I guess KDE means using SDDM. Would this help ? https://wiki.archlinux.org/title/SDDM#Login_session_appears_on_an_unexpected_display
this post was submitted on 15 Jun 2024
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(Edited for clarity) This was interesting. It gave me arandr to generate a script which is great for lazy me. That script "works" in that it doesn't give any errors when I test it, but it actually doesn't have any effect on the login screen. In fact with more digging i discovered that xrandr just doesn't work at all. I tried setting the display to a lower resolution (default is 3440x1440 so I used 1920x1080) in the control panel to test the xrandr command but xrandr tells me the mode (3440x1440) is not found. I looked again in xrandr and saw that any resolution higher 1920x1080 is not listed any more. I reset the resolution back to 3440x1440 in the control panel then looked in xrandr again and all the expected resolutions are listed again.
xrandr errors when I try to set my display to anything other than the setting it is currently using. Either I'm don't something stupid with the syntax (99.999% confident I'm doing it right), or xrandr is broken with my setup. Maybe kde plasma 6 and wayland is giving me grief here? My PC has an AMD 7900XT GPU, so maybe it just doesn't like my GPU for some reason.
Here is the output from xrandr for my current settings:
DP-1 connected primary 3440x1440+0+1080 (normal left inverted right x axis y axis) 800mm x 330mm
HDMI-A-1 connected 1920x1080+758+0 (normal left inverted right x axis y axis) 520mm x 290mm
Here are the commands I'm using in the Xsetup script.
xrandr --output HDMI-A-1 --mode 1920x1080 --pos 758x0 --rotate normal
xrandr --output DP-1 --primary --mode 3440x1440 --pos 0x1080 --rotate normal
xrandr is Xorg only, it doesn't work with Wayland. You should be able to make SDDM use your Plasma display configuration - https://wiki.archlinux.org/title/SDDM#Match_Plasma_display_configuration
No clue if that's going to fix your issues, but at least it's supposed to work with Wayland.
Ok that explains it. I tried applying the plasma config earlier. Didn't fix.
I think I've read somewhere that xrandr only works with Xorg and not with Wayland.
I have almost the exact same setup, but just say “meh”, type my password blindly while looking at my main screen and press Enter, and after login it’s arranged as it should be.
Yeah, it’s an issue, but it’s a non-issue
Yeah that's where I'm at as well. Irritating not world ending.
I know it's bad form to suggest using other software that handles the same functionality instead of suggesting a fix, but it looks like sddm doesn't have the functionality to change displays at the time of writing.
GDM seems to have a workaround
But it looks like every display manager chooses whichever display based on arbitrary criteria.
Have a look at /etc/sddm.conf
It is blank right now. I'm looking at xrandr right now, but a basic check into sddm.conf suggests I can't set resolution in there, but can't call scripts. Might come back to this though.
Do you have a /etc/sddm.conf.d/ then? You need to have an SDDM config XD
But for sure may ne that you cant set it there.
Fedora uses SDDM on Plasma 6 with Wayland now, not sure if EndeavorOS does too. So no xrandr