Bug 485269

Summary: 'Unify output' using the OSD or widget leaves the system with no display output
Product: [Plasma] plasmashell Reporter: Matthias <shalokshalom>
Component: Display Configuration widget and OSDAssignee: Plasma Bugs List <plasma-bugs-null>
Status: RESOLVED WORKSFORME    
Severity: major CC: nate
Priority: NOR Keywords: multiscreen
Version First Reported In: 6.0.3   
Target Milestone: 1.0   
Platform: Other   
OS: Linux   
Latest Commit: Version Fixed In:
Sentry Crash Report:

Description Matthias 2024-04-09 11:44:35 UTC 
SUMMARY
I had a TV connected to my laptop, and chose only it as the shown output. Then I hit Fn +  F7 to open the screen layout widget, and chose "Unify output". 

The result was a black screen on both the laptop and the TV. Removing the cable connection, was not restoring the display output on the laptop. Rebooting booted straight into a black screen as well.

I booted into my second installation (first is KaOS, second NixOS) and tried the same thing there again, with the same outcome. 

This has to be due to a recent change, as I use both systems on a rolling release, and had used that feature in the past with the same hardware, and no such issue occurred. 

In this case, no user error was involved. Still, I managed to reach a similar bad state (with only the TV being inaccessible) with a bad configuration, that involved me confirming a display resolution for the TV as valid, that wasnt. 

In both cases, the simple usage of a multi monitor setup meant partly, or complete loss of display functionality. 

To make matters worse, kscreen is not a declarative file anymore. I think that is a very big mistake, and I strongly suggest to restore that functionality. Today, it seems that the entire display configuration is created by a binary, that then creates a yaml file. That one cannot be edited and reloaded. This goes against the UNIX philosophy and makes it very hard to restore from such a case. I would need to do dark magic, or have a rollback feature on filesystem level enabled, to recover from this. 

I thought about several mechanisms to prevent such issues. 

1) Ask if the configuration is fine for the 'Screen Layout' widget as well. 
At least when the configuration involves new settings. Maybe when the API and/or hardware changes. 

2.) Implement a shortcut, that resets the configuration to its default state. 

3.) Implement such a button to reset the configuration in the KScreen KCM.
This could have helped with the second case, where only the external display was inaccessible.

I put this on major, and think it could be ranked more severe even. 


STEPS TO REPRODUCE
1. 
2. 
3. 

OBSERVED RESULT


EXPECTED RESULT


SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION
Comment 1 Nate Graham 2024-04-09 14:57:31 UTC 
Sorry to hear this happened.

You're definitely right about needing a reset timer for changes made by the OSD and widget. Can you submit a second bug report asking for that so it can be tracked separately?

About this issue, if you use the KScreen KCM in System Settings to unify the outputs by dragging one on top of another so one is centered on the other one, does the issue still happen?
Comment 2 Nate Graham 2024-04-09 20:16:05 UTC 
I just noticed Bug 484592 that you also opened earlier; how does this differ from it?
Comment 3 Matthias 2024-04-09 21:37:13 UTC 
I have no idea, what caused this error. The error in 484592 is known and reproducible. 
This error also disables the main laptop screen, and renders the entire installation of the OS essentially inaccessible. 
The error in 484592 only renders the specific external device unusable.
Comment 4 Matthias 2024-04-10 12:41:35 UTC 
So, I just got this issue on Arch as well. 
Makes three independent distributions.

This is definitely due to a recent update.
I did this on a LG E9. Who knows, how many devices could possibly also effected.

3 Installations rendered unusable. 
I need another way of bugtracking this 😅
Comment 5 Matthias 2024-04-10 13:55:31 UTC 
So, I could reproduce this now on the Garuda and KaOS live ISOs. Both show again the same behavior: 

Wayland sessions get every time into a black screen on both the laptop and the TV. 
I tried it as well on X11, and both Garuda and KaOS show the same behavior as well.
In this case, the OSD disappears, but no change is applied, and that counts for all options of the OSD. 

With Wayland, only the Unify button misbehaves, in X11 all of them show no effect at all. 
I should mention, that with both, Wayland and X11, I get an extended to the side view, when I start the live mode with the TV attached. 
That one works perfectly.
Comment 6 Nate Graham 2025-05-22 19:00:24 UTC 
A lot of things have changed in Plasma 6; is anyone still able to experience this in a Wayland session in Plasma 6.3.5 or later? Thanks a lot!
Comment 7 Nate Graham 2025-05-22 19:01:04 UTC 
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Comment 8 Bug Janitor Service 2025-06-06 03:48:07 UTC 
🐛🧹 ⚠️ 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!
Comment 9 Bug Janitor Service 2025-06-21 03:47:40 UTC 
🐛🧹 This bug has been in NEEDSINFO status with no change for at least 30 days. Closing as RESOLVED WORKSFORME.