Difference between nohup and setsid

• nohup과 setsid 모두 터미널이 종료된 이후에도 process가 background에서 동작하도록 하는데 사용하는 command이다.
• nohup은 SIGHUP signal을 무시하도록 해 프로세스가 백그라운드에서 동작하도록 한다.
• setsid는 system call을 통해 새로운 session을 만들고 해당 프로세스가 session leader가 되게 함으로써 process의 종료를 막는다.
• setsid does not redirect the output to file

What is difference between nohup and setsid

Both nohup and setsid are used to keep a process running in the background even after the terminal is closed. They differ mainly in their approach and usage.

nohup is a command that comes with Unix-like operating systems. It stands for “no hangup”. When you prefix a command with nohup, the system ignores the HUP (hangup) signal, allowing the command to continue running after the terminal is closed. Here’s how you use it:

nohup command

This command will create a nohup.out file in the current directory where the standard output and standard error of the command will be redirected Source 0, Source 2.

On the other hand, setsid is a system call that creates a new session and makes the process the leader of that session. This effectively detaches the process from the terminal. Unlike nohup, setsid does not redirect the output to a file. Here’s how you use it:

setsid command

In this case, the process that calls the setsid function will create a new session if it is not the leader of a process group. The process becomes the session leader of the new session, which is the only process in the new session. The process also becomes the leader process of a new process group, and the new process group ID is the PID of the process Source 0.

In summary, the key differences between nohup and setsid are:

• nohup ignores the HUP signal, allowing the command to continue running after the terminal is closed. It also redirects the output to a file.
• setsid creates a new session and makes the process the leader of that session, effectively detaching the process from the terminal. It does not redirect the output to a file.

About &

• In fact, on newer versions of bash, bash does not send SIGHUP commands to background programs. That means that any process running in the background ending with & will not be exited by the SIGHUP signal for terminal exit.

Reference

• The difference between nohup, setsid and disown - SoByte