Question

20

Mounting Disk Image in Raw format

rated 0 times [ 20] [ 0] / answers: 1 / hits: 98279 / 3 Years ago, fri, september 3, 2021, 4:41:39

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

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ormlai

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answered 3 Years ago wenceslockro · Accepted Answer

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.