Thursday, October 5, 2017

Mounting bootable image file under linux with offset

Use fdisk to see the partitions and their offset of the image file:
# fdisk -l router-devuan-jessie-diskless-2017.img
Disk router-devuan-jessie-diskless-2017.img: 3.7 GiB, 3980394496 bytes, 7774208 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x7b19da02

Device                                                 Boot Start     End Sectors  Size Id Type
router-devuan-jessie-diskless-2017.img    *     2048 7772159 7770112  3.7G 83 Linux
According to fdisk each sector of the image has 512 bytes. We need that so we can calculate the right offset when mounting it.

The image has one linux partition starting at offset of 2048. The right offset is 512*2048.

Here is how to mount it:
# mount -o loop,offset=$((2048*512)) router-devuan-jessie-diskless-2017.img /mnt/

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