Maximising VirtualBox guest machine window size I am running Ubuntu 16.04 LTS inside VirtualBox on a MacBook Air 7,2, but the guest screen window size is less than the host display size. I have seen a suggestion that this is possible by installing something called a Guest Additions inside the VB instance from the Devices menu - I tried to this but I get the following error.
Open Terminal and run the following to install VirtualBox Guest Additions:

sudo apt-get install virtualbox-guest-utils