How to mount partitions from a disk image

Nov 02

smachadoLinux No Comments

You can use the dd command to create images of disk drives, removable usb disks and so on.

If the disk you are making the image of has multiple partitions you cannot simply type “mount -o loop <image> <mount point>” to mount the resulting disk image file.

First you need to find the partitions offsets with the sfdisk command:

# sfdisk -l -uB image.iso
Disk image.iso: cannot get geometry
Disk image.iso: 973 cylinders, 255 heads, 63 sectors/track
Warning: The partition table looks like it was made
for C/H/S=*/4/32 (instead of 973/255/63).
For this listing I'll assume that geometry.
Units = blocks of 1024 bytes, counting from 0
Device Boot   Start       End    #blocks   Id  System
image.iso1   *       16     31231      31216    e  W95 FAT16 (LBA)
image.iso2        32256   7265599    7233344   83  Linux
image.iso3            0         -          0    0  Empty
image.iso4            0         -          0    0  Empty

With this information you can calculate the starting offset of each partition by multiplying the start block by the block units in bytes (1024 bytes in this case):

# echo $(( 32256 * 1024 ))
33030144
# echo $(( 16 * 1024 ))
16384

Mounting is easy now, you specify the file system type and the partition offset. To mount the first partition on the example file above:

# mount -o loop,offset=16384 -t vfat image.iso /mnt/

To mount the second partition:

# mount -o loop,offset=33030144 -t ext2 image.iso /mnt/

Here you go! Hope it helps!