dual monitor linux guest in virtualbox
Solution 1:
I use randr as a workaround
xrandr --output VBOX1 --right-of VBOX0
I put it in my autostart. It will be run after you login
Solution 2:
Whats in your conf file? If you haven't explicitly told it that you have multiple monitors it will just clone the output. If you're uncertain how to modify the conf to do this there are several good tutorials around such as the one at the xorg archwiki.