After peeking at the source code (https://invent.kde.org/plasma/plasma-workspace/-/blob/822c8d9444fb29eb96f40fbe8ee337fb907c00e9/shell/outputorderwatcher.cpp#L183), my hunch is that the issue is related to unavailability of RandR on my system (because I'm forced to use xinerama).

Aha, that does makes sense. Unfortunately we do not support Xinerama, sorry.

I'm having difficulty wrapping my head around this: https://planet.kde.org/vlad-zahorodnii-2022-07-23-xinerama-becomes-hard-requirement-of-kwin/. Was Xinerama support dropped in 5.27?

Hah, that's not what I had remembered. Let me ask around and figure this out.

My mistake, it's the opposite!

But you need the randr tools installed; they can co-exist with xinerama I believe; does the issue go away when you install them?

I don't think I could install xorg-server in such a way that RandR is absent. But RandR conflicts with Xinerama, AFAIU, by definition.

$ xrandr
RandR extension missing

My Xorg.0.log has the following entries:

[   315.220] (WW) NVIDIA: Xinerama is enabled, so RandR has likely been disabled by the
[   315.220] (WW) NVIDIA:     X server.

I can disable (not-enable) Xinerama. Then RandR is present. But KDE doesn't seem to honor RandR setup: https://askubuntu.com/questions/894101/how-to-make-kde-use-a-screen-from-xrandr-1-5
I tried it a few months ago. While i3 honored the setting (https://michael.stapelberg.ch/posts/2017-12-11-dell-up3218k/#linux-compatibility--configuration), KDE ignored it. Xinerama seemed to be the only way to go.

If RandR conflicts with Xinerama, then I guess it being missing shouldn't be the problem if we require Xinerama now. Otherwise this would be broken for everyone and that's not the case.

But it does seem like that dbus call is failing and making reply a nullptr.

Created attachment 158533 [details]
Xorg.0.log

Created attachment 158534 [details]
kscreen_backend_launcher

Created attachment 158535 [details]
xorg.conf

I tried to configure virtual monitor using RandR instead of Xinerama. KDE appears to be reconfiguring the screen using RandR on startup discarding configuration from xorg.conf (see kscreen_backend_launcher and compare to Xorg.0.log).

In comparison Openbox doesn't touch the configuration and works out of box using RandR and provided configuration. If KDE could be convinced not to touch preconfigured state, maybe it would work. KScreen doesn't seem to support setting up a virtual monitor.

(In reply to Nate Graham from comment #7)
> If RandR conflicts with Xinerama, then I guess it being missing shouldn't be
> the problem if we require Xinerama now. Otherwise this would be broken for
> everyone and that's not the case.
> 
> But it does seem like that dbus call is failing and making reply a nullptr.

I think it is, for users of certain monitor types (two DP inputs required). See e.g.
- https://askubuntu.com/questions/894101/how-to-make-kde-use-a-screen-from-xrandr-1-5
- https://michael.stapelberg.ch/posts/2017-12-11-dell-up3218k/

(In reply to Maciej Poleski from comment #12)
> (In reply to Nate Graham from comment #7)
> > If RandR conflicts with Xinerama, then I guess it being missing shouldn't be
> > the problem if we require Xinerama now. Otherwise this would be broken for
> > everyone and that's not the case.
> > 
> > But it does seem like that dbus call is failing and making reply a nullptr.
> 
> I think it is, for users of certain monitor types (two DP inputs required).
> See e.g.
> -
> https://askubuntu.com/questions/894101/how-to-make-kde-use-a-screen-from-
> xrandr-1-5
> - https://michael.stapelberg.ch/posts/2017-12-11-dell-up3218k/

Another one: https://altechnative.net/linux-xorg-up2715k-t221-composite-monitor/

Created attachment 167891 [details]
crash on plasma 5

It is happening sometimes, but if you need more info let me know.

I am using xorg on a 3 monitor setup with proprietary nvidia driver.

Since youre on debian system, this might be worth it to report to debian bug tracker as well.

Relevant part from backtrace:

