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Mounting partitions from a dd image

by assafmo on 5/9/18, 9:33 AM with 34 comments

by discreditable on 5/9/18, 2:33 PM
This is doing it the hard way. Make the image a loop device:
```
   losetup /dev/loop0 /path/to/your/image.img
```
Now you can use /dev/loop0 like it's a normal disk. If you're not seeing your partitions (/dev/loop0p1, etc.):
```
    partprobe /dev/loop0
```
When you're done, detach the loop device:
```
    losetup -d /dev/loop0
```
I use this trick to transparently compress ddrescue images with brtfs: https://brashear.me/blog/2017/11/14/how-to-create-a-compress...

by dbolgheroni on 5/9/18, 3:29 PM

OpenBSD uses vnconfig (also FreeBSD; on NetBSD it's vndconfig). An example:

  # vnconfig vnd0 install63.fs

Then you can treat vnd0 as if it was a disk:

  # disklabel vnd0
  # /dev/rvnd0c:
  type: vnd
  disk: vnd device
  label: fictitious
  duid: 138b4f2a2e184426
  flags:
  bytes/sector: 512
  sectors/track: 100
  tracks/cylinder: 1
  sectors/cylinder: 100
  cylinders: 7382
  total sectors: 738240
  boundstart: 1024
  boundend: 737280
  drivedata: 0 
  
  16 partitions:
  #                size           offset  fstype [fsize bsize   cpg]
    a:           736256             1024  4.2BSD   2048 16384 16142 
    c:           738240                0  unused                    
    i:              960               64   MSDOS

For instance, to mount the 'a' partition:

  # mount /dev/vnd0a /mnt

You can also associate an encryption key with the device. All data written to the diskimage will then be encrypted.

by phaedrus on 5/9/18, 3:49 PM
One time I tried to create a tool to do in-place conversion between Linux software RAID volumes (e.g. RAID-0 to RAID-1 (assuming data fits), or RAID-1 to RAID-5, etc.) I used disk image files and the loopback device to test it to avoid having to reformat physical partitions.
Despite reading all of the documentation I could find, and even going so far as to read kernel source code, I could never get the system to recognize my striped block data. That is, I tried to generate three files composing a RAID-5 "by hand", but mdadm would refuse to mount them. I never figured out if there was some additional id-block I was missing, or if my striping algorithm was not correct.
by ckastner on 5/9/18, 2:28 PM
Under Linux, this can also be achieved with kpartx(8).
https://linux.die.net/man/8/kpartx
by rwmj on 5/9/18, 4:22 PM
Or without needing root using guestfish (http://libguestfs.org/guestfish.1.html)
```
    $ guestfish -a img.dd -m /dev/sda1
    ><fs> ll /
```
guestmount works if you want to mount it on a local directory (implemented using libguestfs + FUSE).

by dpedu on 5/9/18, 5:42 PM

I think ZFS has the easiest way to do this sort of thing:

    # fallocate -l 256M disk.bin
    # zpool create filepool /root/disk.bin
    # zfs set mountpoint=/root/filepool filepool
    # df -h /root/filepool
    Filesystem      Size  Used Avail Use% Mounted on
    filepool        208M     0  208M   0% /root/filepool

by theonewolf on 5/9/18, 8:45 PM

You can directly expose the partitions using the tool `kpartx`, which will create a `loop` device for you:

  > sudo kpartx -a test.raw
  > lsblk
  NAME      MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
  loop0       7:0    0     4G  0 loop
  └─loop0p1 253:0    0     4G  0 part
  > sudo kpartx -d test.raw

by Ace17 on 5/9/18, 3:38 PM
> mount -t -o ro,offset=$((51263)) x.dd partition_1
> mount -t -o ro,offset=$((51296390)) x.dd partition_2
Isn't the mount type "-t" value missing?
by pixelbeat__ on 5/9/18, 8:47 PM
libguestfs > losetup > fdisk
I.E. libguestfs is safer when dealing with images of unknown origin, and losetup has inbuilt support now for partition scanning.
Here's an old fdisk/parted wrapper I used to use:
http://www.pixelbeat.org/scripts/lomount.sh
by amelius on 5/9/18, 2:20 PM
Is it also possible to repartition the image with conventional tools?
How about setting a boot flag and writing it back to e.g. an USB stick?