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When you execute a command in the terminal, you need to wait for the command to finish executing. This is called the foreground process.

However, some advanced programs need to run in the background. In Bash scripts, there is an easy way to have your commands run in the background.

The interesting thing about background processes is that you don't need to wait for the command execution to finish. You can run another command in parallel.

But you can't end the background process just by clicking the cross button. You have to use some command to end the background process.

In this article, we will discuss how to create a command that runs in the background. Furthermore, we will discuss the topic by using necessary examples and explanations to make the topic easier to understand.

We will first learn how to create a background process and then see how to terminate an existing process.

Creating Background Processes Using & in Bash

Creating a background process in a Bash script is very easy. All you need to do is include the & symbol at the end of the command.

The general syntax for making a command run in the background is:

YOUR COMMAND &

The following example runs a Bash script as a background process. The code will look like this:

./example.sh &

After executing the above code, you will get the following output:

[1] 20

Here you will see the process number enclosed in the third bracket.

If your process has completed its work, you will be notified like this:

[1]+  Done                    ./example.sh

Killing Background Processes in Bash

To kill a background process, just follow these steps. If you forget the process ID, you can use the command below to find your running process.

jobs -l

This will output a list of running processes.

[1]+ 25177 Running                 ./example.sh &

From the list, you can find the process ID and use it to kill the process using the following command.

kill %1

The general syntax for killing a process is:

kill %ProcessID

Keep the Current Job Running Using disown in Bash

You can also keep the current job running in the background even when the terminal is closed. To do this, we will use a command called disown.

To keep the current job running in the background, you can follow this example command:

disown -h %3

We will keep the process with id 3 alive even if the terminal is closed. Here, -h is the option to keep the process alive.

The general syntax of this command is:

disown -h %ProcessID

Stop the background process from continuing to print messages to the terminal

To prevent a background process from printing messages to the terminal window, you can follow this syntax:

Your_Command 2>/dev/null &

This will stop printing messages in the terminal window.

Use nohup to run the command in the background

If you want a process to run in the background even if the terminal is closed, you must use the nohup command. This command will execute other programs specified as its parameters and ignore all SIGHUP signals.

When you close the terminal, it sends a SIGHUP signal to close all running processes under the controlling terminal. Since this command ignores the SIGHUP command, the process run by the nohup command remains active until it is killed.

You must include the & in this command. You can follow this example:

nohup ./MyScript.sh &

This command runs a background process and writes its output to the nohup.out file.

Convert a running foreground process to a background process in Bash

To move a foreground process to the background, you must perform the following two steps:

• First, you must stop the target process by pressing Ctrl+Z.
• Use the command bg to move the stopped process to the background. You can follow the syntax:

bg %ProcessID

All the codes used in this article are written in Bash. It will only work in Linux Shell environment.