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cd /usr/share/lightdm/light.conf.d/
Global lightdm settings here
cd /etc/lightdm/ sudo nano lightdm.conf
Lightdm ubuntu-MATE greeter and lock screen issues
/usr/share/common/backgrounds/ubuntu-mate-common/Ubuntu-Mate-Cold.jpg /etc/lightdm/lightdm-gtk-greeter.conf
The .conf file w/ some common sense parameters
[SeatDefaults] allow-guest=false greeter-hide-users=true
To set the global dark theme from the command line for gdm3
nano ~/.config/gtk-3.0/settings.ini [Settings] gtk-application-prefer-dark-theme=1
This tutorial is a designated “Invariant Section” of the “Technotronic” section of Haack's Wiki as described on the Start Page.
— oemb1905 2019/01/13 19:17