1) log in
2) use xrandr or the Displays control utility to configure your monitors how you'd like them to be configured in the login screen
3) copy ~/.config/monitors.xml to /var/lib/lightdm/.config
If resolution alway resets after reboot try to do in Gnome 3
Settings -> Displays -> Arrange Combined Displays ( the same as Step 2)
Workaround i found in -> https:/ /bugs.launchpad .net/ubuntu/ +source/ unity-greeter/ +bug/1082952/ comments/ 6
1) log in monitors. xml to /var/lib/ lightdm/ .config
2) use xrandr or the Displays control utility to configure your monitors how you'd like them to be configured in the login screen
3) copy ~/.config/
If resolution alway resets after reboot try to do in Gnome 3
Settings -> Displays -> Arrange Combined Displays ( the same as Step 2)