(Unix) The Unix command ps displays a list of processes on your system. If you type this at the command line with no arguments, you will only see your own processes (recall that there might be other users on the system). The output might look something like this:

  PID  TT  STAT      TIME COMMAND
84453  p0  Is     0:00.14 -bash (bash)
84552  p0  S+     0:02.10 emacs c03.html
84497  p2  Ss     0:00.09 -bash (bash)
84600  p2  R+     0:00.00 ps

This output lists information about four processes. PID stands for Process ID. On Unix systems (and most other Operating Systems) each process is identified by a unique number. TT stands for teletype and it refers to the controlling terminal or IO channel. We can ignore this for the moment.

STAT refers to the State of the process (I is idle (sleeping for more than 20 seconds), S is Sleeping for less than 20 seconds, R is running).

TIME is total execution time that the process has used.

COMMAND is the user command which initiated the process. In this case bash refers to the shell (user interface) process, emacs refers to the text editor which happens to be in use, and ps refers to the actual ps process which generated the listing.

To get a listing of all processes running on the machine, use the -A option. Make sure that you pipe the output through more because the output will fill more than one screen.

ps -A | more

Note that there are 40 or more processes listed. Almost all of these are associated with the kernel.

You can use the ps command to get more information about each process. The -j flag provides the same information as the default, but also shows the process id of the parent process (PPID), the owner of the process (UID), and the time that the process was started (STIME). Other information is also available. See the man page for ps for details.

On Windows XP, you can get similar information by looking at the Task Manager. You can invoke the Task Manager either by typing cntl-alt-del or by right-clicking an empty space on the tool bar at the bottom of the screen and choosing task manager from the popup menu.

The Task Manager window has five tabs, labeled Applications, Processes, Performance, Networking, and Users. The first shows only user processes (similar to using ps with no arguments) while the second shows information about all processes (similar to ps -A).