For personal computers you may want to disable or remove the guest session from the login screen in Ubuntu 15.04 Vivid Vervet. This can be easily done by adding a rule into the configuration file of LightDM display manager.
To get started:
1. Open Ubuntu Software Center, search for and install gksu, which allows to run graphical commands as root:
2. Open terminal from the Dash or by pressing Ctrl+Alt+T on keyboard. When it opens, run below command:
gksu gedit /etc/lightdm/lightdm.conf
When the file opens, add below lines if it’s empty or add the third line:
[SeatDefaults] greeter-session=unity-greeter allow-guest=false
so the file looks like:
Save the file and restart your computer to apply changes.