When installing VirtualBox-guest-additions on Ubuntu/Xubuntu/Lubuntu 12.10, the following error appears.
Warning: unknown version of the X Window System installed. Not installing
X Window System drivers.
The result is that it does not install the X driver and the virtual machine does not change the screen size, always remaining at 1024 × 768 pixels.
Solution.
sudo apt-get install virtualbox-guest-x11
With this we install it by hand, reboot and ready.