[System] Title Bars on Windows Disappear at Random Times

[SilverFox41]

I'm having a problem that occurs at random, mostly when I start a full screen application but sometimes when starting windowed applications too. The title bars of all of the windows disappear, and then the keyboard can no longer switch between applications. I can still click on the start menu at the bottom to reboot the system though, which is the only way I've found to get my system working again after this happens. Any ideas on how to fix this?
Kubuntu 18.04
KDE Plasma version 5.12.7
KDE Framework version 5.44.0
Qt version 5.9.5
CPU i5 4690K
Ram 16Gb DDR3
I also have a 500Mb EFI partition mounted at /boot.

[oshunluvr]

Sounds like a kwin crash. Next time it happens, try typing ALT-F2 and in the dialog box at the top of your screen enter:

kquitapp5 plasmashell && kstart5 plasmashell

This should restart your desktop without having to reboot.

It's impossible to troubleshoot this with so little info. How full is RAM when it happens? How busy is your CPU? Are there any log messages?

You can start by disabling various desktop effects you may have enabled in System Settings > Desktop Behavior > Desktop Effects.

[claydoh]

It sounds like Kwin, the window manager part of Plasma has crashed, instead of Plasmashell, possibly. Plasmashell would take the panel with it if it went south.

Using the alt-f2 as Oshunluvr mentions, enter "kwin_x11 --replace" to restart it.

Are you by any chance using any custom window decorations? That is another area that have an effect.

[SilverFox41]

In reply to oshunluvr, where would the log messages be located at? I'll make sure I do everything you suggested to try and prevent it from happening again.

[oshunluvr]

In reply to oshunluvr, where would the log messages be located at? I'll make sure I do everything you suggested to try and prevent it from happening again.

There's a couple potential places. Logs are located in /var/log. There's a GUI program available called KSystemLog that will allow you to read log files from the desktop.

The most common first place to check is to use a terminal (Konsole) and enter the one word command: dmesg

This will print out the highlights of what's happening in the system. Here's what I'd do:

Boot up and open Konsole immediately.
In Konsole, type dmesg ENTER and note the last few lines of output.
Leave Konsole open and do whatever you would normally do.
When shenanigans begin, go back to the Konsole window, refresh your memory of what's there, and run dmesg again. Take note of what is new in the output.
Then enter free and see how much memory is being used.
Then enter top and see what process(s) are using your CPU

Then come back here and report what you find.

This (kwin or aka plasmashell) kind of crash usually is some mis-configured or buggy desktop effect or a graphic issue. The place to look at graphical errors is ~/.xsession-errors and /var/log/Xorg.0.log

[SilverFox41]

It sounds like Kwin, the window manager part of Plasma has crashed, instead of Plasmashell, possibly. Plasmashell would take the panel with it if it went south.

Using the alt-f2 as Oshunluvr mentions, enter "kwin_x11 --replace" to restart it.

Are you by any chance using any custom window decorations? That is another area that have an effect.

I'm not using any custom window decorations. It's all stock.

[WWDERW]

Could also enable ctrl+alt+backspace to kill and restart X when that happens without having to do a re-boot.

I actually would suggest disabling kwin. Loose some eye-candy, but KDE became a lot more stable when I did that. I too wasn't running any specialty effects either, but it was crashing 4 times a week and that was just too much.

[claydoh]

Could also enable ctrl+alt+backspace to kill and restart X when that happens without having to do a re-boot.

I actually would suggest disabling kwin. Loose some eye-candy, but KDE became a lot more stable when I did that. I too wasn't running any specialty effects either, but it was crashing 4 times a week and that was just too much.

You disable kwin, you get no window management at all, or window decorations, or alt-tab, etc.

[SilverFox41]

You disable kwin, you get no window management at all, or window decorations, or alt-tab, etc.

I use alt+tab frequently, so this would be far from ideal.

[WWDERW]

Evidently what all kwin provides, I'm not missing. If I was missing it and I had to have kwin enabled, I would be on something else as it was far from stable on my setup and since it is my main production rig, spending time troubleshooting is far from ideal. Which would suck, because I prefer KDE to other DEs out there.

[SilverFox41]

It happened again. Here's what the dmesg output was after the crash https://pastebin.com/PMsQ40UC, and here's what the dmesg output was from a fresh reboot https://pastebin.com/dsDQHNjM.

I don't know what it is I should be looking for on these, so could someone take a look, and show me what they think the problem is? Sadly, I forgot to check RAM and CPU usage when this happened so I don't have that information. If it happens again, I'll make sure I check it.