes standard input. -h, --help Print options to make command. -i, --ignore-errors Ignore command error codes (same as .IGNORE). -j [jobs], --jobs [=jobs] Attempt to execute jobs jobs simultaneously, or, if no number is specified, as many jobs as possible. -k, --keep-going Abandon the current target when it fails, but keep working with unrelated targets. -l [load], --load-average [=load], --max-load [=load] Attempt to keep load below load, which should be a floating-point number. Used with -j. -n, --just-print, --dry-run, --recon Print commands but don't execute (used for testing). -o file, --old-file=file, --assume-old=file Never remake file or cause other files to be remade on account of it. -p, --print-data-base Print rules and variables in addition to normal execution. -q, --question Query; return 0 if file is up-to-date; nonzero otherwise. -r, --no-built-in-rules Do not use default rules. -s, --silent, --quiet Do not display command lines (same as .SILENT). -t, --touch Touch the target files, without remaking them. -v, --version Show version of make. -w, --print-directory Display the current working directory before and after execution. --warn -undefined -variables Print warning if a macro is used without being defined. -C directory, --directory directory cd to directory before beginning make operations. A subsequent -C directive will cause make to attempt to cd into a directory relative to the current working directory. -I directory, --include-dir directory Include directory in list of directories that contain included files. -S, --no-keep-going, --stop Cancel previous -k options. Useful in recursive makes. -W file, --what-if file, --new-file file, --assume-new file Behave as though file has been recently updated. #### Description file lines Instructions in the description file are interpreted as single lines. If an instruction must span more than one input line, use a backslash (\) at the end of the line so that the next line is considered as a continuation. The description file may contain any of the following types of lines: Blanklines Blank lines are ignored. Commentlines A pound sign (#) can be used at the beginning of a line or anywhere in the middle. make ignores everything after the #. Dependencylines Depending on one or more targets, certain commands that follow will be executed. Possible formats include:
  >     targets : dependencies
  >     targets : dependencies ; command
  > Subsequent commands are executed if dependency files (the names of which may contain wildcards) do not exist or are newer than a target. If no prerequisites are supplied, then subsequent commands are always executed (whenever any of the targets are specified). No tab should precede any targets. Suffixrules These specify that files ending with the first suffix can be prerequisites for files ending with the second suffix (assuming the root filenames are the same). Either of these formats can be used:
  >     .suffix.suffix:
  >     .suffix:
  > The second form means that the root filename depends on the filename with the corresponding suffix. Commands Commands are grouped below the dependency line and are typed on lines that begin with a tab. If a command is preceded by a hyphen (-), make ignores any error returned. If a command is preceded by an at sign (@), the command line won't echo on the display (unless make is called with -n). macrodefinitions These have the following form:
  >     name = string
  > or
  >     define name
  >     string
  >     endef
  > Blank space is optional around the =. includestatements Similar to the C include directive, these have the form:
  >     include files
> #### Internal macros $? The list of prerequisites that have been changed more recently than the current target. Can be used only in normal description file entries -- not suffix rules. $@ The name of the current target, except in description file entries for making libraries, where it becomes the library name. Can be used both in normal description file entries and in suffix rules. $< The name of the current prerequisite that has been modified more recently than the current target. $* The name -- without the suffix -- of the current prerequisite that has been modified more recently than the current target. Can be used only in suffix rules. $% The name of the corresponding .o file when the current target is a library module. Can be used both in normal description file entries and in suffix rules. $^ A space-separated list of all dependencies, with no duplications. $+ A space-separated list of all dependencies, including duplications. #### Pattern rules These are a more general application of the idea behind suffix rules. If a target and a dependency both contain %, GNU make will substitute any part of an existing filename. For instance, the standard suffix rule:
>     $(cc) -o $@ $<
> can be written as the following pattern rule:
>     %.o : %.c
>     $(cc) -o $@ $<
  > #### Macro modifiers D The directory portion of any internal macro name except $?. Valid uses are:
  >     $(*D)   $$(@D)   $(?D)   $(<D)
  >     $(%D)   $(@D)    $(^D)
  > F The file portion of any internal macro name except $?. Valid uses are:
  >     $(*F)   $$(@F)   $(?F)   $(<F)
  >     $(%F)   $(@F)    $(^F)
#### Functions $(subst from, to, string) Replace all occurrences of from with to in string. $(patsubst pattern, to, string) Similar to subst, but treat % as a wildcard within pattern. Substitute to for any word in string that matches pattern. $(strip string) Remove all extraneous whitespace. $(findstring substring, mainstring) Return substring if it exists within mainstring; otherwise, return null. $(filter pattern, string) Return those words in string that match at least one word in pattern. patterns may include the wildcard %. $(filter-out pattern, string) Remove those words in string that match at least one word in pattern. patterns may include the wildcard %. $(sort list) Return list, sorted in lexical order. $(dir list) Return the directory part (everything up to the last slash) of each filename in list. $(notdir list) Return the nondirectory part (everything after the last slash) of each filename in list. $(suffix list) Return the suffix part (everything after the last period) of each filename in list. $(basename list) Return everything but the suffix part (everything up to the last period) of each filename in list. $(addsuffix suffix,list) Return each filename given in list with suffix appended. $(addprefix prefix,list) Return each filename given in list with prefix prepended. $(join list1,list2) Return a list formed by concatenating the two arguments, word by word (e.g., $(join a b,.c .o) becomes a.c b.o). $(word n,string) Return the nth word of string. $(words string) Return the number of words in string. $(firstword list) Return the first word in the list list. $(wildcard pattern) Return a list of existing files in the current directory that match pattern. $(origin variable) Return one of the following strings that describes how variable was defined: undefined, default, environment, environment override, file, command line, override, or automatic. $(shell command) Return the results of command. Any newlines in the result are to be converted to spaces. This function works similarly to backquotes in most shells. #### Macro string substitution $(macro:s1=s2) Evaluates to the current definition of $(macro), after substituting the string s2 for every occurrence of s1 that occurs either immediately before a blank or tab or at the end of the macro definition. #### Special target names .DEFAULT: Commands associated with this target are executed if make can't find any description file entries or suffix rules with which to build a requested target. .EXPORT_ALL_VARIABLES: If this target exists, export all macros to all child processes. .IGNORE: Ignore error codes. Same as the -i option. .PHONY: Always execute commands under a target, even if it is an existing, up-to-date file. .PRECIOUS: Files you specify for this target are not removed when you send a signal (such as an interrupt) that aborts make or when a command line in your description file returns an error. .SILENT: Execute commands, but do not echo them. Same as the -s option. .SUFFIXES: Suffixes associated with this target are meaningful in suffix rules. If no suffixes are listed, the existing list of suffix rules is effectively "turned off."
> makedbm | makedbm [options] infile outfile NFS/NIS command. Make NIS dbm file. makedbm takes infile and converts it to a pair of files in ndbm format, namely outfile.pag and outfile.dir. Each line of the input file is converted to a single dbm record. All characters up to the first TAB or SPACE form the key, and the rest of the line is the data. If line ends with \&, the data for that record is continued on to the next line. It is left for the NIS clients to interpret #; makedbm does not treat it as a comment character. infile can be -, in which case the standard input is read. makedbm generates a special entry with the key yp_last_modified, which is the date of infile (or the current time, if infile is -). #### Options -b Interdomain. Propagate a map to all servers using the interdomain name server named. -d yp_domain_name Create a special entry with the key yp_domain_name. -i yp_input_file Create a special entry with the key yp_input_file. -l Convert keys of the given map to lowercase. -m yp_master_name Create a special entry with the key yp_master_name. If no master hostname is specified, yp_master_name is set to the local hostname. -o yp_output_file Create a special entry with the key yp_output_name. -s Secure map. Accept connections from secure NIS networks only. -u dbm filename Undo a dbm file -- print out a dbm file, one entry per line, with a single space separating keys from values. #### Example It is easy to write shell scripts to convert standard files such as /etc/passwd to the key value form used by makedbm. For example, the awk program:
>     BEGIN { FS =":";OFS = "\t";}
>     { print $1, $0}
takes the /etc/passwd file and converts it to a form that can be read by makdbm to make the NIS file passwd.byname. That is, the key is a username and the value is the remaining line in the /etc/passwd file.
makemap | makemap [options] type name System administration command. Transfer from standard input to sendmail's database maps. Input should be formatted as: key value You may comment lines with #, may substitute parameters with %n, and must escape literal % by entering it as %%. The type must be dbm, btree, or hash. The name is a filename to which makemap appends standard suffixes. #### Options -d Allow duplicate entries. Valid only with btree type maps. -f Suppress conversion of uppercase to lowercase. -N Append a zero byte to each key. -o Append to existing file instead of replacing it. -r If some keys already exist, replace them. (By default, makemap will exit when encountering a duplicated key.) -s Ignore safety checks. -v Verbose mode.
man | man [options] [section] [title] Display information from the online reference manuals. man locates and prints the named title from the designated reference section. #### Options -7, --ascii Expect a pure ASCII file, and format it for a 7-bit terminal or terminal emulator. -a, --all Show all pages matching title. -b Leave blank lines in output. -d, --debug Display debugging information. Suppress actual printing of manual pages. -f, --whatis Same as whatis command. -k, --apropos Same as apropos command. -l, --local-file Search local files, not system files, for manual pages. If i is given as filename, search standard input. -m systems, --systems=systems Search systems' manual pages. systems should be a comma-separated list. -p preprocessors, --preprocessor=preprocessors Preprocess manual pages with preprocessors before turning them over to nroff, troff, or groff. Always runs soelim first. -r prompt, --prompt=prompt Set prompt if less is used as pager. -t, --troff Format the manual page with /usr/bin/groff -Tgv -mandoc. Implied by -T and -Z. -u, --update Perform a consistency check between manual page cache and filesystem. -w, --where, --location Print pathnames of entries on standard output. -D, --default Reset all options to their defaults. -L locale, --locale=locale Assume current locale to be locale; do not consult the setlocale() function. -M path, --manpath=path Search for manual pages in path. Ignore -m option. -P pager, --pager=pager Select paging program pager to display the entry. -T device, --troff-device[=device] Format groff or troff output for device, such as dvi, latin1, X75, and X100. -Z, --ditroff Do not allow postprocessing of manual page after groff has finished formatting it. #### Section names Manual pages are divided into sections, depending on their intended audience: 1 Executable programs or shell commands 2 System calls (functions provided by the kernel) 3 Library calls (functions within system libraries) 4 Special files (usually found in /dev) 5 File formats and conventions (e.g., /etc/passwd) 6 Games 7 Macro packages and conventions 8 System administration commands (usually only for a privileged user) 9 Kernel routines (nonstandard)
manpath | manpath [options] Attempt to determine path to manual pages. Check $MANPATH first; if that is not set, consult /etc/man.conf, user environment variables, and the current working directory. The manpath command is a symbolic link to man, but most of the options are ignored for manpath. #### Options -d, --debug Print debugging information. -h Print help message and then exit.
> merge | merge [options] file1 file2 file3 Perform a three-way file merge. merge incorporates all changes that lead from file2 to file3 and puts the results into file1. merge is useful for combining separate changes to an original. Suppose file2 is the original, and both file1 and file3 are modifications of file2. Then merge combines both changes. A conflict occurs if both file1 and file3 have changes in a common segment of lines. If a conflict is found, merge normally outputs a warning and puts brackets around the conflict, with lines preceded by <<<<<<< and >>>>>>>. A typical conflict looks like this:
>     <<<<<<< file1
>     relevant lines from file1
>     =======
>     relevant lines from file3
>     >>>>>>> file3
  > If there are conflicts, the user should edit the result and delete one of the alternatives. #### Options -e Don't warn about conflicts. -p Send results to standard output instead of overwriting file1. -q Quiet; do not warn about conflicts. -A Output conflicts using the -A style of diff3. This merges all changes leading from file2 to file3 into file1 and generates the most verbose output. -E Output conflict information in a less verbose style than -A; this is the default. -L label Specify up to three labels to be used in place of the corresponding filenames in conflict reports. That is:
  >     merge -L x -L y -L z file_a file_b file_c
generates output that looks as if it came from x, y, and z instead of from file_a, file_b, and file_c. -V Print version number.
mesg | mesg [option] Change the ability of other users to send write messages to your terminal. With no options, display the permission status. #### Options n Forbid write messages. y Allow write messages (the default).
mimencode | mimencode [options] [filename] [-o output_file] mimencode [options] [filename] [-o output_file] Translate to and from MIME encoding formats, the proposed standard for Internet multimedia mail formats. By default, mimencode reads standard input and sends a base64-encoded version of the input to standard output. #### Options -b Use the (default) base64 encoding. -o output_file Send output to the named file rather than to standard output. -p Translate decoded CRLF sequences into the local newline convention during decoding and do the reverse during encoding; meaningful only when the default base64 encoding is in effect. -q Use the quoted-printable encoding instead of base64. -u Decode the standard input rather than encode it.
> mkdir | mkdir [options] directories Create one or more directories. You must have write permission in the parent directory in order to create a directory. See also rmdir. The default mode of the new directory is 0777, modified by the system or user's umask. #### Options -m, --mode mode Set the access mode for new directories. See chmod for an explanation of acceptable formats for mode. -p, --parents Create intervening parent directories if they don't exist. --verbose Print a message for each directory created. --help Print help message and then exit. --version Print version number and then exit. #### Examples Create a read-only directory named personal:
>     mkdir -m 444 personal
> The following sequence:
>     mkdir work; cd work
>     mkdir junk; cd junk
>     mkdir questions; cd ../..
> can be accomplished by typing this:
>     mkdir -p work/junk/questions
mke2fs | mke2fs [options] device [blocks] mkfs.ext2 [options] device [blocks] System administration command. Format device as a Linux Second Extended Filesystem. You may specify the number of blocks on the device or allow mke2fs to guess. #### Options -b block-size Specify block size in bytes. -c Scan device for bad blocks before execution. -f fragment-size Specify fragment size in bytes. -i bytes-per-inode Create an inode for each bytes-per-inode of space. bytes-per-inode must be 1024 or greater; it is 4096 by default. -l filename Consult filename for a list of bad blocks. -m percentage Reserve percentage percent of the blocks for use by privileged users. -q Quiet mode. -v Verbose mode. -S Write only superblock and group descriptors; suppress writing of inode table and block and inode bitmaps. Useful only when attempting to salvage damaged systems.
mkfs | mkfs [options] [fs-options] filesys [blocks] System administration command. Construct a filesystem on a device (such as a hard disk partition). filesys is either the name of the device or the mountpoint. mkfs is actually a frontend that invokes the appropriate version of mkfs according to a filesystem type specified by the -t option. For example, a Linux Second Extended Filesystem uses mkfs.ext2 (which is the same as mke2fs); MS-DOS filesystems use mkfs.msdos. fs-options are options specific to the filesystem type. blocks is the size of the filesystem in 1024-byte blocks. #### Options -V Produce verbose output, including all commands executed to create the specific filesystem. -t fs-type Tells mkfs what type of filesystem to construct. filesystem-specific options These options must follow generic options and not be combined with them. Most filesystem builders support these three options: -c Check for bad blocks on the device before building the filesystem. -l file Read the file file for the list of bad blocks on the device. -v Produce verbose ouput.
mkfs.minix | mkfs.minix [options] device size System administration command. Creates a MINIX filesystem. See mkfs.
mklost+found | mklost+found System administration command. Create a lost+found directory in the current working directory. Intended for Linux Second Extended Filesystems.
mkraid | mkraid [options] devices System administration command. Set up RAID array devices as defined in the /etc/raidtab configuration file. mkraid can be used to initialize a new array or upgrade older RAID device arrays for the new kernel. Initialization will destroy any data on the disk devices used to create the array. #### Options -c file, --configfile file Use file instead of /etc/raidtab. -f, --force Initialize the devices used to create the RAID array even if they currently have data. -h, --help Print a usage message and then exit. -o, --upgrade Upgrade an older array to the current kernel's RAID version. Preserve data on the old array. -V, --version Print version information and then exit.
mkswap | mkswap [option] device [size] System administration command. Create swap space on device. You may specify its size in blocks; each block is a page of about 4KB. #### Option -c Check for bad blocks before creating the swap space.
modprobe | modprobe [options] [modules] System administration command. With no options, attempt to load the specified module, as well as all modules on which it depends. If more than one module is specified, attempt to load further modules only if the previous module failed to load. #### Options -a Load all listed modules, not just the first one. -l [pattern] List all existing modules. This option may be combined with -t to specify a type of module, or you may include a pattern to search for. -r Remove the specified modules, as well as the modules on which they depend. -t type Load only a specific type of module. Consult /etc/conf.modules for the directories in which all modules of that type reside. #### Files /etc/conf.modules Information about modules: which ones depend on others, which directories correspond to particular types of modules. /sbin/insmod, /sbin/rmmod, /sbin/depmod Programs that modprobe relies on.
> more | more [options] [files] Display the named files on a terminal, one screenful at a time. See less for an alternative to more. Some commands can be preceded by a number. #### Options +num Begin displaying at line number num. -num number Set screen size to number lines. +/pattern Begin displaying two lines before pattern. -c Repaint screen from top instead of scrolling. -d Display the prompt "Hit space to continue, Del to abort" in response to illegal commands; disable bell. -f Count logical rather than screen lines. Useful when long lines wrap past the width of the screen. -l Ignore form-feed (Ctrl-L) characters. -p Page through the file by clearing each window instead of scrolling. This is sometimes faster. -r Force display of control characters, in the form ^x. -s Squeeze; display multiple blank lines as one. -u Suppress underline characters. #### Commands All commands in more are based on vi commands. An argument can precede many commands. SPACE Display next screen of text. z Display next lines of text, and redefine a screenful to lines lines. Default is one screenful. RETURN Display next lines of text, and redefine a screenful to lines lines. Default is one line. d, ^D Scroll lines of text, and redefine scroll size to lines lines. Default is one line. q, Q, INTERRUPT Quit. s Skip forward one line of text. f Skip forward one screen of text. b, ^B Skip backward one screen of text. ' Return to point where previous search began. = Print number of current line. /pattern Search for pattern, skipping to numth occurrence if an argument is specified. n Repeat last search, skipping to numth occurrence if an argument is specified. !cmd, :!cmd Invoke shell and execute cmd in it. v Invoke vi editor on the file, at the current line. ^L Redraw screen. :n Skip to next file. :p Skip to previous file. :f Print current filename and line number. . Reexecute previous command. #### Examples Page through file in "clear" mode, and display prompts:
>     more -cd file
> Format doc to the screen, removing underlines:
>     nroff doc | more -u
> View the manpage for the grep command; begin near the word "BUGS" and compress extra whitespace:
>     man grep | more +/BUGS -s
mount | mount [options] [special-device] [directory] System administration command. Mount a file structure. mount announces to the system that a removable file structure is present on special-device. The file structure is mounted on directory, which must already exist and should be empty; it then becomes the name of the root of the newly mounted file structure. If mount is invoked with no arguments, it displays the name of each mounted device, the directory on which it is mounted, whether the file structure is read-only, and the date it was mounted. Only a privileged user can use the mount command. #### Options -a Mount all filesystems listed in /etc/fstab. Note: this is the only option that cannot take a special-device or node argument. -f Fake mount. Go through the motions of checking the device and directory, but do not actually mount the filesystem. -n Do not record the mount in /etc/mtab. -o option Note: this is the only option to mount that requires a special-device or node argument. Qualify the mount with one of the specified options: async Read input and output to the device asynchronously. auto Allow mounting with the -a option. defaults Use all options' default values (async, auto, dev, exec, nouser, rw, suid). dev Interpret any special devices that exist on the filesystem. exec Allow binaries to be executed. noauto Do not allow mounting via the -a option. nodev Do not interpret any special devices that exist on the filesystem. noexec Do not allow the execution of binaries on the filesystem. nosuid Do not acknowledge any suid or sgid bits. nouser Only privileged users will have access to the filesystem. remount Expect the filesystem to have already been mounted, and remount it. ro Allow read-only access to the filesystem. rw Allow read/write access to the filesystem. suid Acknowledge suid and sgid bits. sync Read input and output to the device synchronously. user Allow unprivileged users to mount the filesystem. Note that the defaults on such a system will be nodev, noexec, and nosuid, unless otherwise specified. check=relaxed|normal|strict Specify how strictly to regulate the integration of an MS-DOS filesystem when mounting it. conv=binary|text|auto Specify method by which to convert files on MS-DOS and ISO 9660 filesystems. debug Turn debugging on for MS-DOS and ext2fs filesystems. errors=continue|remount|ro|panic Specify action to take when encountering an error. ext2fs filesystems only. -r Mount filesystem read-only. -t type Specify the filesystem type. Possible values are: minix, ext, ext2, xiafs, hpfs, msdos, umsdos, vfat, proc, nfs, iso9660, smbfs, ncpfs, affs, ufs, romfs, sysv, xenix, and coherent. Note that ext and xiafs are valid only for kernels older than 2.1.21 and that sysv should be used instead of xenix and coherent. -v Display mount information verbosely. -w Mount filesystem read/write. This is the default. #### Files /etc/fstab List of filesystems to be mounted and options to use when mounting them. /etc/mtab List of filesystems that are currently mounted and the options with which they were mounted.
mountd | rpc.mountd [options] NFS/NIS command. NFS mount request server. mountd reads the file /etc/exports to determine which filesystems are available for mounting by which machines. It also provides information as to what filesystems are mounted by which clients. See also nfsd. #### Options -d, --debug Debug mode. Output all debugging information via syslogd. -f file, --exports-file file Read the export permissions from file instead of /etc/exports. -n, --allow-non-root Accept even those mount requests that enter via a non-reserved port. -p, --promiscuous Accept requests from any host that sends them. -r, --re-export Allow re-exportation of imported filesystems. -v, --version Print the version number. #### File /etc/exports Information about mount permissions.
mv | mv [option] sources target Move or rename files and directories. The source (first column) and target (second column) determine the result (third column):
Source | Target | Result
--- | --- | ---
File | name (nonexistent) | Rename file to name.
