Ubuntu – Mount single partition from image of entire disk (device)

backupdddiskdisk-imagemount

I made an image of my entire disk with

dd if=/dev/sda of=/media/external_media/sda.img

Now the problem is I'd like to mount an ext4 filesystem that was on that disk but

mount -t ext4 -o loop /media/external_media/sda.img /media/sda_image

obviously gives a superblock error since the image contains the whole disk (MBR, other partitions) not just the partition I need. So I guess I should find a way to make the disk image show up in the /dev/ folder…

Does anyone know how to do that?

PS: I can always dd back the image to the original disk, but that would be very inconvenient (I updated the OS and I'd like to keep it as it is)

Best Answer

Get the partition layout of the image

$ sudo fdisk -lu sda.img
...
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
...
  Device Boot      Start         End      Blocks   Id  System
sda.img1   *          56     6400000     3199972+   c  W95 FAT32 (LBA)

Calculate the offset from the start of the image to the partition start

Sector size * Start = (in the case) 512 * 56 = 28672

Mount it on /dev/loop0 using the offset

sudo losetup -o 28672 /dev/loop0 sda.img

Now the partition resides on /dev/loop0. You can fsck it, mount it etc

sudo fsck -fv /dev/loop0
sudo mount /dev/loop0 /mnt

Unmount

sudo umount /mnt
sudo losetup -d /dev/loop0
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