Ubuntu 11.10 Oneiric Ocelot has released its second alpha. In Ubuntu Oneiric, it starts using LightDM as default to instead Gnome Display Manager(GDM).

If you have upgraded to or new installed Ubuntu 11.10 Oneiric, you might want to change the LightDM login screen background.
And it’s easy, just open up a terminal window and edit the configuration file with the command below(Here unity-greeter.conf is the default theme’s configuration file, it changes depend on what greeter theme you’re using):

gksu gedit /etc/lightdm/unity-greeter.conf

Find the similar line:

background=/PATH/TO/Login/Background

change the path to any image as you like.