Fixing the Login Screen Background Not Changing on Ubuntu Unity

How many days and nights did this problem torment me? Finally solved!

Ecstatic.

The cause: under Ubuntu Unity, the login screen background normally follows your user’s desktop wallpaper. Every time you change your wallpaper, the lock screen and login screen backgrounds switch to that user’s wallpaper too.

But ever since Ubuntu ditched Unity, that feature was gone, and there was no known way to fix it. I practically wore out the LightDM documentation with no luck. Then, after emailing around for help, some random guy finally replied.

Turns out it’s just one command — enable the plugin:

gsettings set org.gnome.settings-daemon.plugins.background active true

Problem solved. So stupid — no idea why it’s disabled by default.