If you want to use an existing VirtualBox hard disk (.vdi) for multiple machines you can't just copy the .vdi as you can't have multiple virtual hard disks with the same UUID on the same computer. But luckily you can easily clone an existing VirtualBox hard disk - here's how to do it. Firstly you'll need to know the path to the .vdi you want to clone. These are usually under ~/VirtualBox VMs (for