Note: Tested on ubuntu 16.04 / 17.10 / 18.04 (bionic)
1) go to native terminal
ctrl+alt+F1
2) disable windows manager (step 1)
sudo lightdm stop
3) create new xorg config file (step 2)
sudo Xorg -configure
4) backup old xorg file ... (optional step for peace of mind)
sudo mv /etc/X11/xorg.conf /etc/X11/xorg.conf.bak
5) copy new configuration (step 3)
sudo mv /root/xorg.conf.new /etc/X11/xorg.conf
6) start lightdm (didn't work for me)
sudo lightdm start
7) reboot - this actually works!
reboot
and that's it ;-)
