Seat seat0: Display server ready, starting session authentication
[+20.61s] DEBUG: Session pid=1375: Started with service 'lightdm-greeter', username 'lightdm'
[+20.67s] DEBUG: Session pid=1375: Authentication complete with return value 0: Success
lightdm-greeter is now named lightdm-gtk-greeter into the xenial archive (not installed) but unity-greeter is used
note: a gnome-shell session should used its own greeter, a unity session its own too; but mixing with not updated package name is building a mess.
lightdm.log shows some confusing log:
Seat seat0: Display server ready, starting session authentication
[+20.61s] DEBUG: Session pid=1375: Started with service 'lightdm-greeter', username 'lightdm'
[+20.67s] DEBUG: Session pid=1375: Authentication complete with return value 0: Success
lightdm-greeter is now named lightdm-gtk-greeter into the xenial archive (not installed) but unity-greeter is used
note: a gnome-shell session should used its own greeter, a unity session its own too; but mixing with not updated package name is building a mess.