File | Existing file | Overwrite existing file with source file.
Directory | name (nonexistent) | Rename directory to name.
Directory | Existing directory | Move directory to be a subdirectory of existing directory.
One or more files | Existing directory | Move files to directory.
#### Options -b, --backup Back up files before removing. -f, --force Force the move, even if target file exists; suppress messages about restricted access modes. --help Print a help message and then exit. -i, --interactive Query user before removing files. -u, --update Do not remove a file or link if its modification date is the same as or newer than that of its replacement. -v, --verbose Print the name of each file before moving it. --version Print version information and then exit. -S suffix, --suffix=suffix Override the SIMPLE_BACKUP_SUFFIX environment variable, which determines the suffix used for making simple backup files. If the suffix is not set either way, the default is a tilde (~). -V value, --version-control=value Override the VERSION_CONTROL environment variable, which determines the type of backups made. The acceptable values for version control are: t, numbered Always make numbered backups. nil, existing Make numbered backups of files that already have them, simple backups of the others. The default. never, simple Always make simple backups.
named | named [options] TCP/IP command. Internet domain name server. named is used by resolver libraries to provide access to the Internet distributed naming database. With no arguments, named reads /etc/named.boot for any initial data and listens for queries on a privileged port. See RFC 1034 and RFC 1035 for more details. There are several named binaries available at different Linux archives, displaying various behaviors. If your version doesn't behave like the one described here, never fear -- it should have come with documentation. #### Options -d debuglevel Print debugging information. debuglevel is a number indicating the level of messages printed. -p port Use port as the port number. Default is 42. [-b] bootfile File to use instead of named.boot. The -b is optional and allows you to specify a filename that begins with a leading dash. #### File /etc/named.boot Read when named starts up.
namei | namei [options] pathname [pathname . . .] Follow a pathname until a terminal point is found (e.g., a file, directory, char device, etc.). If namei finds a symbolic link, it shows the link and starts following it, indenting the output to show the context. namei prints an informative message when the maximum number of symbolic links this system can have has been exceeded. #### Options -m Show the mode bits of each file type in the style of ls; for example: "rwxr-xr-x". -x Show mountpoint directories with a D, rather than a d. #### File type characters For each line of output, namei prints the following characters to identify the file types found: - A regular file ? An error of some kind b A block device c A character device d A directory f: The pathname namei is currently trying to resolve l A symbolic link (both the link and its contents are output) s A socket
netdate | netdate [options] [protocol] hostname... TCP/IP command. Set the system time according to the time provided by one of the hosts in the list hostname. netdate tries to ascertain which host is the most reliable source. When run by an unprivileged user, netdate reports the current time, without attempting to set the system clock. You may specify the protocol -- udp (the default) or tcp -- once, or several times for various hosts. #### Options -l time The most reliable host is chosen from the list by sorting the hosts into groups based on the times they return when questioned. The first host from the largest group is then polled a second time. The differences between its time and the local host's time on each poll are recorded. These two differences are then compared. If the gap between them is greater than time (the default is five seconds), the host is rejected as inaccurate. -v Display the groups into which hosts are sorted.
netstat | netstat [options] TCP/IP command. Show network status. For all active sockets, print the protocol, the number of bytes waiting to be received, the number of bytes to be sent, the port number, the remote address and port, and the state of the socket. #### Options -a Show the state of all sockets, not just active ones. -c Display information continuously, refreshing once every second. -i Include statistics for network devices. -n Show network addresses as numbers. -o Include additional information such as username. -r Show routing tables. -t List only TCP sockets. -u List only UDP sockets. -v Print the version number and exit. -w List only raw sockets. -x List only Unix domain sockets.
newgrp | newgrp [group] Change user's group identification to the specified group. If no group is specified, change to the user's login group. The new group is then used for checking permissions.
newusers | newusers file System administration command. Create or update system users from entries in file. Each line in file has the same format as an entry in /etc/passwd, except passwords are unencrypted, and group IDs can be given as a name or number. During an update, the password age field is ignored if the user already exists in the /etc/shadow password file. If a group name or ID does not already exist, it will be created. If a home directory does not exist, it will be created.
nfsd | rpc.nfsd [options] System administration command. Daemon that starts the NFS server daemons that handle client filesystem requests. These daemons are user-level processes. The options are exactly the same as in mountd.
nice | nice [option] [command [arguments]] Execute a command (with its arguments) with lower priority (i.e., be "nice" to other users). With no arguments, nice prints the default scheduling priority (niceness). If nice is a child process, it prints the parent process's scheduling priority. Niceness has a range of -20 (highest priority) to 19 (lowest priority). #### Options --help Print a help message and then exit. -n adjustment, -adjustment, --adjustment=adjustment Run command with niceness incremented by adjustment (1-19); default is 10. A privileged user can raise priority by specifying a negative adjustment (e.g., -5). --version Print version information and then exit.
nm | nm [options] [objfiles] Print the symbol table (name list) in alphabetical order for one or more object files. If no object files are specified, perform operations on a.out. Output includes each symbol's value, type, size, name, and so on. A key letter categorizing the symbol can also be displayed. If no object file is given, use a.out. #### Options -a, --debug-syms Print debugger symbols. -f format Specify output format (bsd, sysv, or posix). Default is bsd. -g, --extern-only Print external symbols only. -n, -v, --numeric-sort Sort the external symbols by address. -p, --no-sort Don't sort the symbols at all. -r, --reverse-sort Sort in reverse, alphabetically or numerically. --size-sort Sort by size. -u, --undefined-only Report only the undefined symbols. -A, -o, -print-file-name Print input filenames before each symbol. -C, --demangle Translate low-level symbol names into readable versions. -D, --dynamic Print dynamic, not normal, symbols. Useful only when working with dynamic objects (some kinds of shared libraries, for example). -P, --portability Same as -f posix. -V, --version Print nm's version number on standard error.
nohup | nohup command [arguments] Run the named command with its optional command arguments, continuing to run it even after you log out (make command immune to hangups; i.e., no hangup). TTY output is appended to the file nohup.out by default. Modern shells preserve background commands by default; this command is necessary only in the original Bourne shell.
  nslookup | nslookup [-option...] [host_to_find | - [server ]] TCP/IP command. Query Internet domain name servers. nslookup has two modes: interactive and noninteractive. Interactive mode allows the user to query name servers for information about various hosts and domains or to print a list of hosts in a domain. It is entered either when no arguments are given (default name server will be used) or when the first argument is a hyphen and the second argument is the hostname or Internet address of a name server. Noninteractive mode is used to print just the name and requested information for a host or domain. It is used when the name of the host to be looked up is given as the first argument. Any of the keyword=value pairs listed under the interactive set command can be used as an option on the command line by prefacing the keyword with a -. The optional second argument specifies a name server. #### Options All of the options under the set interactive command can be entered on the command line, with the syntax -keyword[=value]. #### Interactive commands exit Exit nslookup. finger [name] [>|>>filename] Connect with finger server on current host, optionally creating or appending to filename. help, ? Print a brief summary of commands. host [server] Look up information for host using the current default server or using server if specified. ls -[ahd] domain [>|>>filename] List information available for domain, optionally creating or appending to filename. The -a option lists aliases of hosts in the domain. -h lists CPU and operating system information for the domain. -d lists all contents of a zone transfer. lserver domain Change the default server to domain. Use the initial server to look up information about domain. root Change default server to the server for the root of the domain namespace. server domain Change the default server to domain. Use the current default server to look up information about domain. set keyword[=value] Change state information affecting the lookups. Valid keywords are: all Print the current values of the frequently used options to set. class=name Set query class to IN (Internet), CHAOS, HESIOD, or ANY. Default is IN. domain=name Change default domain name to name. [no]debug Turn debugging mode on or off. [no]d2 Turn exhaustive debugging mode on or off. [no]defname Append default domain name to every lookup. [no]ignoretc Ignore truncate error. [no]recurse Tell name server to query or not query other servers if it does not have the information. [no]search With defname, search for each name in parent domains of current domain. [no]vc Always use a virtual circuit when sending requests to the server. port=port Connect to name server using port. querytype=value See type=value. retry=number Set number of retries to number. root=host Change name of root server to host. srchlist=domain Set search list to domain. timeout=number Change timeout interval for waiting for a reply to number seconds. type=value Change type of information returned from a query to one of:
  A | Host's Internet address
  ANY | Any available information
  CNAME | Canonical name for an alias
  HINFO | Host CPU and operating system
  | type
  MD | Mail destination
  MG | Mail group member
  MINFO | Mailbox or mail list
  | information
  MR | Mail rename domain name
  MX | Mail exchanger
  NS | Nameserver for the named zone
  PTR | Hostname or pointer to other
  | information
  SOA | Domain start-of-authority
  TXT | Text information
  UINFO | User information
  WKS | Supported well-known services
view filename Sort and list output of previous ls command(s) with more.
passwd | passwd [user] Create or change a password associated with a user name. Only the owner or a privileged user may change a password. Owners need not specify their user name.
> paste | paste [options] files Merge corresponding lines of one or more files into tab- separated vertical columns. See also cut, join, and pr. #### Options - Replace a filename with the standard input. -d char, --delimiters=char Separate columns with char instead of a tab. Note: you can separate columns with different characters by supplying more than one char. --help Print a help message and then exit. --version Print version information and then exit. -s, --serial Merge lines from one file at a time. #### Examples Create a three-column file from files x, y, and z:
>     paste x y z > file
> List users in two columns:
>     who | paste - -
> Merge each pair of lines into one line:
>     paste -s -d"\t\n" list
> patch | patch [options] [original [patchfile]] Apply the patches specified in patchfile to original. Replace the original with the new, patched version; move the original to original.orig or original~. #### Options + [options] [original2] Apply patches again, with different options or a different original file. -b, --backup Back up the original file. -z suffix, --suffix=suffix Back up the original file in original.suffix. -B prefix, --prefix=prefix Prepend prefix to the backup filename. -c, --context Interpret patchfile as a context diff. -d dir, --directory=dir cd to directory before beginning patch operations. -D string, --ifdef=string Mark all changes with:
>         #ifdef
>            string
>         #endif
-e, --ed Treat the contents of patchfile as ed commands. -E, --remove-empty-files If patch creates any empty files, delete them. -f, --force Force all changes, even those that look incorrect. Skip patches if the original file does not exist; force patches for files with the wrong version specified; assume patches are never reversed. -i file, --input=file Read patch from file instead of stdin. -t, --batch Skip patches if the original file does not exist. -F num, --fuzz=num Specify the maximum number of lines that may be ignored (fuzzed over) when deciding where to install a hunk of code. The default is 2. Meaningful only with context diffs. -l, --ignore-whitespace Ignore whitespace while pattern matching. -n, --normal Interpret patch file as a normal diff. -N, --forward Ignore patches that appear to be reversed or to have already been applied. -o file, --output=file Print output to file. -p[num], --strip[=num] Specify how much of preceding pathname to strip. A num of 0 strips everything, leaving just the filename. 1 strips the leading /; each higher number after that strips another directory from the left. -r file, --reject-file=file Place rejects (hunks of the patch file that patch fails to place within the original file) in file. Default is original.rej. -R, --reverse Do a reverse patch: attempt to undo the damage done by patching with the old and new files reversed. -s, --silent, --quiet Suppress commentary. -u, --unified Interpret patch file as a unified context diff. -V method, --version-control=method Specify method for creating backup files (overridden by -B): t, numbered Make numbered backups. nil, existing Back up files according to preexisting backup schemes, with simple backups as the default. This is patch's default behavior. never, simple Make simple backups. #### Environment variables TMPDIR Specify the directory for temporary files, /tmp by default. SIMPLE_BACKUP_SUFFIX Suffix to append to backup files instead of .orig or ~. VERSION_CONTROL Specify what method to use in naming backups (see -V).
pathchk | pathchk [ option ] filenames Determine validity and portability of filenames. Specifically, determine if all directories within the path are searchable and if the length of the filenames is acceptable. #### Options -p, --portability Check portability for all POSIX systems. --help Print a help message and then exit. --version Print version information and then exit.
> pcnfsd | /usr/sbin/rpc.pcnfsd NFS/NIS command. NFS authentication and print request server. pcnfsd is an RPC server that supports ONC clients on PC systems. pcnfsd reads the configuration file /etc/pcnfsd.conf, if present, then services RPC requests directed to program number 150001. This current release of the pcnfsd daemon (as of this printing) supports both Version 1 and Version 2 of the pcnfsd protocol. Requests serviced by pcnfsd fall into three categories: authentication, printing, and other. Only the authentication and printing services have administrative significance. #### Authentication When pcnfsd receives a PCNFSD_AUTH or PCNFSD2_AUTH request, it will log in the user by validating the username and password, returning the corresponding user ID, group IDs, home directory, and umask. At this time, pcnfsd will also append a record to the wtmp database. If you do not want to record PC logins in this way, add the line:
>     wtmp off
> to the /etc/pcnfsd.conf file. #### Printing pcnfsd supports a printing model based on the use of NFS to transfer the actual print data from the client to the server. The client system issues a PCNFSD_PR_INIT or PCNFSD2_PR_INIT request, and the server returns the path to a spool directory that the client may use and that is exported by NFS. pcnfsd creates a subdirectory for each of its clients; the parent directory is normally /usr/spool/pcnfs and the subdirectory is the hostname of the client system. If you want to use a different parent directory, add the line:
>     spooldir path
> to the /etc/pcnfsd.conf file. Once a client has mounted the spool directory and has transferred print data to a file in this directory, pcnfsd will issue a PCNFSD_PR_START or PCNFSD2_PR_START request. pcnfsd constructs a command based on the printing services of the server operating system and executes the command using the identity of the PC user. Every print request includes the name of the printer to be used. pcnfsd interprets a printer as either a destination serviced by the system print spooler or as a virtual printer. Virtual printers are defined by the following line in the /etc/pcnfsd.conf file:
>     printer name alias-for command
where name is the name of the printer you want to define, alias-for is the name of a real printer that corresponds to this printer, and command is a command that will be executed whenever a file is printed on name.
perl | perl A powerful text-processing language that combines many of the most useful features of shell programs, C, awk, and sed, as well as adding extended features of its own. For more information, see Learning Perl by Randal L. Schwartz and Programming Perl, 2d ed., by Larry Wall, Tom Christiansen, and Randal L. Schwartz.
pidof | pidof [options] programs Display the process IDs of the listed program or programs. pidof is actually a symbolic link to killall5. #### Options -o pids Omit all processes with the specified process ID. You may list several process IDs. -s Return a single process ID. -x Also return process IDs of shells running the named scripts.
ping | ping [options] host System administration command. Confirm that a remote host is online and responding. ping is intended for use in network testing, measurement, and management. Because of the load it can impose on the network, it is unwise to use ping during normal operations or from automated scripts. #### Options -c count Stop after sending (and receiving) count ECHO_RESPONSE packets. -d Set SO_DEBUG option on socket being used. -f Flood ping-output packets as fast as they come back or 100 times per second, whichever is more. This can be very hard on a network and should be used with caution; only a privileged user may use this option. -i wait Wait wait seconds between sending each packet. Default is to wait 1 second between each packet. This option is incompatible with the -f option. -l preload Send preload number of packets as fast as possible before falling into normal mode of behavior. -n Numeric output only. No attempt will be made to look up symbolic names for host addresses. -p digits Specify up to 16 pad bytes to fill out packet sent. This is useful for diagnosing data-dependent problems in a network. digits are in hex. For example, -p ff will cause the sent packet to be filled with all 1s. -q Quiet output -- nothing is displayed except the summary lines at startup time and when finished. -r Bypass the normal routing tables and send directly to a host on an attached network. -s packetsize Specify number of data bytes to be sent. Default is 56, which translates into 64 ICMP data bytes when combined with the 8 bytes of ICMP header data. -v Verbose -- list ICMP packets received other than ECHO_RESPONSE. -R Set the IP record route option, which will store the route of the packet inside the IP header. The contents of the record route will be printed if the -v option is given, and will be set on return packets if the target host preserves the record route option across echoes or the -l option is given.
pop2d | in.pop2d System administration command. Allow users to connect to port 109 and request the contents of their mailbox in /var/spool/mail. pop2d requires a username and password before providing mail and can serve individual messages. See also pop3d. #### Commands Each command must be entered on a separate line. HELO Prompt for username and password. FOLD Open /var/spool/mail/$USER. HOST Open /var/spool/pop/$USER. READ Read a message. RETR Retrieve a message. ACKS Save the last message retrieved and move to next message. ACKD Delete the last message retrieved and move to next message. NACK Save the last message retrieved and expect to resend it. QUIT Exit.
pop3d | in.pop3d System administration command. pop3d is a more recent version of pop2d. It behaves similarly but accepts a slightly different list of commands. #### Commands USER Prompt for name. PASS Prompt for password. STAT Display the number of messages in the mailbox and its total size. LIST Display individual messages' sizes. DELE Delete a message. NOOP Perform a null operation. LAST Print the number of the most recently received message that has been read. RSET Reset: clear all deletion marks. TOP Print the first part of a message. QUIT Exit.
portmap | rpc.portmap [option] NFS/NIS command. RPC program number to IP port mapper. portmap is a server that converts RPC program numbers to IP port numbers. It must be running in order to make RPC calls. When an RPC server is started, it tells portmap what port number it is listening to and what RPC program numbers it is prepared to serve. When a client wishes to make an RPC call to a given program number, it first contacts portmap on the server machine to determine the port number where RPC packets should be sent. portmap must be the first RPC server started. #### Option -d Run portmap in debugging mode. Does not allow portmap to run as a daemon.
powerd | powerd device System administration command. Monitor the connection to an uninterruptible power supply, which the user must specify via device. When power goes low, signal init to run its powerwait and powerfail entries; when full power is restored, signal init to run its powerokwait entries.
