What is a process in Linux?

A process is a task that your Linux machine is currently working on. For example, when you open a browser, your machine creates a process for it.

Let’s try to understand this by running a simple command such as ps. Here’s the syntax:

ps [options]

When you run ps in your shell, it will give you the following output.

  PID TTY          TIME CMD
    8 tty1     00:00:00 bash
   71 tty1     00:00:00 ps

Explanation

ps gives you information about active processes. By default, it displays all processes associated with the same effective user.

It displays the:

• Process ID PID
• The terminal linked to the process TTY
• The cumulated CPU TIME in hh:mm:ss format
• The executable name CMD

Output is unsorted by default.

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For more information on the processes, you can use the ps aux command.

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root         1  0.0  0.0   8936   100 ?        Ssl  Sep27   0:00 /init
root         7  0.0  0.0   8936    96 tty1     Ss   Sep30   0:00 /init
kedar        8  0.0  0.0  18076  2464 tty1     S    Sep30   0:00 -bash
kedar       81  0.0  0.0  18664  1896 tty1     R    00:53   0:00 ps aux

Explanation

In the command aux:

1. a represents all users
2. u represents the user/owner
3. x displays processes executed outside of the terminal

It also displays some extra fields in results as compared to our previous command, which are:

• USER represents the user that initiated the process.

• %CPU is the CPU utilization of the process.

• %MEM shows the memory usage.

• VSZ means the virtual memory size of the process in KiB.

• RSS is the non-swapped physical memory that a process has used (in kilobytes).

• STAT shows the process state.

• START represents the time at which the command started.

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To stop the process, you can use the kill command. Here’s the syntax:

kill PID

For example, kill 20.

To learn more about the ps command or any other commands in Linux, I encourage you to try the man (manual) command.

The syntax is as follows:

man command

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