gdm3 -V (return code: 1)
GDM 3.18.3
gdm3 --help (return code: 0)
Usage:
gdm3 [OPTION...] GNOME Display Manager
Help Options:
-h, --help Show help options
Application Options:
--fatal-warnings Make all warnings fatal
--timed-exit Exit after a time (for debugging)
--version Print GDM version