2019 Update! – I am not using Ubuntu-MATE at this time. The guide below may no longer work with current versions of the OS. I don’t know for certain so use with caution.
In this how-to guide, I will explain how I disabled, and removed the guest session from my login screen. I did not need or want the guest login, because this was my personal computer.
This guide should only work on your Ubuntu-MATE install. In my case, I was using version 15.10 of the Ubuntu-MATE Linux operating system.
To begin, first type Alt+F2. Then run the following command: gksu pluma /etc/lightdm/lightdm.conf
After entering your password, you will be able to edit your lightdm.conf file with Pluma. Which is the default text editor in Ubuntu Mate 15.10
Add the following lines to the file:
[SeatDefaults]
greeter-session=lightdm-gtk-greeter
allow-guest=false
Save the file, then restart your computer. The changes should be applied.
If you have any questions or issues, check with the Ubuntu-MATE community. The UbuntuForums are another good site to visit.