This is actually distinct enough from bug 2121017, so let's not consider
it duplicate. To copy my comment from that bug:
The user in bug 2125403 is using "compat" rather than "files" for
passwd, group, and shadow[1]. I don't grok the generated postinst well
enough to be sure, but I think that means that since we have
"after=files" in libnss-systemd.nss, the sed expressions don't match the
existing content of /etc/nsswitch.conf:
root@q:~# cat /var/lib/dpkg/info/libnss-systemd\:amd64.postinst
#!/bin/sh
set -e
# Automatically added by dh_installnss/1.7
if [ "$1" = "configure" ] && [ -f
"${DPKG_ROOT}/etc/nsswitch.conf.nss.${DPKG_MAINTSCRIPT_PACKAGE}-will-install" ]
&& [ -e "${DPKG_ROOT}/etc/nsswitch.conf" ] ; then
if ! grep -q -E -e '^group:[^#]*\s(systemd)(\s|#|$)' -e
'^gshadow:[^#]*\s(systemd)(\s|#|$)' -e '^passwd:[^#]*\s(systemd)(\s|#|$)' -e
'^shadow:[^#]*\s(systemd)(\s|#|$)' "${DPKG_ROOT}/etc/nsswitch.conf" ; then
# Installing passwd/systemd from libnss-systemd in position
after=files
sed -E -i "${DPKG_ROOT}/etc/nsswitch.conf" -e
'/^passwd:\s[^#]*$/ s/(\s)(files(\s+\[[^]]+\])?)(\s|$)/\1\2 systemd /' -e
'/^passwd:\s.*#/ s/(\s)(files(\s+\[[^]]+\])?)(\s|#)/\1\2 systemd \3/' -e 's/
$//'
# Installing group/systemd from libnss-systemd in position
after=files
sed -E -i "${DPKG_ROOT}/etc/nsswitch.conf" -e
'/^group:\s[^#]*$/ s/(\s)(files(\s+\[[^]]+\])?)(\s|$)/\1\2 systemd /' -e
'/^group:\s.*#/ s/(\s)(files(\s+\[[^]]+\])?)(\s|#)/\1\2 systemd \3/' -e 's/ $//'
# Installing shadow/systemd from libnss-systemd in position
after=files
sed -E -i "${DPKG_ROOT}/etc/nsswitch.conf" -e
'/^shadow:\s[^#]*$/ s/(\s)(files(\s+\[[^]]+\])?)(\s|$)/\1\2 systemd /' -e
'/^shadow:\s.*#/ s/(\s)(files(\s+\[[^]]+\])?)(\s|#)/\1\2 systemd \3/' -e 's/
$//'
# Installing gshadow/systemd from libnss-systemd in position
after=files
sed -E -i "${DPKG_ROOT}/etc/nsswitch.conf" -e
'/^gshadow:\s[^#]*$/ s/(\s)(files(\s+\[[^]]+\])?)(\s|$)/\1\2 systemd /' -e
'/^gshadow:\s.*#/ s/(\s)(files(\s+\[[^]]+\])?)(\s|#)/\1\2 systemd \3/' -e 's/
$//'
fi
rm
"${DPKG_ROOT}/etc/nsswitch.conf.nss.${DPKG_MAINTSCRIPT_PACKAGE}-will-install"
fi
# End automatically added section
In other words, since the user did not have "files" listed for those
dbs, "systemd" does not get added. It's also unclear to me from the
docs[2] what to do in this case.
Can we just add "after=compat" entries as a fallback to libnss-
systemd.nss?
[1] https://bugs.launchpad.net/ubuntu/+source/gdm3/+bug/2125403/comments/4
[2] https://manpages.debian.org/unstable/dh-nss/dh_installnss.1.en.html
** This bug is no longer a duplicate of bug 2121017
gdm3 49~beta doesn't start [unix_chkpwd: could not obtain user info
(gdm-greeter)] on systems installed before 2024
** Summary changed:
- Graphics mode won't be started from gdm3
+ Graphics mode won't be started from gdm3 when 'compat' is used instead of
'files' in /etc/nsswitch.conf
** Changed in: gdm3 (Ubuntu)
Status: New => Triaged
** Changed in: gdm3 (Ubuntu)
Importance: Undecided => Critical
** Changed in: gdm3 (Ubuntu)
Assignee: (unassigned) => Nick Rosbrook (enr0n)
** Changed in: gdm3 (Ubuntu)
Milestone: None => ubuntu-25.10
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https://bugs.launchpad.net/bugs/2125403
Title:
Graphics mode won't be started from gdm3 when 'compat' is used instead
of 'files' in /etc/nsswitch.conf
Status in gdm3 package in Ubuntu:
Triaged
Bug description:
That one is really odd.
25.04 was working perfectly - and then I upgraded the (expendable)
machine to beta test 25.10 and ... the graphical login won't work at
all.
gdm will start, but I see no graphical activity AT ALL. No flickering,
nothing.
The only log line which might be of interest is:
gdm-launch-environment] [3328]: pam_unix(gdm-launch-
environment:account): could not identify user (from getpwname(gdm-
greeter))
ProblemType: Bug
DistroRelease: Ubuntu 25.10
Package: gdm3 49~rc-0ubuntu2
ProcVersionSignature: Ubuntu 6.17.0-4.4-generic 6.17.0-rc5
Uname: Linux 6.17.0-4-generic x86_64
ApportVersion: 2.33.1-0ubuntu2
Architecture: amd64
CasperMD5CheckResult: unknown
Date: Mon Sep 22 15:14:57 2025
ProcEnviron:
LANG=en_US.UTF-8
PATH=(custom, no user)
SHELL=/bin/bash
TERM=linux
SourcePackage: gdm3
UpgradeStatus: Upgraded to questing on 2025-09-18 (4 days ago)
To manage notifications about this bug go to:
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