Bug#993821: After upgrading libc, some services are unable to restart (including systemd-resolved)

[Michael Hudson-Doyle]

On Tue, 7 Sept 2021 at 10:21, Michael Biebl <biebl at debian.org> wrote:

> Am 06.09.21 um 23:45 schrieb Vincent Bernat:
>  > Package: systemd
>  > Version: 247.9-1
>  > Severity: normal
>  >
> > Hey!
> >
> > After upgrading to libc6 2.32-1, some services are unable to restart.
> > In my case, systemd-resolved, systemd-timesyncd and colord. Using
> > "systemctl daemon-reexec" fixes the issue. Unsure if there is really
> > something to be fixed but as I didn't find anything about that, a bug
> > report may help others. I suppose the problem is related to NSS.
> >
> > Sep 06 23:06:43 chocobo systemd[1]: Starting Network Time
> Synchronization...
> > Sep 06 23:06:43 chocobo systemd[236983]: systemd-timesyncd.service:
> Failed to determine user credentials: No such process
> > Sep 06 23:06:43 chocobo systemd[236983]: systemd-timesyncd.service:
> Failed at step USER spawning /lib/systemd/systemd-timesyncd: No such process
> >
> >
>
>
> @libc maintainers: any ideas what could be causing this? If this is
> triggered by a libc6 update, should this be reassigned to glibc?
>

We went through this in Ubuntu recently and decided that restarting systemd
in glibc's postinst was the safest option:
https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1942276

What's happening is that systemd is running with the old glibc, forks and
then does NSS things that cause the new glibc's NSS modules to load and
they don't necessarily work, leading to failures in any unit that specifies
User=. At least for Ubuntu's builds the NSS modules seem to be ABI
compatible between 2.32 and 2.33 (I didn't try 2.31 vs 2.32) but they are
definitely not between 2.33 and 2.34.

Cheers,
mwh
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