This is for when installing Linux Mint guest os into a virtualbox host (eg on windows). After starting your Linux Mint virtual machine on your Windows virtualbox host (ie, Windows for me) install THIS package in Mint, which means there is no need to install Linux headers, build essential, etc, all the stuff required to install Guest additions. After installation of THIS package is complete, on the virtual machine menu, click "devices", insert guest additions - this has the effect of automatically adding a cd into Mint; Virtualbox will automatically get the correct ISO, it takes care of it all. This should autorun/show a prompt to allow autorun. Go through the installation process (about 2 minutes). After installation complete, sign out/shutdown of Mint. When the virtual machine has stopped running, eject the guest additions cd from the machine (settings, storage). Start Mint machine, log in, wait for Mint to ready itself. Then, you should be able to resize the main virtual machine window (drag a corner), and Mint desktop will automatically refit (it might take two or three goes). After this drag-corner resize has worked successfully, you should now be able to do full screen mode (Virtual machine "View" menu" ).