There is a ton of information available on the web to help with installing VirtualBox. Too much, maybe. It’s a bit daunting to find the right set of instructions to follow. This machine is running Ubuntu 14.04, start here: https://www.virtualbox.org/wiki/Linux_Downloads

But don’t start at the top, it is not really necessary to download a package as described there. I went to the Debian-based Linux distributions section and did:

• Added this to the end of the /etc/apt/sources.list file:

  ## added to support virtualbox installation
  deb http://download.virtualbox.org/virtualbox/debian trusty contrib

  The trusty part will need to be changed if the host OS is not version 14.04

• Fetched the Oracle public key in to my Downloads directory (from the “here” link)

• sudo apt-key add ~/Downloads/oracle_vbox.asc

• Did not do the combine downloading and registering line

• sudo apt-get update
  sudo apt-get install virtualbox-4.3

• And also picked up the other recommended package:

  sudo apt-get install dkms

I did not experience any of the signature bad messages shown.

Now the system is ready to create a virtual box using the VirtualBox Manager and install a copy of a guest OS. Done, So VirtualBox runs fine and the guest OS installation went fine, BUT when the new virtual system was started up it’s display area was confined to a tiny 640×480 space on the screen!

After a bit more googling I found: http://youtu.be/JH29ALyraG4

Which advises on installing under Windows 8.1. No, not what I wanted, but the good applicable part comes just after 10:30 in the video. This is where the fix for the tiny window problem is described.

In the virtual system on a terminal window run:

sudo apt-get install virtualbox-guest-utils virtualbox-guest-x11 virtualbox-guest-dkms

Fixed! Virtual box display now resizes as desired.

Tip: change the background image for the virtual system to avoid confusion with the host OS.