When you are working on your system, there will be times when you will want to run commands or jobs that survive to a logout or to an unexpectedly session termination. The command for handling this task is the nohup unix command.
Imagine you have to sort a big file, but you have no time to see the process terminate and you have to logoff to protect your terminal session. Simply run your sort command as follows:
nohup sort really_big_file.txt > /tmp/new_file &
Now when you logout nohup will take care of making your command to be immune to SIGHUP signal sent by the system.
If the standard output is a terminal, it is redirected to the file nohup.out. The standard error is redirected to follow the standard output.. This file will be created in $HOME (your home directory) if it cannot be created in the current working directory.