Mounting Disk Image in Raw format

Question

While trying to mount a disk image in Raw(dd) format using the following command

mount  nps-2010-emails.dd /media/manu/

I get the following error message

mount: you must specify the filesystem type

I know that using -t we can specify the file system but what is the terminology for a RAW (dd) file, which can be passed as an argument to the mount command. If my method to mount this file system is wrong please help me out in doing the same.

$ file -s nps-2010-emails.dd
nps-2010-emails.dd: x86 boot sector; 
partition 1: ID=0xb, starthead 254, startsector 1, 20479 sectors, extended partition table (last)\011, code offset 0x0

$ fdisk -l nps-2010-emails.dd
Disk nps-2010-emails.dd: 10 MB, 10485760 bytes
255 heads, 63 sectors/track, 1 cylinders, total 20480 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: 0x00000000

             Device Boot      Start         End      Blocks   Id  System
nps-2010-emails.dd1               1       20479       10239+   b  W95 FAT32 

Solution 1

From http://major.io/2010/12/14/mounting-a-raw-partition-file-made-with-dd-or-dd_rescue-in-linux/, there's a suggestion to use an offset. First obtain the offset via fdisk(8) and then specify it with the offset option to mount. Use fdisk to determine the starting sector of the partition and the sector size. Then calculate offset in bytes using the starting sector number and sector size in bytes. See Mount single partition from image of entire disk (device) for an example. Finally:

mount -o offset=<offset in bytes> nps-2010-emails.dd /media/manu/

In a typical hard disk, the cells holding the data are grouped. The groupings are called sectors. The way we usually partition things, the first few sectors are kept aside for giving information about the partitions, leaving a gap. So if we have an image of an entire disk, these sectors also get included. Now, the mount command cannot directly start at the first byte, as the partition doesn't start at the first byte. So, we will have to tell mount how many bytes to skip (so that it can avoid the extra information)and get to the actual partition. This is called the offset. Now each sector can store a certain amount of information in bytes, which is called the size of a sector. We take the total size of information that can be stored in this gap by multiplying the size of a sector, with the size of the gap in number of sectors.

From the output of fdisk there, you can see the sector size is 512 bytes and it starts at sector 1. So the offset is 1*512=512. Try the following command:

mount -t vfat -o offset=512 ps-2010-emails.dd /media/manu/

I added the filesystem type since fdisk gave it as FAT32. To mount it for writing as well, use -o offset=512,rw instead.

Solution 2

You can also have the computer automatically scan all the partitions in a dump and automatically prepare all loop devices, as described here.

So, lets say you dumped your entire /dev/sda into something called sda.img. You can access its partitions as follows:

losetup -f -P sda.img

On my system, it then shows up as follows:

In non-GUI environments, you can list the created device with losetup -l, which will tell you the name of the loop device, example:

# losetup -l
NAME       SIZELIMIT OFFSET AUTOCLEAR RO BACK-FILE
/dev/loop0         0      0         0  0 /path/mmcblk0

You can then mount say, the first partition, with:

mount /dev/loop0p1 /mnt/mypartition

Hope that helps.

Solution 3

Can't add a comment because of lack of reputation, but want to tell to those of you who have GPT disk when testing it with fdisk, use gdsik instead to get start sector and count proper offset. It helped me.

fdisk -l gave me:

      Device Boot      Start         End      Blocks   Id  System
vm2080737.bak1   *           1        3901    31457279+  ee  GPT

and it couldn't be mounted with 512 offset with an error 'mount: you must specify the filesystem type'

gdisk -l gave me good result:

Number  Start (sector)    End (sector)  Size       Code  Name
   1              34             545   256.0 KiB   A501  gpboot
   2             546          993825   485.0 MiB   A502  swap
   3          993826        62914526   29.5 GiB    A503  rootfs

Comments

[steeldriver]

Can you add the output of the command file -s nps-2010-emails.dd to your post please?

[muru]

I took a look at your profile, and saw the other question. Perhaps this blog post might be of help.

[spaceman_spiff]

@steeldriver Output added...

[Hannu]

Easier options for mounting - available/described here: askubuntu.com/questions/69363/…

[spaceman_spiff]

Post updated to include the output of fdisk -l nps-2010-emails.dd.

[spaceman_spiff]

thanx, my background has been in theorotical computer science (I am a math major), is there any reference to understand this topic on a general note?

[muru]

'This' topic being disks, sectors, filesystems and all that? Perhaps you could start with the IO/Storage chapter of an Operating Systems textbook, like Tannenbaum's. Other than those basics, and the FAT32 mount type, everything I posted on the answer is from tholinks.

[muru]

Or use parted.

[praveen pathak]

Worked for me perfectly.

[RoundSparrow hilltx]

Along these same lines, on Ubuntu 18.04 I had no trouble doing "gparted backup.img" and getting a list of partitions. "fdisk -l backup.img" also shows useful information.

[Flimm]

How do you undo the losetup command?

[aggregate1166877]

@Flimm I believe it's losetup -d your_loop_device