fuente: https://www.programbr.com/ubuntu/how-to-switch-between-gdm-and-lightdm
How to Switch Between GDM and LightDM or other display managers in Ubuntu.
To switch between gdm3 and LightDM. Your system should have already installed gdm3 and lightdm. Earlier LightDM was default display manager of Ubuntu. But from Ubuntu 20.04 comes with gdm3 as the default display manager.
To install gdm use this command sudo apt install gdm3 or to install LightDM use this command sudo apt install lightdm in terminal.
Switching Between GDM3 and LightDM
Read also: gdm3 vs lightdm
To switch between gdm3 and lightdm, run the below command in terminal.
sudo dpkg-reconfigure gdm3
Using the above mentioned command will take you to a warning page. Enter to go to next screen. After that On the next screen, you will see all the available display managers. Select your preferred display manager and then press enter, Once you have selected it, press the tab to go to ok and press enter again. Then, restart your computer.
You can got this error (gdm.service is not active, cannot reload. invoke-rc.d: initscript gdm3, action “reload” failed.)
gdm.service is not active, cannot reload.
invoke-rc.d: initscript gdm3, action "reload" failed.
The error that you’re receiving just means that gdm3 wasn’t already running, so it couldn’t reload it. reboot it or run below command in terminal.
sudo systemctl start gdm3.service
sudo dpkg-reconfigure gdm3
Conclusion
you can run the same command sudo dpkg-reconfigure gdm to switch to any display manager between LightDM, MDM, KDM, Slim, GDM.
