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Detach Processes With Disown and Nohup
Many system administrators make a practice of using GNU Screen or tmux to manage jobs running in the terminal. If you have a long-running job that you want to "detach" from the terminal, you can simply use your terminal multiplexer to do it. But what if you don't use tmux or Screen, or you just forgot? For those times, there's
When I'm going to be working at a project for any amount of time, I'm usually running
tmux (I usually default to
screen, but I have been spending more time with
tmux lately to become more familiar with it). But sometimes I'll log into my server or another system and start a job -- like a backup, or copying a really large file -- and realize that I want to close the connection for one reason or another. (One of the downsides in working from a laptop at a coffee shop ...)
If you haven't started the job yet, there's
nohup. Short for "no hangup,"
nohup will detach the program from the current shell and send its output to
nohup.out. If you quit the shell or whatever, the process will continue to run until it completes.
Ah, but what if you forget to use
nohup, or if you didn't expect to be leaving the computer but get called away? Then there's
The use of disown is a bit more complex. While the command is running, use
Ctrl-z to stop it and then use
bg to put it in the background. Then you'll use
disown %n where
n is the job number (jobspec). And, of course, you can find the job number using the
jobs command. Run
jobs again to verify that the job has been detached -- and you can use
top to verify that the job is actually still running.
And that's all there is to it. Complex? No. But you'd be surprised how many new admins -- especially those coming from Windows environments -- are unfamiliar with these utilities.
disown is specific to GNU Bash, so you may not find it on some systems. The
nohup command is implemented as a Bash built-in, but also as a separate utility on some systems, so be sure to check if its behavior differs from what's described here.
Joe 'Zonker' Brockmeier is a freelance writer and editor with more than 10 years covering IT. Formerly the openSUSE Community Manager for Novell, Brockmeier has written for Linux Magazine, Sys Admin, Linux Pro Magazine, IBM developerWorks, Linux.com, CIO.com, Linux Weekly News, ZDNet, and many other publications. You can reach Zonker at firstname.lastname@example.org and follow him on Twitter.