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| Chapter 39 |

# 39. Time and Performance

Contents:
Which Time Is It?
Timing Programs
The csh time variable
Average Command Runtimes with runtime
Why Is the System So Slow?
lastcomm: What Commands Are Running and How Long Do They Take?
Checking System Load: uptime
A Big Environment Can Slow You Down
Know When to Be "nice" to OTher Users...and When Not to
A nice Gotcha
Changing a Job's Priority Under BSD UNIX
What Makes Your Computer Slow? How Do You Fix It?

## 39.1 Which Time Is It?

When we talk about "time" on UNIX systems, we could be talking about two things:

1. What time it is, as shown by the date (51.10) command, and recorded in countless ways - as file creation and modification times, as the time of last login, and so on.

2. How long things take.

This chapter is concerned with the latter. It talks about how long programs take to run, what makes them faster or slower, and what you can (or more often can't) do about it.

- TOR

38.18 nohup |  | 39.2 Timing Programs