Possible Duplicate: How do I change the default session for LightDM when using auto-logins? When I auto-login it gives me unity 3D. How do I change the default to the 2D counterpart?
When autologon is active, lightdm will start the Unity 3D session, not the 2D (or any other shell that I want to auto-login to). Is there a way to start the shell I want automatically (autologon)? ...