Notice: Tested for Ubuntu releases up to Ubuntu 10.10 (Maverick Meerkat)
Every Linux distribution now days sets its default theme and wallpaper. That theme and wallpaper is usually login screen theme and wallpaper. What if you don't like it? You can change theme and wallpaper for your user account but login screen theme stays the same. Lets do something about it...
This is the plan. In a way GDM (Gnome Display Manager) is like every other user. It can have theme, wallpaper and programs to be run when it starts. Why not adjusting Gnome appearance properties (gnome-appearance-properties) window to start at login screen? Then we can adjust things like theme, fonts, wallpaper and everything Gnome appearance properties allows us to do. So first step is to enter this at your terminal (following code is single command):
sudo ln -s /usr/share/applications/gnome-appearance-properties.desktop /usr/share/gdm/autostart/LoginWindow/gnome-appearance-properties.desktop
Next step is to logout. Gnome appearance properties window will start together with GDM login screen and you can adjust everything as you like. The last step is to undo what we have done in the last step. So after next login enter this at your terminal to stop Gnome appearance properties window form showing its face every time you're at GDM login screen:
sudo rm /usr/share/gdm/autostart/LoginWindow/gnome-appearance-properties.desktop
Next time you need to change your login screen appearance you repeat this process. That's it. No more steps.