It is easy to mount a cdrom or hard drive PARTITION image under
linux.
mount -o loop,ro,noatime cdrom_image.iso mountpoint/
mount -o loop,ro,noatime partition_image.img mountpoint/
However, directly trying to mount a hard drive image fails, because
the start of a disk is not the start of the first partition.
The first sector of a typical hard drive looks something like
( Description of MSDOS-style partition table and master boot record as
+ gleaned
from the soure of /parted/ and /grub/. )
---------------------------------------------------------------- 0 - 6
+3
boot code boot code boot code boot code boot code boot code
---------------------------------------------------------------- 64 -
+127
boot code boot code boot code boot code boot code boot code
---------------------------------------------------------------- 128 -
+ 191
boot code boot code boot code boot code boot code boot code
---------------------------------------------------------------- 192 -
+ 255
boot code boot code boot code boot code boot code boot code
---------------------------------------------------------------- 256 -
+ 319
boot code boot code boot code boot code boot code boot code
---------------------------------------------------------------- 320 -
+ 383
boot code boot code boot code boot code boot code boot code
---------------------------------------------------------------- 384 -
+ 447
boot code boot code boot code boot code (to 440) AAAABB(
---------------------------------------------------------------- 448 -
+ 511
partion one )(partion two )(partion three )(partion four )CC
AAAA = mbr_sig
BB = unknown
CC = magic
Each 16 byte partion entry is
---------------- 0 - 15
ABBBCDDDEEEEFFFF
C = type
BBB,DDD =
EEEE = start sector from 0
FFFF = length in sectors
The sector counts are little-endian integers, easily parsable with
unpack("V").
Using the offset of the partition, it is possible to mount a partition
within a hard drive image file.
mount -o ro,noatime,loop,offset=<sector offset * 512> hard_drive_image
+.img mountpoint/
On some older systems, mount only accepts offsets up to 2gb. A simple
way to check if this is a problem is to run
losetup -o 5100200300 /dev/loop5 small_file
followed by
losetup /dev/loop5
A system that limits offsets to 2gb will print
/dev/loop5: [XXX]:XXXXXX (small_file) offset 2147483647, no encryption
A system that supports large offsets will print
/dev/loop5: [XXX]:XXXXXX (small file) offset 5100200300, no encryption
