@Till > Robie, thanks for the investigations. I have looked into what the file /var/cache/cups/org.cups.cupsd (CUPS calls it "keepalive" file) is good for and what CUPS does with it. The file is created by the CUPS daemon cupsd when it needs to keep running, having active jobs, being in the course of a reload, having the web interface active or sharing printers, otherwise the file is removed. CUPS updates presence/no presence on start-up and shutdown of the daemon and it does exactly the same in both cases, so it can remain present after shutdown, depending on CUPS' configuration. CUPS never reads this file (or checks its presence), meaning that it is purely for advising external processes.
> So for me it looks like that there is a certain system service manager (what one usually runs as PID 1 under Linux) which checks for the presence of keepalive files and decides based on this which daemons to kill and which to keep running. Right - I believe this is launchd (under OS X). I do not know everything about systemd. Does systemd care about keepalive files? > AFAIK, no, not at all. You can configure systemd to start cupsd when a named file appears ("systemd.path"). I can't find anything documented about systemd stopping any service ever. The source that handles "systemd.path" doesn't ever appear to stop a service. Upstream appears to have configured this in their supplied systemd units, but I believe it may be unnecessary. > The CUPS upstream *.path makes cupsd being triggered by creating the file, but only if the file is not there already. What is this good for? Exactly :-) AFAICT, it serves no purpose. > Does this *.path also take down cupsd if one removes the keepalive file or is systemd supposed to do so? For me cupsd does not get stopped by that. AFAICT, removing the file isn't supposed to cause any action. Nothing should happen when the file is removed, and nothing does happen (apart from perhaps some state change within systemd, or some timing delay helping us trigger the race). > And why does shutdown of CUPS fail after removing the keepalive file (with "Job for cups.service canceled.")? As CUPS does not care about it, systemd seems to depend on it. This I'm not sure about. It may be a systemd race or bug. I pinged pitti to take a look, but he was busy. But if we definitely don't need cups.path, perhaps removing it will fix the problem (whether that's working around a bug in systemd or in the current CUPS systemd arrangements I don't know). > And what in the prerm script of the CUPS Debian package deletes the keepalive file? Nothing, AFAICT. It's only cupsd that deletes it on exit. The prerm stops cups.path, then stops cups.service. I don't know that my example above reproduces the root cause. But it does seem to reproduce a race that produces the same symptoms that seems to fit reasonably well. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1642966 Title: package cups-daemon 2.1.3-4 failed to install/upgrade: subprocess new pre-removal script returned error exit status 1 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/cups/+bug/1642966/+subscriptions -- ubuntu-bugs mailing list firstname.lastname@example.org https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs