Linux Command Basics: 7 commands for process management    

Suppose you find yourself exploring the Linux command line for the first time or entering into Linux administration. In that case, a low-level understanding of how to get around the terminal and complete basic tasks is essential. To help you grasps those concepts, check out my previous two articles:

• 10 commands to get you started at the terminal

• 10 more commands for manipulating files

However, if you feel comfortable with those concepts, we will advance your Linux knowledge a bit further in this article. We will be looking at processes and how to manage them.

So, what exactly is a process?

In Linux, a process is any active (running) instance of a program. But what is a program? Well, technically, a program is any executable file held in storage on your machine. Anytime you run a program, you have created a process. At a basic level, this is pretty easy to manage, and that is what we are going to take a look at today.

What you need to get started

I recommend that you follow along on your favorite virtual machine. That way, you can try and fail without consequence (which is definitely the best way to get comfortable at the terminal).

For this demo, I am going to start the sleep process for 500 seconds. This approach allows you to see the process without me making meaningful changes to my system.

[tcarrigan@client ~]$ sleep 500
^Z
[1]+  Stopped                 sleep 500

I then stopped the process with Ctrl+Z so that we can use our terminal.

1. List processes

To display your currently active processes, use the ps command:

[tcarrigan@client ~]$ ps
    PID TTY          TIME CMD
   2648 pts/0    00:00:00 bash
   3293 pts/0    00:00:00 sleep
   3300 pts/0    00:00:00 ps

Here you get a little information about the active processes on your system. You will want to pay attention to the PID (unique process ID), the TIME (amount of time that the process has been running), and the CMD (the command executed to launch the process).

2. Verbose list (processes)

To see an incredibly detailed list of processes, you can use the ps aux command.

• a - all users
• u - shows the user/owner
• x - displays processes not executed in the terminal (making the output rather long)

You can see the command here (output edited for length):

[tcarrigan@client ~]$ ps aux
USER         PID %CPU %MEM   VSZ    RSS   TTY  STAT  START    TIME   COMMAND
tcarrig+    3293  0.0  0.0 215292   520 pts/0    T    13:41   0:00 sleep 500
root        3380  0.0  0.0      0     0 ?        I    13:45   0:00 [kworker/1:1-mm_percpu_wq]
root        3381  0.0  0.0      0     0 ?        I    13:45   0:00 [kworker/1:3]
root        3398  0.0  0.0      0     0 ?        I    13:46   0:00 [kworker/3:2-ata_sff]
root        3481  0.0  0.0      0     0 ?        I    13:50   0:00 [kworker/u8:2-flush-253:0]
root        3482  0.0  0.0      0     0 ?        I    13:50   0:00 [kworker/0:1-events]
root        3483  0.0  0.0      0     0 ?        I    13:50   0:00 [kworker/0:2]
root        3508  0.0  0.0      0     0 ?        I    13:51   0:00 [kworker/3:0-ata_sff]
root        3511  0.0  0.0  18892  7732 ?        S    13:52   0:00 systemd-userwork
root        3512  0.0  0.0  18892  7656 ?        S    13:52   0:00 systemd-userwork
root        3513  0.0  0.0  18892  7656 ?        S    13:52   0:00 systemd-userwork
root        3566  0.4  0.0 432792  8024 ?        Ssl  13:54   0:00 /usr/libexec/fprintd
tcarrig+    3598  0.0  0.0 228208  3948 pts/0    R+   13:54   0:00 ps aux

3. Kill by PID

Inevitably, a process will get hung, and you will need to kill it. The more time you spend at the CLI, the more likely it is you will need the kill command. The most accurate way to identify a process is by process ID (PID).

Use the following syntax:

[tcarrigan@client ~]$ kill PID

This command sends the SIGTERM signal. However, if you are dealing with a stuck process, add the -9 option.

[tcarrigan@client ~]$ ps
    PID TTY          TIME CMD
   2648 pts/0    00:00:00 bash
   3293 pts/0    00:00:00 sleep
   4684 pts/0    00:00:00 sleep
  40527 pts/0    00:00:00 sleep
  40540 pts/0    00:00:00 ps
[tcarrigan@client ~]$ sudo kill -9 3293
[sudo] password for tcarrigan: 
[1]   Killed                  sleep 500

4. Kill by name/keyword

Use the killall command to kill a process by name. This command will kill all processes with the keyword/name that you specify.

The syntax is:

[tcarrigan@client ~]$ killall sleep

This would kill all sleep processes active on the system (the -9 option works here as well). Here is an example:

[tcarrigan@client ~]$ ps
    PID TTY          TIME CMD
   2648 pts/0    00:00:00 bash
   4684 pts/0    00:00:00 sleep
  40527 pts/0    00:00:00 sleep
  40540 pts/0    00:00:00 ps
[tcarrigan@client ~]$ killall -9 sleep 
[2]-   Killed                  sleep 500
[3]+   Killed                  sleep 500

These next two commands go hand in hand. They allow you to move/manage background commands. I will give a basic look at the syntax below; however, for an in-depth look at these commands, see my previous article on the subject.

5. List background jobs and resume background jobs

To list and manage background jobs, we will use the bg command. I started a new sleep 500 process and then stopped it, sending it to the background. Thus we see it listed when running bg below:

[tcarrigan@client ~]$ bg
[1]+ sleep 500 &

6. Bring the most recent job to the foreground

To do this, we are going to use the fg command. This brings the most recently run job/process to the foreground. The following example is a continuation of the above command. The sleep 500 process that is in the background is now active in the background. Let's bring it into the light...

[tcarrigan@client ~]$ fg
sleep 500

This command brings us to our final command in this list.

7. Bring a specific job to the foreground

Use the fg command again, but select a specific job to bring to the foreground (instead of the most recent). To do this, we are just going to add the job/process name to the command.

[tcarrigan@client ~]$ fg XXXample

This brings job XXXample to the foreground.

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Wrapping up

In today's Linux Command Basics, we looked at processes and how to manage them. You can now complete general process management tasks—everything from listing and killing to moving between the background and foreground. If there are other general Linux administration areas that you would like to see a dedicated list of commands for, email the team at enable-sysadmin@redhat.com, and I will do my best to flesh that out for you.