After Upgrade to Mate 18.04 boot problems - not trusted key

[wolfman]

See my last answer here to you here.

How to install graphics card drivers in Ubuntu

Hi @mate2go, leave the 340 package installed and install the following package (or at least try it), the terminal command (Ctrl + Alt + t) is as follows: sudo apt install nvidia-driver-390 This is on the assumption it will work for you???.