What are gmd/lightdm Display mangers and how to switch between them?

Switch Between GDM and LightDM in Ubuntu

Display Manager?

What is a display manager? In the X Window System, an X display manager is a graphical login manager which starts a session on an X server from the same or another computer. A display manager presents the user with a login screen. A session starts when a user successfully enters a valid combination of username and password.Also known as a "login manager", a display manager is responsible for starting the display server and loading the desktop. This happens right after your correctly enter your username and password

How to switch between GDM and Lightdm display managers in ubuntu?

Lightdm was the default display manager of ubuntu.From ubuntu 20.04 gdm3 is set as the default one.If you don't have already installed the two kinds of display managers,do it by using this command sudo apt-get install gdm3 and sudo apt-get install lightdm in terminal.

Switching between GDM3 and LIGHTDM

To switch between the two display managers use this command: sudo dpkg-reconfigure gdm3

A pop up window will appear and you have to choose between gdm3 and lightdm.pick your choice and restart your device!

Some issues and errors

"gdm.service is not active,cannot reload.invoke-rc.d:initscript gdm3, action "reload" faied."!It is a common gdm error in ubuntu.So you have to reboot or to run this command: sudo systemctl start gdm3.service sudo dpkg-reconfigure gdm3

Note:

This command sudo dpkg-reconfigure gdm is usefull to switch between any display manager you have installed like mdm ,kdm ,slim ...