Obtain a binary image

We have a USB key with a file system on it, and we want to save its content. We do a binary image using:

1 $ dd if=/dev/sda1 of=/home/kevin/usb_key.img

Mount the image file

Get information about the file system of the image file using:

1 $ fdisk -l -u /home/kevin/usb_key.img

This show you something like that:

Disque usb_key.img: 0 Mo, 0 octets
9 têtes, 56 secteurs/piste, 0 cylindres, total 0 sectors
Unités = secteurs de 1 * 512 = 512 octets

Périphérique Boot   Start   End      Blocks   Id   System
usb_key.img1        56      511559   255752   83   Linux

Get the sector number where the partition start (56) and the size of sectors (512). Multiply the two values:

56 * 512 = 28672

Then setup a loopback block device based on the image:

1 $ losetup -o 28672 /dev/loop0 /home/kevin/usb_key.img

Now you can mount your USB key:

1 $ mount /dev/loop0 /mnt/usb_key/