This problem can be only from two sources, in this case:
- Incorrect settings in Display manager (unlikely)
- Kernel-Display driver conflict that got accentuated when the new resolution was set.
(1). To test the first, I deleted lightdm from Qubes, which deleted these specific packages (~2MB) in dom0 user shell via tty.
$sudo systemctl -n999 status lightdm
$sudo systemctl stop lightdm.service
$sudo systemctl disable lightdm.service
$sudo dnf remove lightdm
Package
lightdm-1.30.0-9.fc32.x86_64
Dependent Package
lightdm-gtk-2.0.7-1.fc32.x86_64
qubes-gui-dom0-4.1.23-1.fc32.x86_64
Unused Dependencies
accountsservice-0.6.55-2.fc32.x86_64
lightdm-gobject-1.30.0-9.fc32.x86_64
qubes-gui-daemon-4.1.23-1.fc32.x86_64
Re-installation does not work with dnf install command.
$sudo qubes-dom0-update lightdm
This installed ~277MB of packages. the qubes related dependencies had to be separately installed.
I also installed kde, sddm, plasma-workspace, latte-dock, dolphin through:
$sudo qubes-dom0-update plasma-workspace latte-dock dolphin sddm
This also installs dependencies usually, else install separately.
The original instructions for kde installation at qubes-os.org/doc/kde do not work. ($sudo qubes-dom0-update @kde-desktop-qubes)
After reinstalling lightdm as well as sddm, I tried the sddm service first.
$sudo nano /etc/sddm.conf
Added the line as per qubes-os.org/doc/kde
[XDisplay]
ServerArguments=-nolisten tcp -background none
$sudo systemctl enable sddm.service
$sudo systemctl start sddm.service
Three sessions were available: Deepin, Plasma, Xfce
Xfce failed as before. So did Deepin.
Plasma showed the same black screen, but with a mouse arrow and dropdown qubes window for disk usage at a corner; practically nothing else was working. Tried shortcuts to access display settings, and found win+E gave explorer access and from there I obtained terminal access in dom0.
xrandr output (to check resolution and alias for the next commands) showed the following:
Screen 0: minimum 320x200, Current 1920x1080, Maximum 16384x16384
eDP-1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 344mm x 193mm
I used xrandr to set new mode 1920x1080_144.00 after gtf output for the modeline for this setting.
#xrandr --newmode “1920x1080_144.00” xyz.xx 1920 2040 2248 2576 1080 1081 1084 1118 -HSync +Vsync
#xrandr --addmode eDP-1 “1920x1080_144.00”
if it doesn’t work, force with
#xrandr --output eDP-1 --mode "1920x1080_144.00"
Navigating to a folder containing jpg file, I used right click to force open through settings app to obtain access to the settings display window which had resolution dropdown fixed at 1920x1080 at 144Hz.
No matter the changes after login into the session, the display problem stubbornly remained.
So, this was not a DM/service problem.
(2). To check whether kernel was the problem, I checked kernel versions. 5.15-52 and 5.15-57, with the latter currently activated. Kernel was temporarily reset to previous version via editing during boot. This allowed Plasma session to function decently (with a dashboard, taskbar and all usual widgets with access to qubes applications), but not xfce session.
Plasma display settings showed that there was a driver conflict with kernel upgrade, by defaulting to OpenGL2.0 instead of xrenderer.
I have set default kernel used by all qubes to 5.15-52.
My next tasks:
- Revert default kernel version for dom0 to 5.15-52, and retain it. Remove 5.15-57. Prevent system from updating kernels.
- Reset drivers to previous versions, if required, to rescue Xfce.