The ps command on Linux/Unix systems (and, yes, that includes Mac OS X) is a command-line utility for displaying information about currently running processes.

Unix has had the ps command for decades, but because Unix has a varied past with contributions from different parties, there are a couple of different camps on ps. It basically boils down to the System V camp and the BSD camp. Fortunately for users of operating systems such as Linux that use GNU libraries, the ps installed provides the options of both the System V and BSD versions.

* The way most people use ps*

Most people use ps one of the following ways:

• ps -ef
• ps aux

The first is a common System V way of listing all processes. The latter is a BSD way.

* Show parent-child relationships *

The BSD f option is really handy for showing parent-child process relationships. It produces a tree-like structure.

Here is an excerpt of the output of ps -ef f:

UID        PID  PPID  C STIME TTY      STAT   TIME CMD
root      2617     1  0  2010 ?        Ss     9:38 /usr/sbin/sshd
root     12502  2617  0 19:52 ?        Ss     0:00  \_ sshd: fozz [priv]
fozz     12504 12502  0 19:52 ?        S      0:04      \_ sshd: fozz@pts/0 
fozz     12505 12504  0 19:52 pts/0    Rs     0:00          \_ -zsh
fozz     14877 12505  0 20:08 pts/0    R+     0:00              \_ ps -ef f
fozz     14878 12505  0 20:08 pts/0    R+     0:00              \_ [less]