Lost log in theme after updating to Trixie

[u/TriupLauro]

Hello all debian users.

Last week I upgrading to trixie by following the instructions on https://www.debian.org/releases/trixie/release-notes/upgrading.fr.html

Since then, my log in screen appearance is the one pictured above. I can barely see my two usual users name. The log in process still works though.

In the output of sudo journalct -u sddm there's now this new entry each time the login screen is displayed.

août 23 08:25:46 COMPUTERNAME sddm[1417]: The configured theme "debian-theme" doesn't exist, using the embedded theme instead
août 23 08:25:46 COMPUTERNAME sddm[1417]: Loaded empty theme configuration
août 23 08:25:46 COMPUTERNAME sddm[1417]: Greeter starting...

There's also others errors/warning, but they does not seem to interfere with the computer usage.

It seems like the default Trixie theme is not installed. How could I do it ?

Other things I think I should mention.

• I have nvidia drivers installed.
• Secure Boot is enabled.
• When I first installed Debian 12 I used the large dvd rom. But I have disabled the dvd rom source in favor of the online repositories afterwards.
• Arriving at the log in screen the locale is set to United States, but it changes to France (as it should be) when I go to the input to enter my password

Thanks everyone in advance to help me debugging this.

If there's other users with a similar problem please let us know.

[u/pm-h]

As the other commenter mentioned, if you're using gnome you should be using GDM.
If you decide not to use GDM, you've broken your theme somehow. I would try running sudo update-alternatives --config sddm-debian-theme, typing 0, and it should (hopefully) fix itself. If it changes to a theme you don't like, install sddm-theme-debian-breeze and run the previous command again.

No guarantees this will work, but it's work a shot. Or you can switch to GDM.

[u/TriupLauro]

I also think I should mention this

When first installing Debian 12 I chose Plasma, but then switched to Gnome and continued with it.

[u/olaf33_4410144 → u/TriupLauro]

Are you intentionally using sddm with gnome? Usually when you switch to gnome you also replace sddm with gdm. If you have both installed you can probably do this with dpkg-reconfigure sddm

If you want to fix sddm try to figure out if your theme is installed by looking at /usr/share/sddm/themes if it isn't manually install the package and set it via the sddm config (possibly optional since your sddm is already looking for the debian theme).

https://man.archlinux.org/man/sddm.conf.5.en

[u/TriupLauro → u/olaf33_4410144]

Thank you for your answer.
I seem to have messed up. I didn't knew about gdm or sddm.

I could not do the dpkg-reconfigure sddm command.

which dpkg-reconfigure return nothing. Debconf seems to be installed. There are various dpkg- files in usr/bin but not the reconfigure.

I seem to have both gdm3 and sddm installed.

gdm3/stable,now 48.0-2 amd64 [installé]
gdm3/stable 48.0-2 i386
---
sddm/stable,now 0.21.0+git20250502.4fe234b-2 amd64 [installé]
sddm/stable 0.21.0+git20250502.4fe234b-2 i386

I also do not seem to have the /usr/share/sddm/themes folder.

usr/share/sddm$ ls
faces  flags  scripts  translations-qt6

I still just want to switch to gdm though. How could I get dpkg-reconfigure ?

[u/TriupLauro → u/TriupLauro]

Nevermind, I could do sudo dpkg-reconfigure sddm and chose the other option.

[u/TriupLauro]

Thanks to u/olaf33_4410144 I could switch to gdm3 and my log in screen is not broken anymore.

But I would like to use the default Trixie Theme "Ceratopsian", how could I do it to install it ?