Friday, 4 March 2011

Booting VirtualBox from USB

If you have a Live OS installed onto a USB Key, you may want to test it by booting it from VirtualBox. It turns out that this is a real pain in the arse. There is apparently no way to do this natively, but there is a work around. What you have to do is use a command line (yay!) utility to make a fake hard disk image which points to the USB Key. So VirtualBox THINKS it is booting from a hard disk image but is ACTUALLY booting from the USB Key.

Anyway. The appropriate command in Ubuntu looks like this:

sudo VBoxManage internalcommands createrawvmdk -filename ~/test_usb.vmdk -rawdisk /dev/sdc

That works if you want the new fake disk image to be called [test_usb] and to be stored in [~/] home. Also it links to a USB disk mounted at [/dev/sdc]. The [.vmdk] bit is just the file type for VirtualBox disks.

If you want to do this on Windows, you run a very similar command which looks like this:

VBoxManage internalcommands createrawvmdk -filename "%USERPROFILE%\test_usb.vmdk" -rawdisk \\.\PhysicalDrive1

Apparently [%USERPROFILE%] is the Windows equivalent of [~]. The tricky bit is going to be [PhysicalDrive1]. You are going to have to work out what the number that goes on the end of that is, just as you would have to find out where a USB Key had been mounted in Linux. To do this in Windows run the command line [diskpart] program and then the command [list disk] and it should pop out with a list of the disks attached to the machine with their numbers. It looks like this on my virtual XP:

Microsoft DiskPart version 5.1.3565

Copyright (C) 1999-2003 Microsoft Corporation.
On computer: SB-VIRTUAL

DISKPART> list disk

  Disk ###  Status      Size     Free     Dyn  Gpt
  --------  ----------  -------  -------  ---  ---
  Disk 0    Online        10 GB      0 B


So I would want to use PhysicalDrive0 in that case. That would be monumentally stupid though, because I would mount the disk I was using to run my OS from in another machine AT THE SAME TIME. I do not want to imagine what the crash would look like.

You will also need to navigate to the install directory for VirtualBox to run the command (the VBoxManage command, not the diskpart command). Linux sticks the program file in the path, but Windows doesn't.

If it didn't go without saying all you do next is just add the .vmdk file as the principal hard disk to your virtual machine.

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