How to Run Linux Commands in the Background
Running commands in the background allows users to continue working on other tasks while the command runs. This feature is particularly useful for long-running tasks that need to continue even after logging out or closing the terminal window. In this section, we will discuss various methods to run Linux commands in the background.
Method 1: Using Ampersand Sign (&)
The easiest way to run a command in the background is to append an ampersand sign (&) at the end of the command. This will start the command in the background and immediately return the shell prompt.
$ command &
For example, to run a script called backup.sh
in the background, you can use the following command:
$ ./backup.sh &
Advantages and Disadvantages
The ampersand method is simple and easy to remember. However, the main disadvantage is that the command’s output will still be printed to the terminal. This can be distracting, particularly if the command is producing a lot of output.
Examples of Commands to Run in the Background
Here are some examples of commands that can be run in the background using the ampersand method:
$ ping google.com &
– Run theping
command in the background to check if the host is reachable.$ firefox &
– Run the Firefox browser in the background.$ python script.py &
– Run a Python script in the background.
Method 2: Using bg Command
The bg
command is used to move a stopped or suspended process to the background. This method is useful when you have accidentally stopped a process or when a process has been suspended due to a keyboard shortcut or signal.
$ bg
Advantages and Disadvantages
The bg
command is useful when you have accidentally stopped a process, and you want to resume it in the background. However, it cannot be used to start new processes in the background.
Examples of Commands to Run in the Background
Here are some examples of commands that can be moved to the background using the bg
command:
$ cp file1 file2 &
– Copy a file in the background.$ cat file1 > file2 &
– Redirect the output of a command to a file in the background.$ sudo apt-get upgrade &
– Run a system upgrade in the background.
Method 3: Using nohup Command
The nohup
command is used to run a command that will continue to run even after you log out or close the terminal window. This method is useful when you want to start a long-running process that you want to continue running even when you are not logged in.
$ nohup command &
Advantages and Disadvantages
The nohup
command is useful when you want to start a long-running process that you want to continue running even after you log out. However, it cannot be used to interact with the process once it has started.
Examples of Commands to Run in the Background
Here are some examples of commands that can be run in the background using the nohup
command:
$ nohup python script.py &
– Run a Python script in the background.$ nohup sudo apt-get upgrade &
– Run a system upgrade in the background.$ nohup ping google.com &
– Run theping
command in the background.
Method 4: Using disown Command
The disown
command is used to detach a job from the shell, which means that it will not be terminated when the shell exits. This method is useful when you want to start a long-running process that you want to continue running even when you log out or close the terminal.
$ command &
$ disown
Advantages and Disadvantages
The disown
command is useful when you want to start a long-running process that you want to continue running even after you log out. However, it cannot be used to interact with the process once it has started.
Examples of Commands to Run in the Background
Here are some examples of commands that can be run in the background using the disown
command:
$ python script.py &
– Run a Python script in the background.$ sudo apt-get upgrade &
– Run a system upgrade in the background.$ ping google.com &
– Run theping
command in the background.
Method 5: Using tmux
tmux
is a terminal multiplexer that allows you to run multiple sessions in a single terminal window. This method is useful when you want to run multiple commands in the background and switch between them.
Explanation of What tmux Is
tmux
is a terminal multiplexer that allows you to run multiple terminal sessions in a single terminal window. You can detach and reattach sessions, which means that you can keep your sessions running even after you log out or close the terminal window.
Step-by-Step Instructions
To start a new tmux
session, use the following command:
$ tmux new-session
Once you are in the tmux
session, you can start running commands in the background by appending an ampersand sign (&) at the end of the command.
To detach a tmux
session, press Ctrl-b d
. To reattach a tmux
session, use the following command:
$ tmux attach-session
Advantages and Disadvantages
The main advantage of using tmux
is that you can run multiple commands in the background and switch between them. However, the learning curve for tmux
can be steep, and it can take some time to get used to the interface.
Examples of Commands to Run in the Background
Here are some examples of commands that can be run in the background using tmux
:
$ ping google.com &
– Run theping
command in the background.$ top &
– Monitor system processes in the background.$ python script.py &
– Run a Python script in the background.
