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on Sep 15th 2009 at 2:14 pm tech

Mounting a xen disk image file on dom0

If you need to get in and edit some files on your xen domU instance, i.e. it isn’t booting up properly, etc, here’s how to mount it on dom0. In this case, we want to mount the second partion on the virtual disk (our root partition):

  • Print out the partition layout:
    fdisk -l /path/to/img/file.img

    Disk System.img: 0 MB, 0 bytes
    255 heads, 63 sectors/track, 0 cylinders
    Units = cylinders of 16065 * 512 = 8225280 bytes

    Device Boot Start End Blocks Id System
    System.img1 1 4 32098+ 83 Linux
    System.img2 * 5 619 4939987+ 83 Linux
    System.img3 620 750 1052257+ 82 Linux swap / Solaris

  • create directory to mount image under: mkdir /mnt/tmp
  • mount the image using the offset from the fdisk output, the start block (in this case 5)
    mount mount -o loop,offset=$((512*5) /path/to/img/file.img /mnt/tmp
  • Edit files as needed, and unmount when done.

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