GDM (GNOME Display Manager) are login managers. They both provide graphical login capabilities (the GUI with the list of the system’s users) as well as remote logins using the XDMCP protocol.
Ubuntu comes with LightDM as default display manager. But if you experiment with various display managers or various desktop environments such as to install Gnome shell in Ubuntu 14.04 , you may end up with GDM as default display manager. It is a matter of choice but if you want to get back to another display managers, you can easily do that.
In this quick post, we shall see how to switch between LightDM and GDM in Ubuntu 14.04.
Switch between LightDM and GDM in Ubuntu 14.04
Open a terminal and use the following command:
sudo dpkg-reconfigure gdm
You can in fact use lightdm instead of gdm, the procedure is same for both. Using the above mentioned command will take you to a warning page. Enter to get back to next screen:
On the next screen, you’ll see all the available display managers. Use tab to select your preferred one and then press enter, Once you have selected it, press tab to go to ok and press enter again.
Restart the system and you will find your selected display manager at login. The same procedure can be applied to switch between GDM, LightGDM, MDM, KDM etc.