How to: Clone a VM for VirtualBox

 The following is the command for cloning a .vdi virtual hdd for VirtualBox

Mac OS/Linux:
Open the terminal
Type:

VBoxManage clonehd source.vdi target.vdi

Example:
Suppose you have a virtual machine with a hdd called: "virtualhdd.vdi"
"virtualhdd.vdi" is located on /Users
You will make a clone of this hdd called: "clone.vdi" on /Users
You will type:
VBoxManage clonehd /Users/virtualhdd.vdi /Users/clone.vdi

Alternatively you could do:
cd /Users
VBoxManage clonehd virtualhdd.vdi clone.vdi

For Windows the command is the same but you must navigate cmd into the directory that contains VBoxManage