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| Chapter 2 UNIX Commands |

## chmod

    chmod [option] mode files

Change the access `mode` of one or more `files`. Only the owner of a file or a privileged user may change its mode. Create `mode` by concatenating the characters from `who`, `opcode`, and `permission`. `who` is optional (if omitted, default is a); choose only one `opcode`.

### OptionXF

-R

  Recursively descend directory arguments while setting modes.

-f

  suppress error message upon failure to change a file's mode.

### Who

u

  User

g

  Group

o

  Other

a

  All (default)

### Opcode

+

  Add permission

-

  Remove permission

=

  Assign permission (and remove permission of the unspecified fields)

### Permission

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

l

  Mandatory locking

Alternatively, specify permissions by a 3-digit sequence. The first digit designates owner permission; the second, group permission; and the third, others 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

2

  Set group ID on execution or set mandatory locking

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

Reference: chkey |  | Reference: chown