SDDM

Kanade ships a login screen theme for SDDM, drawn like the lock screen, and kanade sddm writes what SDDM reads for it. It does not replace SDDM or any greeter: SDDM stays your login manager, and Kanade only writes a theme and a picture. Nothing here needs the shell to run.

kanade sddm enable    # writes the theme and picture, then prints the root commands
# run the commands it prints as root, once
kanade sddm status    # what is written, what SDDM reads, anything still missing

Command	Does
kanade sddm status	What is written, what SDDM reads, and the root commands still missing
kanade sddm setup	Run as root; stages and atomically installs the built-in executable theme
kanade sddm sync	Writes only the mutable backdrop data from the sddm.* keys
kanade sddm enable	sync, then the root commands that make SDDM read the overlay
kanade sddm disable	Removes the picture, stops following the wallpaper, prints the root commands that undo enable
kanade sddm theme list|info <name>|use <name>	The installed themes, what Kanade finds in one, or sets sddm.theme

Kanade never runs sudo and never writes /etc or /usr; it prints the root steps for you to run. enable prints the setup needed, then refreshes the mutable picture data.

The picture

sddm.background says what shows behind the clock: the wallpaper, an image from sddm.background_path, the solid color sddm.surface, or none. The picture is blurred by sddm.blur and darkened by sddm.dim as the lock screen does, sized to the largest output, and re-encoded so it holds none of the original’s metadata.

Caution

The picture is readable by the sddm user and by anyone who can read /usr/local/share/kanade-sddm-data/, so it holds a picture of your desktop. That is why sddm.sync is off by default. A picture you set by hand in the overlay’s theme.conf.user is not checked by Kanade, and a Qt 5 greeter decodes it whatever its size, which can stall or crash the greeter.

When it breaks

If the login screen is already broken, from a text console (Ctrl+Alt+F3) log in and run:

sudo rm /etc/sddm.conf.d/zz-kanade.conf
sudo systemctl restart sddm

That puts SDDM back on its own theme. The file is named zz- so SDDM reads it after any other there; a file read later (/etc/sddm.conf, or a zzz- name) wins, and status and kanade doctor name it.

See also

SDDM configuration, maintenance CLI, and lock and idle gaps.