Auto Login in Ubuntu Mate

Auto-login could pose security risks to your environment. At a minimum, the auto-login enabled computer would be prone to unauthorised access of whoever passes it by. But, there might be situations you want to take the risk, for example at your home lab. If you need to enable Ubuntu Mate to login automatically then edit the following configuration file:

/usr/share/lightdm/lightdm.conf.d/60-lightdm-gtk-greeter.conf

Use you favourite text editor to add line below to the aforementioned config file

autologin-user=username

What is Lightdm?

LightDM was the default display manager for Ubuntu up to version 16.04 LTS. GDM took its place in the Ubuntu releases afterwards. It is still the default DM in several Ubuntu flavours.

Reference
What is LightDM?