One of the things I don’t like about the default login screen in Linux Mint Cinnamon Version 18.3 (Sylvia) is the availability of a guest session. Fortunately, it’s easy to disable this function:
(1) Navigate to Menu – Administration – Login Window
(2) Enter the root password in the “Login Window” pop-up dialogue box
(3) Navigate to Users – Guest sessions – Allow guest sessions, and toggle the switch to Off
Another useful tweak in this same command window is to navigate to Appearance – Background – Draw a grid, and toggle its switch to Off. This gives the login screen a much cleaner look.
How To Disable The Guest Session In Linux Mint 18