mount >

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Pradeep’s blog ∞

2007-06-06

https://web.archive.org/web/20070613005140/http://ppadala.blogspot.com/2007/06/linux-tips-mounting-disk-image-with.html

How do you mount a disk image with multiple partitions? If an image contains a single partition, we can simply use a command like the following.

mount -o loop image_file /mnt

This will not work if the image_file is a complete disk image containing multiple partitions. I found a neat trick here that explains how to do it. The idea is to get the partition offset and then mount it as follows.

mount -o loop,offset=some_number image_file /mnt

The offset can be found by running fdisk -ul image_file. Detailed information is available here. Enjoy!

2. Mounting the disk image ∞

From Creating and using disk images mini-HOWTO

The clean way ∞

First, we need to determine the offset of the partition. This is quite easy: just type fdisk -ul <device>. The option -ul means list the partitions on the device and assume a unit size of 512 byte. This looks something like this:

fdisk -ul /dev/sda

Disk /dev/sda: 256 MB, 256376832 bytes
8 heads, 62 sectors/track, 1009 cylinders, total 500736 sectors
Units = sectors of 1 * 512 = 512 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *          62       19839        9889    4  FAT16 <32M
/dev/sda2           19840      231135      105648   83  Linux
/dev/sda3          231136      442431      105648   83  Linux
/dev/sda4          442432      471199       14384   83  Linux

Now all we need to do is a little math to get the offset: we need to multiply the start block by 512. E.g. if we wanted to mount the first partition we’d have an offset of 62 * 512 = 31744. The second partition has an offset of 19840 * 512 = 10158080.

Now that we have the offset we can mount the partition:

mount -o loop,offset=10158080 image.bootable /mnt

This would mount the second partition on /mnt. Linux recognizes it as ext3 if it is formatted as ext3 and the kernel supports ext3, so no need for a -t ext3 option to mount.

The dirty way ∞

There is also a hard way to find the formatted partitions if you can’t calculate the offsets for some reason:

for <span class="footnote_referrer" ><a><sup id="footnote_plugin_tooltip_61530_1" class="footnote_plugin_tooltip_text" onclick="footnote_moveToAnchor_61530('footnote_plugin_reference_61530_1');" >[ 1 ]</sup ></a><span id="footnote_plugin_tooltip_text_61530_1" class="footnote_tooltip" >i=0 ; $i < 10000 ; i=$i + 1</span ></span><script type="text/javascript"> jQuery('#footnote_plugin_tooltip_61530_1').tooltip({ tip: '#footnote_plugin_tooltip_text_61530_1', tipClass: 'footnote_tooltip', effect: 'fade', predelay: 0, fadeInSpeed: 200, delay: 400, fadeOutSpeed: 200, position: 'top center', relative: true, offset: [1, 0], });</script> ; do
    mount -o loop,offset=$<span class="footnote_referrer" ><a><sup id="footnote_plugin_tooltip_61530_2" class="footnote_plugin_tooltip_text" onclick="footnote_moveToAnchor_61530('footnote_plugin_reference_61530_2');" >[ 2 ]</sup ></a><span id="footnote_plugin_tooltip_text_61530_2" class="footnote_tooltip" >$i * 512</span ></span><script type="text/javascript"> jQuery('#footnote_plugin_tooltip_61530_2').tooltip({ tip: '#footnote_plugin_tooltip_text_61530_2', tipClass: 'footnote_tooltip', effect: 'fade', predelay: 0, fadeInSpeed: 200, delay: 400, fadeOutSpeed: 200, position: 'top center', relative: true, offset: [1, 0], });</script> image.bootable /mnt && break
done

If there is a partition within the first 10000 blocks, it gets mounted eventually :-) Just type mount to get the offset…