Změna pozadí u lightdm
In my case this solved the problem.
The org.gnome.settings-daemon.plugins.background
setting had been disabled but I cannot determine why. Once I checked this checkbox in dconf-editor
and changed my wallpaper, it was reflected on the login screen.
I just solved this by copying my background image into the folder /usr/share/backgrounds (with a pkexec nautilus
— lazy me, or in a better way with sudo cp /path/to/image.jpg /usr/share/backgrounds
). After that, I changed the background image from Unity in a regular way. You have to do this last change for any of the desktop manager you have on your system. Also, I think image has to be outside of the user’s folder.
It worked for me.