You can display extra text on the login screen, such as who to contact for support, by setting the org.gnome.login-screen.banner-message-enable and org.gnome.login-screen.banner-message-text GSettings keys.
Create the gdm profile which contains the following lines:
user-db:user system-db:gdm file-db:/usr/share/gdm/greeter-dconf-defaults
gdm is the name of a dconf database.
Create a gdm keyfile for machine-wide settings in /etc/dconf/db/gdm.d/01-banner-message:
[org/gnome/login-screen]
banner-message-enable=true
banner-message-text='Type the banner message here.'
Update the system databases:
# dconf update
There is no character limit for the banner message. gnome-shell autodetects longer stretches of text and enters two column mode.
The banner message cannot be read from an external file.
Got a comment? Spotted an error? Found the instructions unclear? Send feedback about this page.