pppd | pppd [options] [tty] [speed] System administration command. PPP stands for the Point-to-Point Protocol; it allows datagram transmission over a serial connection. pppd attempts to configure tty for PPP (searching in /dev) or, by default, the controlling terminal. You can also specify a baud rate of speed. #### Options asyncmap map Specify which control characters cannot pass over the line. map should be a 32-bit hex number, where each bit represents a character to escape. For example, bit 00000001 represents the character 0x00; bit 80000000 represents the character 0x1f or _. You may specify multiple characters. auth Require self-authentication by peers before allowing packets to move. connect command Connect as specified by command, which may be a binary or shell command. debug, -d Increment the debugging level. defaultroute Add a new default route in which the peer is the gateway. When the connection shuts down, remove the route. -detach Operate in the foreground. By default, pppd forks and operates in the background. disconnect command Close the connection as specified by command, which may be a binary or shell command. domain d Specify a domain name of d. escape character-list Escape all characters in character-list, which should be a comma-separated list of hex numbers. You cannot escape 0x20-0x3f or 0x5e. file file Consult file for options. lock Allow only pppd to access the device. mru bytes Refuse packets of more than bytes bytes. name name Specify a machine name for the local system. netmask mask Specify netmask (for example, 255.255.255.0). passive, -p Do not exit if peer does not respond to attempts to initiate a connection. Instead, wait for a valid packet from the peer. silent Send no packets until after receiving one. [local_IP_address]:[remote_IP_address] Specify the local and/or remote interface IP addresses, as hostnames or numeric addresses. #### Files /var/run/pppn.pid pppd's process ID. The n in pppn.pid is the number of the PPP interface unit corresponding to this pppd process. /etc/ppp/ip-up Binary or script to be executed when the PPP link becomes active. /etc/ppp/ip-down Binary or script to be executed when the PPP link goes down. /etc/ppp/pap-secrets Contains usernames, passwords, and IP addresses for use in PAP authentication. /etc/ppp/options System defaults. Options in this file are set before the command-line options. ~/.ppprc The user's default options. These are read before command-line options but after the system defaults. /etc/ppp/options.ttyname Name of the default serial port.
pr | pr [files] Convert a text file or files to a paginated, columned version, with headers. If - is provided as the filename, read from standard input. #### Options +beg_pag[:end-pag], --pages=[beg_pag[:end-pag] Begin printing on page beg_pag and end on end-pag if specified. -num_cols, --columns=num_cols Print in num_cols number of columns, balancing the number of lines in the columns on each page. -a, --across Print columns horizontally, not vertically. -c, --show-control-chars Convert control characters to hat notation (such as ^C) and other unprintable characters to octal backslash format. -d, --double-space Double space. -e[tab-char[width]], --expand-tabs=[tab-char[width]] Convert tabs (or tab-chars) to spaces. If width is specified, convert tabs to width characters (default is 8). -f, -F, --form-feed Separate pages with form feeds, not newlines. -h header, --header=header Use header for the header instead of the filename. -i[out-tab-char[out-tab-width]], --output-tabs[=out-tab-char[out-tab-width]] Replace spaces with tabs on output. Can specify alternative tab character (default is tab) and width (default is 8). -J, --join-lines Merge full lines; ignore -W if set. -l lines, --length=lines Set page length to lines (default 66). If lines is less than 10, omit headers and footers. -m, --merge Print all files, one file per column. -n[delimiter[digits]], --number-lines[=delimiter[digits]] Number columns, or, with the -m option, number lines. Append delimiter to each number (default is a tab) and limit the size of numbers to digits (default is 5). -o width, --indent=width Set left margin to width. -r, --no-file-warnings Continue silently when unable to open an input file. -s[delimiter], --separator[=delimiter] Separate columns with delimiter (default is a tab) instead of spaces. -S[string], --sep-string[=string] Separate columns with string. Default is a tab with -J and a space otherwise. -t, --omit-header Suppress headers, footers, and fills at end of pages. -T, --omit-pagination Like -t but also suppress form feeds. -v, --show-non-printing Convert unprintable characters to octal backslash format. -w page_width, --width=page_width Set the page width to page_width characters for multi-column output. Default is 72. -W page_width, --page-width=page_width Set the page width to always be page_width characters. Default is 72. --help Print a help message and then exit. --version Print version information and then exit.
praliases | praliases [option] System administration command. praliases prints the current sendmail mail aliases. (Usually defined in the /etc/aliases or /etc/aliases.db file.) #### Option -f file Read the aliases from the specified file instead of sendmail's default alias files.
printenv | printenv [variables] Print values of all environment variables or, optionally, only the specified variables.
> printf | printf formats [strings] Print strings using the specified formats. formats can be ordinary text characters, C-language escape characters, or more commonly, a set of conversion arguments listed here. #### Arguments %s Print the next string. %n$s Print the nth string. %[-]m[.n]s Print the next string, using a field that is m characters wide. Optionally, limit the field to print only the first n characters of string. Strings are right-adjusted unless the left-adjustment flag, -, is specified. #### Examples
>     printf '%s %s\n' "My files are in" $HOME
>     printf '%-25.15s %s\n' "My files are in" $HOME
ps | ps [options] Report on active processes. Note that you do not need to include a - before options. In options, list arguments should either be separated by commas or be put in double quotes. In comparing the amount of output produced, note that e prints more than a and l prints more than f. #### Options pids Include only specified processes, which are given in a comma-delimited list. a List all processes. c Consult task_struct for command name. e Include environment. f "Forest" family tree format. h Suppress header. j Jobs format. l Produce a long listing. m Memory format. n Print user IDs and WCHAN numerically. r Exclude processes that are not running. s Signal format. --sort delimiter[+|-]key[,[+|-]key[,...]] Similar to O, but designed to protect multiletter sort keys. See the later list, "Sort keys". t tty Display only processes running on tty. u Include username and start time. v vm format. w Wide format. Don't truncate long lines. x Include processes without an associated terminal. O[+|-]key[,[+|-]key[,...]] Sort processes. (See the following list, "Sort keys.") + Return key to default direction. - Reverse default direction on key. S Include child processes' CPU time and page faults. #### Sort keys c, cmd Name of executable. C, cmdline Whole command line. f, flags Flags. g, pgrp Group ID of process. G, tpgid Group ID of associated tty. j, cutime Cumulative user time. J, cstime Cumulative system time. k, utime User time. K, stime System time. m, min_flt Number of minor page faults. M, maj_flt Amount of major page faults. n, cmin_flt Total minor page faults. N, cmaj_flt Total major page faults. o, session Session ID. p, pid Process ID. P, ppid Parent's process ID. r, rss Resident set size. R, resident Resident pages. s, size Kilobytes of memory used. S, share Number of shared pages. t, tty tty. T, start_time Process's start time. U, uid User ID. u, user User's name. v, vsize Bytes of VM used. y, priority Kernel's scheduling priority. #### Fields PRI Process's scheduling priority. A higher number indicates lower priority. NI Process's nice value. A higher number indicates less CPU time. SIZE Size of virtual image. RSS Resident set size (amount of physical memory), in kilobytes. WCHAN Kernel function in which process resides. STAT Status: R Runnable T Stopped D Asleep and not interruptible S Asleep Z Zombie W No resident pages (second field) N Positive nice value (third field) TT Associated tty. PAGEIN Number of major page faults. TRS Size of resident text. SWAP Amount of swap used, in kilobytes. SHARE Shared memory.
psupdate | psupdate [mapfile] System administration command. Update the psupdate database (on some systems /boot/psupdate; on others, /etc/psdatabase), which contains information about the kernel image system map file. If no mapfile is specified, psupdate uses the default (which is either /usr/src/linux/vmlinux or /usr/src/linux/tools/zSystem, depending on the distribution).
pwck | pwck [option] [files] System administration command. Remove corrupt or duplicate entries in the /etc/passwd and /etc/shadow files. pwck will prompt for a "yes" or "no" before deleting entries. If the user replies "no," the program will exit. Alternate passwd and shadow files can be checked. If correctable errors are found, the user will be encouraged to run the usermod command. #### Option -n Noninteractive mode. Don't prompt for input, and delete no entries. Return appropriate exit status. #### Exit status 0 Success. 1 Syntax error. 2 One or more bad password entries found. 3 Could not open password files. 4 Could not lock password files. 5 Could not write password files.
pwconv | pwconv pwunconv System administration command. Convert unshadowed entries in /etc/passwd into shadowed entries in the /etc/shadow file. Replace the encrypted password in /etc/password with an x. Shadowing passwords keeps them safe from password cracking programs. pwconv creates additional expiration information for the /etc/shadow file from entries in your /etc/login.defs file. If you add new entries to the /etc/passwd file, you can run pwconv again to transfer the new information to /etc/shadow. Already shadowed entries are ignored. pwunconv restores the encrypted passwords to your /etc/passwd file and removes the /etc/shadow file. Some expiration information is lost in the conversion.
pwd | pwd Print the full pathname of the current working directory. See also the dirs shell command, built in to both bash and csh/tcsh.
quota | quota [options] [user|group] Display disk usage and total space allowed for a designated user or group. With no argument, the quota for the current user is displayed. This command reports quotas for all filesystems listed in /etc/fstab. #### Options -g Given with a user argument, display the quotas for the groups of which the user is a member, instead of the user's quotas. -q Display information only for filesystems in which the user is over quota. -u The default behavior. When used with -g, display both user and group quota information. -v Display quotas for filesystems even if no storage is currently allocated.
raidstart | raidstart [options] [devices] raidstop [options] [devices] System administration command. Start or stop RAID devices as defined in the RAID configuration file, /etc/raidtab. If option -a (or --all) is used, no devices need to be given; the command will be applied to all the devices defined in the configuration file. #### Options -a, --all Apply command to all devices defined in the RAID configuration file. -c file, --configfile file Use file instead of /etc/raidtab. -h, --help Print usage message and exit. -V, --version Print version and exit.
ramsize | ramsize [option] [image [size [offset]]] System administration command. If no options are specified, print usage information for the RAM disk. The pair of bytes at offset 504 in the kernel image normally specify the RAM size; with a kernel image argument, print the information found at that offset. To change that information, specify a new size (in kilobytes). You may also specify a different offset. Note that rdev -r is the same as ramsize. #### Option -o offset Same as specifying an offset as an argument.
ranlib | ranlib filename Generate an index for archive file filename. Same as running ar -s.
rarp | rarp [options] System administration command. Administer the Reverse Address Resolution Protocol table (usually /proc/net/rarp). #### Options -a [hostname] Show all entries. If hostname is specified, show only the entries relevant to hostname, which may be a list. -d hostname Remove the entries relevant to hostname, which may be a list. -s hostname hw_addr Add a new entry for hostname, with the hardware address hw_addr. -t type Check only for type entries when consulting or changing the table. type may be ether (the default) or ax25. -v Verbose mode.
rcp | rcp [options] file1 file2 rcp [options] file ... directory Copy files between two machines. Each file or directory is either a remote filename of the form rname@rhost:path or a local filename. #### Options -k Attempt to get tickets for remote host; query krb_realmofhost to determine realm. -p Preserve modification times and modes of the source files. -r If any of the source files are directories, rcp copies each subtree rooted at that name. The destination must be a directory. -x Turns on DES encryption for all data passed by rcp.
rdate | rdate [options] [host...] TCP/IP command. Retrieve the date and time from a host or hosts on the network and optionally set the local system time. #### Options -p Print the retrieved dates. -s Set the local system time from the host; must be specified by root.
rdev | rdev [options] [image [value [offset]]] System administration command. If no arguments are specified, display a line, in /etc/mtab syntax, that describes the root filesystem. Otherwise, change the values of the bytes in the kernel image that describe the RAM disk size (by default located at decimal byte offset 504 in the kernel), VGA mode (default 506), and root device (default 508). You must specify the kernel image to change and may specify a new value and a different offset. #### Options -o offset Same as specifying an offset as an argument. The offset is given in decimal. -r Behave like ramsize. -s Behave like swapdev. -v Behave like vidmode. -R Behave like rootflags.
rdist | rdist [options] [names] System administration command. Remote file distribution client program. rdist maintains identical copies of files over multiple hosts. It reads commands from a file named distfile to direct the updating of files and/or directories. An alternative distfile can be specified with the -f option or the -c option. #### Options -a num Do not update filesystems with fewer than num bytes free. -c name [login@]host[:dest] Interpret the arguments as a small distfile, where login is the user to log in as, host is the destination host, name is the local file to transfer, and dest is the remote name where the file should be installed. -d var=value Define var to have value. This option defines or overrides variable definitions in the distfile. Set the variable var to value. -f file Read input from file (by default, distfile). If file is -, read from standard input. -l options Specify logging options on the local machine. -m machine Update only machine. May be specified multiple times for multiple machines. -n Suppress normal execution. Instead, print the commands that would have been executed. -o options Specify one or more options, which must be comma-separated. chknfs Suppress operations on files that reside on NFS filesystems. chkreadonly Check filesystem to be sure it is not read-only before attempting to perform updates. chksym Do not update files that exist on the local host but are symbolic links on the remote host. compare Compare files; use this comparison rather than age as the criteria for determining which files should be updated. follow Interpret symbolic links, copying the file to which the link points instead of creating a link on the remote machine. ignlnks Ignore links that appear to be unresolvable. nochkgroup Do not update a file's group ownership unless the entire file needs updating. nochkmode Do not update file mode unless the entire file needs updating. nochkowner Do not update file ownership unless the entire file needs updating. nodescend Suppress recursive descent into directories. noexec Suppress rdist of executables that are in a.out format. numchkgroup Check group ownership by group ID instead of by name. numchkowner Check file ownership by user ID instead of by name. quiet Quiet mode; do not print commands as they execute. remove Remove files that exist on the remote host but not the local host. savetargets Save updated files in name.old. verify Print a list of all files on the remote machine that are out of date, but do not update them. whole Preserve directory structure by creating subdirectories on the remote machine. For example, if you rdist the file /foo/bar into the directory /baz, it would produce the file /baz/foo/bar, instead of the default, /baz/bar. younger Do not update files that are younger than the master files. -p path Specify the path to search for rdistd on the remote machine. -t seconds Specify the timeout period (default 900 seconds) after which rdist will sever the connection if the remote server has not yet responded. -A num Specify the minimum number of inodes that rdist requires. -D Debugging mode. -F Execute all commands sequentially, without forking. -L options Specify logging options on the remote machine. -M num Do not allow more than num child rdist processes to run simultaneously. Default is 4. -P path Specify path to rsh on the local machine.
rdistd | rdistd options System administration command. Start the rdist server. Note that you must specify the -S option, unless you are simply querying for version information with -V. #### Options -D Debugging mode. -S Start the server. -V Display the version number and exit immediately.
reboot | reboot [options] System administration command. Close out filesystems, shut down the system, then reboot the system. Because this command immediately stops all processes, it should be run only in single-user mode. If the system is not in runlevel 0 or 6, reboot calls shutdown -nf. #### Options -d Suppress writing to /var/log/wtmp. -f Call reboot even when shutdown would normally be called. -n Suppress normal call to sync. -w Suppress normal execution; simply write to /var/log/wtmp.
renice | renice [priority] [options] [target] Control the scheduling priority of various processes as they run. May be applied to a process, process group, or user (target). A privileged user may alter the priority of other users' processes. priority must, for ordinary users, lie between 0 and the environment variable PRIO_MAX (normally 20), with a higher number indicating increased niceness. A privileged user may set a negative priority, as low as PRIO_MIN, to speed up processes. #### Options +num Specify number by which to increase current priority of process, rather than an absolute priority number. -num Specify number by which to decrease current priority of process, rather than an absolute priority number. -g Interpret target parameters as process group IDs. -p Interpret target parameters as process IDs (default). -u Interpret target parameters as usernames.
reset | reset Clear screen (reset terminal).
rev | rev [file] Reverse the lines of a file onto standard output. The order of characters on each line is also reversed. If no file is specified, rev reads from standard input.
rexecd | rexecd command-line TCP/IP command. Server for the rexec routine, providing remote execution facilities with authentication based on usernames and passwords. rexecd is started by inetd and must have an entry in inetd's configuration file, /etc/inetd.conf. When rexecd receives a service request, the following protocol is initiated: The server reads characters from the socket up to a null byte. The resulting string is interpreted as an ASCII number, base 10. If the number received in step 1 is nonzero, it is interpreted as the port number of a secondary stream to be used for stderr. A second connection is then created to the specified port on the client's machine. A null-terminated username of at most 16 characters is retrieved on the initial socket. A null-terminated, unencrypted password of at most 16 characters is retrieved on the initial socket. A null-terminated command to be passed to a shell is retrieved on the initial socket. The length of the command is limited by the upper bound on the size of the system's argument list. rexecd then validates the user, as is done at login time and, if the authentication was successful, changes to the user's home directory and establishes the user and group protections of the user. A null byte is returned on the connection associated with stderr, and the command line is passed to the normal login shell of the user. The shell inherits the network connections established by rexecd. #### Diagnostics Username too long Name is longer than 16 characters. Password too long Password is longer than 16 characters. Command too long Command passed is too long. Login incorrect No password file entry for the username exists. Password incorrect Wrong password was supplied. No remote directory chdir to home directory failed. Try again fork by server failed. <shellname>:... fork by server failed. User's login shell could not be started.
rlogin | rlogin rhost [options] Remote login. rlogin connects the terminal on the current local host system to the remote host system rhost. The remote terminal type is the same as your local terminal type. The terminal or window size is also copied to the remote system if the server supports it. #### Options -8 Allow an 8-bit input data path at all times. -e c Specify escape character c (default is ~). -d Debugging mode. -k Attempt to get tickets from remote host, requesting them in the realm as determined by krb_realm-ofhost. -l username Specify a different username for the remote login. Default is the same as your local username. -x Turns on DES encryption for all data passed via the rlogin session. -E Do not interpret any character as an escape character. -K Suppress all Kerberos authentication. -L Allow rlogin session to be run without any output postprocessing (i.e., run in litout mode).
rlogind | rlogind [options] TCP/IP command. Server for the rlogin program, providing a remote login facility, with authentication based on privileged port numbers from trusted hosts. rlogind is invoked by inetd when a remote login connection is requested and executes the following protocol: The server checks the client's source port. If the port is not in the range 0-023, the server aborts the connection. The server checks the client's source address and requests the corresponding hostname. If the hostname cannot be determined, the dot-notation representation of the host address is used. The login process propagates the client terminal's baud rate and terminal type, as found in the environment variable, TERM. #### Options -a Verify hostname. -l Do not authenticate hosts via a nonroot .rhosts file. -n Suppress keep-alive messages.
rm | rm [options] files Delete one or more files. To remove a file, you must have write permission in the directory that contains the file, but you need not have permission on the file itself. If you do not have write permission on the file, you will be prompted (y or n) to override. #### Options -d, --directory Remove directories, even if they are not empty. Available only to a privileged user. -f, --force Remove write-protected files without prompting. --help Print a help message and then exit. -i, --interactive Prompt for y (remove the file) or n (do not remove the file). -r, -R, --recursive If file is a directory, remove the entire directory and all its contents, including subdirectories. Be forewarned: use of this option can be dangerous. -v, --verbose Turn on verbose mode. (rm prints the name of each file before removing it.) --version Print version information and then exit. -- Mark the end of options. Use this when you need to supply a filename beginning with -.
rmail | rmail user... TCP/IP command. Handle remote mail received via uucp, collapsing From lines in the form generated by mail into a single line of the form return-path!sender and passing the processed mail onto sendmail. rmail is explicitly designed for use with uucp and sendmail.
rmdir | rmdir [options] directories Delete the named directories (not the contents). directories are deleted from the parent directory and must be empty (if not, rm -r can be used instead). See also mkdir. #### Options --help Print a help message and then exit. --ignore-fail-on-non-empty Ignore failure to remove directories that are not empty. -p, --parents Remove directories and any intervening parent directories that become empty as a result; useful for removing subdirectory trees. --verbose Turn on verbose mode; print message for each directory as it is processed. --version Print version information and then exit.
rmmod | rmmod [option] modules System administration command. Unload a module or list of modules from the kernel. This command is successful only if the specified modules are not in use and no other modules are dependent on them. #### Option -r Recursively remove stacked modules (all modules that use the specified module).
rootflags | rootflags [option] image [flags [offset]] System administration command. Sets flags for a kernel image. If no arguments are specified, print flags for the kernel image. flags is a 2-byte integer located at offset 498 in a kernel image. Currently the only effect of flags is to mount the root filesystem in read-only mode if flags is non-zero. You may change flags by specifying the kernel image to change, the new flags, and the byte-offset at which to place the new information (the default is 498). Note that rdev -R is a synonym for rootflags. If LILO is used, rootflags is not needed. flags can be set from the LILO prompt during a boot. #### Option -o offset Same as specifying an offset as an argument.
