Bug#1116563: gdm3: Version 49 does not start properly

[Dmitry Shachnev]

On Sun, Sep 28, 2025 at 06:21:32PM +0100, Simon McVittie wrote:
> On Sun, 28 Sep 2025 at 20:08:07 +0300, Dmitry Shachnev wrote:
> > Sep 28 19:58:28 l3 unix_chkpwd[1094]: could not obtain user info (gdm-greeter)
> 
> What modules does your /etc/nsswitch.conf have registered for the passwd,
> group, shadow and gshadow databases? A typical setup would look like this:
> 
> passwd:         files systemd
> group:          files systemd
> shadow:         files systemd
> gshadow:        files systemd

Oh, for me the last two lines don't have systemd:

passwd:         files systemd
group:          files systemd
shadow:         files
gshadow:        files

And adding systemd there helped, thanks a lot!

> The new gdm version requires libnss-systemd ("systemd" in
> /etc/nsswitch.conf) for its handling of dynamic creation/deletion of
> temporary user IDs.
>
> gdm3 Depends on libnss-systemd, and installing that package *should* set it
> up in nsswitch.conf automatically, but one possible reason for the gdm
> "greeter" (login prompt) not to start up successfully is that this somehow
> hasn't happened.

I am now looking at libnss-systemd postinst, which has the following code:

# 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|#|$)' -e '^shadow:[^#]*\s(systemd)(\s|#|$)' "${DPKG_ROOT}/etc/nsswitch.conf" ; then
        # Installing passwd/systemd from libnss-systemd in position last
        sed -E -i "${DPKG_ROOT}/etc/nsswitch.conf" -e '/^passwd:\s[^#]*$/ s/$/ systemd/' -e '/^passwd:\s.*#/ s/#/ systemd #/'
        # Installing group/systemd from libnss-systemd in position last
        sed -E -i "${DPKG_ROOT}/etc/nsswitch.conf" -e '/^group:\s[^#]*$/ s/$/ systemd/' -e '/^group:\s.*#/ s/#/ systemd #/'
        # Installing shadow/systemd from libnss-systemd in position last
        sed -E -i "${DPKG_ROOT}/etc/nsswitch.conf" -e '/^shadow:\s[^#]*$/ s/$/ systemd/' -e '/^shadow:\s.*#/ s/#/ systemd #/'
        # Installing gshadow/systemd from libnss-systemd in position last
        sed -E -i "${DPKG_ROOT}/etc/nsswitch.conf" -e '/^gshadow:\s[^#]*$/ s/$/ systemd/' -e '/^gshadow:\s.*#/ s/#/ systemd #/'
    fi
    rm "${DPKG_ROOT}/etc/nsswitch.conf.nss.${DPKG_MAINTSCRIPT_PACKAGE}-will-install"
fi
# End automatically added section

In my case there is match for the first two expressions but not for the last
two, however grep will still exit 0 in this case, so sed won't be called.

I found a related dh-nss bug #1113745, but it was marked as wontfix by the
dh-nss maintainer.

--
Dmitry Shachnev
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