4

I have a disk image file I'm trying to mount locally using a loop device. Using parted I can see the image has two partitions, however, I'm not able to mount the first partition and losetup thinks the second partition doesn't exist. Anyone know how I can mount the second partition?

/m/sf_VMShare ❯❯❯ sudo losetup /dev/loop0 ./imm_image-2017-05-28.img
/m/sf_VMShare ❯❯❯ sudo losetup -a
/dev/loop0: [0023]:99 (/media/sf_VMShare/imm_image-2017-05-28.img)
/m/sf_VMShare ❯❯❯ sudo parted /dev/loop0 print
Model: Loopback device (loop)
Disk /dev/loop0: 1206MB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start   End     Size   Type     File system  Flags
 1      10.5MB  360MB   349MB  primary  ext4
 2      361MB   1205MB  844MB  primary  ext4

/m/sf_VMShare ❯❯❯ sudo mount -t ext4 /dev/loop0p2 /tmp/vdisk
mount: special device /dev/loop0p2 does not exist
/m/sf_VMShare ❯❯❯ sudo mount -t ext4 /dev/loop0p1 /tmp/vdisk 
mount: wrong fs type, bad option, bad superblock on /dev/loop0p1,
       missing codepage or helper program, or other error
       In some cases useful info is found in syslog - try
       dmesg | tail  or so

/m/sf_VMShare ❯❯❯ mount | grep /tmp/vdisk
/m/sf_VMShare ❯❯❯
/m/sf_VMShare ❯❯❯ ls /dev/loop*
/dev/loop0    /dev/loop1  /dev/loop3  /dev/loop5  /dev/loop7
/dev/loop0p1  /dev/loop2  /dev/loop4  /dev/loop6  /dev/loop-control
/m/sf_VMShare ❯❯❯ lsblk -f
NAME      FSTYPE LABEL MOUNTPOINT
sda                    
├─sda1                 /
├─sda2                 
└─sda5                 [SWAP]
sdb                    
└─sdb1                 /home/foo/workspace
sr0                    
loop0                  
└─loop0p1              
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  • 1
    What does ls /dev/loop* show?
    – John
    Jun 19, 2017 at 17:34
  • 1
    What is the output of lsblk -f?
    – Mio Rin
    Jun 19, 2017 at 18:28

2 Answers 2

11

How to mount a partition in a full disk image that contains a msdos partition table.

Tools:

  • fdisk
  • mount
  • calculator

Get the partition layout of the image.

sudo fdisk -l -u=sectors /work/loop_test/disk_image.img

Example output:

Disk /work/loop_test/disk_image.img: 29 MB, 29629952 bytes
255 heads, 63 sectors/track, 3 cylinders, total 57871 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: 0x0009d7e5

                     Device Boot      Start         End      Blocks   Id  System
/work/loop_test/disk_image.img1       2048       18431        8192   83  Linux
/work/loop_test/disk_image.img2       18432      57343       19456    7  HPFS/NTFS/exFAT

Calculate the offset from the start of the image to the partition start. In this case the ntfs partition.

formula:

Sector size * Start = Offset
512 * 18432 = 9437184

Mount the image, passing the offset for the desired partition.

In this example the ntfs partition.

sudo mount -o loop,offset=9437184 /work/loop_test/disk_image.img /mnt/ntfs_partition
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  • 4
    Instead of calculating the offset by yourself, you could even use bash's arithemtic evaluation: sudo mount -o loop,offset=$((512*18432)) ...
    – Murmel
    Oct 16, 2018 at 13:13
3

Running losetup -P will automatically detect partitions and create appropriate /dev/loop0pX devices for you. No need to perform the calculations manually.

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