Mounting a partition in a loop device

Your requirement

You have created an image of a hard disk. The hard disk is partitioned. You want to mount one of the partitions from the image file.

The problem here

Linux can use /dev/loop? to turn an image file into a block device which can then be mounted. However the /dev/loop? devices do not recognise partitions.

The Solution

When mounting, you can use the offset= and sizelimit= options to limit the range in the image file when mounting using loopback. If you place this area exactly on the boundaries of a partition, you can mount it.

You can determine the size and location of the partitions with sfdisk (in this example the image of a USB stick with only one partition):

root@linux# sfdisk -d /tmp/image
# Partitionstabelle von /tmp/image
unit: sectors

/tmp/image1 : start=       32, size=    20448, Id=83, bootable
/tmp/image2 : start=        0, size=        0, Id= 0
/tmp/image3 : start=        0, size=        0, Id= 0
/tmp/image4 : start=        0, size=        0, Id= 0

The data here are in blocks of 512 bytes. The conversion can be done for you by the shell, for example. The mounting is performed with the following command:

root@linux# echo $((32 * 512)) $((20448 * 512))
16384 10469376
root@linux# mount -o loop,offset=16384,sizelimit=10469376 /tmp/image /mnt