How to Start Linux Command in Background and Detach Process in Terminal

In this guide, we shall bring to light a simple yet important concept in process handling in a Linux system, that is how to completely detach a process from its controlling terminal.

When a process is associated with a terminal, two problems might occur:

  1. your controlling terminal is filled with so much output data and error/diagnostic messages.
  2. in the event that the terminal is closed, the process together with its child processes will be terminated.

To deal with these two issues, you need to totally detach a process from a controlling terminal. Before we actually move to solve the problem, let us briefly cover how to run processes in the background.

How to Start a Linux Process or Command in Background

If a process is already in execution, such as the tar command example below, simply press Ctrl+Z to stop it then enter the command bg to continue with its execution in the background as a job.

You can view all your background jobs by typing jobs. However, its stdin, stdout, stderr are still joined to the terminal.

$ tar -czf home.tar.gz .
$ bg
$ jobs
Run Linux Command in Background
Run Linux Command in Background

You can as well run a process directly from the background using the ampersand, & sign.

$ tar -czf home.tar.gz . &
$ jobs
Start Linux Process in Background
Start Linux Process in Background

Take a look at the example below, although the tar command was started as a background job, an error message was still sent to the terminal meaning the process is still connected to the controlling terminal.

$ tar -czf home.tar.gz . &
$ jobs
Linux Process Running in Background Message
Linux Process Running in Background Message

Keep Linux Processes Running After Exiting Terminal

We will use disown command, it is used after the a process has been launched and put in the background, it’s work is to remove a shell job from the shell’s active list jobs, therefore you will not use fg, bg commands on that particular job anymore.

In addition, when you close the controlling terminal, the job will not hang or send a SIGHUP to any child jobs.

Suggested Read: 5 Ways to Keep Remote SSH Sessions and Processes Running

Let’s take a look at the below example of using diswon bash built-in function.

$ sudo rsync Templates/* /var/www/html/files/ &
$ jobs
$ disown  -h  %1
$ jobs
Keep Linux Process Running After Closing Terminal
Keep Linux Process Running After Closing Terminal

You can also use nohup command, which also enables a process to continue running in the background when a user exits a shell.

$ nohup tar -czf iso.tar.gz Templates/* &
$ jobs
Put Linux Process in Background After Closing Shell
Put Linux Process in Background After Closing Shell

Detach a Linux Processes From Controlling Terminal

Therefore, to completely detach a process from a controlling terminal, use the command format below, this is more effective for graphical user interface (GUI) applications such as firefox:

$ firefox </dev/null &>/dev/null &

In Linux, /dev/null is a special device file which writes-off (gets rid of) all data written to it, in the command above, input is read from, and output is sent to /dev/null.

Suggested Read: 10 Screen Command Examples to Detach Terminal Sessions

As a concluding remark, provided a process is connected to a controlling terminal, as a user, you will see several output lines of the process data as well as error messages on your terminal. Again, when you close the a controlling terminal, your process and child processes will be terminated.

Importantly, for any questions or remarks on the subject, reach us by using the comment form below.

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8 thoughts on “How to Start Linux Command in Background and Detach Process in Terminal”

  1. I see this is an old post but I think my question is sort of in the ballpark. what I would like to do is open the console of the process that was started with systemd with a no GUI flag. what this pertains to the Minecraft server.

    so I made a systemd service file and the execution command is “java -jar server.jar nogui” now once the system is up and running, I would like to open the GUI or console of the Minecraft server to issue commands without having to open a Minecraft launcher like you would play the game. I know I have done something like this in the past on other platforms but I just don’t know enough about Minecraft/java to make this happen.

    I am using ubuntu 18.04 and the current version of the Minecraft is 1.15.2

    Reply
  2. How to see the jobs running in the previous session? I have submitted jobs in nohup and logged out. After logging again if i wanna see the jobs and if I wanna kill, how to do so

    Reply
  3. Hi,

    I am running a script that copy files from one server to 3 other servers. The output I get is warning from other servers when make ssh even when I run the script with & on the end or if I move it in background with ^Z and bg. So my question is can you please give me some advice how can I prevent that output from showing. Thank You in advance.

    Regards,
    Vladimir Todorov

    Reply
  4. This was very useful! Thank you very much.
    I always used 2, 3 terminals to run different apps like android studio, ract-native, node, webstorm, etc. at the same time.
    These commands helped me to just have one terminal with all of these running in the background.

    Reply

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