ligthtdm webkit greeter
After spending hours (days!) troubleshooting the lightdm webkit greeter which would just show a mouse cursor on a black screen, I decided to start from scratch on my home machine. Re-installed Ubuntu MATE, configured lightdm webkit greeter and got ... the same result. Just by chance I noticed the greeter on my laptop screen, which usually has the lid closed ... d'oh ... This is the hard way to find out that the webkit greeter only uses a single monitor. Found the relevant info searching the net: Need to get the display IDs using xrandr , HDMI-3 in my case Modify /etc/lightdm/lightdm.conf : Add display-setup-script=xrandr --output HDMI-3 --primary to the [Seat:*] section. Done!