Thread 1 (Thread 0x7fae3173aa00 (LWP 3677)):
[KCrash Handler]
#5  X11OutputOrderWatcher::refresh (this=0x55908691ffa0) at ./shell/outputorderwatcher.cpp:188
#6  0x00007fae365062b2 in QtPrivate::QSlotObjectBase::call (a=0x7fff0a8af390, r=0x55908691ffa0, this=0x55908690cd00) at ../../include/QtCore/../../src/corelib/kernel/qobjectdefs_impl.h:398
#7  doActivate<false> (sender=0x559086910820, signal_index=3, argv=0x7fff0a8af390) at kernel/qobject.cpp:3925
#8  0x00007fae364febe7 in QMetaObject::activate (sender=<optimized out>, m=m@entry=0x7fae3676f2e0 <QTimer::staticMetaObject>, local_signal_index=local_signal_index@entry=0, argv=argv@entry=0x7fff0a8af390) at kernel/qobject.cpp:3985
#9  0x00007fae3650a2ce in QTimer::timeout (this=<optimized out>, _t1=...) at .moc/moc_qtimer.cpp:205
#10 0x00007fae364f984b in QObject::event (this=0x559086910820, e=0x7fff0a8af4e0) at kernel/qobject.cpp:1369
#11 0x00007fae37362f32 in QApplicationPrivate::notify_helper (this=<optimized out>, receiver=0x559086910820, e=0x7fff0a8af4e0) at kernel/qapplication.cpp:3640
#12 0x00007fae364cc748 in QCoreApplication::notifyInternal2 (receiver=0x559086910820, event=0x7fff0a8af4e0) at kernel/qcoreapplication.cpp:1064
#13 0x00007fae364cc922 in QCoreApplication::sendEvent (receiver=<optimized out>, event=<optimized out>) at kernel/qcoreapplication.cpp:1462
#14 0x00007fae365270c9 in QTimerInfoList::activateTimers (this=0x559086329210) at kernel/qtimerinfo_unix.cpp:643
#15 0x00007fae365279cc in timerSourceDispatch (source=<optimized out>) at kernel/qeventdispatcher_glib.cpp:183
#16 0x00007fae34f1f1f4 in g_main_dispatch (context=context@entry=0x7fae2c000ec0) at ../../../glib/gmain.c:3476
#17 0x00007fae34f22317 in g_main_context_dispatch_unlocked (context=0x7fae2c000ec0) at ../../../glib/gmain.c:4284
#18 g_main_context_iterate_unlocked (context=context@entry=0x7fae2c000ec0, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at ../../../glib/gmain.c:4349
#19 0x00007fae34f22930 in g_main_context_iteration (context=0x7fae2c000ec0, may_block=1) at ../../../glib/gmain.c:4414
#20 0x00007fae36527d4a in QEventDispatcherGlib::processEvents (this=0x559086328c40, flags=...) at kernel/qeventdispatcher_glib.cpp:423
#21 0x00007fae364cb0fb in QEventLoop::exec (this=this@entry=0x7fff0a8af720, flags=..., flags@entry=...) at ../../include/QtCore/../../src/corelib/global/qflags.h:69
#22 0x00007fae364d38a4 in QCoreApplication::exec () at ../../include/QtCore/../../src/corelib/global/qflags.h:121
#23 0x00007fae36933210 in QGuiApplication::exec () at kernel/qguiapplication.cpp:1863
#24 0x00007fae37362ea9 in QApplication::exec () at kernel/qapplication.cpp:2832
#25 0x0000559085651db4 in main (argc=<optimized out>, argv=<optimized out>) at ./shell/main.cpp:235

*** Bug 468991 has been marked as a duplicate of this bug. ***

Well as I can see it isn't a bug of the debian package but something depending on KDE itself.

On Matrix some devs said that had to check if the issue is present on Plasma 6 so I am just waiting for Debian Sid to get the plasma 6 packages to test it myself...

> On Matrix some devs said that had to check if the issue is present on Plasma 6 so I am just waiting for Debian Sid to get the plasma 6 packages to test it myself...

Thats a good idea. Hopefully it's fixed for you in Plasma 6. If you encounter it again, do keep us posted!

(Sidenote, I don't have Nvidia card so I can't really test this myself sadly)

Setting this waitingforinfo so if you encounter this bug again with Plasma 6, feel free to report here again even if it closes or make a new bug :) Thanks!

Dear Bug Submitter,

This bug has been in NEEDSINFO status with no change for at least
15 days. Please provide the requested information as soon as
possible and set the bug status as REPORTED. Due to regular bug
tracker maintenance, if the bug is still in NEEDSINFO status with
no change in 30 days the bug will be closed as RESOLVED > WORKSFORME
due to lack of needed information.

For more information about our bug triaging procedures please read the
wiki located here:
https://community.kde.org/Guidelines_and_HOWTOs/Bug_triaging

If you have already provided the requested information, please
mark the bug as REPORTED so that the KDE team knows that the bug is
ready to be confirmed.

Thank you for helping us make KDE software even better for everyone!

This bug has been in NEEDSINFO status with no change for at least
30 days. The bug is now closed as RESOLVED > WORKSFORME
due to lack of needed information.

For more information about our bug triaging procedures please read the
wiki located here:
https://community.kde.org/Guidelines_and_HOWTOs/Bug_triaging

Thank you for helping us make KDE software even better for everyone!

I am still waiting for Debian Sid to update to the latest version to check if the issue is fixed.

*** Bug 494239 has been marked as a duplicate of this bug. ***

>I am still waiting for Debian Sid to update to the latest version to check if the issue is fixed.

Ok, lets reopen it then

🐛🧹 ⚠️ This bug has been in NEEDSINFO status with no change for at least 15 days. Please provide the requested information, then set the bug status to REPORTED. If there is no change for at least 30 days, it will be automatically closed as RESOLVED WORKSFORME.

For more information about our bug triaging procedures, please read https://community.kde.org/Guidelines_and_HOWTOs/Bug_triaging.

Thank you for helping us make KDE software even better for everyone!

🐛🧹 This bug has been in NEEDSINFO status with no change for at least 30 days. Closing as RESOLVED WORKSFORME.