Linux - How to Nohup
The nohup command is the no hangup command. It prevents a process from being terminated when the shell that launched it is killed. An example scenario where you might use this is if you launch a command on a remote server and want it to continue running after you close your terminal and reboot your laptop.
You can run nohup on Linux like this:
nohup ./test.sh &
The nohup command will cause the process not to be terminated and the ampersand will place it in the background. It will write to the file nohup.out in the same directory. If you open another terminal you will be able to watch the output of the program by watching this file. This works great if you want to come back later and check the status of the process. For example, you could tail the nohup file like this:
tail -f nohup.out
You could verify that the process is running like this:
ps -ef |grep -i test
If you want to force it to stop you can just use the kill command like this:
If that doesn’t work you can always use kill -9 like this:
kill -9 55972
If you haven’t killed the original terminal yet, you can use the fg command to bring it back to the foreground ( it will still write to nohup ). You can also specify the job ID to bring to the foreground if you have more than one in the background. You can list running jobs with the jobs command.
jobs # list jobs fg # bring job to foreground fg 1 # bring job with ID 1 ( not PID ) to foreground
If you run a job like this without the ampersand:
You can first move it to a stopped state by pressing [ctrl] - z. Then use the bg command to move it to the background ( running ).
jobs # find job ID bg 1 # specify ID bg # don't need ID if only one job
Redirecting stdout and stderr
You can choose to direct stdout and stderr to a file of your choosing like this:
nohup ./test.sh > out.log 2>&1 &
nohup vs disown vs &
- & just puts the process in the background
- disown removes the process from the shell’s job list. It won’t receive a SIGHUP and won’t die when the shell dies. It doesn’t disconnect it from the terminal so if the terminal is killed the process will keep running until it tries to use stdin or stdout. At this point it will fail.
- nohup disconnects the process from the terminal and stops it from receiving SIGHUP so it will survive after the shell is killed. It will also redirect stdout to a file called nohup.out. It will stay in the job control list until the shell is killed.