nohup, &

nohup and &

Ampersand (&)

The ampersand (&) is an operator that is used to send the execution of a command to the background.

Syntax:

[command] &

For example, the command sleep 5 & will start the sleep command in the background. You can then run other commands without having to wait for the sleep command to finish.

The nohup command

The nohup command is used to run a command in the background without any interruption, even when the terminal session is closed.

Syntax:

nohup [command]

For example, the command nohup sleep 5 & will start the sleep command in the background and will continue to run even if you close the terminal session.

Difference between nohup and &

The nohup and & commands are both used to run commands in the background. However, there are some key differences between the two commands.

• nohup prevents the command from being interrupted by the HUP signal, even if the terminal session is closed. The HUP signal is typically sent to a process when the terminal session is closed. This can cause the process to stop running. However, the nohup command catches the HUP signal and ignores it, so that the command continues to run even after the terminal session is closed.
• & does not prevent the command from being interrupted by the HUP signal. If you run a command with the & operator and then close the terminal session, the command will stop running.

Differences between the nohup and & commands:

	nohup	&
Prevents HUP signal	Yes	No
Redirects output to file	Yes	No
Suitable for	Running commands that need to continue running even after the terminal session is closed	Running commands that don't need to continue running after the terminal session is closed