What is the purpose of nohup in Unix?

In Unix, nohup command can be used to run a command in background. But it is different from & option to run a process in background.

Nohup stands for No Hangup. A nohup process does not stop even if the Unix user that started the process has logged out from the system.

But the process started with option & will stop when the user that started the process logs off.