Information
GDM is the GNOME Display Manager which handles graphical login for GNOME based
systems.
Rationale:
Warning messages inform users who are attempting to login to the system of their legal
status regarding the system and must include the name of the organization that owns the
system and any monitoring policies that are in place.
Solution
Edit or create the file /etc/gdm3/greeter.dconf-defaults and add the following:
[org/gnome/login-screen]
banner-message-enable=true
banner-message-text='Authorized uses only. All activity may be monitored and
reported.'
Notes:
Additional options and sections may appear in the /etc/dconf/db/gdm.d/01-banner-
message file.
If a different GUI login service is in use, consult your documentation and apply an
equivalent banner.