Mount partition from a raw disk image
In this post, I will share how you can mount a raw disk image such as an image generated with dd. Raw disk image or RAW Image Format is a bit-for-bit copy of disk data, without any metadata information on files. In Linux, dd is a popular tool for data transfer by duplicating entire disk for instance. Let us create a disk image of a mount with an EXT3 file system –
[root@kauai src]# dd if=/dev/sdb of=disk.img 7233761+0 records in 7233760+0 records out 3703685120 bytes (3.7 GB) copied, 236.166 s, 15.7 MB/s [root@kauai src]# ls -alh disk.img -rw-r--r--. 1 root root 3.5G Jan 15 18:44 disk.img
We have copied a mount with multiple files into a single disk.img file which we can copy to another system. Now let us examine the raw disk layout, that we can use to mount as a file system –
[root@kauai src]# fdisk -lu disk.img You must set cylinders. You can do this from the extra functions menu. Disk disk.img: 0 MB, 0 bytes 124 heads, 62 sectors/track, 0 cylinders, total 0 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: 0xdebbbd93 Device Boot Start End Blocks Id System disk.img 630416 945623 157604 83 Linux
As we can see the raw disk has 512 byte size sectors and it starts at offset 630416, given this information we can use mount command to mount the disk image –
[root@kauai src]# mount -o loop,offset=$((630416*512)) disk.img /mnt/hdisk/ [root@kauai src]# ls -al /mnt/hdisk/ total 37 drwxr-xr-x. 3 root root 1024 Jan 15 18:39 . drwxr-xr-x. 4 root root 4096 Nov 17 20:04 .. -rw-r--r--. 1 root root 15 Jan 15 18:39 file21 -rw-r--r--. 1 root root 15 Jan 15 18:39 file22 -rw-r--r--. 1 root root 15 Jan 15 18:39 file23 -rw-r--r--. 1 root root 15 Jan 15 18:39 file24 -rw-r--r--. 1 root root 15 Jan 15 18:39 file25 -rw-r--r--. 1 root root 15 Jan 15 18:39 file26 -rw-r--r--. 1 root root 15 Jan 15 18:39 file27 -rw-r--r--. 1 root root 15 Jan 15 18:39 file28 -rw-r--r--. 1 root root 15 Jan 15 18:39 file29 -rw-r--r--. 1 root root 15 Jan 15 18:39 file30 drwx------. 2 root root 12288 Jan 15 18:37 lost+found [root@kauai src]# cat /mnt/hdisk/file26 File number 26
Here we were able to mount the disk image and be able to read the content of one of the text files.
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