background jobs and ssh connections
- by petrelharp
This question has come up quite a lot (really a lot), but I'm finding the answers to be generally incomplete. The general question is "Why does/doesn't my job get killed when I exit/kill ssh?", and here's what I've found. The first question is: How general is the following information? The following seems to be true for modern Debian linux, but I am missing some bits; and what do others need to know?
All child processes, backgrounded or not of a shell opened over an ssh connection are killed with SIGHUP when the ssh connection is closed only if the huponexit option is set: run shopt huponexit to see if this is true.
If huponexit is true, then you can use nohup or disown to dissociate the process from the shell so it does not get killed when you exit.
If huponexit is false, which is the default on at least some linuxes these days, then backgrounded jobs will not be killed on normal logout.
But even if huponexit is false, then if the ssh connection gets killed, or drops (different than normal logout), then backgrounded processes will still get killed. This can be avoided by disown or nohup as in (2).
There is some distinction between (a) processes whose parent process is the terminal and (b) processes that have stdin, stdout, or stderr connected to the terminal. I don't know what happens to processes that are (a) and not (b), or vice versa.
Final question: How can I avoid behavior (3)? In other words, by default in Debian backgrounded processes run along merrily by themselves after logout but not after the ssh connection is killed. I'd like the same thing to happen to processes regardless of whether the connection was closed normally or killed. Or, is this a bad idea?
