A display manager is a program that provides graphical login capabilities for the X window system. Ubuntu uses LightDM as its default display manager since Ubuntu 11.10 Unity.
If you installed Gnome Shell, Cinnamon, and/or other desktops on Ubuntu, you may have multiple display manager packages on your system. However, only one display manager can manage a given X server and here’s how to switch between them in Ubuntu 14.04.
To get started, press Ctrl+Alt+T on keyboard to open a terminal window. When it opens, run:
sudo dpkg-reconfigure lightdm
Type in your password if asked. Then:
- If you only have one display manager, nothing will happen.
- Two or more? You’ll see below screen.
Press Enter and you’ll able to choose a display manager in below screen:
Highlight the one you want to use and hit Enter and done.