Bug#922647: systemd --user no longer running

[Eduard Bloch]

Package: libpam-systemd
Version: 240-5
Severity: normal

Hi,

a few days ago some user services started failed - I mainly noticed that pulseaudio was no longer available.
This looked very strange, and while checking other systems, I saw that
"systemd --user" is not launched, which would have started pa and some
other user-session daemons.

So I started looking around, what "systemd --user" doing and how it is
started? Here, the first issue emerges. The manual explains --user but
a) does not tell you who/what is supposed to run this
b) in case you run systemd --user manually, it aborts with 
"Trying to run as user instance, but $XDG_RUNTIME_DIR is not set."
This does not help me at all - how shall a user guess where it's coming
from and how this is required for --user? There is NO explanation or
hint in the manpage.

Ok, so I guess that it must be some special thing triggered by login.
Which probably means pam. So I found libpam-systemd by looking through
the package list. And the manpage is interesting. But nothing tells me
what might be going wrong when the thing is NOT spawning systemd--user.
So I checked a few hints in the "SEE ALSO" section, like logind.conf(5),
and still nothing tells me how to debug a problem where systemd --user
is not run.

I checked the journal, and still cannot find much about/from PAM there.
And the only matches for /login/ are:

| Feb 18 19:54:58 zombie systemd[1]: Condition check resulted in getty on tty2-tty6 if dbus and logind are not available being skipped.

This phrase I not understand. Missing a comma somewhere? Missing some background explanation for regular users? Is this my problem and if yes, what to do about it?

The rest looks harmless:

| Feb 18 19:54:58 zombie systemd-logind[996]: New seat seat0.
| Feb 18 19:54:58 zombie systemd-logind[996]: Watching system buttons on /dev/input/event9 (Power Button)
| Feb 18 19:54:58 zombie systemd-logind[996]: Watching system buttons on /dev/input/event8 (Power Button)
| Feb 18 19:54:58 zombie systemd-logind[996]: Watching system buttons on /dev/input/event0 (Microsoft Natural® Ergonomic Keyboard 4000)
| Feb 18 19:54:58 zombie systemd-logind[996]: Watching system buttons on /dev/input/event1 (Microsoft Natural® Ergonomic Keyboard 4000)
| Feb 18 19:54:58 zombie systemd-logind[996]: Watching system buttons on /dev/input/event2 (A4TECH USB Device Keyboard)
| Feb 18 19:54:58 zombie systemd-logind[996]: Watching system buttons on /dev/input/event3 (A4TECH USB Device System Control)
| Feb 18 19:54:58 zombie systemd-logind[996]: Watching system buttons on /dev/input/event4 (A4TECH USB Device Consumer Control)
| Feb 18 19:55:00 zombie systemd-logind[996]: New session c1 of user lightdm.
| Feb 18 19:55:09 zombie systemd-logind[996]: Removed session c1.

Still does not tell me much if I don't know what to look for. There are
no exceptions/error/hints which would look somehow linked to login
sequence problems.

Any ideas?

NOTE: this issue might be related to #921687 because it started at
approximately the same time.

Best regards,
Eduard.

-- System Information:
Debian Release: buster/sid
  APT prefers unstable-debug
  APT policy: (500, 'unstable-debug'), (500, 'unstable'), (1, 'experimental-debug'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.20.7 (SMP w/12 CPU cores)
Kernel taint flags: TAINT_UNSIGNED_MODULE
Locale: LANG=de_DE.UTF-8, LC_CTYPE=de_DE.UTF-8 (charmap=UTF-8), LANGUAGE=de_DE.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages libpam-systemd depends on:
ii  dbus            1.12.12-1
ii  libc6           2.28-7
ii  libpam-runtime  1.3.1-5
ii  libpam0g        1.3.1-5
ii  systemd         240-5
ii  systemd-sysv    240-5

libpam-systemd recommends no packages.

libpam-systemd suggests no packages.

-- no debconf information