How to install Ubuntu Server 14.04 LTS in VirtualBox using a net install.
Virtualbox: https://www.virtualbox.org/wiki/Downloads
Network Install Ubuntu ISOs:
32-bit: http://archive.ubuntu.com/ubuntu/dists/trusty-updates/main/installer-i386/current/images/netboot/mini.iso
64-bit: http://archive.ubuntu.com/ubuntu/dists/trusty-updates/main/installer-amd64/current/images/netboot/mini.iso
