Install the build essentials package in order to be able to compile the kernel modules.

apt-get install build-essential

Install the guest additions ISO image package:

apt-get install virtualbox-guest-additions-iso

Allow Ubuntu to use the proprietary extensions:

software-properties-gtk --open-tab 4

Check the “x86 virtualization solution” radio button and apply the changes. Reboot the guest system.

Check whether the vboxvideo driver gets used:

/usr/lib/nux/unity_support_test -p

If there is a line reading:

Not software rendered: no

That means, the driver is not used yet.

In Ubuntu 14.04 there are problems with guest additions prior to: VBoxGuestAdditions_4.3.13-94438.iso

<note important>The download of the ISO image VBoxGuestAdditions_4.3.13-94438.iso is clearly labeled as test software! See https://www.virtualbox.org/download/testcase/VBoxGuestAdditions_4.3.13-94438.iso </note>

Since at the time of this writing packaged guest additions in this version or higher are not on the Ubuntu repository, you have to manually download the ISO image, add the ISO as virtual CD drive in your VM setup and install it.

After rebooting you should now see that Unity 3D is supported.

Warning: this driver produced glitches in the display though.

Add the entry vboxvideo to the file /etc/modules.

Reboot.