bug#55444: elogind startup race between shepherd and dbus-daemon

[Liliana Marie Prikler <liliana.prikler@gmail.com>]

Hi,

Am Montag, dem 16.05.2022 um 10:26 +0200 schrieb Ludovic Courtès:
> [...]
> So it would seem that the solution to this is to prevent dbus-daemon
> from starting elogind.  We can do that by changing
> org.freedesktop.login1.service so that it has “Exec=true” instead of
> “Exec=elogind --daemon”.
> 
> “Exec=true” is a bit crude because it doesn’t guarantee that elogind
> is really started; if that isn’t good enough, we could instead wait
> for the PID file or something (as of Shepherd 0.9.0, invoking ‘herd
> start elogind’ potentially leads shepherd to start a second instance
> if the first one is still being started, so we can’t really do that).
Why does shepherd race with itself here?  That sounds like a very evil
bug.  Rather than waiting for a log file, I'd suggest writing an ad-hoc
Guile script that communicates with shepherd and blocks until shepherd
signals that elogind has been started, but this script too would have
to work around shepherd racing against itself.

> Depending on what we end up with, we might also revisit whether
> xorg-server needs to explicitly depend on elogind.
At least in the case of GDM I think it does heavily depend on elogind.
For the future, I think we also should take over dbus-daemon's
autostart in the same way systemd already has.

Cheers