Personalize monitor position before login

I was experiencing this too. So long as you have your monitors configured as you want them in your user space then you should be able to follow these steps to set your monitors up the same way on the log in screen:

• Open a terminal
• Type sudo cp ~/.config/monitors.xml /var/lib/lightdm/.config/
• Enter user password
• Reboot your computer

Kudos goes to this post over here for pointing me in the right direction: Wrong Login Screen Resolution

At least with Ubuntu 16.04, which includes lightdm-gtk-greeeter 2.0.1, the following entry in /etc/lightdm/lightdm-gtk-greeter.conf can be used to fix the initial position of the login dialog on a certain monitor. This setting isn't available via the settings UI.

[greeter]
active-monitor=0

The monitors.xml workaround didn't work here, too.