[Bug 1877528] Re: Applet does not terminate at end of X desktop session

[Daniel Richard G.]

Aaaand the upstream has decided they can't/won't fix this issue.

One thing that bothers me about this whole situation is that, in order
for background services like this one to be cleaned up after logout,
they need to behave "correctly." From my point of view, this is
backwards.

When the system is preparing to reboot, it first sends SIGTERM to all
user processes, waits a few seconds, and then sends SIGKILL. Processes
that behave correctly are allowed to close down cleanly, and those that
don't, are terminated forcibly. If you didn't have that SIGKILL part,
then one badly-behaving process could delay the reboot indefinitely. By
doing things this way, good behavior is rewarded, but not required.

Something like that should be the case for user sessions, although there
are exceptions (screen, tmux, nohup), and SIGKILL might be excessive.
The upstream bug mentioned a few other processes that remained visible
under session-status, and I myself have seen similar behavior from at-
spi2-core (haven't determined yet if a bug report is in order for that
one).

We're going to be fighting a losing battle if every single desktop
background service in Ubuntu has to do things correctly in order to
avoid keeping the session open after logout. There needs to be a
failsafe of some kind.

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https://bugs.launchpad.net/bugs/1877528

Title:
  Applet does not terminate at end of X desktop session

Status in System Config Printer:
  New
Status in lightdm package in Ubuntu:
  New
Status in sddm package in Ubuntu:
  New
Status in system-config-printer package in Ubuntu:
  Triaged
Status in systemd package in Ubuntu:
  Invalid
Status in system-config-printer package in Debian:
  Unknown

Bug description:
  This concerns system-config-printer 1.5.12-0ubuntu1 in Ubuntu focal.

  I log into the Xfce desktop, and then logout. The screen returns to
  the LightDM login screen.

  A few minutes later, "loginctl list-sessions" shows the following:

      SESSION  UID USER    SEAT  TTY  
            9    0 root               
           c2 1000 skunk   seat0      
           c3  116 lightdm seat0      

      3 sessions listed.

  Output from "loginctl session-status c2":

      c2 - skunk (1000)
                 Since: Fri 2020-05-08 03:09:05 EDT; 9min ago
                Leader: 2530
                  Seat: seat0; vc7
               Display: :0
               Service: lightdm; type x11; class user
               Desktop: xubuntu
                 State: closing
                  Unit: session-c2.scope
                        └─2856 /usr/bin/python3 /usr/share/system-config-printer/applet.py

  This process sticks around forever until I kill it, or its parent
  "systemd --user" process. Only then does the session disappear from
  list-sessions.

  When I run "session-status" while I'm logged in, I see a list of
  nearly 30 desktop-related processes. All of them except this one go
  away on logout. This one should too.

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