SDDM not starting if usb mouse connected

Bazzite
1

I’ve just replaced my mouse with a wireless usb dongle mouse, and now 9 times out of ten when starting my laptop, I get a black screen when SDDM normally shows the login gui. unplugging the mouse and restarting, then reconnecting the mouse after logging in works ok.
When the black screen occurs I can switch to another tty, and run sudo service sddm restart, and the login screen appears.
It seems to be related to the Black screen since latest update

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Black screen since latest update
2

I started the Black screen since latest update topic and still experience the issue.

I’m using a Logitech wireless mouse and keyboard combo. I just tested this by removing the logi bolt receiver from my PC before booting and it worked! I’m puzzled. Wondering what to do with this new information haha

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3

I found a possible fix SDDM display manager fails to start · Issue #3376 · ublue-os/bazzite · GitHub
but I was unsure to try in case it breaks something now or later on.

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4

Workaround (not a definitive fix): Random SDDM black screen – forcing X11 greeter

Note: I’m not claiming this is the root cause or the “official” solution.
This is simply a workaround that has been reliable for me.

Symptoms

  • Random black screen instead of SDDM login screen

  • Happens intermittently (often when USB mouse/keyboard is connected at boot)

  • Switching to a TTY and running systemctl restart sddm makes the login screen appear

  • Plasma Wayland works normally once logged in

Environment

  • Bazzite / Universal Blue

  • KDE Plasma

  • SDDM

  • Wayland sessions enabled

What worked for me (workaround)

I forced X11 only for the SDDM login screen, while keeping Wayland for Plasma sessions.

From a TTY or terminal:

sudo nano /etc/sddm.conf.d/20-x11-greeter.conf

Add:

[General]
DisplayServer=x11

Save the file, then restart SDDM:

sudo systemctl restart sddm

(or reboot)

Result (in my case)

  • SDDM login screen became stable

  • No more random black screens

  • USB devices no longer affected login

  • Plasma Wayland sessions continued to work normally

Notes

  • This does not disable Wayland system-wide

  • Only the SDDM greeter runs on X11

  • This seems to avoid a race condition between the SDDM Wayland greeter and USB/input initialization

How to undo

sudo rm /etc/sddm.conf.d/20-x11-greeter.conf
sudo systemctl restart sddm

Again, this may not apply to everyone, but it’s been a solid workaround for me so far.

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Black screen since latest update
5

Thank you for sharing this link. I followed this comment SDDM display manager fails to start · Issue #3376 · ublue-os/bazzite · GitHub and the issue is finally resolved.

Black screen since latest update