I am predominantly a mac user and have been used to the ability to plug in a usb hard drive in to my mac and whilst booted in to my machine run backup software that makes a full, file-by-file backup of all my system and private files and make it bootable in the event that my hardware dies I can just plug it in to another mac and boot straight up off it.

Is this possible in ubuntu? I have seen many guides showing this done booted from a live cd but not when booted in your OS.

Any advice would be gratefully received.