> route | route [option] [command] TCP/IP command. Manually manipulate the routing tables normally maintained by routed. route accepts two commands: add, to add a route, and del, to delete a route. The two commands have the following syntax:
>     add [-net | -host] address [gw gateway]
>         [netmask mask] [mss tcp-mss] [dev device]
>     del address
address is treated as a plain route unless -net is specified or address is found in /etc/networks. -host can be used to specify that address is a plain route whether or not it is found in /etc/networks. The keyword default means to use this route for all requests if no other route is known. You can specify the gateway through which to route packets headed for that address, its netmask, TCP mss, and the device with which to associate the route. Only a privileged user may modify the routing tables. If no command is specified, route prints the routing tables. #### Option -n Show numerical addresses; do not look up hostnames. (Useful if DNS is not functioning properly.)
routed | routed [options] [logfile] TCP/IP command. Network routing daemon. routed is invoked by a privileged user at boot time to manage the Internet routing tables. The routing daemon uses a variant of the Xerox NS Routing Information Protocol in maintaining up-to-date kernel routing-table entries. When routed is started, it uses the SIOCGIFCONF ioctl call to find those directly connected interfaces configured into the system and marked up. routed transmits a REQUEST packet on each interface, then enters a loop, listening for REQUEST and RESPONSE packets from other hosts. When a REQUEST packet is received, routed formulates a reply based on the information maintained in its internal tables. The generated RESPONSE packet contains a list of known routes. Any RESPONSE packets received are used to update the routing tables as appropriate. When an update is applied, routed records the change in its internal tables, updates the kernel routing table, and generates a RESPONSE packet reflecting these changes to all directly connected hosts and networks. #### Options -d Debugging mode. Log additional information to the logfile. -g Offer a route to the default destination. -q Opposite of -s option. -s Force routed to supply routing information, whether it is acting as an internetwork router or not. -t Stop routed from going into background and releasing itself from the controlling terminal, so that interrupts from the keyboard will kill the process.
rpcgen | rpcgen [options] file Parse file, which should be written in the RPC language, and produce a program written in C that implements the RPC code. Place header code generated from file.x in file.h, XDR routines in file_xdr.c, server code in file_svc.c, and client code in file_clnt.c. Lines preceded by % are not parsed. By default, rpcgen produces SunOS 4.1-compatible code. -a Produce all files (client and server). -5 Produce SVR4-compatible code. -c Create XDR routines. Cannot be used with other options. -C Produce ANSI C code (default). -D name[=value] Define the symbol name, and set it equal to value or 1. -h Produce a header file. With -T, make the file support RPC dispatch tables. Cannot be used with other options. -I Produce an inetd-compatible server. -K secs Specify amount of time that the server should wait after replying to a request and before exiting. Default is 120. A secs of -1 prevents the program from ever exiting. -l Produce client code. Cannot be used with other options. -m Produce server code only, suppressing creation of a "main" routine. Cannot be used with other options. -N New style. Allow multiple arguments for procedures. Not necessarily backward compatible. -o [file] Print output to file or standard output. -Ss Create skeleton server code only. -t Create RPC dispatch table. Cannot be used with other options. -T Include support for RPC dispatch tables.
> rpcinfo | rpcinfo [options] [host] [program] [version] NFS/NIS command. Report RPC information. program can be either a name or a number. If a version is specified, rpcinfo attempts to call that version of the specified program. Otherwise, it attempts to find all the registered version numbers for the specified program by calling Version 0, and it attempts to call each registered version. #### Options -b program version Make an RPC broadcast to the specified program and version, using UDP, and report all hosts that respond. -d program version Delete the specified version of program's registration. Can be executed only by the user who added the registration or a privileged user. -n portnum Use portnum as the port number for the -t and -u options, instead of the port number given by the portmapper. -p [host] Probe the portmapper on host and print a list of all registered RPC programs. If host is not specified, it defaults to the value returned by hostname. -t host program [version] Make an RPC call to program on the specified host, using TCP, and report whether a response was received. -u host program [version] Make an RPC call to program on the specified host, using UDP, and report whether a response was received. #### Examples To show all of the RPC services registered on the local machine, use:
>     $ rpcinfo -p
> To show all of the RPC services registered on the machine named klaxon, use:
>     $ rpcinfo -p klaxon
> To show all machines on the local net that are running the Network Information Service (NIS), use:
>     $ rpcinfo -b ypserv version | uniq
where version is the current NIS version obtained from the results of the -p switch earlier in this list.
rpm | rpm [options] The Red Hat Package Manager. A freely available packaging system for software distribution and installation. RPM packages are built, installed, and queried with the rpm command. For detailed information on rpm, see Chapter 5, "Red Hat and Debian Package Managers".
rsh | rsh [options] host [command] Execute command on remote host, or, if no command is specified, begin an interactive shell on the remote host using rlogin. #### Options -d Enable socket debugging. -k Cause rsh to obtain tickets for the remote host in realm instead of the remote host's realm as determined by krb_realmofhost(3). -l username Attempt to log in as username. By default, the name of the user executing rsh is used. -n Redirects the input to rsh from the special device /dev/null. (This should be done when backgrounding rsh from a shell prompt, to direct the input away from the terminal.) -x Turns on DES encryption for all data exchange. -K Suppress Kerberos authentication.
rshd | rshd [options] TCP/IP command. Remote shell server for programs such as rcmd and rcp, which need to execute a noninteractive shell on remote machines. rshd is started by inetd and must have an entry in inetd's configuration file, /etc/inetd.conf. All options are exactly the same as those in rlogind, except for -L, which is unique to rshd. #### Option -L Log all successful connections and failed attempts via syslogd.
rstat | rstat host TCP/IP command. Summarize host's system status: the current time, uptime, and load averages -- the average number of jobs in the run queue. Queries the remote host's rstat_svc daemon.
run-parts | run-parts [options] [directory] System administration command. Run, in lexical order, all scripts found in directory. Exclude scripts whose filenames include nonalphanumeric characters (besides underscores and hyphens). #### Options -- Interpret all subsequent arguments as filenames, not options. --test Print information listing which scripts would be run, but suppress actual execution of them. --umask=umask Specify umask. The default is 022.
runlevel | runlevel System administration command. Display the previous and current system runlevels.
ruptime | ruptime [options] TCP/IP command. Provide information on how long each machine on the local network has been up and which users are logged in to each. If a machine has not reported in for 11 minutes, assume it is down. The listing is sorted by hostname. #### Options -a Include users who have been idle for more than one hour. -l Sort machines by load average. -r Reverse the normal sort order. -t Sort machines by uptime. -u Sort machines by the number of users logged in.
rusers | rusers [options] [host] TCP/IP command. List the users logged on to host, or to all local machines, in who format (hostname, usernames). #### Options -a Include machines with no users logged in. -l Include more information: tty, date, time, idle time, remote host.
rwall | rwall host [file] TCP/IP command. Print a message to all users logged on to host. If file is specified, read the message from it; otherwise, read from standard input.
rwho | rwho [option] Report who is logged on for all machines on the local network (similar to who). #### Option -a List users even if they've been idle for more than one hour.
rwhod | rwhod TCP/IP command. System status server that maintains the database used by the rwho and ruptime programs. Its operation is predicated on the ability to broadcast messages on a network. As a producer of information, rwhod periodically queries the state of the system and constructs status messages, which are broadcast on a network. As a consumer of information, it listens for other rwhod servers' status messages, validates them, then records them in a collection of files located in the directory /var/spool/rwho. Messages received by the rwhod server are discarded unless they originated at an rwhod server's port. Status messages are generated approximately once every 3 minutes.
script | script [option] [file] Fork the current shell and make a typescript of a terminal session. The typescript is written to file. If no file is given, the typescript is saved in the file typescript. The script ends when the forked shell exits, usually with Ctrl-D or exit. #### Option -a Append to file or typescript instead of overwriting the previous contents.
sed | sed [options] [command] [files] Stream editor -- edit one or more files without user interaction. See Chapter 12, "The sed Editor", for more information.
sendmail | sendmail [flags] [address...] System administration command. sendmail is a mail transfer agent (MTA) or, more simply, a mail router. It accepts mail from a user's mail program, interprets the mail address, rewrites the address into the proper form for the delivery program, and routes the mail to the correct delivery program. #### Command-line flags -b x Set operation mode to x. Operation modes are: a Run in ARPAnet mode. d Run as a daemon. i Initialize the alias database. m Deliver mail (default). p Print the mail queue. s Speak SMTP on input side. t Run in test mode. v Verify addresses; do not collect or deliver. -C file Use configuration file file. -d level Set debugging level. -F name Set full name of user to name. -f name Sender's name is name. -h cnt Set hop count (number of times message has been processed by sendmail) to cnt. -n Do not alias or forward. -o x value Set option x to value value. Options are described below. -p protocol Receive messages via the protocol protocol. -q [time] Process queued messages immediately, or at intervals indicated by time (for example, -q30m for every half hour). -r name Obsolete form of -f. -t Read head for To:, Cc:, and Bcc: lines, and send to everyone on those lists. -v Verbose. -X file Log all traffic to file. Not to be used for normal logging. #### Configuration options The following options can be set with the -o flag on the command line or the O line in the configuration file: 7 Format all incoming messages in 7 bits. a min If the D option is set, wait min minutes for the aliases file to be rebuilt before returning an alias database out-of-date warning. A file Use alternate alias file. b minblocks[/maxsize] Require at least minblocks to be free, and optionally set the maximum message size to maxsize. If maxsize is omitted, the slash is optional. B char Set unquoted space replacement character. c On mailers that are considered "expensive" to connect to, don't initiate immediate connection. C num Checkpoint the queue when mailing to multiple recipients. sendmail will rewrite the list of recipients after each group of num recipients has been processed. d x Set the delivery mode to x. Delivery modes are d for deferred delivery, i for interactive (synchronous) delivery, b for background (asynchronous) delivery, and q for queue only -- i.e., deliver the next time the queue is run. D Try to automatically rebuild the alias database if necessary. e x Set error processing to mode x. Valid modes are m to mail back the error message, w to write back the error message, p to print the errors on the terminal (default), q to throw away error messages, and e to do special processing for the BerkNet. E text Set error message header. text is either text to add to an error message or the name of a file. A filename must include its full path and begin with a /. f Save Unix-style From lines at the front of messages. F mode Set default file permissions for temporary files. If this option is missing, default permissions are 0644. G Compare local mail names to the GECOS section in the password file. g n Default group ID to use when calling mailers. H file SMTP help file. h num Allow a maximum of num hops per message. i Do not take dots on a line by themselves as a message terminator. I arg Use DNS lookups and tune them. Queue messages on connection refused. The arg arguments are identical to resolver flags without the RES_ prefix. Each flag can be preceded by a plus or minus to enable or disable the corresponding name server option. There must be a whitespace between the I and the first flag. j Use MIME format for error messages. J path Set an alternative .forward search path. k num Specify size of the connection cache. K time Time out connections after time. l Do not ignore Errors-To header. L n Specify log level. m Send to me (the sender) also if I am in an alias expansion. M Xvalue Define a macro's value in command line. Assign value to macro X. n When running newaliases, validate the right side of aliases. o If set, this message may have old-style headers. If not set, this message is guaranteed to have new-style headers (i.e., commas instead of spaces between addresses). p what,what,... Tune how private you want the SMTP daemon. The what arguments should be separated from one another by commas. The what arguments may be any of the following: public Make SMTP fully public (default). needmailhelo Require site to send HELO or ELHO before sending mail. needexpnhelo Require site to send HELO or ELHO before answering an address expansion request. needvrfyhelo Like preceding argument but for verification requests. noexpn Deny all expansion requests. novrfy Deny all verification requests. authwarnings Insert special headers in mail messages advising recipients that the message may not be authentic. goaway Set all of the previous arguments (except public). restrictmailq Allow only users of the same group as the owner of the queue directory to examine the mail queue. restrictqrun Limit queue processing to root and the owner of the queue directory. P user Send copies of all failed mail to user (usually postmaster). q fact Multiplier (factor) for high-load queuing. Q queuedir Select the directory in which to queue messages. R Don't prune route addresses. S file Save statistics in the named file. s Always instantiate the queue file, even under circumstances in which it is not strictly necessary. T time Set the timeout on undelivered messages in the queue to the specified time. t stz, dtz Set name of the time zone. U database Consult the user database database for forwarding information. u N Set default user ID for mailers. v Run in verbose mode. V host Fall-back MX host. host should be the fully qualified domain name of the fallback host. w Use a record for an ambiguous MX. x load Queues messages when load level is higher than load. X load Refuse SMTP connections when load is higher than load. y factor Penalize large recipient lists by factor. Y Deliver each job that is run from the queue in a separate process. This helps limit the size of running processes on systems with very low amounts of memory. z factor Multiplier for priority increments. This determines how much weight to give to a message's precedence header. sendmail's default is 1800. Z inc Increment priority of items remaining in queue by inc after each job is processed. sendmail uses 90,000 by default. #### sendmail support files /usr/lib/sendmail Binary of sendmail. /usr/bin/newaliases Link to /usr/lib/sendmail; causes the alias database to be rebuilt. /usr/bin/mailq Prints a listing of the mail queue. /etc/sendmail.cf Configuration file, in text form. /etc/sendmail.hf SMTP help file. /usr/lib/sendmail.st Statistics file. Doesn't need to be present. /etc/aliases Alias file, in text form. /etc/aliases.{pag,dir} Alias file in dbm format. /var/spool/mqueue Directory in which the mail queue and temporary files reside. /var/spool/mqueue/qf Control (queue) files for messages. /var/spool/mqueue/df Data files. /var/spool/mqueue/lf Lockfiles. /var/spool/mqueue/tf Temporary versions of af files, used during queue-file rebuild. /var/spool/mqueue/nf Used when creating a unique ID. /var/spool/mqueue/xf Transcript of current session.
setfdprm | setfdprm [options] device [name] Load disk parameters used when autoconfiguring floppy devices. #### Options -c device Clear parameters of device. -n device Disable format-detection messages for device. -p device [name | parameter] Permanently reset parameters for device. You can use name to specify a configuration, or you can specify individual parameters. The parameters that can be specified are dev, size, sect, heads, tracks, stretch, gap, rate, spec1, or fmt_gap. Consult /etc/fdprm for the original values. -y device Enable format-detection messages for device.
setsid | setsid command [arguments] System administration command. Execute the named command and optional command arguments in a new session.
sh | sh [options] [file [arguments]] The standard Unix shell, a command interpreter into which all other commands are entered. On Linux, this is just another name for the bash shell. For more information, see Chapter 7, "bash: The Bourne-Again Shell", .
shar | shar [options] files shar -S [options] Create shell archives (or shar files) that are in text format and can be mailed. These files may be unpacked later by executing them with /bin/sh. Other commands may be required on the recipient's system, such as compress, gzip, and uudecode. The resulting archive is sent to standard output, unless the -o option is given. #### Options -a, --net-headers Allows automatic generation of headers. The -n option is required if the -a option is used. -b bits, --bits-per-code=bits Use -b bits as a parameter to compress (when doing compression). Default value is 12. The -b option automatically turns on -Z. -c, --cut-mark Start the shar file with a line that says "Cut here." -d delimiter, --here-delimiter=delimiter Use delimiter for the files in the shar instead of SHAR_EOF. -f, --basename Causes only simple filenames to be used when restoring, which is useful when building a shar from several directories or another directory. (If a directory name is passed to shar, the substructure of that directory will be restored whether or not -f is used.) -g level, --level-for-gzip=level Use -level as a parameter to gzip (when doing compression). Default is 9. The -g option turns on the -z option by default. --help Print a help summary on standard output, then exit. -l nn, --whole-size-limit=nn Limit the output file size to nn kilobytes but don't split input files. Requires use of -o. -m, --no-timestamp Don't generate touch commands to restore the file modification dates when unpacking files from the archive. -n name, --archive-name=name Name of archive to be included in the header of the shar files. Required if the -a option is used. --no-i18n Do not produce internationalized shell archives; use default English messages. By default, shar produces archives that will try to output messages in the unpacker's preferred language (as determined by LANG/LC_MESSAGES). -o prefix, --output-prefix=prefix Save the archive to files prefix.01 through prefix.nn (instead of sending it to standard output). This option must be used when either -l or -L is used. -p, --intermix-type Allow positional parameter options. The options -B, -T, -z, and -Z may be embedded, and files to the right of the option will be processed in the specified mode. --print-text-domain-dir Print the directory shar looks in to find messages files for different languages, then immediately exit. -q, --quiet, --silent Turn off verbose mode. -s who@where, --submitter=who@where Supply submitter name and address, instead of allowing shar to determine it automatically. --version Print the version number of the program on standard output, then exit. -w, --no-character-count Do not check each file with wc -c after unpacking. The default is to check. -x, --no-check-existing Overwrite existing files without checking. Default is to check and not overwrite existing files. If -c is passed as a parameter to the script when unpacking (sh archive -c), existing files will be overwritten unconditionally. See also -X. -z, --gzip gzip and uuencode all files prior to packing. Must be unpacked with uudecode and gunzip (or zcat). -B, --uuencode Treat all files as binary; use uuencode prior to packing. This increases the size of the archive, and it must be unpacked with uudecode. -D, --no-md5-digest Do not use md5sum digest to verify the unpacked files. The default is to check. -F, --force-prefix Force the prefix character to be prepended to every line even if not required. May slightly increase the size of the archive, especially if -B or -Z is used. -L nn, --split-size-limit=nn Limit output file size to nn kilobytes and split files if necessary. The archive parts created with this option must be unpacked in correct order. Requires use of -o. -M, --mixed-uuencode Pack files in mixed mode (the default). Distinguishes files as either text or binary; binaries are uuencoded prior to packing. -P, --no-piping Use temporary files instead of pipes in the shar file. -Q, --quiet-unshar Disable verbose mode. -S, --stdin-file-list Read list of files to be packed from standard input rather than from the command line. Input must be in a form similar to that generated by the find command, with one filename per line. -T, --text-files Treat all files as text. -V, --vanilla-operation Produce shars that rely only upon the existence of sed and echo in the unsharing environment. -X, --query-user Prompt user to ask if files should be overwritten when unpacking. -Z, --compress Compress and uuencode all files prior to packing.
  > showmount | showmount [options] [host] NFS/NIS command. Show information about an NFS server. This information is maintained by the mountd server on host. The default value for host is the value returned by hostname. With no options, show the clients that have mounted directories from the host. showmount is usually found in /usr/sbin, which is not in the default search path. #### Options -a, --all Print all remote mounts in the format:
  >          hostname:directory
where hostname is the name of the client and directory is the root of the filesystem that has been mounted. -d, --directories List directories that have been remotely mounted by clients. -e, --exports Print the list of exported filesystems. -h, --help Provide a short help summary. --no-headers Do not print headers. -v, --version Report the current version number of the program.
shutdown | shutdown [options] when [message] System administration command. Terminate all processing. when may be a specific time (in hh:mm format), a number of minutes to wait (in +m format), or now. A broadcast message notifies all users to log off the system. Processes are signaled with SIGTERM, to allow them to exit gracefully. /etc/init is called to perform the actual shutdown, which consists of placing the system in runlevel 1. Only privileged users can execute the shutdown command. Broadcast messages, default or defined, are displayed at regular intervals during the grace period; the closer the shutdown time, the more frequent the message. #### Options -c Cancel a shutdown that is in progress. -f Reboot fast, by suppressing the normal call to fsck when rebooting. -h Halt the system when shutdown is complete. -k Print the warning message, but suppress actual shutdown. -n Perform shutdown without a call to init. -r Reboot the system when shutdown is complete. -t sec Ensure a sec-second delay between killing processes and changing the runlevel.
size | size [options] [objfile...] Print the number of bytes of each section of objfile and its total size. If objfile is not specified, a.out is used. #### Options -d Display the size in decimal and hexadecimal. --format format Imitate the size command from either System V (--format sysv) or BSD (--format berkeley). -o Display the size in octal and hexadecimal. --radix num Specify how to display the size: in hexadecimal and decimal (if num is 10 or 16) or hexadecimal and octal (if num is 8). -x Display the size in hexadecimal and decimal. -A Imitate System V's size command. -B Imitate BSD's size command.
slattach | slattach [options] [tty] TCP/IP command. Attach serial lines as network interfaces, thereby preparing them for use as point-to-point connections. Only a privileged user may attach or detach a network interface. #### Options -c command Run command when the connection is severed. -d Debugging mode. -e Exit immediately after initializing the line. -h Exit when the connection is severed. -l Create UUCP-style lockfile in /var/spool/uucp. -L Enable 3-wire operation. -m Suppress initialization of the line to 8 bits raw mode. -n Similar to mesg -n. -p protocol Specify protocol, which may be slip, adaptive, ppp, or kiss. -q Quiet mode; suppress messages. -s speed Specify line speed.
sleep | sleep amount[units] Wait a specified amount of time before executing another command. The default for units is seconds.
