LightDM ubuntu display manager
How to remove quest login from LightDM
open with an editor lightdm.conf
sudo gedit /etc/lightdm/lightdm.conf add this row at the end
allow-guest=false
new lightdm.conf is now like that [SeatDefaults]
greeter-session=unity-greeter
user-session=ubuntu
allow-guest=false restart LightDM
sudo service lightdm restart