Mount entire DD image

Linux Logo Yesterday, my Raspberry Pi running Arch Linux was not able to boot with error: Kernel Panic, not syncing: no init found. I spent a night on it, but could not find a working solution. The last option is easy: reinstall the system. That is really the last resort, for I do not want to re-setup everything I have done: samba server, Time Machine server, Xunlei Offline Downloader…

Unable to mount the SD card

The system does not boot, so I need to find a way to get into the file system to identify what is wrong, or at least backup all the configuration files. I cannot directly mount it on my Mac, due to the unsupported Ext4 format, although the boot partition can be mounted, as it is in FAT format. I did tried with ext4fuse and fuse-ext2 without luck. I could neither connect the inter SD card reader to Parallel Desktop VM running Ubuntu, what a pity!

Use DD to make the SD card to an image

This is really a workaround, but it indeed is the best solution I am having.

  • Locate the SD card by running diskutil list. It is disk2
  • Make image file using dd: 
    sudo dd if=/dev/disk2 of=~/Desktop/pi.img bs=1m

Mount the image in Ubuntu

I did this in my Parallel Desktop running Ubuntu.
Use fdisk to list partition information of the image.

fdisk -u -l pi.img

the result I got was:

Disk pi.img: 15.9 GB, 15931539456 bytes
255 heads, 63 sectors/track, 1936 cylinders, total 31116288 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
Disk identifier: 0x0004f23a

 Device Boot      Start         End      Blocks   Id  System
pi.img1   *        2048      186367       92160    c  W95 FAT32 (LBA)
pi.img2          186368    31116287    15464960   83  Linux

We will be using this command to mount the image:

mount -o loop, offset=[offset value] [path to image file] [path to mount point]

Take note of the unit size, 512 byte here and the Start sector for each partition, which are used to calculate the offset. Here I want to mount the second partition, pi.img2. With a simple calculation: 512 * 186368 = 95420416

sudo mount -o loop,offset=95420416 pi.img /media/pi

Ok, that’s it. Now I am able to explore the files.