Managing Background Processes
Once you have started a process in the background, you can manage it using various commands. This section will cover how to check the status of background processes, bring them to the foreground, terminate them, and keep them running even after a shell session ends.
Checking the Status of Background Processes
To check the status of background processes, you can use the jobs
command. This command will display a list of all the jobs that are running in the background.
$ jobs
The output will display the job number, status, and command name. This information was obtained from linuxhint.com.
Bringing Background Processes to the Foreground
To bring a background process to the foreground, you can use the fg
command. This command will bring the last job that was run in the background to the foreground.
$ fg
If you have multiple jobs running in the background, you can bring a specific job to the foreground by specifying the job number.
$ fg %job_number
Terminating Background Processes
To terminate a background process, you can use the kill
command. This command will send a signal to the process to terminate it.
$ kill %job_number
Alternatively, you can use the pkill
command to terminate a process by name.
$ pkill process_name
These commands and their usage information were obtained from linuxize.com and tecmint.com.
Keeping Processes Running After a Shell Session Ends
When you log out of your shell session or close the terminal window, any background processes that are still running will be terminated. To keep processes running even after a shell session ends, you can use the nohup
command.
$ nohup command &
Another way to keep processes running after a shell session ends is to use a terminal multiplexer like tmux
. This method allows you to detach from a session and reattach to it later, even after logging out.
$ tmux new-session
You can then start running commands in the background as usual. To detach from the tmux
session, press Ctrl-b d
. To reattach to the session, use the following command:
$ tmux attach-session
These methods will ensure that your background processes continue to run even after you log out or close the terminal window. This information was obtained from linuxhandbook.com and linuxconfig.org.
Using Screen or Tmux for Multiple Interactive Sessions
Screen and Tmux are terminal multiplexers that allow you to have multiple interactive sessions within a single terminal window. This section will cover how to use these programs to run multiple sessions and keep them running even after you log out.
Screen
Screen is a terminal multiplexer that allows you to have multiple terminal sessions within a single window. To start a new screen session, run the following command:
$ screen
This will start a new session. You can then run commands within this session as usual. To detach from the session, press Ctrl-a d
. This will return you to the main terminal window. To reattach to the session, use the following command:
$ screen -r
This will reattach you to the last screen session that you detached from.
Tmux
Tmux is another terminal multiplexer that allows you to have multiple terminal sessions within a single window. To start a new Tmux session, run the following command:
$ tmux new-session
This will start a new session. You can then run commands within this session as usual. To detach from the session, press Ctrl-b d
. This will return you to the main terminal window. To reattach to the session, use the following command:
$ tmux attach-session
This will reattach you to the last Tmux session that you detached from.
Both Screen and Tmux are useful for running multiple sessions within a single terminal window. This can be especially useful when working on remote servers or when you need to keep multiple sessions running at the same time. These programs are also useful for keeping sessions running even after you log out or close the terminal window.
Conclusion
Running Linux commands in the background is a powerful feature that allows you to continue working on other tasks while a command is running. There are several ways to run commands in the background, including using the &
operator, bg
, nohup
, and disown
. You can also use terminal multiplexers like Screen or Tmux to run multiple sessions within a single terminal window.
When running background processes, it’s important to manage them properly. This includes checking the status of background processes, bringing them to the foreground, and terminating them when necessary. You should also ensure that processes continue to run even after you log out or close the terminal window.
By using the methods outlined in this article, you can effectively run Linux commands in the background and manage background processes with ease.
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Frequently Asked Questions
What is the best way to run a Linux command in the background?
Use the &
operator at the end of the command.
How can I check the status of a background process?
Use the jobs
command to display a list of running jobs.
What happens to background processes when I log out of the shell?
They are terminated, unless you use nohup
or a terminal multiplexer.
How can I bring a background process to the foreground?
Use the fg
command to bring the last job to the foreground.
What are some ways to keep a process running after a shell session ends?
Use nohup
to run a command in the background, or use a terminal multiplexer like Screen or Tmux.
Why do I need to manage background processes properly?
To prevent them from consuming system resources and to avoid unexpected behavior.