Time | Units
s | seconds
m | minutes
h | hours
d | days
> sort | sort [options] [files] Sort the lines of the named files. Compare specified fields for each pair of lines, or, if no fields are specified, compare them by byte, in machine collating sequence. See also uniq, comm, and join. #### Options -b Ignore leading spaces and tabs. -c Check whether files are already sorted, and, if so, produce no output. -d Sort in dictionary order. -f Fold -- ignore uppercase/lowercase differences. --help Print a help message and then exit. -i Ignore nonprinting characters (those outside ASCII range 040-176). -m Merge (i.e., sort as a group) input files. -n Sort in arithmetic order. -o file Put output in file. -r Reverse the order of the sort. -t c Separate fields with c (default is a tab). -u Identical lines in input file appear only one (unique) time in output. -z recsz Provide recsz bytes for any one line in the file. This option prevents abnormal termination of sort in certain cases. +n [-m] Skip n fields before sorting, and sort up to field position m. If m is missing, sort to end of line. Positions take the form a.b, which means character b of field a. If .b is missing, sort at the first character of the field. -k n[,m] Similar to +. Skip n-1 fields and stop at m-1 fields (i.e., start sorting at the nth field, where the fields are numbered beginning with 1). --version Print version information and then exit. -M Attempt to treat the first three characters as a month designation (JAN, FEB, etc.). In comparisons, treat JAN < FEB and any valid month as less than an invalid name for a month. -T tempdir Directory pathname to be used for temporary files. #### Examples List files by decreasing number of lines:
>     wc -l * | sort -r
> Alphabetize a list of words, remove duplicates, and print the frequency of each word:
>     sort -fd wordlist | uniq -c
> Sort the password file numerically by the third field (user ID):
>     sort +2n -t: /etc/passwd
> split | split [option] [infile] [outfile] Split infile into equal-sized segments. infile remains unchanged, and the results are written to outfile aa, outfile ab, and so on. (default is xaa, xab, etc.). If infile is - (or missing), standard input is read. See also csplit. #### Options -n, -l n, --lines=n Split infile into n-line segments (default is 1000). -b n[bkm], --bytes=n[bkm] Split infile into n-byte segments. Alternate blocksizes may be specified: b 512 bytes k 1 kilobyte m 1 megabyte -C bytes[bkm], --line-bytes=bytes[bkm] Put a maximum of bytes into file; insist on adding complete lines. --help Print a help message and then exit. --verbose Print a message for each output file. --version Print version information and then exit. - Take input from the standard input. #### Examples Break bigfile into 1000-line segments:
>     split bigfile
> Join four files, then split them into 10-line files named new.aa, new.ab, and so on. Note that without the -, new. would be treated as a nonexistent input file:
>     cat list[1-4] | split -10 - new.
> stat | stat filename [filenames . . . ] Print out the contents of an inode as they appear to the stat system call in a human-readable format. The error messages "Can't stat file" or "Can't lstat file" usually mean the file doesn't exist. "Can't readlink file" generally indicates that something is wrong with a symbolic link. #### Output Sample output from the command:
>     stat /
>       File: "/"
>       Size: 1024         Filetype: Directory
>       Mode: (0755/drwxr-xr-x)  Uid: (  0/  root) Gid: (  0/  system)
>     Device: 3,3   Inode: 2        Links: 21
>     Access: Tue Apr 11 04:02:01 2000(00000.11:47:35)
>     Modify: Wed Nov 17 11:46:38 1999(00146.03:02:58)
>     Change: Wed Nov 17 11:46:38 1999(00146.03:02:58)
    strace | strace [options] command [arguments] Trace the system calls and signals for command and arguments. strace shows you how data is passed between the program and the system kernel. With no options, strace prints a line to stderr for each system call. It shows the call name, arguments given, the return value, and any error messages generated. A signal is printed with both its signal symbol and a descriptive string. #### Options -a n Align the return values in column n. -c Count all calls and signals and create a summary report when the program has ended. -d Debug mode. Print debugging information for strace on stderr. -e keyword[=[!]values Pass an expression to strace to limit the types of calls or signals that are traced or change how they are displayed. The values for these expressions can be given as a comma-separated list. Preceding the list with an exclamation mark (!) negates the list. The special values of all and none are valid, as are the values listed with the following keywords. abbrev=names Abbreviate output from large structures for system calls listed in names. read=descriptors Print all data read from the given file descriptors. signal=symbols Trace the listed signal symbols (for example, signal=SIGIO,SIGHUP). trace=values Trace the listed values. values may be a list of system call names or one of the following sets of system calls:
    file | Calls that take a filename as an argument
    ipc | Interprocess communication
    network | Network-related
    process | Process management
    signal | Signal-related
verbose=names Unabbreviate structures for the given system call names. Default is none. write=descriptors Print all data written to the given file descriptors. -f Trace forked processes. -ff Write system calls for forked processes to separate files named filename.pid when using the -o option. -h Print help and exit. -i Print instruction pointer with each system call. -o filename Write output to filename instead of stderr. If filename starts with the pipe symbol |, treat the rest of the name as a command to which output should be piped. -O n Override strace's built-in timing estimates, and just subtract n microseconds from the timing of each system call to adjust for the time it takes to measure thestentry> call. -p pid Attach to the given process ID and begin tracking. strace can track more than one process if more than one option -p is given. Type Ctrl-c to end the trace. -q Quiet mode. Suppress attach and detach messages from strace. -r Relative timestamp. Print time in microseconds between system calls. -s n Print only the first n characters of a string. Default value is 32. -S value Sort output of -c option by the given value. value may be calls, name, time, or nothing. By default it is sorted by time. -T Print time spent in each system call. -t Print time of day on each line of output. -tt Print time of day with microseconds on each line of output. -ttt Print timestamp on each line as number of seconds since the Epoch. -u username Run command as username. Needed when tracing setuid and setgid programs. -V Print version and exit. -v Verbose. Do not abbreviate structure information. -x Print all non-ASCII strings in hexadecimal. -xx Print all strings in hexadecimal.
strfile | strfile [options] input_file [output_file] unstr [-c delimiter] input_file[.ext] [output_file] strfile creates a random-access file for storing strings. The input file should be a file containing groups of lines separated by a line containing a single percent sign (or other specified delimiter character). strfile creates an output file that contains a header structure and a table of file offsets for each group of lines, allowing random access of the strings. The output file, if not specified on the command line, is named sourcefile.dat. unstr undoes the work of strfile, printing out the strings contained in the input file in the order that they are listed in the header file data. If no output file is specified, unstr prints to standard output; otherwise, it prints to the file specified. unstr can also globally change the delimiter character in a strings file. #### Options Of the following options, only -c can be used with unstr. All other options apply to strfile alone. -c delimiter Change the delimiting character from the percent sign to delimiter. Valid for both strfile and unstr. -i Ignore case when ordering the strings. -o Order the strings alphabetically. -r Randomize access to the strings. -s Run silently; don't give a summary message when finished. -x Set the STR_ROTATED bit in the header str_flags field.
strings | strings [options] files Search each file specified and print any printable character strings found that are at least four characters long and followed by an unprintable character. #### Options -, -a, --all Scan entire object files; default is to scan only the initialized and loaded sections for object files. -f, --print-file-name Print the name of the file before each string. -min-len, -n min-len, --bytes=min-len Print only strings that are at least min-len characters. -t base, --radix=base Print the offset within the file before each string, in the format specified by base: d Decimal o Octal x Hexadecimal --target=format Specify an alternative object code format to the system default. -o Same as -t o. --help Print help message and then exit. -v, --version Print version information and then exit.
strip | strip [options] files Remove symbols from object files, thereby reducing file sizes and freeing disk space. #### Options -F format, --target=format Expect the input file to be in the format format. -O format, --output-target=format Write output file in format. -R section, --remove-section=section Delete section. -s, --strip-all Strip all symbols. -S, -g,--strip-debug Strip debugging symbols. -x, --discard-all Strip nonglobal symbols. -X, --discard-locals Strip local symbols that were generated by the compiler. -v, --verbose Verbose mode.
stty | stty [options] [modes] Set terminal I/O options for the current standard input device. Without options, stty reports the terminal settings that differ from those set by running stty sane, where a ^ indicates the Ctrl key and ^` indicates a null value. Most modes can be negated using an optional - (shown in brackets). The corresponding description is also shown in brackets. Some arguments use non-POSIX extensions; these are marked with a *. #### Options -a, --all Report all option settings. -g Report settings in hex. #### Control modes n Set terminal baud rate to n (e.g., 2400). [-]clocal [Enable] disable modem control. [-]cread [Disable] enable the receiver. cs bits Set character size to bits, which must be 5, 6, 7, or 8. [-]cstopb [1] 2 stop bits per character. [-]hup [Do not] hang up connection on last close. [-]hupcl Same as previous. ispeed n Set terminal input baud rate to n. ospeed n Set terminal output baud rate to n. [-]parenb [Disable] enable parity generation and detection. [-]parodd Use [even] odd parity. [-]crtscts* [Disable]enable RTS/CTS handshaking. #### Flow control modes The following flow control modes are available by combining the ortsfl, ctsflow, and rtsflow flags:
Flag Settings | Flow Control Mode
--- | ---
ortsfl rtsflow ctsflow | Enable unidirectional flow control.
ortsfl rtsflow -ctsflow | Assert RTS when ready to send.
ortsfl -rtsflow ctsflow | No effect.
ortsfl -rtsflow -ctsflow | Enable bidirectional flow control.
-ortsfl rtsflow ctsflow | Enable bidirectional flow control.
-ortsfl rtsflow -ctsflow | No effect.
-ortsfl -rtsflow ctsflow | Stop transmission when CTS drops.
-ortsfl -rtsflow -ctsflow | Disable hardware flow control.
#### Input modes [-]brkint [Do not] signal INTR on break. [-]icrnl [Do not] map CR to NL on input. [-]ignbrk [Do not] ignore break on input. [-]igncr [Do not] ignore CR on input. [-]ignpar [Do not] ignore parity errors. [-]inlcr [Do not] map NL to CR on input. [-]inpck [Disable] enable input parity checking. [-]istrip [Do not] strip input characters to 7 bits. [-]iuclc* [Do not] map uppercase to lowercase on input. [-]ixany* Allow [XON] any character to restart output. [-]ixoff [-]tandem [Do not] send START/STOP characters when queue is nearly empty/full. [-]ixon [Disable] enable START/STOP output control. [-]parmrk [Do not] mark parity errors. [-]imaxbel* When input buffer is too full to accept a new character, [flush the input buffer] beep without flushing the input buffer. #### Output modes bs n Select style of delay for backspaces (0 or 1). cr n Select style of delay for carriage returns (0-3). ff n Select style of delay for formfeeds (0 or 1). nl n Select style of delay for linefeeds (0 or 1). tab n Select style of delay for horizontal tabs (0-3). vt n Select style of delay for vertical tabs (0 or 1). [-]ocrnl* [Do not] map CR to NL on output. [-]ofdel* Set fill character to [NULL] DEL. [-]ofill* Delay output with [timing] fill characters. [-]olcuc* [Do not] map lowercase to uppercase on output. [-]onlcr* [Do not] map NL to CR-NL on output. [-]onlret* On the terminal, NL performs [does not perform] the CR function. [-]onocr* Do not [do] output CRs at column 0. [-]opost [Do not] postprocess output. #### Local modes [-]echo [Do not] echo every character typed. [-]echoe, [-]crterase [Do not] echo ERASE character as BS-space-BS string. [-]echok [Do not] echo NL after KILL character. [-]echonl [Do not] echo NL. [-]icanon [Disable] enable canonical input (ERASE, KILL, WERASE, and RPRINT processing). [-]iexten [Disable] enable extended functions for input data. [-]isig [Disable] enable checking of characters against INTR, SUSPEND, and QUIT. [-]noflsh [Enable] disable flush after INTR or QUIT. [-]tostop* [Do not] send SIGTTOU when background processes write to the terminal. [-]xcase* [Do not] change case on local output. [-]echoprt, [-]prterase* When erasing characters, echo them backward, enclosed in \ and /. [-]echoctl. [-]ctlecho* Do not echo control characters literally. Use hat notation (e.g., ^Z). [-]echoke [-]crtkill* Erase characters as specified by the echoprt and echoe settings (default is echoctl and echok settings). #### Control assignments ctrl-char c Set control character to c. ctrl-char is dsusp (flush input and then send stop), eof, eol, eol2 (alternate end-of-line), erase, intr, lnext (treat next character literally), kill, rprnt (redraw line), quit, start, stop, susp, swtch, or werase (erase previous word). c can be a literal control character, a character in hat notation (e.g., ^Z), in hex (must begin with 0x), in octal (must begin with 0), or in decimal. Disable the control character with values of ^- or undef. min n Set the minimum number of characters that will satisfy a read until the time value has expired when -icanon is set. time n Set the number of tenths of a second before reads time out if the min number of characters have not been read when -icanon is set. line i Set line discipline to i (1-126). #### Combination modes cooked Same as -raw. [-]evenp [-]parity Same as [-]parenb and cs[8]7. [-]parity Same as [-]parenb and cs[8]7. ek Reset ERASE and KILL characters to Ctrl-h and Ctrl-u, their defaults. [-]lcase [Un] set xcase, iuclc, and olcuc. [-]LCASE Same as [-]lcase. [-]nl [Un] set icrnl and onlcr. -nl also unsets inlcr, igncr, ocrnl, and onlret, icrnl, onlcr. [-]oddp Same as [-]parenb, [-]parodd, and cs7[8]. [-]raw [Disable] enable raw input and output (no ERASE, KILL, INTR, QUIT, EOT, SWITCH, or output postprocessing). sane Reset all modes to reasonable values. [-]tabs* [Expand to spaces] preserve output tabs. [-]cbreak Same as -icanon. [-]pass8 Same as -parenb -istrip cs8. [-]litout Same as -parenb -istrip cs8. [-]decctlq* Same as -ixany. crt Same as echoe echoctl echoke. dec Same as echoe echoctl echoke -ixany. Additionally, set INTERRUPT to ^C, ERASE to DEL, and KILL to ^U. #### Special settings ispeed speed Specify input speed. ospeed speed Specify output speed. rows rows* Specify number of rows. cols columns, columns columns* Specify number of columns. size* Display current row and column settings. line discipline* Specify line discipline. speed Display terminal speed.
  > su | su [option] [user] [shell_args] Create a shell with the effective user-ID user. If no user is specified, create a shell for a privileged user (that is, become a superuser). Enter EOF to terminate. You can run the shell with particular options by passing them as shell_args (e.g., if the shell runs sh, you can specify -c command to execute command via sh or -r to create a restricted shell). #### Options -, -l, --login Go through the entire login sequence (i.e., change to user's environment). -c command, --command=command Execute command in the new shell and then exit immediately. If command is more than one word, it should be enclosed in quotes -- for example:
  >     su -c 'find / -name \*.c -print' nobody
-f, --fast Start shell with -f option. In csh and tcsh, this suppresses the reading of the .cshrc file. In bash, this suppresses filename pattern expansion. -m, -p, --preserve-environment Do not reset environment variables. -s shell, --shell=shell Execute shell, not the shell specified in /etc/passwd, unless shell is restricted. --help Print a help message and then exit. --version Print version information and then exit.
sum | sum [options] files Calculate and print a checksum and the number of (1KB) blocks for file. Useful for verifying data transmission. #### Options -r The default setting. Use the BSD checksum algorithm. -s, --sysv Use alternate checksum algorithm as used on System V. The blocksize is 512 bytes. --help Print a help message and then exit. --version Print the version number and then exit.
swapdev | swapdev [option] [image [swapdevice [offset]]] System administration command. If no arguments are given, display usage information about the swap device. If just the location of the kernel image is specified, print the information found there. To change that information, specify the new swapdevice. You may also specify the offset in the kernel image to change. Note that rdev -s is a synonym for swapdev. #### Option -o offset Synonymous to specifying an offset as an argument.
swapoff | swapoff -a | device ... System administration command. Stop making the listed devices available for swapping and paging. #### Option -a Consult /etc/fstab for devices marked sw. Use those in place of the device argument.
swapon | swapon [options] device ... System administration command. Make the listed devices available for swapping and paging. #### Options -a Consult /etc/fstab for devices marked sw. Use those in place of the device argument. -p priority Specify a priority for the swap area. Higher priority areas will be used up before lower priority areas are used.
sync | sync System administration command. Write filesystem buffers to disk. sync executes the sync() system call. If the system is to be stopped, sync must be called to ensure filesystem integrity. Note that shutdown automatically calls sync before shutting down the system. sync may take several seconds to complete, so the system should be told to sleep briefly if you are about to manually call halt or reboot. Note that shutdown is the preferred way to halt or reboot your system, since it takes care of sync-ing and other housekeeping for you.
sysklogd | sysklogd System administration command. sysklogd, the Linux program that provides syslogd functionality, behaves exactly like the BSD version of syslogd. The difference should be completely transparent to the user. However, sysklogd is coded very differently and supports a slightly extended syntax. It is invoked as syslogd. See also klogd. #### Options -d Turn on debugging. -f configfile Specify alternate configuration file. -h Forward messages from remote hosts to forwarding hosts. -l hostlist Specify hostnames that should be logged with just their hostname, not their fully qualified domain name. Multiple hosts should be separated with a colon (:). -m markinterval Select number of minutes between mark messages. -n Avoid autobackgrounding. This is needed when starting syslogd from init. -p socket Send log to socket instead of /dev/log. -r Receive messages from the network using an Internet domain socket with the syslog service. -s domainlist Strip off domain names specified in domainlist before logging. Multiple domain names should be separated by a colon (:).
syslogd | syslogd TCP/IP command. Log system messages into a set of files described by the configuration file /etc/syslog.conf. Each message is one line. A message can contain a priority code, marked by a number in angle braces at the beginning of the line. Priorities are defined in <sys/syslog.h>. syslogd reads from an Internet domain socket specified in /etc/services. To bring syslogd down, send it a terminate signal.
systat | systat [options] host System administration command. Get information about the network or system status of a remote host by querying its netstat, systat, or daytime service. #### Options -n, --netstat Specifically query the host's netstat service. -p port, --port port Specify port to query. -s, --systat Specifically query the host's systat service. -t, --time Specifically query the host's daytime service.
tac | tac [options] [file] Named for the common command cat, tac prints files in reverse. Without a filename or with -, it reads from standard input. By default, it reverses the order of the lines, printing the last line first. #### Options -b, --before Print separator (by default a newline) before string that it delimits. -r, --regex Expect separator to be a regular expression. -s string, --separator=string Specify alternate separator (default is newline). --help Print a help message and then exit. --version Print version information and then exit.
