I lately ran into a problem where my system would greet me with black screens (I use three monitors and a GTX 970 with proprietary drivers) and fully functional cursor as soon if I wake it up from suspend.

When I tried to start a console session with "Alt+F3" and entered

Code: Select all

kquitapp5 plasmashell && kstart5 plasmashell

to restart my plasmashell my system informed firstly that "xcb" had an error and couldn't detect a display and then after reinstalling "xcb" that the command "plasmashell" did not exist.

This error with the black screens happens several times per day and can only be fixed by rebooting. I've never had such issues with KDE so I suspect one of the latest updates could be the culprit.

Does anyone know where to look for the issue and possibly how to fix it?

Same here - drives me crazy.
Something else I (think) noticed is that if you put the machine to sleep and then wake it up almost immediately, it comes back fine. But if you leave it for over 10 mins - blank screen.
Curiously, I have another system on another disk on the same machine - and at the same level, but in that case the screens return (mostly) but the network cannot be started - even by swearing at it.

Any feedback on this issue?
It is a dealbreaker for me - I'll probably have to move to something else very soon - and that's from being a KDE user in one form or another for many years.
Pity.

Both of you: which distribution, which exact Plasma version?

@Mamarok

Distribution: KDE neon 5.19 User Edition
KDE-Plasma-Version: 5.19.5
KDE-Frameworks-Version: 5.74.0
Qt-Version: 5.15.0
Kernel-Version: 5.4.0-48-generic (64-bit)

I was subscribed to this thread because I have the same issue but I'll add another data point:

Operating System: KDE neon Testing Edition
KDE Plasma Version: 5.19.90
KDE Frameworks Version: 5.75.0
Qt Version: 5.15.0
Kernel Version: 5.4.0-48-generic

Another datapoint same issues as OP. Disto is Manjaro. This happens after user logout/new user login or sometimes after long screenlock times. Cursor and yakuake still work, but nothing else does. Weird in that you can issue systemctl -shutdown -i from yakuake, and the shutdown starts but will then hang. From that point, only a magic sysreq will work.

Operating System: Manjaro Linux
KDE Plasma Version: 5.19.5
KDE Frameworks Version: 5.74.0
Qt Version: 5.15.1
Kernel Version: 5.8.11-1-MANJARO
OS Type: 64-bit
Processors: 4 × AMD A6-3620 APU with Radeon(tm) HD Graphics
Memory: 7.3 GiB of RAM
Graphics Processor: AMD SUMO

If it will help, here are journal items that may be related:
10/7/20 10:57 AM kglobalaccel5 qt.qpa.xcb: could not connect to display :0
10/7/20 10:57 AM kglobalaccel5 This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: wayland-org.kde.kwin.qpa, eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-glx, xcb.
10/7/20 10:57 AM systemd-coredump Process 13055 (kglobalaccel5) of user 1001 dumped core.

Stack trace of thread 13055:
#0 0x00007f482bc00615 raise (libc.so.6 + 0x3d615)
#1 0x00007f482bbe9862 abort (libc.so.6 + 0x26862)
#2 0x00007f482bffb9ac _ZNK14QMessageLogger5fatalEPKcz (libQt5Core.so.5 + 0x909ac)
#3 0x00007f482c5ee666 _ZN22QGuiApplicationPrivate25createPlatformIntegrationEv (libQt5Gui.so.5 + 0x131666)
#4 0x00007f482c5eeb01 _ZN22QGuiApplicationPrivate21createEventDispatcherEv (libQt5Gui.so.5 + 0x131b01)
#5 0x00007f482c225936 _ZN23QCoreApplicationPrivate4initEv (libQt5Core.so.5 + 0x2ba936)
#6 0x00007f482c5f1b40 _ZN22QGuiApplicationPrivate4initEv (libQt5Gui.so.5 + 0x134b40)
#7 0x00007f482c5f2aa8 _ZN15QGuiApplicationC1ERiPPci (libQt5Gui.so.5 + 0x135aa8)
#8 0x000056014792b08f n/a (kglobalaccel5 + 0x208f)
#9 0x00007f482bbeb152 __libc_start_main (libc.so.6 + 0x28152)
#10 0x000056014792b3fe n/a (kglobalaccel5 + 0x23fe)

10/7/20 10:57 AM sddm-greeter QObject: Cannot create children for a parent that is in a different thread.
(Parent is QGuiApplication(0x7ffe65fedb40), parent's thread is QThread(0x55d911c84e80), current thread is QThread(0x55d911e1ed30)

hello i have same issue
it happens some times after i unlock the pc

OS: Manjaro Linux x86_64
Kernel: 5.4.74-1-MANJARO
Resolution: 1920x1080, 1920x1080
DE: Plasma 5.20.2

I'm having similar issue on Arch with latest KDE Plasma. My main issue is when I resume from suspend, with a Thunderbolt dock connected while sleeping (ie coming from home to office), I can see the cursor and I can switch to a different terminal (ie to reboot), but there's no KDE UI, no plasmashell, no right click, I can't do anything. The only way out is to reboot.

I've got the same issue with KDE Neon.

KDE Plasma : 5.21.0
Graphic card : GeForce GTX 970
KDE Framework : 5.79.0

It's better for me after manually update the linux kernel to 5.8.
However, I need to press Ctrl + Alt + F1 to return to my desktop.
Have you got an idea to fix it ?

Robiocop wrote:It's better for me after manually update the linux kernel to 5.8.
However, I need to press Ctrl + Alt + F1 to return to my desktop.
Have you got an idea to fix it ?

I also have this issue on Arch linux.