Virtualbox 5.0, Ubuntu 14.04:
1.
wget -q http://download.virtualbox.org/virtualbox/debian/oracle_vbox.asc -O- | sudo apt-key add -
2.
sudo sh -c 'echo "deb http://download.virtualbox.org/virtualbox/debian trusty contrib" >> /etc/apt/sources.list.d/virtualbox.list'
3.
sudo apt-get update
4.
sudo apt-get install virtualbox-5.0
5. Oracle VM VirtualBox Extension Pack (https://www.virtualbox.org/wiki/Downloads)
6.
sudo apt-get install dkms
7.
sudo apt-get install gnome-system-tools
8. Users and Groups > Manage Groups > vboxusers > Properties > OK.