ARM Virtual machine on Ubuntu

Question

I'm following this guide to install a virtual ARM environment on Ubuntu.

• I installed linaro and qemu packages:

sudo add-apt-repository ppa:linaro-maintainers/tools
sudo apt-get install linaro-image-tools qemu-user-static qemu-system

• Cross compilers:

sudo apt-get install gcc-arm-linux-gnueabi g++-arm-linux-gnueabi

• Downloaded a Linaro release and hardware pack:

wget http://releases.linaro.org/platform/linaro-n/nano/alpha-3/linaro-natty-nano-tar-20110302-0.tar.gz
wget http://releases.linaro.org/platform/linaro-n/hwpacks/alpha-3/hwpack_linaro-vexpress_20110302-0_armel_supported.tar.gz

• Created a VM disk image:

linaro-media-create --image_file vexpress.img --dev vexpress \
--binary linaro-natty-nano-tar-20110302-0.tar.gz \
--hwpack hwpack_linaro-vexpress_20110302-0_armel_supported.tar.gz

I'm failing at Extracting the kernel and initrd. The instructions say to run:

sudo mount -o loop,offset="$(file vexpress.img | awk 'BEGIN { RS=";"; } /partition 2/ { print $7*512; }')" \
-t auto vexpress.img /mnt/tmp

But I'm getting the error:

mount: failed to parse mount options

There's a note in the guide that says:

The actual names of the files might vary slightly in your build.

So does anyone know how to modify this last line to fit on Ubuntu?

Answer 1

sudo mount -o loop,offset="$(file vexpress.img | awk 'BEGIN { RS=";"; } \
/partition 2/ { print $7*512; }')" \
-t auto vexpress.img /mnt/tmp

What the above command is doing is actually simple: It finds the starting sector of partition 2 of the image vexpress.img, multiply it by 512, and take the result as offset to mount as a loop device.

The mount command accepts offset value in byte. Each sector has 512 bytes, so multiplying start sector offset by 512 will yield the start offset in bytes.

Here's an alternative way to do this: (I take a raw raspbian image as example)

1. Find the offset:

   $ fdisk -lu 2016-09-23-raspbian-jessie-lite.img 
   Disk 2016-09-23-raspbian-jessie-lite.img: 1.3 GiB, 1389363200 bytes, 2713600 sectors
   Units: sectors of 1 * 512 = 512 bytes
   Sector size (logical/physical): 512 bytes / 512 bytes
   I/O size (minimum/optimal): 512 bytes / 512 bytes
   Disklabel type: dos
   Disk identifier: 0x5a7089a1
   
   Device                               Boot  Start     End Sectors  Size Id Type
   2016-09-23-raspbian-jessie-lite.img1        8192  137215  129024   63M  c W95 FAT32 (LBA)
   2016-09-23-raspbian-jessie-lite.img2      137216 2713599 2576384  1.2G 83 Linux
   

The start offset of partition two is 137216. Like your vexpress.img, partition 2 is the root partition that we are interested in.

2. Simple math:

   $ perl -e "print 137216*512"
   70254592
   

3. Mount it:

   sudo mount -o loop,offset=70254592 vexpress.img /mnt/tmp