"systemd --user" and child processes fail to exit when user logs out

Thank you for your bug report, do you have that user logged in from a VT or ssh maybe?
What's the output of
$ loginctl list-sessions
(log as another user to try the comment)

This occurs whether the user logs in (through lightdm) on the console, or remotely via xrdp.

Running that command, as root, after the user (skunk) has logged in via lightdm:

    # loginctl list-sessions
    SESSION UID USER SEAT TTY
          2 0 root
         c2 1000 skunk seat0

    2 sessions listed.

After logout:

    # loginctl list-sessions
    SESSION UID USER SEAT TTY
          2 0 root
         c2 1000 skunk seat0
         c3 107 lightdm seat0

    3 sessions listed.

Even after SIGINT to "systemd --user", even after all the user processes go away, the c2 session remains present.

The output from loginctl for an xrdp login is similar. After logout:

    # loginctl list-sessions
    SESSION UID USER SEAT TTY
          2 0 root
         c1 107 lightdm seat0
         c2 1000 skunk

Thank you for your bug report, I can't confirm the bug on focal

Using an uptodate system
- start to gdm
- login is 'userone'
- create a 'dbguser'
- logout from the 'userone' session
- ssh dbguser@

$ loginctl list-sessions
SESSION UID USER SEAT TTY
     27 1001 dbguser pts/0
     c3 124 gdm seat0 tty1

What's the output of
$ loginctl user-status skunk
for you?
(you need to ssh as another user otherwise the fact that you connect with the user to start the command is going to interfer)

Could you try this using lightdm? It's possible that this may be a display-manager issue.

I did notice that in a different (customized) configuration of Xubuntu, the user processes still remained after logout, but then killing the "systemd --user" process resulted in the login session ending.

Anyway, here is the output you requested, in the original test environment:

# LC_ALL=C loginctl user-status skunk | cat
skunk (1000)
    Since: Fri 2020-04-10 18:40:19 EDT; 3min 11s ago
    State: closing
 Sessions: *c2
   Linger: no
     Unit: user-1000.slice
    |-session-c2.scope
    | |-1288 /usr/libexec/geoclue-2.0/demos/agent
    | `-1345 /usr/bin/python3 /usr/share/system-config-printer/applet.py
    `-user@1000.service
      |-at-spi-dbus-bus.service
      | |-1131 /usr/libexec/at-spi-bus-launcher
      | `-1136 /usr/bin/dbus-daemon --config-file=/usr/share/defaults/at-spi2/accessibility.conf --nofork --print-address 3
      |-dbus.service
      | |-1042 /usr/bin/dbus-daemon --session --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
      | |-1140 /usr/lib/x86_64-linux-gnu/xfce4/xfconf/xfconfd
      | |-1291 /usr/lib/x86_64-linux-gnu/tumbler-1/tumblerd
      | |-1302 /usr/libexec/dconf-service
      | |-1391 /usr/libexec/goa-daemon
      | `-1404 /usr/libexec/goa-identity-service
      |-evolution-addressbook-factory.service
      | `-1438 /usr/libexec/evolution-addressbook-factory
      |-evolution-calendar-factory.service
      | `-1396 /usr/libexec/evolution-calendar-factory
      |-evolution-source-registry.service
      | `-1374 /usr/libexec/evolution-source-registry
      |-gvfs-afc-volume-monitor.service
      | `-1501 /usr/libexec/gvfs-afc-volume-monitor
      |-gvfs-daemon.service
      | |-1153 /usr/libexec/gvfsd
      | |-1158 /usr/libexec/gvfsd-fuse /run/user/1000/gvfs -f -o big_writes
      | `-1509 /usr/libexec/gvfsd-trash --spawner :1.13 /org/gtk/gvfs/exec_spaw/0
      |-gvfs-goa-volume-monitor.service
      | `-1497 /usr/libexec/gvfs-goa-volume-monitor
      |-gvfs-gphoto2-volume-monitor.service
      | `-1493 /usr/libexec/gvfs-gphoto2-volume-monitor
      |-gvfs-metadata.service
      | `-1515 /usr/libexec/gvfsd-metadata
      |-gvfs-mtp-volume-monitor.service
      | `-1489 /usr/libexec/gvfs-mtp-volume-monitor
      |-gvfs-udisks2-volume-monitor.service
      | `-1484 /usr/libexec/gvfs-udisks2-volume-monitor
      |-init.scope
      | |-1017 /lib/systemd/systemd --user
      | `-1018 (sd-pam)
      `-obex.service
        `-1464 /usr/lib/bluetooth/obexd

Apr 10 18:41:21 test-ubuntu64 systemd[1017]: Stopped Indicator Application Service.
Apr 10 18:41:21 test-ubuntu64 systemd[1017]: indicator-keyboard.service: Succeeded.
Apr 10 18:41:21 test-ubuntu64 systemd[1017]: Stopped Indicator Keyboard Backend.
Apr 10 18:41:21 test-ubuntu64 systemd[1017]: Stopping Indicator Session Service...
Apr 10 18:41:21 test-ubuntu64 systemd[1017]: indicator-session.service: Succeeded.
Apr 10 18:41:21 test-ubuntu64 systemd[1017]: Stopped Indicator Session Service.
Apr 10 18:41:22 test-ubuntu64 indicator-sound[1250]: g_object_ref: assertion 'old_val > 0' failed
Apr 10 18:41:22 test-ubuntu64 systemd[1017]: pulseaudio.service: S...

Related: LP: #1877528

Also related: LP: #1877532

It's possible that all the lingering processes are due to a couple of misbehaving applications.

This isn't a great state of affairs (the cleanup process should not be so fragile that non-cooperative processes can stop it completely), but it might explain what's going on.

please reopen if this is still an issue

Yes, it is still an issue in focal. Was there an update since last year that should have addressed this?

Status changed to 'Confirmed' because the bug affects multiple users.

Confirmed that this is still an issue in focal.

It is only an issue if I log onto a XFCE session and then log out, these two processes stay around:
    /usr/libexec/geoclue-2.0/demos/agent
    /usr/bin/python3 /usr/share/system-config-printer/applet.py

When I remove the geoclue-2.0 from the system:
    sudo apt -y purge geoclue-2.0 --autoremove
The issue no longer shows up. I don't see neither processes hanging around any more.

I think those two are related to the two autostart programs:
    /etc/xdg/autostart/geoclue-demo-agent.desktop
    /etc/xdg/autostart/print-applet.desktop

I think in terms of workaround, two options here:
    1. remove geoclue - but the catch here is that if you autoremove, gnome dependencies may get removed, which could have unexpected outcome
    2. remove autostart files