[systemd-devel] sigpwr.target - intended usage?

[Lennart Poettering]

On Mon, 18.07.16 14:41, Michael Biebl (mbiebl at gmail.com) wrote:

> 2016-07-18 14:00 GMT+02:00 Michael Biebl <mbiebl at gmail.com>:
> > 2016-07-18 13:54 GMT+02:00 Lennart Poettering <lennart at poettering.net>:
> >> On Mon, 18.07.16 13:37, Michael Biebl (mbiebl at gmail.com) wrote:
> >>
> >>> Apparently SIGPWR is used by lxc-stop to shut down LXC containers.
> >>> What interface would you recommend instead?
> >>>
> >>> https://lists.linuxcontainers.org/pipermail/lxc-users/2015-May/009279.html
> >>
> >> Is that actually really used? I mean, upstart is pretty much dead
> >> afaics...
> >>
> >> systemd since day one shuts down cleanly on SIGRTMIN+4, and it's
> >> probably what a container manager should use (it is what machined
> >> uses). See the "Signals" section in systemd(1).
> >
> > lxc containers require sigpwr.target to be hooked up properly,
> > otherwise lxc-stop does not shutdown the container.
> 
> SIGPWR is wired up in sysvinit and upstart by default to initiate a
> shutdown. Afaics both do not react on SIGRTMIN+4.

Well, many sysvinit distros where set up to log something about
"IMPENDING POWER FAILURE" on SIGPWR... It sounds really wrong to
trigger this in a container just to shut it down...

> So the problem here is that lxc doesn't know what runs inside the
> container: could be an older version of Debian (using syvinit), and
> older version of Ubuntu (using upstart) or systemd.

Well, if they don't want to make SIGRTMIN+4 the default because they
think sysvinit/Upstart is more relevant than systemd, then that's
their right. But I think making the kill signal configurable per
container would probably be a good idea. That's what we do in nspawn,
where SIGRTMIN+3 is the default, but you can override it with
--kill-signal= on the cmdline (or KillSignal= in .nspawn files), for
compat with sysv.

Lennart

-- 
Lennart Poettering, Red Hat