KDE plasma 6 fail to lock after updating

Ask Fedora
, ,
1

Hi, I’m having with screen locking after updating on my Fedora 42 laptop. Here’re details about my machine:

  • OS: Fedora Linux 42 (KDE Plasma Desktop Edition) x86_64
  • Bootmgr: Fedora - shimx64.efi
  • Kernel: Linux 6.15.3-200.fc42.x86_64
  • Init System: systemd 257.6-1.fc42
  • LM: sddm 0.21.0 (Wayland)
  • DE: KDE Plasma 6.4.1

I was following this guide https://unix.stackexchange.com/questions/721343/how-to-fix-broken-kde-screen-locker, the output from /usr/libexec/kscreenlocker_greet --testing is:

Locked at 1751125159
qml: The backend got an unknown wallpaper provider type. The wallpaper will now fall back to the default. Please check your wallpaper configuration!
org.kde.plasma.libtaskmanager: The PlasmaWindowManagement protocol hasn't activated in time. The client possibly got denied by kwin? Check kwin output.
file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/lockscreen/LockOsd.qml:10:1: "../osd": no such directory
Segmentation fault (core dumped)

I tried to search for this problem but nothing came up.
Thank you in advance :folded_hands:

1 Like
2

I am so sorry for wasting your time. I found a fix to this problem here KDE Plasma 6.4 and Screen Locker error | oakleys.org.uk. Apparently, just simply changing theme fix the issue.

2 Likes
3

Thanks for the link!

I found that:

  • Changing the theme Breeze apparently fixed the issue
  • When I changed back to Fedora, I got the same issue again
  • However, if I change the lock screen wallpaper, then at first it seemed like the Fedora theme worked without problems, but later the same thing appeared again.

From what I’m seeing in my logs, it looks like this KDE bug: 506316 – Locked screen cannot be unlocked

The package I’m most suspicious of is qt6-qtwayland (6.9.1-2) because:

  • In the last update transaction I did on the affected system, that was the only package that seems at all related to the desktop environment. No Plasma packages were upgraded.
  • I have another system where I haven’t yet upgraded that package, and I’m not seeing the lock screen issue there.

Update: Downgrading qt6-qtwayland to 6.9.1-1 appears to fix the issue.

1 Like
4

Yeah, the bug reports exactly what I got as well.
And for the fix, I didnt get any issue from changing the lock screen wallpaper, but maybe it’ll cause issue after a few reboot.
For the fedora theme, I haven’t tried it, I’ll prob just delete that theme and stick to breeze for now, thanks for sharing

1 Like
5

Hi, it’s my blog post. Glad it helped. Before I applied Breeze, I was getting the screen locker error every time I locked the session. The fact that I managed to lock the session without fault led me to believe I’d solved the problem. Sadly, it still happens, now sometimes.

I then tried changing the lockscreen wallpaper, but that also seems a red-herring.

Prompted by @pg-tips post above, I’ve just downgraded qt6-qtwayland. Because the problem is now intermittent, I need to give it some time to see if this has solved the problem. I’m keeping the blog post updated.

1 Like
6

Interesting, that’s the situation I was also in before downgrading.

1 Like
7

Is there a bug filed against qt6-qtwayland? I’ve not found one, but that doesn’t mean it’s not there.

8

Yep: https://bugzilla.redhat.com/show_bug.cgi?id=2375356

A 6.9.1-3 (which backs out the patch in 6.9.1-2 so should be binary identical to 6.9.1-1) is in the process of being tested for release: FEDORA-2025-6842ac8bfa — bugfix update for qt6-qtwayland — Fedora Updates System

See also this thread: KDE Plasma users - beware of new qt6-qtwayland version 6.9.1-2 (breaks lockscreen, may cause app crashes)

1 Like