You can use debuginfo to get debug symbols for powerdevil. Please do so and then attach a backtrace that shows the crashing thread.

The backtrace was sloppy the first time because I had built the package from AUR with `!debug` and `strip` enabled by default. I updated it to the latest powerdevil and built it with debug symbols this time. systemd-coredumpd does not seem to catch the backtrace again, but I'll give it another shot.

I simplified the crash to a much simpler case. powerdevil crashes and aborts on logging out. Here's the rough timeline. Logs attached at the end.

1. Cold boot
2. Log in: SDDM is still on X11 because wayland does not work for me
3. Log out: no errors related to powerdevil until this point

org_kde_powerdevil[1136]: The Wayland connection broke. Did the Wayland compositor die?
systemd[890]: Starting Powerdevil...
systemd[890]: plasma-powerdevil.service: Scheduled restart job, restart counter is at 1.
org_kde_powerdevil[1596]: Failed to create wl_display (No such file or directory)
org_kde_powerdevil[1596]: This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem. Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-glx, xcb.
org_kde_powerdevil[1596]: qt.qpa.plugin: Could not load the Qt platform plugin "wayland" in "" even though it was found.
systemd[890]: Failed to start Powerdevil.
systemd[890]: plasma-powerdevil.service: Failed with result 'core-dump'.
systemd[890]: plasma-powerdevil.service: Main process exited, code=dumped, status=6/ABRT

Note: A lot of other kde services such as kdeconnectd, krunner, kactivitymanagerd, plasmashell, kwalletd5, kded5 die with similar error message. plasmashell produces a core dump when systemd tries to restart it: `plasma-plasmashell.service: Scheduled restart job, restart counter is at 1.`

To summarize, can we reduce the scope of this bug to finding the reason why services automatically start after a logout?

https://bbs.archlinux.org/viewtopic.php?id=263885 appears related

> This is what journalctl reports (option -p 3) about the time of the attempted logout. <snip>
> Lots of KDE related task notifying the end of the Wayland connection, some several times
> and lots of coredumps of KDE related tasks ...

The full backtrace using debuginfod. `bt full` did not add anything useful so I am posting the short version `bt`

#0  __pthread_kill_implementation (threadid=<optimized out>, signo=signo@entry=6, no_tid=no_tid@entry=0) at pthread_kill.c:44
#1  0x00007fa4cf28e8a3 in __pthread_kill_internal (signo=6, threadid=<optimized out>) at pthread_kill.c:78
#2  0x00007fa4cf23e668 in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26
#3  0x00007fa4cf2264b8 in __GI_abort () at abort.c:79
#4  0x00007fa4cfaa0098 in qt_message_fatal (message=<synthetic pointer>..., context=<optimized out>) at global/qlogging.cpp:1919
#5  QMessageLogger::fatal(char const*, ...) const (this=this@entry=0x7ffecd96d6c0, msg=msg@entry=0x7fa4d05737de "%s") at global/qlogging.cpp:898
#6  0x00007fa4d013f3f2 in init_platform (argv=<optimized out>, argc=@0x7ffecd96d90c: 1, platformThemeName=..., platformPluginPath=..., pluginNamesWithArguments=...) at kernel/qguiapplication.cpp:1254
#7  QGuiApplicationPrivate::createPlatformIntegration() (this=0x5588235f0b90) at kernel/qguiapplication.cpp:1484
#8  0x00007fa4d013fa69 in QGuiApplicationPrivate::createEventDispatcher() (this=<optimized out>) at kernel/qguiapplication.cpp:1501
#9  0x00007fa4cfc9c195 in QCoreApplicationPrivate::init() (this=this@entry=0x5588235f0b90) at kernel/qcoreapplication.cpp:835
#10 0x00007fa4d013fb16 in QGuiApplicationPrivate::init() (this=0x5588235f0b90) at kernel/qguiapplication.cpp:1530
#11 0x00007fa4d014084c in QGuiApplication::QGuiApplication(int&, char**, int) (this=this@entry=0x7ffecd96d940, argc=@0x7ffecd96d90c: 1, argv=0x7ffecd96dac8, flags=flags@entry=331530, this=<optimized out>, argc=<optimized out>, argv=<optimized out>, flags=<optimized out>)
    at ../../include/QtGui/../../src/gui/kernel/qguiapplication.h:203
#12 0x0000558821d420a5 in PowerDevilApp::PowerDevilApp(int&, char**) (argv=<optimized out>, argc=@0x7ffecd96d90c: 1, this=0x7ffecd96d940) at /usr/src/debug/powerdevil-ddcutil/powerdevil-5.27.7/daemon/powerdevilapp.cpp:48
#13 main(int, char**) (argc=<optimized out>, argv=<optimized out>) at /usr/src/debug/powerdevil-ddcutil/powerdevil-5.27.7/daemon/powerdevilapp.cpp:155

> #6  0x00007fa4d013f3f2 in init_platform (argv=<optimized out>, argc=@0x7ffecd96d90c: 1, platformThemeName=..., platformPluginPath=..., pluginNamesWithArguments=...) at kernel/qguiapplication.cpp:1254
> #7  QGuiApplicationPrivate::createPlatformIntegration() (this=0x5588235f0b90) at kernel/qguiapplication.cpp:1484

This means there is some kind of subtle misconfiguration on your system. Given that you're using an AUR package, I suspect it's not built correctly. The next step would be to report this to the author of that package.

> This means there is some kind of subtle misconfiguration on your system. Given that you're using an AUR package, I suspect it's not built correctly. The next step would be to report this to the author of that package.

I agree that this is a misconfiguration somewhere, as indicated by the journal as well - "org_kde_powerdevil[1136]: The Wayland connection broke. Did the Wayland compositor die?". In my understanding, plasma uses systemd user units to start powerdevil. When I log out, plasma does not "tell" systemd that powerdevil need not be restarted?

There is nothing noteworthy in my PKGBUILD: `cmake -B build -S $_pkgname-$pkgver -DCMAKE_INSTALL_LIBEXECDIR=lib -DBUILD_TESTING=OFF -DHAVE_DDCUTIL=On`. Upstream does not package ddcutil but I require it. That's why I use the AUR package. I now see DDCUTIL is turned on in the upstream package as well, so I am going to try it next.

We can't offer more support for this issue, sorry.

That's okay, I understand. Since the systemd unit files are provided by KDE and not arch, where do you suggest I open another issue about plasma's interaction with systemd? The file in question `plasma-powerdevil.service` is indeed owned by powerdevil: https://invent.kde.org/plasma/powerdevil/-/blob/master/daemon/plasma-powerdevil.service.in; If this service does not terminate properly when wayland dies, then would you consider it a bug in powerdevil?

So on Wayland, it's currently expected that when the compositor dies and the wayland socket is severed, everything dies. So Powerdevil is not unique there. Not ideal, but not worse than anything else.

In Plasma 6 with Qt 6.6 however, it's another story: all Qt-based software should survive and not die or crash. Very cool.

So if you're using 5.27.7, I'd say the dies-when-the-compositor-crashes behavior you're seeing is expected, so there's no need for a bug report. If you still see it happening in Plasma 6 with Qt 6.6 though, that wold be worth a bug report.

Got it. Thank you for the explanation! Looking forward to plasma 6 :)

You're welcome!