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

On Tue, 7 Sept 2021 at 10:21, Michael Biebl <biebl@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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