When you run a command in the background on a Linux system and then log out, the process you were running will stop abruptly. If you elect to run the command with a no-hangup command, on the other hand, it will continue running and will store its output in a file.
Here’s how this works. The nohup command instructs your process to ignore the SIGHUP signal that would normally shut it down. That allows you to leave time-consuming processes to complete on their own without you having to remain logged in. By default, the output of the command you are running will be left in a file named nohup.out so that you can find your data the next time you log in.
From: Network World