Disable the Guest Account In Ubuntu

If you wish to remove or disable the guest session from the login screen, open a shell terminal (use the Dash to search for “terminal”), then type sudo gedit /etc/lightdm/lightdm.conf. That command will open LightDM’s configuration file (after you authenticate) in Gedit, a text editor. By default, that file reads:

[SeatDefaults]
greeter-session=unity-greeter
user-session=ubuntu

Append allow-guest=false to it, so that it reads:

[SeatDefaults]
greeter-session=unity-greeter
user-session=ubuntu
allow-guest=false