This blog post has been an incredible help, but I stumbled at the very last hurdle – modifying the contents of the SD card.

You see, my compile system (Ubuntu 13.04) was in a virtual machine (VM) – VirtualBox running on Windows 7.

Windows 7 doesn’t know how to read the various linux filesystems, so they’re invisible, which means I needed to access to the whole, raw disk directly from the VM.

Here’s a step-by-step guide to directly mounting raw SD card in your virtual machine, so you can edit it.

1. Get the DeviceID for you SD Card reader

Open a command window as an administrator. (Press Start, type cmd, right click on cmd.exe in the list, and choose “Run as administrator”)

type

wmic diskdrive list brief

and if your system is anything like mine you’ll get something like this:

C:\Users\Sandy Scott>wmic diskdrive list brief
Caption                      DeviceID            Model                        Partitions  Size
WDC WD7500BPKT-75PK4T0       \\.\PHYSICALDRIVE0  WDC WD7500BPKT-75PK4T0       3           750153761280
O2Micro SD SCSI Disk Device  \\.\PHYSICALDRIVE1  O2Micro SD SCSI Disk Device  1           3964584960

The top item is the main hard drive, the lower one is the SD card.

The bit we’re interested in is the DeviceID, in this case \\.\PHYSICALDRIVE1

2. Navigate to the VirtualBox directory

Next thing you’ll need to find is the installation directory for VirtualBox. This is usually C:\Program Files\Oracle\VirtualBox\. You’ll know it’s the right one if it has lots of files starting with VBox in it.

Go there by entering this command

cd C:\Program Files\Oracle\VirtualBox

3. Create the link file to the SD card

VBoxManage internalcommands createrawvmdk -filename "%USERPROFILE%/Desktop/sdcard.vmdk" -rawdisk "\\.\PHYSICALDRIVE1"

The file you’ve just created (sdcard.vmdk, on your Desktop) is a special link that lets a virtual machine access the SD card.

4. Connect the VM to the SD card using the link

Now, open VirtualBox as Administrator, and open the Settings for your virtual machine. Go to Storage -> Controller: SATA -> (right click) Add Hard Disk -> Choose Existing Disk and open the file you just created.

Fire up the VM and you should be able to access the SD card in all it’s glory!