Install and Enable GNOME as default Display Manager in Ubuntu

GNOME Display Manager
As per wikipedia, GNOME Diplay Manager (GDM) is a display manager for windowing systems X11 and Wayland. The X Windows System by default used the XDM display manager. GDM allows users to customize or troubleshoot setting without having to resort to a command line. Users can pick their session type on a per-login basis.



Installation
1.  Update the repository and install GDM
sudo apt-get update
sudo apt-get -d install --reinstall gdm
sudo apt-get remove --purge gdm
sudo apt-get install gdm


2. Reconfigure GDM Package
sudo dpkg-reconfigure gdm

 Now GDM is configured as default display manager. To verify check the content of "/etc/X11/default-display-manager"
cat /etc/X11/default-display-manager
It should contain "/usr/sbin/gdm"


By default, lightdm display manager is installed on  latest versions of Ubuntu. We need to first stop the old display manager and start the gdm by executing following commands.
sudo service lightdm stop
sudo service gdm start

3.Reboot the system
reboot