In Ubuntu 12.04, lightDM login screen uses user’s desktop wallpaper as its background. If you don’t prefer this feature in your machine, here’s a way to set lightdm login screen background different to User’s desktop wallpaper.

First open up a terminal window (search terminal from the dash, or press Ctrl+Alt+T) and do following commands.

  • Allow the user lightdm to create a connection to the X server
    sudo xhost +SI:localuser:lightdm
  • Switch user to lightdm
    sudo su lightdm -s /bin/bash
  • Turn off the dynamic switching of the background
    gsettings set com.canonical.unity-greeter draw-user-backgrounds false
  • Now you can change login background via a gui tool like Ubuntu Tweak, and see effect!

    If you want to re-enable this feature, in a new terminal window re-run previous commands but change the third to:

    gsettings reset com.canonical.unity-greeter draw-user-backgrounds