> tail | tail [options] [file] Print the last 10 lines of the named file (or standard input if - is specified) on standard output. #### Options -n[k] Begin printing at nth item from end-of-file. k specifies the item to count: l (lines, the default), b (blocks), or c (characters). -k Same as -n, but use the default count of 10. +n[k] Like -n, but start at nth item from beginning of file. +k Like -k, but count from beginning of file. -c num{bkm}, --bytes num{bkm} Print last num bytes. An alternate blocksize may be specified: b 512 bytes k 1 kilobyte m 1 megabyte -f Don't quit at the end of file; "follow" file as it grows. End when user presses Ctrl-C. -n num, --lines num Print last num lines. -q, --quiet, --silent Suppress filename headers. --version Print version information and then exit. #### Examples Show the last 20 lines containing instances of .Ah:
>     grep '\.Ah' file | tail -20
> Show the last 10 characters of variable name:
>     echo "$name" | tail -c
> Print the last two blocks of bigfile:
>     tail -2b bigfile
talk | talk person [ttyname] Talk to another user. person is either the login name of someone on your own machine or user@host on another host. To talk to a user who is logged in more than once, use ttyname to indicate the appropriate terminal name. Once communication has been established, the two parties may type simultaneously, with their output appearing in separate windows. To redraw the screen, type Ctrl-L. To exit, type your interrupt character; talk then moves the cursor to the bottom of the screen and restores the terminal.
talkd | talkd [option] TCP/IP command. Remote user communication server. talkd notifies a user that somebody else wants to initiate a conversation. A talk client initiates a rendezvous by sending a CTL_MSG of type LOOK_UP to the server. This causes the server to search its invitation tables for an existing invitation for the client. If the lookup fails, the caller sends an ANNOUNCE message, causing the server to broadcast an announcement on the callee's login ports requesting contact. When the callee responds, the local server responds with the rendezvous address, and a stream connection is established through which the conversation takes place. #### Option -d Write debugging information to the syslogd log file.
> tar | tar [options] [tarfile] [other-files] Copy files to or restore files from an archive medium. If any files are directories, tar acts on the entire subtree. Options need not be preceded by - (though they may be). The exception to this rule is when you are using a long-style option (such as --modification-time). In that case, the exact syntax is:
>     tar --long-option -function-options files
> For example:
>     tar --modification-time -xvf tarfile.tar
> #### Function options You must use exactly one of these, and it must come before any other options: -c, --create Create a new archive. -d, --compare Compare the files stored in tarfile with other-files. Report any differences: missing files, different sizes, different file attributes (such as permissions or modification time). -r, --append Append other-files to the end of an existing archive. -t, --list Print the names of other-files if they are stored on the archive (if other-files are not specified, print names of all files). -u, --update Add files if not in the archive or if modified. -x, --extract, --get Extract other-files from an archive (if other-files are not specified, extract all files). -A, --catenate, --concatenate Concatenate a second tar file on to the end of the first. #### Options n Select device n, where n is 0,...,9999. The default is found in /etc/default/tar. [drive][density] Set drive (0-7) and storage density (l, m, or h, corresponding to low, medium, or high). --atime-preserve Preserve original access time on extracted files. -b, --block-size=n Set block size to n × 512 bytes. --checkpoint List directory names encountered. --exclude=file Remove file from any list of files. -f arch, --file=filename Store files in or extract files from archive arch. Note that filename may take the form hostname:filename. --force-local Interpret filenames in the form hostname:filename as local files. -g, --listed-incremental Create new-style incremental backup. -h, --dereference Dereference symbolic links. -i, --ignore-zeros Ignore zero-sized blocks (i.e., EOFs). --ignore-failed-read Ignore unreadable files to be archived. Default behavior is to exit when encountering these. -k, --keep-old-files When extracting files, do not overwrite files with similar names. Instead, print an error message. -l, --one-file-system Do not archive files from other file systems. -m, --modification-time Do not restore file modification times; update them to the time of extraction. --null Allow filenames to be null-terminated with -T. Override -C. --old, --portability, --preserve Equivalent to invoking both the -p and -s options. -p, --same-permissions, --preserve-permissions Keep ownership of extracted files same as that of original permissions. --remove-files Remove originals after inclusion in archive. --rsh-command=command Do not connect to remote host with rsh; instead, use command. -s, --same-order, --preserve-order When extracting, sort filenames to correspond to the order in the archive. --totals Print byte totals. --use-compress-program=program Compress archived files with program, or uncompress extracted files with program. -v, --verbose Verbose. Print filenames as they are added or extracted. -w, --interactive Wait for user confirmation (y) before taking any actions. -z, --gzip, --ungzip Compress files with gzip before archiving them, or uncompress them with gunzip before extracting them. -C, --directory=directory cd to directory before beginning tar operation. -F, --info-script, --new-volume-script=script Implies -M (multiple archive files). Run script at the end of each file. -G, --incremental Create old-style incremental backup. -K file, --starting-file file Begin tar operation at file file in archive. -L, --tape-length=length Write a maximum of length × 1024 bytes to each tape. -M, --multivolume Expect archive to multivolume. With -c, create such an archive. -N date, --after-date date Ignore files older than date. -O, --to-stdout Print extracted files on standard out. -P, --absolute-paths Do not remove initial slashes (/) from input filenames. -R, --record-number Display archive's record number. -S, --sparse Treat short file specially and more efficiently. -T filename, --files-from filename Consult filename for files to extract or create. -V name, --label=name Name this volume name. -W, --verify Check archive for corruption after creation. -X file, --exclude file Consult file for list of files to exclude. -Z, --compress, --uncompress Compress files with compress before archiving them, or uncompress them with uncompress before extracting them. #### Examples Create an archive of /bin and /usr/bin (c), show the command working (v), and store on the tape in /dev/rmt0:
>     tar cvf /dev/rmt0 /bin /usr/bin
> List the tape's contents in a format like ls -l:
>     tar tvf /dev/rmt0
> Extract the /bin directory:
>     tar xvf /dev/rmt0 /bin
> Create an archive of the current directory and store it in a file backup.tar:
>     tar cvf - `find . -print > backup.tar
(The - tells tar to store the archive on standard output, which is then redirected.)
tcpd | tcpd TCP/IP command. Monitor incoming TCP/IP requests (such as those for telnet, ftp, finger, exec, rlogin). Provide checking and logging services; then pass the request to the appropriate daemon.
tcpdchk | tcpdchk [options] TCP/IP command. Consult the TCP wrapper configuration (in /etc/hosts.allow and /etc/hosts.deny); display a list of all possible problems with it; attempt to suggest possible fixes. #### Options -a Include a list of rules; do not require an ALLOW keyword before allowing sites to access the local host. -d Consult ./hosts.allow and ./hosts.deny instead of /etc/hosts.allow and /etc/hosts.deny. -i conf-file Specify location of inetd.conf or tlid.conf file. These are files that tcpdchk automatically uses in its evaluation of TCP wrapper files. -v Verbose mode.
tcpdmatch | tcpdmatch [options] daemon client TCP/IP command. Predict the TCP wrapper's response to a specific request. You must specify which daemon the request is made to (the syntax may be daemon@host for requests to remote machines) and the client from which the request originates (the syntax may be user@client for a specific user or a wildcard). Consult /etc/hosts.allow and /etc/hosts.deny to determine the TCP wrapper's actions. #### Options -d Consult ./hosts.allow and ./hosts.deny instead of /etc/hosts.allow and /etc/hosts.deny. -i conf-file Specify location of inetd.conf or tlid.conf file. These are files that tcpdmatch automatically uses in its evaluation of TCP wrapper files.
tcsh | tcsh [options] [file [arguments]] An extended version of the C shell, a command interpreter into which all other commands are entered. For more information, see Chapter 8, "csh and tcsh".
> tee | tee [options] files Accept output from another command and send it both to the standard output and to files (like a T or fork in a road). #### Options -a, --append Append to files; do not overwrite. -i, --ignore-interrupts Ignore interrupt signals. --help Print a help message and then exit. --version Print version information and then exit. #### Example
>     ls -l | tee savefile    View listing and save for later
telinit | telinit [option] [runlevel] System administration command. Signal init to change the system's runlevel. telinit is actually just a link to init, the ancestor of all processes. #### Option -t seconds Send SIGKILL seconds after SIGTERM. Default is 20. #### Runlevels The default runlevels vary from distribution to distribution, but these are standard: 0 Halt the system. 1, s, S Single user. 6 Reboot the system. a, b, c Process only entries in /etc/inittab that are marked with run level a, b, or c. q, Q Reread /etc/inittab. Check the /etc/inittab file for runlevels on your system.
telnet | telnet [options] [host [port ]] Access remote systems. telnet is the user interface that communicates with another host using the Telnet protocol. If telnet is invoked without host, it enters command mode, indicated by its prompt, telnet>, and accepts and executes the commands listed after the following options. If invoked with arguments, telnet performs an open command (shown in the following list) with those arguments. host indicates the host's official name. port indicates a port number (default is the Telnet port). #### Options -a Automatic login into the remote system. -d Turn on socket-level debugging. -e [escape_char] Set initial telnet escape character to escape_char. If escape_char is omitted, there will be no predefined escape character. -l user When connecting to remote system and if remote system understands ENVIRON, send user to the remote system as the value for variable USER. -n tracefile Open tracefile for recording the trace information. -r Emulate rlogin: the default escape character is a tilde (~); an escape character followed by a dot causes telnet to disconnect from the remote host; a ^Z instead of a dot suspends telnet; and a ] (the default telnet escape character) generates a normal telnet prompt. These codes are accepted only at the beginning of a line. -8 Request 8-bit operation. -E Disable the escape character functionality. -L Specify an 8-bit data path on output. -S tos Set the IP type-of-service (TOS) option for the Telnet connection to the value tos. #### Commands CTRL-Z Suspend telnet. ! [command] Execute a single command in a subshell on the local system. If command is omitted, an interactive subshell will be invoked. ? [command] Get help. With no arguments, print a help summary. If a command is specified, print the help information for just that command. close Close a Telnet session and return to command mode. display argument ... Display all, or some, of the set and toggle values. environ [arguments [...]] Manipulate variables that may be sent through the TELNET ENVIRON option. Valid arguments for environ are: ? Get help for the environ command. define variable value Define variable to have a value of value. undefine variable Remove variable from the list of en vi ronment variables. export variable Mark variable to have its value exported to the remote side. unexport variable Mark variable to not be exported unless explicitly requested by the remote side. list Display current variable values. logout If the remote host supports the logout command, close the telnet session. mode [type] Depending on state of Telnet session, type is one of several options: ? Print out help information for the mode command. character Disable TELNET LINEMODE option, or, if remote side does not understand the option, enter "character-at-a-time" mode. [-]edit Attempt to [disable] enable the EDIT mode of the TELNET LINEMODE option. [-]isig Attempt to [disable]enable the TRAPSIG mode of the LINEMODE option. line Enable LINEMODE option, or, if remote side does not understand the option, attempt to enter "old line-by-line" mode. [-]softtabs Attempt to [disable] enable the SOFT_TAB mode of the LINEMODE option. [-]litecho [Disable]enable LIT_ECHO mode. open[-l user] host [port] Open a connection to the named host. If no port number is specified, attempt to contact a Telnet server at the default port. quit Close any open Telnet session and then exit telnet. status Show current status of telnet. This includes the peer one is connected to as well as the current mode. send arguments Send one or more special character sequences to the remote host. Following are the arguments that may be specified: ? Print out help information for send command. abort Send Telnet ABORT sequence. ao Send Telnet AO sequence, which should cause the remote system to flush all output from the remote system to the user's terminal. ayt Send Telnet AYT (Are You There) sequence. brk Send Telnet BRK (Break) sequence. do cmd dont cmd will cmd wont cmd Send Telnet DO cmd sequence, where cmd is a number between 0 and 255 or a symbolic name for a specific telnet command. If cmd is ? or help, this command prints out help (including a list of symbolic names). ec Send Telnet EC (Erase Character) sequence, which causes the remote system to erase the last character entered. el Send Telnet EL (Erase Line) sequence, which causes the remote system to erase the last line entered. eof Send Telnet EOF (End Of File) sequence. eor Send Telnet EOR (End Of Record) sequence. escape Send current Telnet escape character (initially ^). ga Send Telnet GA (Go Ahead) sequence. getstatus If the remote side supports the Telnet STATUS command, getstatus sends the subnegotiation request that the server send its current option status. ip Send Telnet IP (Interrupt process) sequence, which causes the remote system to abort the currently running process. nop Send Telnet NOP (No operation) sequence. susp Send Telnet SUSP (Suspend process) sequence. synch Send Telnet SYNCH sequence, which causes the remote system to discard all previously typed (but not read) input. set argument value unset argument value Set any one of a number of telnet variables to a specific value or to TRUE. The special value off disables the function associated with the variable. unset disables any of the specified functions. The values of variables may be interrogated with the aid of the display command. The variables that may be specified are: ? Display legal set and unset commands. ayt If telnet is in LOCALCHARS mode, this character is taken to be the alternate AYT character. echo This is the value (initially ^E) which, when in "line-by-line" mode, toggles between doing local echoing of entered characters and suppressing echoing of entered characters. eof If telnet is operating in LINEMODE or in the old "line-by-line" mode, entering this character as the first character on a line will cause the character to be sent to the remote system. erase If telnet is in LOCALCHARS mode and operating in the "character-at-a-time" mode, then when this character is entered, a Telnet EC sequence will be sent to the remote system. escape This is the Telnet escape character (initially ^[), which causes entry into the Telnet command mode when connected to a remote system. flushoutput If telnet is in LOCALCHARS mode and the flushoutput character is entered, a Telnet AO sequence is sent to the remote host. forw1 If Telnet is in LOCALCHARS mode, this character is taken to be an alternate end-of-line character. forw2 If Telnet is in LOCALCHARS mode, this character is taken to be an alternate end-of-line character. interrupt If Telnet AO is in LOCALCHARS mode and the interrupt character is entered, a Telnet IP sequence is sent to the remote host. kill If Telnet IP is in LOCALCHARS mode and operating in the "character-at-a-time" mode, then when this character is entered, a Telnet EL sequence is sent to the remote system. lnext If Telnet EL is in LINEMODE or in the old "line-by-line" mode, then this character is taken to be the terminal's lnext character. quit If Telnet EL is in LOCALCHARS mode and the quit character is entered, a Telnet BRK sequence is sent to the remote host. reprint If Telnet BRK is in LINEMODE or in the old "line-by-line" mode, this character is taken to be the terminal's reprint character. rlogin Enable rlogin mode. Same as using -r command-line option. start If the Telnet TOGGLE-FLOW-CONTROL option has been enabled, this character is taken to be the terminal's start character. stop If the Telnet TOGGLE-FLOW-CONTROL option has been enabled, this character is taken to be the terminal's stop character. susp If Telnet is in LOCALCHARS mode, or if the LINEMODE is enabled and the suspend character is entered, a Telnet SUSP sequence is sent to the remote host. tracefile File to which output generated by netdata is written. worderase If Telnet BRK is in LINEMODE or in the old "line-by-line" mode, this character is taken to be the terminal's worderase character. Defaults for these are the terminal's defaults. slc [state] Set state of special characters when Telnet LINEMODE option has been enabled. ? List help on the slc command. check Verify current settings for current special characters. If discrepancies are discovered, convert local settings to match remote ones. export Switch to local defaults for the special characters. import Switch to remote defaults for the special characters. toggle arguments [...] Toggle various flags that control how Telnet responds to events. The flags may be set explicitly to true or false using the set and unset commands listed previously. The valid arguments are: ? Display legal toggle commands. autoflush If autoflush and LOCALCHARS are both true, then when the ao or quit characters are recognized, Telnet refuses to display any data on the user's terminal until the remote system acknowledges that it has processed those Telnet sequences. autosynch If autosynch and LOCALCHARS are both true, then when the intr or quit character is entered, the resulting Telnet sequence sent is followed by the Telnet SYNCH sequence. Initial value for this toggle is false. binary Enable or disable the Telnet BINARY option on both the input and the output. inbinary Enable or disable the Telnet BINARY option on the input. outbinary Enable or disable the Telnet BINARY option on the output. crlf If this toggle value is true, carriage returns are sent as CR-LF. If false, carriage returns are sent as CR-NUL. Initial value is false. crmod Toggle carriage return mode. Initial value is false. debug Toggle socket level debugging mode. Initial value is false. localchars If the value is true, flush, interrupt, quit, erase, and kill characters are recognized locally, then transformed into appropriate Telnet control sequences. Initial value is true. netdata Toggle display of all network data. Initial value is false. options Toggle display of some internal telnet protocol processing pertaining to Telnet options. Initial value is false. prettydump When netdata is enabled, and if prettydump is enabled, the output from the netdata command is reorganized into a more user-friendly format, spaces are put between each character in the output, and an asterisk precedes any Telnet escape sequence. skiprc Toggle whether to process `~`/.telnetrc file. Initial value is false, meaning the file is processed. termdata Toggle printing of hexadecimal terminal data. Initial value is false. z Suspend telnet; works only for the csh.
telnetd | telnetd [options] TCP/IP command. Telnet protocol server. telnetd is invoked by the Internet server for requests to connect to the Telnet port (port 23 by default). telnetd allocates a pseudoterminal device for a client, thereby creating a login process that has the slave side of the pseudoterminal serving as stdin, stdout, and stderr. telnetd manipulates the master side of the pseudoterminal by implementing the Telnet protocol and by passing characters between the remote client and the login process. #### Options -debug [port] Start telnetd manually instead of through inetd. port may be specified as an alternate TCP port number on which to run telnetd. -D modifier(s) Debugging mode. This allows telnet to print out debugging information to the connection, enabling the user to see what telnet is doing. Several modifiers are available for the debugging mode: exercise Has not been implemented yet. netdata Display data stream received by telnetd. options Print information about the negotiation of the Telnet options. ptydata Display data written to the pseudo terminal device. report Print options information, as well as some additional information about what processing is going on.
test | test expression [expression] Also exists as a built-in in most shells. Evaluate an expression and, if its value is true, return a zero exit status; otherwise, return a nonzero exit status. In shell scripts, you can use the alternate form [expression]. This command is generally used with conditional constructs in shell programs. #### File testers The syntax for all of these options is test option file. If the specified file does not exist, they return false. Otherwise, they will test the file as specified in the option description. -b Is the file block special? -c Is the file character special? -d Is the file a directory? -e Does the file exist? -f Is the file a regular file? -g Does the file have the set-group-ID bit set? -k Does the file have the sticky bit set? -L Is the file a symbolic link? -p Is the file a named pipe? -r Is the file readable by the current user? -s Is the file nonempty? -S Is the file a socket? -t [file-descriptor] Is the file associated with file-descriptor (or 1, standard output, by default) connected to a terminal? -u Does the file have the set-user-ID bit set? -w Is the file writable by the current user? -x Is the file executable? -O Is the file owned by the process's effective user ID? -G Is the file owned by the process's effective group ID? #### File comparisons The syntax for file comparisons is test file1 option file2. A string by itself, without options, returns true if it's at least one character long. -nt Is file1 newer than file2? Check modification, not creation, date. -ot Is file1 older than file2? Check modification, not creation, date. -ef Do the files have identical device and inode numbers? #### String tests The syntax for string tests is test option string. -z Is the string 0 characters long? -n Is the string at least 1 character long? = string Are the two strings equal? != string Are the strings unequal? #### Expression tests Note that an expression can consist of any of the previous tests. ! expression Is the expression false? expression -a expression Are the expressions both true? expression -o expression Is either expression true? #### Integer tests The syntax for integer tests is test integer1 option integer2. You may substitute -l string for an integer; this evaluates to string's length. -eq Are the two integers equal? -ne Are the two integers unequal? -lt Is integer1 less than integer2? -le Is integer1 less than or equal to integer2? -gt Is integer1 greater than integer2? -ge Is integer1 greater than or equal to integer2?
