SIGHUP for "session has gone away", not SIGTERM/SIGKILL

Posted Jun 9, 2016 16:10 UTC (Thu) by cortana (subscriber, #24596)
In reply to: SIGHUP for "session has gone away", not SIGTERM/SIGKILL by Cyberax
Parent article: Distributors ponder a systemd change

Probably some kind of command that moves the disowned process (BTW, what's the difference between SIGSTOP, bg & exiting the shell, and SIGSTOP, bg, disown and exiting?) into its own scope unit. So a bit like 'systemd-run --scope --user' except with an existing process, rather than a new process that the user's systemd instance launched.

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SIGHUP for "session has gone away", not SIGTERM/SIGKILL

Posted Jun 9, 2016 16:50 UTC (Thu) by viro (subscriber, #7872) [Link]

disown doesn't do anything to the process; it's a shell builtin that makes shell forget about that job, so that when it comes to shell-sent SIGHUP the job in question won't be affected.

The point is that back when you had launched that sucker you had no idea that it might need to be left to run - otherwise you would've used nohup to start it in the first place. And yes, there's a bunch of real-world situations where you really don't want to kill the damn thing and restart it from scratch, this time with nohup. Consider a case when what you expected to be a couple of hours of calculations you've started in ssh session on a big fast box at 1pm, only to discover at 11pm, when you get around to checking what it has produced that it's only ~2/3 way through. And you really have to disconnect the laptop you'd been using and leave. Killing that sucker and starting it with nohup means that results won't be there until 2pm tomorrow instead of waiting for you when you get back there in the morning. Sure, you ought to have added checkpointing, etc., but the whole problem is that it was supposed to be a one-off thing, and a reasonably quick one. I've no idea whether that's the scenario original poster had in mind, but it definitely does happen. disown can save you a lot of PITA in such case.