libgdm1 3.20.1-1ubuntu3 (arm64 binary) in ubuntu zesty

 GDM provides the equivalent of a "login:" prompt for X displays: it
 asks for a login and starts graphical sessions.
 .
 It supports multiple seats and switching between multiple users.
 .
 The greeter is based on the GNOME libraries and applications, and its
 look and design are the same as those of a GNOME session.
 .
 This package contains the shared library required by gnome-shell.