> tftp | tftp [host [port]] User interface to the TFTP (Trivial File Transfer Protocol), which allows users to transfer files to and from a remote machine. The remote host may be specified, in which case tftp uses host as the default host for future transfers. #### Commands Once tftp is running, it issues the prompt:
>     tftp>
and recognizes the following commands: ? [command-name...] Print help information. ascii Shorthand for mode ASCII. binary Shorthand for mode binary. connect hostname [port] Set the hostname, and optionally the port, for transfers. get filename get remotename localname get filename1 filename2 filename3...filenameN Get a file or set of files from the specified remote sources. mode transfer-mode Set the mode for transfers. transfer-mode may be ASCII or binary. The default is ASCII. put filename put localfile remotefile put filename1 filename2...filenameN remote-directory Transfer a file or set of files to the specified remote file or directory. quit Exit tftp. rexmt retransmission-timeout Set the per-packet retransmission timeout, in seconds. status Print status information: whether tftp is connected to a remote host (i.e., whether a host has been specified for the next connection), the current mode, whether verbose and tracing modes are on, and the values for retransmission timeout and total transmission timeout. timeout total-transmission-timeout Set the total transmission timeout, in seconds. trace Toggle packet tracing. verbose Toggle verbose mode.
tftpd | tftpd [homedir] TCP/IP command. Trivial File Transfer Protocol server. tftpd is normally started by inetd and operates at the port indicated in the tftp Internet service description in the /etc/inetd.conf file. By default, the entry for tftpd in /etc/inetd.conf is commented out; the comment character must be deleted to make tfptd operational. Before responding to a request, the server attempts to change its current directory to homedir; the default value is tftpboot.
tload | tload [options] [tty] Display system load average in graph format. If tty is specified, print it to that tty. #### Options -d delay Specify the delay, in seconds, between updates. -s scale Specify scale (number of characters between each graph tick). A smaller number results in a larger scale.
top | top [options] Provide information (frequently refreshed) about the most CPU-intensive processes currently running. See ps for explanations of the field descriptors. #### Options -b Run in batch mode; don't accept command-line input. Useful for sending output to another command or to a file. -c Show command line in display instead of just command name. -d delay Specify delay between refreshes. -i Suppress display of idle and zombie processes. -n num Update display num times, then exit. -p pid Monitor only processes with the specified process ID. -q Refresh without any delay. If user is privileged, run with highest priority. -s Secure mode. Disable some (dangerous) interactive commands. -S Cumulative mode. Print total CPU time of each process, including dead child processes. #### Interactive commands space Update display immediately. c Toggle display of command name or full command line. f, F Add fields to display or remove fields from the display. h, ? Display help about commands and the status of secure and cumulative modes. k Prompt for process ID to kill and signal to send (default is 15) to kill it. i Toggle suppression of idle and zombie processes. l Toggle display of load average and uptime information. m Toggle display of memory information. n, # Prompt for number of processes to show. If 0 is entered, show as many as will fit on the screen (default). o, O Change order of displayed fields. q Exit. r Apply renice to a process. Prompt for PID and renice value. Suppressed in secure mode. s Change delay between refreshes. Prompt for new delay time, which should be in seconds. Suppressed in secure mode. t Toggle display of processes and CPU states information. A Sort by age, with newest first. ^L Redraw screen. M Sort tasks by resident memory usage. N Sort numerically by process ID. P Sort tasks by CPU usage (default). S Toggle cumulative mode. (See the -S option.) T Sort tasks by time/cumulative time. W Write current setup to ~/.toprc. This is the recommended way to write a top configuration file.
touch | touch [options] files For one or more files, update the access time and modification time (and dates) to the current time and date. touch is useful in forcing other commands to handle files a certain way; e.g., the operation of make, and sometimes find, relies on a file's access and modification time. If a file doesn't exist, touch creates it with a filesize of 0. #### Options -a, --time=atime, --time=access, --time=use Update only the access time. -c, --no-create Do not create any file that doesn't already exist. -d time, --date time Change the time value to the specified time instead of the current time. time can use several formats and may contain month names, time zones, a.m. and p.m. strings, as well as others. -m, --time=mtime, --time=modify Update only the modification time. -r file, --reference file Change times to be the same as those of the specified file, instead of the current time. -t time Use the time specified in time instead of the current time. This argument must be of the format: [[cc]yy]mmddhhmm[.ss], indicating optional century and year, month, date, hours, minutes, and optional seconds. --help Print help message and then exit. --version Print the version number and then exit.
> tr | tr [options] [string1 [string2]] Translate characters -- copy standard input to standard output, substituting characters from string1 to string2 or deleting characters in string1. #### Options -c, --complement Complement characters in string1 with respect to ASCII 001-377. -d, --delete Delete characters in string1 from output. -s, --squeeze-repeats Squeeze out repeated output characters in string2. -t, --truncate-set1 Truncate string1 to the length of string2 before translating. --help Print help message and then exit. --version Print the version number and then exit. #### Special characters Include brackets ([]) where shown. \a ^G (bell) \b ^H (backspace) \f ^L (form feed) \n ^J (newline) \r ^M (carriage return) \t ^I (tab) \v ^K (vertical tab) \nnn Character with octal value nnn. \\ Literal backslash. char1-char2 All characters in the range char1 through char2. If char1 does not sort before char2, produce an error. [char1-char2] Same as char1-char2 if both strings use this. [char*] In string2, expand char to the length of string1. [char*number] Expand char to number occurrences. [x*4] expands to xxxx, for instance. [:class:] Expand to all characters in class, where class can be: alnum Letters and digits alpha Letters blank Whitespace cntrl Control characters digit Digits graph Printable characters except space lower Lowercase letters print Printable characters punct Punctuation space Whitespace (horizontal or vertical) upper Uppercase letters xdigit Hexadecimal digits [=char=] The class of characters in which char belongs. #### Examples Change uppercase to lowercase in a file:
>     cat file | tr '[A-Z]' '[a-z]'
> Turn spaces into newlines (ASCII code 012):
>     tr ' ' '\012' < file
> Strip blank lines from file and save in new.file (or use 011 to change successive tabs into one tab):
>     cat file | tr -s "" "\012" > new.file
> Delete colons from file; save result in new.file:
>     tr -d : < file > new.file
traceroute | traceroute [options] host [packetsize] TCP/IP command. Trace route taken by packets to reach network host. traceroute attempts tracing by launching UDP probe packets with a small TTL (time to live), then listening for an ICMP "time exceeded" reply from a gateway. host is the destination hostname or the IP number of host to reach. packetsize is the packet size in bytes of the probe datagram. Default is 38 bytes. #### Options -d Turn on socket-level debugging. -g addr Enable the IP LSRR (Loose Source Record Route) option in addition to the TTL tests, to ask how someone at IP address addr can reach a particular target. -l Include the time-to-live value for each packet received. -m max_ttl Set maximum time-to-live used in outgoing probe packets to max-ttl hops. Default is 30 hops. -n Show numerical addresses; do not look up hostnames. (Useful if DNS is not functioning properly.) -p port Set base UDP port number used for probe packets to port. Default is (decimal) 33434. -q n Set number of probe packets for each time-to-live setting to the value n. Default is 3. -r Bypass normal routing tables and send directly to a host on an attached network. -s src_addr Use src_addr as the IP address that will serve as the source address in outgoing probe packets. -t tos Set the type-of-service in probe packets to tos (default 0). The value must be a decimal integer in the range 0 to 255. -v Verbose -- received ICMP packets (other than TIME_EXCEEDED and PORT_UNREACHABLE) will be listed. -w wait Set time to wait for a response to an outgoing probe packet to wait seconds (default is 3 seconds).
troff | troff See groff.
true | true A null command that returns a successful (0) exit status. See also false.
tune2fs | tune2fs [options] device System administration command. Tune the parameters of a Linux Second Extended Filesystem by adjusting various parameters. You must specify the device on which the filesystem resides; it must not be mounted read/write when you change its parameters. #### Options -c mount-counts Specify the maximum number of mount counts between two checks on the filesystem. -e behavior Specify the kernel's behavior when encountering errors. behavior must be one of: continue Continue as usual. remount-ro Remount the offending filesystem in read-only mode. panic Cause a kernel panic. -g group Allow group (a group ID or name) to use reserved blocks. -i interval[d|w|m] Specify the maximum interval between filesystem checks. Units may be in days (d), weeks (w), or months (m). If interval is 0, checking will not be time-dependent. -l Display a list of the superblock's contents. -m percentage Specify the percentage of blocks that will be reserved for use by privileged users. -r num Specify the number of blocks that will be reserved for use by privileged users. -u user Allow user (a user ID or name) to use reserved blocks.
tunelp | tunelp device [options] System administration command. Control a lineprinter's device parameters. Without options, print information about device(s). #### Options -a [on|off] Specify whether or not to abort if the printer encounters an error. By default, do not abort. -c n Retry device n times if it refuses a character. (Default is 250.) After exhausting n, sleep before retrying. -i irq Use irq for specified parallel port. Ignore -t and -c. If 0, restore noninterrupt driven (polling) action. -o [on|off] Specify whether to abort if device is not online or is out of paper. -q [on|off] Specify whether to print current IRQ setting. -r Reset port. -s Display printer's current status. -t time Specify a delay of time in jiffies to sleep before resending a refused character to the device. A jiffy is defined as either one tick of the system clock or one AC cycle time; it should be approximately 1/100th of a second. -w time Specify a delay of time in jiffies to sleep before resending a strobe signal. -C [on|off] Specify whether to be extremely careful in checking for printer error.
ul | ul [options] [names] Translate underscores to underlining. The correct sequence with which to do this will vary by terminal type. Some terminals are unable to handle underlining. #### Options -i Translate -, when on a separate line, to underline, instead of translating underscores. -t terminal-type Specify terminal type. By default, TERM is consulted.
umount | umount [options] [special-device/directory] System administration command. Unmount a filesystem. umount announces to the system that the removable file structure previously mounted on device special-device is to be removed. umount also works by specifying the directory. Any pending I/O for the filesystem is completed, and the file structure is flagged as clean. #### Options -a Unmount all filesystems that are listed in /etc/mtab. -n Unmount, but do not record changes in /etc/mtab. -t type Unmount only filesystems of type type.
uname | uname [options] Print information about the machine and operating system. Without options, print the name of the operating system (Linux). #### Options -a, --all Combine all the system information from the other options. -m, --machine Print the hardware the system is running on. -n, --nodename Print the machine's hostname. -r, --release Print the release number of the kernel. -s, --sysname Print the name of the operating system (Linux). -p, --processor Print the type of processor (not available on all versions). -v Print build information about the kernel. --help Display a help message and then exit. --version Print version information and then exit.
uncompress | uncompress [options] files Uncompress files that were compressed (i.e., whose names end in .Z). See compress for the available options; uncompress takes all the same options except -r and -b.
unexpand | unexpand [options] [files] Convert strings of initial whitespace, consisting of at least two spaces and/or tabs to tabs. Read from standard input if given no file or a file named -. #### Options -a, --all Convert all, not just initial, strings of spaces and tabs. -nums, -t nums, --tabs nums nums is a comma-separated list of integers that specify the placement of tab stops. If a single integer is provided, the tab stops are set to every integer spaces. By default, tab stops are 8 spaces apart. With -t and --tabs, the list may be separated by whitespace instead of commas. This option implies -a. --help Print help message and then exit. --version Print the version number and then exit.
> uniq | uniq [options] [file1 [file2]] Remove duplicate adjacent lines from sorted file1, sending one copy of each line to file2 (or to standard output). Often used as a filter. Specify only one of -d or -u. See also comm and sort. #### Options -n, -f n, --skip-fields=n Ignore first n fields of a line. Fields are separated by spaces or by tabs. +n, -s n, --skip-chars=n Ignore first n characters of a field. -c, --count Print each line once, prefixing number of instances. -d, --repeated Print duplicate lines once but no unique lines. -i, --ignore-case Ignore case differences when checking for duplicates. -u, --unique Print only unique lines (no copy of duplicate entries is kept). -w n, --check-chars=n Compare only first n characters per line (beginning after skipped fields and characters). --help Print a help message and then exit. --version Print version information and then exit. #### Examples Send one copy of each line from list to output file list.new:
>     uniq list list.new
> Show which names appear more than once:
>     sort names | uniq -d
unshar | unshar [options] [files] Unpack a shell archive (shar file). unshar scans mail messages looking for the start of a shell archive. It then passes the archive through a copy of the shell to unpack it. unshar accepts multiple files. If no files are given, standard input is used. #### Options -c, --overwrite Overwrite existing files. -d directory, --directory=directory Change to directory before unpacking any files. -e, --exit-0 Sequentially unpack multiple archives stored in same file; uses clue that many shar files are terminated by an exit 0 at the beginning of a line. (Equivalent to -E "exit 0".) -E string, --split-at=string Like -e, but allows you to specify the string that separates archives. -f, --force Same as -c. --help Print help message and then exit. --version Print the version number and then exit.
update | update [options] System administration command. update is a daemon that controls how often the kernel's disk buffers are flushed to disk. update is also known as bdflush. The daemon forks a couple of processes to call system functions flush() and sync(). When called by an unprivileged user, no daemon is created. Instead, update calls sync() and then exits. By default, update will wake up every 5 seconds and flush() some dirty buffers. If that doesn't work, it will try waking up every 30 seconds to sync() the buffers to disk. Not all of the listed options are available in every version of update. #### Options -d Display the kernel parameters. This does not start the update daemon. -f seconds Call flush() at this interval. Default is 5. -h Help. Print a command summary. -s seconds Call sync() at this interval. Default is 30. -S Always use sync() instead of flush. -0 percent Flush buffers when the specified percent of the buffer cache is dirty. -1 blocks The maximum number of dirty blocks to write out per wake cycle. -2 buffers The number of clean buffers to try to obtain each time the free buffers are refilled. -3 blocks Flush buffers if dirty blocks exceed blocks when trying to refill the buffers. -4 percent Percent of buffer cache to scan when looking for free clusters. -5 seconds Time for a data buffer to age before being flushed. -6 seconds Time for a nondata buffer to age before being flushed. -7 constant The time constant to use for load average. -8 ratio How low the load average can be before trimming back the number of buffers.
uptime | uptime Print the current time, amount of time logged in, number of users currently logged in (which may include the same user multiple times), and system load averages. This output is also produced by the first line of the w command.
useradd | useradd [options] [user] System administration command. Create new user accounts or update default account information. Unless invoked with the -D option, user must be given. useradd will create new entries in system files. Home directories and initial files may also be created as needed. #### Options -c comment Comment field. -d dir Home directory. The default is to use user as the directory name under the home directory specified with the -D option. -e date Account expiration date. date is in the format MM/DD/YYYY. Two-digit year fields are also accepted. The value is stored as the number of days since January 1, 1970. This option requires the use of shadow passwords. -f days Permanently disable account this many days after the password has expired. A value of -1 disables this feature. This option requires the use of shadow passwords. -g group Initial group name or ID number. If a different default group has not been specified using the -D option, the default group is 1. -G groups Supplementary groups given by name or number in a comma-separated list with no whitespace. -k [dir] Copy default files to user's home directory. Meaningful only when used with the -m option. Default files are copied from /etc/skel/ unless an alternate dir is specified. -m Make user's home directory if it does not exist. The default is not to make the home directory. -o Override. Accept a nonunique uid with the -u option. (Probably a bad idea.) -s shell Login shell. -u uid Numerical user ID. The value must be unique unless the -o option is used. The default value is the smallest ID value greater than 99 and greater than every other uid. -D [options] Set or display defaults. If options are specified, set them. If no options are specified, display current defaults. The options are: -b dir Home directory prefix to be used in creating home directories. If the -d option is not used when creating an account, the user name will be appended to dir. -e date Expire date. Requires the use of shadow passwords. -f days Number of days after a password expires to disable an account. Requires the use of shadow passwords. -g group Initial group name or ID number. -s shell Default login shell.
userdel | userdel [option] user System administration command. Delete all entries for user in system account files. #### Option -r Remove the home directory of user and any files contained in it.
usermod | usermod [options] user System administration command. Modify user account information. #### Options -c comment Comment field. -d dir Home directory. -e date Account expiration date. date is in the format MM/DD/YYYY. Two-digit year fields are also accepted, but the value is stored as the number of days since January 1, 1970. This option requires the use of shadow passwords. -f days Permanently disable account this many days after the password has expired. A value of -1 disables this feature. This option requires the use of shadow passwords. -g group Initial group name or number. -G groups Supplementary groups given by name or number in a comma-separated list with no whitespace. user will be removed from any groups to which they currently belong that are not included in groups. -l name Login name. This cannot be changed while the user is logged in. -o Override. Accept a nonunique uid with the -u option. -s shell Login shell. -u uid Numerical user ID. The value must be unique unless the -o option is used. Any files owned by user in the user's home directory will have their user ID changed automatically. Files outside of the home directory will not be changed. user should not be executing any processes while this is changed.
users | users [file] Print a space-separated list of each login session on the host. Note that this may include the same user multiple times. Consult file or, by default, /etc/utmp.
usleep | usleep [microseconds] usleep [options] Sleep some number of microseconds (default is 1). #### Options --help Print help information and then exit. --usage Print usage message and then exit. -v, --version Print version information.
uudecode | uudecode [-o outfile] [file] Read a uuencoded file and re-create the original file with the permissions and name set in the file (see uuencode). The -o option specifies an alternate output file.
> uuencode | uuencode [-m] [file] name Encode a binary file. The encoding uses only printable ASCII characters and includes the permissions and name of the file. When file is reconverted via uudecode, the output is saved as name. If the file argument is omitted, uuencode can take standard input, so a single argument is taken as the name to be given to the file when it is decoded. With the -m option, base64 encoding is used. #### Example It's common to encode a file and save it with an identifying extension, such as .uue. This example encodes the binary file flower12.jpg, names it rose.jpg, and saves it to a .uue file:
>     % uuencode flower12.jpg rose.jpg > rose.uue
> Encode flower12.jpg and mail it:
>     % uuencode flower12.jpg flower12.jpg | mail ellen@oreilly.com
1. > vacation | vacation vacation [options] [user] Automatically return a mail message to the sender announcing that you are on vacation. Use vacation with no options to initialize the vacation mechanism. The process performs several steps. Creates a .forward file in your home directory. The .forward file contains:
   >     \user, "|/usr/bin/vacation user"
> user is your login name. The action of this file is to actually deliver the mail to user (i.e., you) and to run the incoming mail through vacation. Creates the .vacation.pag and .vacation.dir files. These files keep track of who has sent you messages, so that they receive only one "I'm on vacation" message from you per week. Starts an editor to edit the contents of .vacation.msg. The contents of this file are mailed back to whomever sends you mail. Within its body, $subject is replaced with the contents of the incoming message's Subject line. Remove or rename the .forward file to disable vacation processing. #### Options The -a and -r options are used within a .forward file; see the example. -a alias Mail addressed to alias is actually mail for the user and should produce an automatic reply. -i Reinitialize the .vacation.pag and .vacation.dir files. Use this right before leaving for your next vacation. -r interval By default, no more than one message per week is sent to any sender. This option changes that interval. interval is a number with a trailing s, m, h, d, or w indicating seconds, minutes, hours, days, or weeks, respectively. If interval is infinite, only one reply is sent to each sender. #### Example Send no more than one reply every three weeks to any given sender:
>     $ cd
>     $ vacation -I
>     $ cat .forward
>     \jp, "|/usr/bin/vacation -r3w jp"
>     $ cat .vacation.msg
>     From: jp@wizard-corp.com (J. Programmer, via the vacation program)
>     Subject: I'm out of the office ...

>     Hi. I'm off on a well-deserved vacation after finishing
>     up whizprog 1.0. I will read and reply to your mail
>     regarding "$SUBJECT" when I return.

>     Have a nice day.
vi | vi [options] [files] A screen-oriented text editor based on ex. For more information on vi, see Chapter 11, "The vi Editor".
vidmode | vidmode [option] image [mode [offset]] System administration command. Sets the video mode for a kernel image. If no arguments are specified, print current mode value. mode is a 1-byte value located at offset 506 in a kernel image. You may change the mode by specifying the kernel image to change, the new mode, and the byte offset at which to place the new information (the default is 506). Note that rdev -v is a synonym for vidmode. If LILO is used, vidmode is not needed. The video mode can be set from the LILO prompt during a boot. #### Modes -3 Prompt -2 Extended VGA -1 Normal VGA 0 Same as entering 0 at the prompt 1 Same as entering 1 at the prompt 2 Same as entering 2 at the prompt 3 Same as entering 3 at the prompt n Same as entering n at the prompt #### Option -o offset Same as specifying an offset as an argument.
w | w [options] [user] Print summaries of system usage, currently logged-in users, and what they are doing. w is essentially a combination of uptime, who, and ps -a. Display output for one user by specifying user. #### Options -f Toggle printing the from (remote hostname) field. -h Suppress headings and uptime information. -s Use the short format. -u Ignore the username while figuring out the current process and CPU times. -V Display version information. #### File /var/run/utmp List of users currently logged on.
wall | wall [file] System administration command. Write to all users. wall reads a message from the standard input until an end-of-file. It then sends this message to all users currently logged in, preceded by "Broadcast Message from..." If file is specified, read input from that, rather than from standard input.
