How To Run Bash Commands In The Background In Linux

Running commands in the background is a powerful feature in Linux that allows users to execute long-running processes without tying up the terminal. This capability is particularly useful for tasks that take a significant amount of time, enabling users to multitask efficiently.

Using Ampersand (&) to Run Commands in the Background

One of the simplest ways to run a command in the background is by appending an ampersand (&) at the end of the command. This method instructs the shell to execute the command as a separate background process.

[command] &

For example, to run the vim text editor in the background, you would use:

vim &

When you run a command with &, the terminal displays the job ID and process ID of the background command. You can check the status of background processes using the jobs command.

To bring a background process back to the foreground, use the fg command followed by the job ID or process ID. For instance:

fg 1%  # Using job ID
fg 2781  # Using process ID

Using bg to Move a Stopped Process to the Background

If a process is already running in the foreground and you need to move it to the background, you can use the bg command. First, stop the process by pressing Ctrl + z, then use bg to continue it in the background.

sudo apt update  # Start the command
Ctrl + z  # Stop the command
bg  # Continue the command in the background

This method is useful when you need to pause a process temporarily and then resume it in the background.

Using nohup to Keep Commands Running After Terminal Closure

The nohup command allows you to run a command in the background and keep it running even after the terminal session is closed. This is particularly useful for long-running processes that should not be interrupted by terminal closure.

To use nohup, combine it with the & symbol and optionally redirect output to /dev/null to prevent the creation of a nohup.out file.

nohup [command] &>/dev/null &

For example:

nohup ping google.com &>/dev/null &

This ensures that the command continues to run even after you close the terminal.

Using disown to Detach Processes from the Shell

The disown command allows you to detach a background process from the shell, so it continues running even if the shell is closed. This is useful when you want to ensure that a process remains active regardless of the shell's state.

First, run the command with &, then use disown to detach it from the shell.

[command] &
disown %1  # Replace %1 with the job ID

This method ensures that the process is not terminated when the shell is closed.

Using Tmux for Advanced Background Management

Tmux is a terminal multiplexer that allows you to manage multiple terminal sessions within a single shell. It is particularly useful for running multiple commands in the background and switching between them efficiently.

To use Tmux, first install it if it is not already installed:

sudo apt install tmux

Then, launch Tmux:

tmux

You can create new windows, split panes, and switch between them using Tmux commands. For example, to split the window vertically:

Ctrl + b, %

To navigate between panes:

Ctrl + b, Right/Left Arrow

Tmux allows you to detach from a session and reattach later, keeping your background processes running:

Ctrl + b, d  # Detach from the session
tmux attach  # Reattach to the session

This provides a robust way to manage background processes and maintain session persistence.

Suppressing Output from Background Processes

When running commands in the background, output from these processes can still appear in your terminal, which might be distracting. To suppress this output, you can redirect it to /dev/null.

For example:

firefox &>/dev/null &

This command runs firefox in the background and redirects its output to /dev/null, preventing it from appearing in your terminal.

By using these methods, you can efficiently manage background processes in Linux, ensuring that your terminal remains available for other tasks while long-running commands execute in the background.