[systemd-devel] [PATCH] Allow PID 1 systemd --user instances to exit

[Michael Marineau]

On Nov 6, 2014 5:17 PM, "Lennart Poettering" <lennart at poettering.net> wrote:
>
> On Thu, 06.11.14 16:59, Vito Caputo (vito.caputo at coreos.com) wrote:
>
> > Because for all intents and purposes it's effectively still a user
> > instance, just having its own PID namespace isn't cause --system
behaviors
> > like disabling systemctl exit for example.
>
> I am pretty sure doing something like this will break at a ton of
> other places.
>
> I really wonder if it's worth supporting this, after all a lot of our
> code checks getpid() == 1 to see if we are run in system mode. I mean,
> once upon a time we had a mode in systemd, where we supported running
> --system system as PID != 1. We removed that because it only ever
> half-worked, because it confused things, because the usecase was
> weak, because nobody really cared and because it bitrotted. Now,
> supporting running systemd --user in a PID namespace kinda feels like
> the same story, just inverted. Which makes me immediately wonder why
> this should be different for this case.
>
> So, what's the real usecase for all of this? Can you elaborate on
> that?

The basic idea is to create a container that has the ability to return a
normal exit code when it exits. System instances don't allow this. User
instances do and also avoid other undesired things like reading extra args
from /proc/cmdline which isn't applicable to a container.

There seems to be a odd fit here between expecting a system instance to
behave nicely like yet another service on a host or a user instance to be
pid 1 in a container.

>
> > Preventing exit from PID 1 makes sense when you're going to panic the
> > kernel, but doesn't --user imply otherwise?
>
> Well, the --user switch as PID 1 is probably something we should
> refuse early on...
>
> Lennart
>
> --
> Lennart Poettering, Red Hat
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