bug#26931: GuixSD rebooting fails when tmux is running

[ng0 <ng0@infotropique.org>]

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Ludovic Courtès transcribed 1.7K bytes:
> Hi,
> 
> Leo Famulari <leo@famulari.name> skribis:
> 
> > On Sun, May 14, 2017 at 11:36:17PM +0200, Ludovic Courtès wrote:
> >> What does /var/log/shepherd.log show around the time where you hit
> >> “halt”?
> >> 
> >> I get something like this:
> >> 
> >> --8<---------------cut here---------------start------------->8---
> >> 18:06:26 Service mcron has been stopped.
> >> 18:06:26 sending all processes the TERM signal
> >
> > For me, this is where it gets stuck:
> >
> > ------
> > 2017-05-16 19:12:53 sending all processes the TERM signal
> > 2017-05-16 19:12:58 waiting for process termination (processes left: (1 494)) 
> > 2017-05-16 19:13:00 waiting for process termination (processes left: (1 494)) 
> > 2017-05-16 19:13:02 waiting for process termination (processes left: (1 494)) 
> > ------
> >
> > In my experience, it will wait here forever.
> >
> > And from `ps aux`:
> >
> > leo        494  0.0  0.1  27232  3676 ?        Ss   19:12   0:00 tmux
> 
> The bug was 100% reproducible in a VM, and AFAICS it is fixed by
> 7f090203d5fb033eb1b64778b03afad5bb35f5f2.
> 
> The problem was that the tmux server process would be left as a zombie,
> and then the loop would always see it because the parent process of the
> tmux server process is PID 1 and for some reason the PID 1 either didn’t
> get SIGCHLD or the handler didn’t run.
> 
> The test that this commit adds does exactly the same thing: launch tmux
> and then invoke “halt”.  I tried to create a synthetic test not
> involving tmux, simply creating a process that gets PID 1 as its parent,
> but it wouldn’t trigger the bug.  I’m unclear as to why tmux triggers it
> and no that other simple test.
> 
> Thanks,
> Ludo’.
> 
> 
> 
> 
I just found this upstream issue: https://github.com/tmux/tmux/issues/311
which has been fixed in tmux 2.5. I think we should take this bug to upstream,
even if it's just to get more insight if it is a tmux bug.
-- 
ng0
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