> wc | wc [options] [files] Print character, word, and line counts for each file. Print a total line for multiple files. If no files are given, read standard input. See other examples under ls and sort. #### Options -c, -bytes, --chars Print character count only. -l, --lines Print line count only. -w, --words Print word count only. --help Print help message and then exit. --version Print the version number and then exit. #### Examples Count the number of users logged in:
>     who | wc -l
> Count the words in three essay files:
>     wc -w essay.[123]
> Count lines in the file named by variable $file (don't display filename):
>     wc -l < $file
whatis | whatis keywords Search the short manual page descriptions in the whatis database for each keyword and print a one-line description to standard output for each match. Like apropos, except that it only searches for complete words. Equivalent to man -f.
> whereis | whereis [options] files Locate the binary, source, and manual page files for specified commands/files. The supplied filenames are first stripped of leading pathname components and any (single) trailing extension of the form .ext (for example, .c). Prefixes of s. resulting from use of source code control are also dealt with. whereis then attempts to locate the desired program in a list of standard Linux directories (e.g., /bin, /etc, /usr/bin, /usr/local/bin/, etc.). #### Options -b Search only for binaries. -f Terminate the last directory list and signal the start of filenames; required when any of the -B, -M, or -S options are used. -m Search only for manual sections. -s Search only for sources. -u Search for unusual entries, that is, files that do not have one entry of each requested type. Thus, the command whereis -m -u * asks for those files in the current directory that have no documentation. -B directories Change or otherwise limit the directories to search for binaries. -M directory Change or otherwise limit the directories to search for manual sections. -S directory Change or otherwise limit the directories to search for sources. #### Example Find all files in /usr/bin that are not documented in /usr/man/man1 but that have source in /usr/src:
>     % cd /usr/bin
>     % whereis -u -M /usr/man/man1 -S /usr/src -f *
> which | which [options] [--] [command] [...] List the full pathnames of the files that would be executed if the named commands had been run. which searches the user's $PATH environment variable. The C shell and tcsh have a built-in which command that has no options. To use the options, specify the full pathname (e.g., /usr/bin/which). #### Options -a, --all Print all matches, not just the first. -i, --read-alias Read aliases from standard input and write matches to standard output. Useful for using an alias for which. --skip-alias Ignore --read-alias if present. Useful for finding normal binaries while using --read-alias in an alias for which. --skip-dot Skip directories that start with a dot. --skip-tilde Skip directories that start with a tilde (`~`) and executables in $HOME. --show-dot If a matching command is found in a directory that starts with a dot, print ./cmdname instead of the full pathname. --show-tilde Print a tilde (`~`) to indicate the user's home directory. Ignored if the user is root. --tty-only Stop processing options on the right if not on a tty. -v, -V, --version Print version information and then exit. #### Example
>     $ which cc ls
>     /usr/bin/cc
>     ls:      aliased to ls -sFC
> who | who [options] [file] who am i Show who is logged in to the system. With no options, list the names of users currently logged in, their terminal, the time they have been logged in, and the name of the host from which they have logged on. An optional system file (default is /etc/utmp) can be supplied to give additional information. #### Options am i Print the username of the invoking user. --help Print a help message and then exit. -i, -u, --idle Include idle times. An idle time of . indicates activity within the last minute; one of old indicates no activity in more than a day. -l, --lookup Attempt to include canonical hostnames via DNS. -m Same as who am i. -q, --count "Quick." Display only the usernames and total number of users. --version Print version information and then exit. -w, -T, --mesg, --message, --writable Include user's message status: + mesg y (write messages allowed) - mesg n (write messages refused) ? Cannot find terminal device -H, --heading Print headings. #### Example This sample output was produced at 8 a.m. on April 17:
>     $ who -uH
>     NAME    LINE   TIME         IDLE   PID  COMMENTS
>     Earvin  ttyp3  Apr 16 08:14 16:25  2240
>     Larry   ttyp0  Apr 17 07:33   .   15182
Since Earvin has been idle since yesterday afternoon (16 hours), it appears that he isn't at work yet. He simply left himself logged in. Larry's terminal is currently in use.
whoami | whoami Print current user ID. Equivalent to id -un.
write | write user [tty] message Initiate or respond to an interactive conversation with user. A write session is terminated with EOF. If the user is logged in to more than one terminal, specify a tty number. See also talk; use mesg to keep other users from writing to your terminal.
> xargs | xargs [options] [command] Execute command (with any initial arguments), but read remaining arguments from standard input instead of specifying them directly. xargs passes these arguments in several bundles to command, allowing command to process more arguments than it could normally handle at once. The arguments are typically a long list of filenames (generated by ls or find, for example) that get passed to xargs via a pipe. #### Options -0, --null Expect filenames to be terminated by NULL instead of whitespace. Do not treat quotes or backslashes specially. -e[string], --eof[=string] Set EOF to _ or, if specified, to string. --help Print a summary of the options to xargs and then exit. -i[string], --replace[=string] Edit all occurrences of {}, or string, to the names read in on standard input. Unquoted blanks are not considered argument terminators. Implies -x and -l 1. -l[lines], --max-lines[=lines] Allow no more than 1, or lines, nonblank input lines on the command line. Implies -x. -n args, --max-args=args Allow no more than args arguments on the command line. May be overridden by -s. -p, --interactive Prompt for confirmation before running each command line. Implies -t. -P max, --max-procs=max Allow no more than max processes to run at once. The default is 1. A maximum of 0 allows as many as possible to run at once. -r, --no-run-if-empty Do not run command if standard input contains only blanks. -s max, --max-chars=max Allow no more than max characters per command line. -t, --verbose Verbose mode. Print command line on standard error before executing. -x, --exit If the maximum size (as specified by -s) is exceeded, exit. --version Print the version number of xargs and then exit. #### Examples grep for pattern in all files on the system:
>     find / -print | xargs grep pattern > out &
> Run diff on file pairs (e.g., f1.a and f1.b, f2.a and f2.b ...):
>     echo $* | xargs -n2 diff
> The previous line would be invoked as a shell script, specifying filenames as arguments. Display file, one word per line (same as deroff -w):
>     cat file | xargs -n1
> Move files in olddir to newdir, showing each command:
>     ls olddir | xargs -i -t mv olddir/{} newdir/{}
yacc | yacc [options] file Given a file containing context-free grammar, convert file into tables for subsequent parsing and send output to y.tab.c. This command name stands for yet another compiler-compiler. See also flex, bison, and lex & yacc by John Levine, Tony Mason, and Doug Brown. #### Options -b prefix Prepend prefix, instead of y, to the output file. -d Generate y.tab.h, producing #define statements that relate yacc's token codes to the token names declared by the user. -l Exclude #line constructs from code produced in y.tab.c. (Use after debugging is complete.) -t Compile runtime debugging code. -v Generate y.output, a file containing diagnostics and notes about the parsing tables.
yes | yes [strings] yes [option] Print the command-line arguments, separated by spaces and followed by a newline, until killed. If no arguments are given, print y followed by a newline until killed. Useful in scripts and in the background; its output can be piped to a program that issues prompts. #### Options --help Print a help message and then exit. --version Print version information and then exit.
ypbind | ypbind [options] NFS/NIS command. NIS binder process. ypbind is a daemon process typically activated at system startup time. Its function is to remember information that lets client processes on a single node communicate with some ypserv process. The information ypbind remembers is called a binding -- the association of a domain name with the Internet address of the NIS server and the port on that host at which the ypserv process is listening for service requests. This information is cached in the file /var/yp/bindings/domainname.version. #### Options -ypset May be used to change the binding. This option is very dangerous and should be used only for debugging the network from a remote machine. -ypsetme ypset requests may be issued from this machine only. Security is based on IP address checking, which can be defeated on networks on which untrusted individuals may inject packets. This option is not recommended.
ypcat | ypcat [options] mname NFS/NIS command. Print values in an NIS database specified by mname, which may be either a map name or a map nickname. #### Options -d domain Specify domain other than default domain. -k Display keys for maps in which values are null or key is not part of value. -t Do not translate mname to map name. -x Display map nickname table listing the nicknames (mnames) known and map name associated with each nickname. Do not require an mname argument.
ypchfn | ypchfn [option] [user] NFS/NIS command. Change your information stored in /etc/passwd and displayed when you are fingered; distribute the change over NIS. Without options, ypchfn enters interactive mode and prompts for changes. To make a field blank, enter the keyword none. The superuser can change the information for any user. See also yppasswd and ypchsh. #### Options -f Behave like ypchfn (default). -l Behave like ypchsh. -p Behave like yppasswd.
ypchsh | ypchsh [option] [user] NFS/NIS command. Change your login shell and distribute this information over NIS. Warn if shell does not exist in /etc/shells. The superuser can change the shell for any user. See also yppasswd and ypchfn. #### Options -f Behave like ypchfn. -l Behave like ypchsh (default). -p Behave like yppasswd.
ypinit | ypinit [options] NFS/NIS command. Build and install an NIS database on an NIS server. ypinit can be used to set up a master or a slave server or slave copier. Only a privileged user can run ypinit. #### Options -c master_name Set up a slave copier database. master_name should be the hostname of an NIS server, either the master server for all the maps or a server on which the database is up-to-date and stable. -m Indicates that the local host is to be the NIS server. -s master_name Set up a slave server database. master_name should be the hostname of an NIS server, either the master server for all the maps or a server on which the database is up-to-date and stable.
ypmatch | ypmatch [options] key...mname NFS/NIS command. Print value of one or more keys from an NIS map specified by mname. mname may be either a map name or a map nickname. #### Options -d domain Specify domain other than default domain. -k Before printing value of a key, print key itself, followed by a colon (:). -t Do not translate nickname to map name. -x Display map nickname table listing the nicknames (mnames) known, and map name associated with each nickname. Do not require an mname argument.
yppasswd | yppasswd [option] [name] NFS/NIS command. Change login password in Network Information Service. Create or change your password, and distribute the new password over NIS. The superuser can change the password for any user. See also ypchfn and ypchsh. #### Options -f Behave like ypchfn. -l Behave like ypchsh. -p Behave like yppasswd (default).
yppasswdd | rpc.yppasswdd [option] NFS/NIS command. Server for modifying the NIS password file. yppasswdd handles password change requests from yppasswd. It changes a password entry only if the password represented by yppasswd matches the encrypted password of that entry and if the user ID and group ID match those in the server's /etc/passwd file. Then it updates /etc/passwd and the password maps on the local server. #### Option -s Support shadow password functions.
yppoll | yppoll [options] mapname NFS/NIS command. Determine version of NIS map at NIS server. yppoll asks a ypserv process for the order number and the hostname of the master NIS server for the named map. #### Options -h host Ask the ypserv process at host about the map parameters. If host is not specified, the hostname of the NIS server for the local host (the one returned by ypwhich) is used. -d domain Use domain instead of the default domain.
yppush | yppush [options] mapnames NFS/NIS command. Force propagation of changed NIS map. yppush copies a new version of an NIS map, mapname, from the master NIS server to the slave NIS servers. It first constructs a list of NIS server hosts by reading the NIS map ypservers with the -d option's domain argument. Keys within this map are the ASCII names of the machines on which the NIS servers run. A "transfer map" request is sent to the NIS server at each host, along with the information needed by the transfer agent to call back the yppush. When the attempt has been completed and the transfer agent has sent yppush a status message, the results may be printed to stdout. Normally invoked by /var/yp/Makefile. #### Options -d domain Specify a domain. -v Verbose -- print message when each server is called and for each response.
ypserv | ypserv [options] NFS/NIS command. NIS server process. ypserv is a daemon process typically activated at system startup time. It runs only on NIS server machines with a complete NIS database. Its primary function is to look up information in its local database of NIS maps. The operations performed by ypserv are defined for the implementor by the NIS protocol specification and for the programmer by the header file <rpcvc/yp_prot.h>. Communication to and from ypserv is by means of RPC calls. #### Options -d NIS service should go to the DNS for more host information. -localonly Indicates ypserv should not respond to outside requests. #### Files and directories /var/yp/[domainname]/ Location of NIS databases. /var/yp/Makefile Makefile that is responsible for creating NIS databases.
ypset | ypset [options] server NFS/NIS command. Point ypbind at a particular server. ypset tells ypbind to get NIS services for the specified domain from the ypserv process running on server. server indicates the NIS server to bind to and can be specified as a name or an IP address. #### Options -d domain Use domain instead of the default domain. -h host Set ypbind's binding on host, instead of locally. host can be specified as a name or an IP address.
ypwhich | ypwhich [options] [host] NFS/NIS command. Return hostname of NIS server or map master. Without arguments, ypwhich cites the NIS server for the local machine. If host is specified, that machine is queried to find out which NIS master it is using. #### Options -d domain Use domain instead of the default domain. -m map Find master NIS server for a map. No host can be specified with -m. map may be a map name or a nickname for a map. -t mapname Inhibit nickname translation. -x Display map nickname table. Do not allow any other options.
ypxfr | ypxfr [options] mapname NFS/NIS command. Transfer an NIS map from the server to the local host by making use of normal NIS services. ypxfr creates a temporary map in the directory /etc/yp/domain (where domain is the default domain for the local host), fills it by enumerating the map's entries, and fetches the map parameters and loads them. If run interactively, ypxfr writes its output to the terminal. However, if it is invoked without a controlling terminal, and if the log file /usr/admin/nislog exists, it appends all its output to that file. #### Options -b Preserve the resolver flag in the map during the transfer. -C tid prog ipadd port This option is for use only by ypserv. When ypserv invokes ypxfr, it specifies that ypxfr should call back a yppush process at the host with IP address ipadd, registered as program number prog, listening on port port, and waiting for a response to transaction tid. -c Do not send a "Clear current map" request to the local ypserv process. -d domain Specify a domain other than the default domain. -f Force the transfer to occur even if the version at the master is older than the local version. -h host Get the map from host, regardless of what the map says the master is. If host is not specified, ypxfr asks the NIS service for the name of the master and tries to get the map from there. host may be a name or an Internet address in the form h.h.h.h. -S Use only NIS servers running as root and using a reserved port. -s domain Specify a source domain from which to transfer a map that should be the same across domains (such as the services.byname map).
zcat | zcat [options] [files] Read one or more files that have been compressed with gzip or compress and write them to standard output. Read standard input if no files are specified or if - is specified as one of the files; end input with EOF. zcat is identical to gunzip -c and takes the options -fhLV described for gzip/gunzip.
zcmp | zcmp [options] files Read compressed files and pass them, uncompressed, to the cmp command, along with any command-line options. If a second file is not specified for comparison, look for a file called file.gz.
zdiff | zdiff [options] files Read compressed files and pass them, uncompressed, to the diff command, along with any command-line options. If a second file is not specified for comparison, look for a file called file.gz.
zdump | zdump [options] [zones] System administration command. Dump a list of all known time zones or, if an argument is provided, a specific zone or list of zones. Include each zone's current time with its name. #### Options -c year Specify a cutoff year to limit verbose output. Meaningful only with -v. -v Verbose mode. Include additional information about each zone.
zforce | zforce [names] Rename all gzipped files to filename.gz, unless file already has a .gz extension.
zgrep | zgrep [options] [files] Uncompress files and pass to grep, along with any command-line arguments. If no files are provided, read from (and attempt to uncompress) standard input. May be invoked as zegrep or zfgrep and will in those cases invoke egrep or fgrep.
> zic | zic [options] [files] System administration command. Create time conversion information files from the file or files specified. If the specified file is -, read information from standard input. #### Options -d directory Place the newly created files in directory. Default is /usr/local/etc/zoneinfo. -l timezone Specify a timezone to use for local time. zic links the zone information for timezone with the zone localtime. -p timezone Set the default rules for handling POSIX-format environment variables to the zone name specified by timezone. -s Store time values only if they are the same when signed as when unsigned. -v Verbose mode. Include extra error checking and warnings. -y command Check year types with command. Default is yearistype. -L file Consult file for information about leap seconds. The source file(s) for zic should be formatted as a sequence of rule lines, zone lines, and link lines. An optional file containing leap second rules can be specified on the command line. Rule lines describe how time should be calculated. They describe changes in time, daylight savings time, war time, and any other changes that might affect a particular time zone. Zone lines specify which rules apply to a given zone. Link lines link similar zones together. Leap lines describe the exact time when leap seconds should be added or subtracted. Each of these lines is made up of fields. Fields are separated from one another by any number of whitespace characters. Comment lines are preceded by a #. The fields used in each line are listed next. #### Rule line fields The format of a rule line is:
>     Rule NAME FROM TO TYPE IN ON AT SAVE LETTERS
> NAME Name this set of rules. FROM Specify the first year to which this rule applies. Gregorian calendar dates are assumed. Instead of specifying an actual year, you may specify minimum or maximum for the minimum or maximum year representable as an integer. TO Specify the last year to which this rule applies. Syntax is the same as for the FROM field. TYPE Specify the type of year to which this rule should be applied. The wildcard - instructs that all years be included. Any given year's type will be checked with the command given with the -y option or the default yearistype year type. An exit status of 0 is taken to mean the year is of the given type; an exit status of 1 means that it is not of the given type (see -y option). IN Specify month in which this rule should be applied. ON Specify day in which this rule should be applied. Whitespace is not allowed. For example: 1 The 1st firstSun The first Sunday Sun>=3 The first Sunday to occur before or on the 3rd AT Specify the time after which the rule is in effect. For example, you may use 13, 13:00, or 13:00:00 for 1:00 p.m.. You may include one of several suffixes (without whitespace between): s Local standard time. u, g, z Universal time. w Wall clock time (default). SAVE Add this amount of time to the local standard time. Formatted like AT, without suffixes. LETTERS Specify letter or letters to be used in time zone abbreviations (for example, S for EST). For no abbreviation, enter -. #### Zone line fields The format of a zone line is:
>     Zone NAME GMTOFF RULES/SAVE FORMAT [UNTIL]
> NAME Time zone name. GMTOFF The amount of hours by which this time zone differs from GMT. Formatted like AT. Negative times are subtracted from GMT; by default, times are added to it. RULES/SAVE Either the name of the rule to apply to this zone or the amount of time to add to local standard time. To make the zone the same as local standard time, specify -. FORMAT How to format time zone abbreviations. Specify the variable part with %s. UNTIL Change the rule for the zone at this date. The next line must specify the new zone information and therefore must omit the string "Zone" and the NAME field. #### Link line fields The format of a link line is:
>     Link LINK-FROM LINK-TO
> LINK-FROM The name of the zone that is being linked. LINK-TO An alternate name for the zone that was specified as LINK-FROM. #### Leap line fields The format of a leap line is:
>     Leap YEAR MONTH DAY HH:MM:SS CORR R/S
YEAR MONTH DAY HH:MM:SS Specify when the leap second happened. CORR Uses a + or a - to show whether the second was added or skipped. R/S An abbreviation of Rolling or Stationary to describe whether the leap second should be applied to local wall clock time or to GMT.
zmore | zmore [files] Similar to more. Uncompress files and print them, one screenful at a time. Works on files compressed with compress, gzip, or pack and with uncompressed files. #### Commands space Print next screenful. i[number] Print next screenful, or number lines. Set i to number lines. d, ^D Print next i, or 11, lines. i z Print next i lines or a screenful. i s Skip i lines. Print next screenful. i f Skip i screens. Print next screenful. q, Q, :q, :Q Go to next file, or, if current file is the last, exit zmore. e, q Exit zmore when the prompt "--More--(Next file: file)" is displayed. s Skip next file and continue. = Print line number. i/expr Search forward for ith occurrence (in all files) of expr, which should be a regular expression. Display occurrence, including the two previous lines of context. i n Search forward for the ith occurrence of the last regular expression searched for. !command Execute command in shell. If command is not specified, execute last shell command. To invoke a shell without passing it a command, enter \!. `.` Repeat the previous command.
znew | znew [options] [files] Uncompress .Z files and recompress them in .gz format. #### Options -9 Optimal (and slowest) compression method. -f Recompress even if filename.gz already exists. -t Test new .gz files before removing .Z files. -v Verbose mode. -K If the original .Z file is smaller than the .gz file, keep it. -P Pipe data to conversion program. This saves disk space.

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