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033-the-ps-command.md

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The ps command

The ps command is used to identify programs and processes that are running on the system and the resources they are using. Its frequently pipelined with other commands like grep to search for a program/process or less so that the user can analyze the output one page at a time.

Let's say you have a program like openshot which is notorious for hogging system resources when exporting a video, and you want to close it, but the GUI has become unresponsive.

Example

  1. You want to find the PID of openshot and kill it.
ps aux | grep openshot
kill - <openshot PID>
  1. To Show all the running processes:
ps -A

Syntax

ps [options]

When run without any options, it's useless and will print: CMD - the executable processes/(program) running, their PID - process ID, TTY - terminal type and Time - How long the process has utilized the CPU or thread.

Common Option

If you are going to remember only one thing from this page let it be these three letter aux: a - which displays all processes running, including those being run by other users. u - which shows the effective user of a process, i.e. the person whose file access permissions are used by the process. x - which shows processes that do not have a TTY associated with them.

Additional Options:

Option Description
a Shows list all processes with a terminal (tty)
-A Lists all processes. Identical to -e
-a Shows all processes except both session leaders and processes not associated with a terminal
-d Select all processes except session leaders
--deselect Shows all processes except those that fulfill the specified conditions. Identical to -N
-e Lists all processes. Identical to -A
-N Shows all processes except those that fulfill the specified conditions. Identical to -deselect
T Select all processes associated with this terminal. Identical to the -t option without any argument
r Restrict the selection to only running processes
--help simple Shows all the basic options
--help all Shows every available options

Another useful command which give a realtime snapshot of the processes and the resources they are using about every ten seconds is top.