[Solved] Cannot start KDE/Wayland session with SDDM

awes · 2025-03-19 20:07:44

Hello!

When I try to open a KDE/Wayland session using SDDM, the screen switches to black text mode and ... that's it.
However, I can successfully:
- open X11 session via SDDM,
- open Wayland session via GDM (!!)

Any help would be much appreciated!

Using kernel 6.13.7-arch1-1
GPU: nvidia RTX 4070
nvidia-open driver: 570.124.04

I've notice an important difference between SDDM and GDM journal entries:
SDDM:

kwin_wayland[3169]: No backend specified, automatically choosing X11 because DISPLAY is set

GDM:

kwin_wayland[4498]: No backend specified, automatically choosing drm

... so it looks like SDDM can't get the correct backend, but I don't know how to specify it or how does GDM do it. I also don't know where the DISPLAY comes from. Surely I do not set it intentionally.

What I've tried:

Removal of ~/.config/kwinoutputconfig.json.

Added /etc/sddm.conf.d/10-wayland.conf:

[General]
DisplayServer=wayland
GreeterEnvironment=QT_WAYLAND_SHELL_INTEGRATION=layer-shell

[Wayland]
CompositorCommand=kwin_wayland --drm --no-lockscreen --no-global-shortcuts --locale1

Added kernel param nvidia_drm.fbdev=1 (although it's default if I'm not mistaken)
Didn't add nvidia-drm.modeset=1 since it's the default for sure:
```
cat /sys/module/nvidia_drm/parameters/modeset -> Y
```

Essential journal entries:

 
19:52:17 sddm[2809]: Greeter session started successfully
19:52:17 sddm-helper-start-wayland[2833]: Starting Wayland process "kwin_wayland --drm --no-lockscreen --no-global-shortcuts --locale1" "sddm"
19:52:17 sddm-helper-start-wayland[2833]: started succesfully "kwin_wayland --drm --no-lockscreen --no-global-shortcuts --locale1"
19:52:18 sddm-helper-start-wayland[2833]: "Accepting client connections on sockets: QList(\"wayland-0\")\n"
19:52:20 sddm-greeter-qt6[2848]: Loading theme configuration from "/usr/share/sddm/themes/breeze/theme.conf"
19:52:20 sddm-greeter-qt6[2848]: Connected to the daemon.
19:52:20 sddm[2809]: Message received from greeter: Connect
19:52:20 sddm-greeter-qt6[2848]: Loading file:///usr/share/sddm/themes/breeze/Main.qml...
19:52:28 sddm-greeter-qt6[2848]: Reading from "/usr/share/wayland-sessions/plasma.desktop"
19:52:28 sddm[2809]: Message received from greeter: Login
19:52:28 sddm[2809]: Reading from "/usr/share/wayland-sessions/plasma.desktop"
19:52:28 sddm[2809]: Session "/usr/share/wayland-sessions/plasma.desktop" selected, command: "/usr/lib/plasma-dbus-run-session-if-needed /usr/bin/startplasma-wayland" for VT 2
19:52:28 sddm-helper[3051]: [PAM] Authenticating...
19:52:28 sddm[2809]: Authentication for user  "awes"  successful
19:52:28 sddm-helper[3051]: pam_unix(sddm:session): session opened for user awes(uid=1000) by awes(uid=0)
19:52:28 sddm-greeter-qt6[2848]: eglSwapBuffers failed with 0x300d, surface: 0x0
19:52:28 sddm-helper[3051]: Starting Wayland user session: "/usr/share/sddm/scripts/wayland-session" "/usr/lib/plasma-dbus-run-session-if-needed /usr/bin/startplasma-wayland"
19:52:28 sddm[2809]: Session started true
19:52:28 sddm-helper-start-wayland[2833]: "kwin_core: Applying output config failed!\n"
19:52:28 sddm-helper-start-wayland[2833]: wayland greeter finished 0 QProcess::NormalExit
19:52:28 sddm-helper-start-wayland[2833]: quitting helper-start-wayland
19:52:28 sddm-helper-start-wayland[2833]: Stopping... "kwin_wayland"
19:52:28 sddm-helper-start-wayland[2833]: "QThreadStorage: Thread 0x57eba0983e10 exited after QThreadStorage 7 destroyed\n"
19:52:28 sddm-helper-start-wayland[2833]: wayland compositor finished 15 QProcess::NormalExit
19:52:28 sddm-helper-start-wayland[2833]: quitting helper-start-wayland
19:52:28 sddm-helper[2819]: [PAM] Closing session
19:52:28 kwin_wayland[3154]: No backend specified, automatically choosing X11 because DISPLAY is set
19:52:28 sddm[2809]: Auth: sddm-helper exited successfully
19:52:28 sddm[2809]: Greeter stopped. SDDM::Auth::HELPER_SUCCESS
--- black screen ---

Additional logs:

full journal from the boot: http://0x0.st/81AY.txt
eglinfo: http://0x0.st/81Ag.txt
glxinfo: http://0x0.st/81AE.txt
nvidia-smi: http://0x0.st/81A6.txt

Installed packages, that might be relevant:

egl-wayland 4:1.1.18-1
kwayland 6.3.3-1
layer-shell-qt 6.3.3-1
plasma-desktop 6.3.3-1
plasma-wayland-protocols 1.16.0-1
sddm 0.21.0-6
sddm-kcm 6.3.3-1
wayland 1.23.1-1
xorg-xwayland 24.1.6-1

Thanks!

Last edited by awes (2025-03-20 08:11:56)

WorMzy · 2025-03-19 20:56:32

Mod note: moving to Apps/DEs, on request.

seth · 2025-03-19 21:36:56

GDM runs on wayland by default, SDDM on X11 - I guess kwin gets the DISPLAY from there.
https://wiki.archlinux.org/title/SDDM#Wayland

Otherwie try "kwin_wayland --drm"

awes · 2025-03-20 06:24:09

I've found source of the problem and it's really stupid. I had DISPLAY set in .bashrc. I must have added it years ago (for some reason) and I always copy this file to the new system installed.
After removing - SDDM successfully starts KDE/Wayland session.
It's still unclear why DISPLAY doesn't affect GDM, but it doesn't matter anymore.
Thanks.

Last edited by awes (2025-03-20 08:11:38)

seth · 2025-03-20 08:48:03

Yes, sorry. And according to the journal this is also fully applied.
So there's no reason for any DISPLAY to be around, did you set it in /etc/profile* or some shell RC (~/.bashrc) and forgot about it?

Arch Linux

#1 2025-03-19 20:07:44

[Solved] Cannot start KDE/Wayland session with SDDM

#2 2025-03-19 20:56:32

Re: [Solved] Cannot start KDE/Wayland session with SDDM

#3 2025-03-19 21:36:56

Re: [Solved] Cannot start KDE/Wayland session with SDDM

#4 2025-03-20 06:24:09

Re: [Solved] Cannot start KDE/Wayland session with SDDM

#5 2025-03-20 08:48:03

Re: [Solved] Cannot start KDE/Wayland session with SDDM

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