I'm using Ubuntu 17.04 and Gnome 3 with gdm3 3.24. I have two external displays connected to my laptop. I usually keep the laptop lid closed, so only the external displays are enabled, and this works fine.
However, when I log out, the login screen with username/password fields is only displayed on the closed laptop screen, and the external displays are blank. (The external displays are enabled but only show the login screen background color, no content.)
I would like to have the login screen content mirrored across all displays when logged out. Is that possible?
I tried configuring my displays for mirroring and copying that
$HOME/.config/monitors.xml file to
/var/lib/gdm3/.config, but that did not produce any change.