Change The Default Login To The Desktop Session - mdeguzis/SteamOS-Tools GitHub Wiki
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About
This is really only useful for testing, or those who must rely on VirtualBox (or wish to) for tinkering with SteamOS. Under VirtualBox, the default steamos-session is very slow. Therefore, it is ideal to use desktop mode as the default session.
How To
The best way would probably be disabling autologin. In desktop open terminal. If you haven't made a password yet, do so now by typing "passwd".
sudo nano /etc/lightdm/lightdm.conf
Scroll the file until you find these two lines
#user-session=default
#autologin-user=
Modify them to be:
user-session=gnome-session
autologin-user=desktop
Source
This was sourced from the Steam Community