Bug#1071462: installing/upgrading libc6 does not work in sbuild when systemd is installed as ischroot declines

[Luca Boccassi]

On Mon, 20 May 2024 at 10:20, Johannes Schauer Marin Rodrigues
<josch at debian.org> wrote:
>
> Hi,
>
> Quoting Chris Hofstaedtler (2024-05-20 10:38:04)
> > * Johannes Schauer Marin Rodrigues <josch at debian.org> [240520 07:35]:
> > > [..] But maybe it [glibc's postinst] should be doing some
> > > more involved checks about what PID 1 is? It could then make sure to only call
> > > systemd telinit if systemd is pid 1. [..]
> >
> > Well, that would probably suck. Putting the knowledge when to call
> > telinit, and a specific telinit, into a ton of different things
> > makes all those things hard to get right, hard to update, the usual.
> >
> > I've checked the sysvinit and the systemd implementations now, and
> > they are not that different. Both try to talk to their respective
> > pid1 daemons first using their respective communication socket.
> >
> > But then, if that doesn't work, they diverge:
> > - sysvinit's telinit just gives up
> > - systemd's telinit, *as an explicit fallback*, sends signals.
> >
> > systemd's telinit (aka systemctl) helpfully exits if it detects
> > being in a chroot, before doing any of that.
> >
> > IWSTM systemd's telinit could, if called as telinit, not do the
> > fallback to stick with sysvinit's behaviour?
> >
> > As a bonus, sysvinit's telinit could also gain the chroot check, and glibc's
> > postinst (and other places) can become simpler again.
>
> via irc, jochen also pointed out: telinit could be the component which checks
> what PID 1 actually is and only do its thing after it confirmed that it is
> indeed an init system like systemd that is providing PID 1?

That's all legacy stuff and I really don't want to touch it anymore.
Going from the other side, maybe libc6.postinst could use something
more reliable than ischroot()? Is systemd-detect-virt able to figure
out the situation a bit better?