Choose lightdm login screen location in multi monitor setup

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:

[greeter]
active-monitor=0

The xrandr workaround didn't work here, too.

This did the trick for me. Find out your primary screen:

$ xrandr

And create the file /usr/bin/dualmon.sh with the following command:

xrandr --output DVI-0 --primary

**Change DVI-0 for your primary screen.*

Make it executable:

sudo chmod +x /usr/bin/dualmon.sh.

And add it to /etc/lightdm/lightdm.conf file:

[SeatDefaults]
display-setup-script=/usr/bin/dualmon.sh
session-setup-script=/usr/bin/dualmon.sh

Regards!