[ILUG] loopback partition tables ?

[Padraig Brady]

John P. Looney wrote:

>  If I have a disk image on disk, can I mount partitions inside that disk
> image, loopback ? I can mount partition images no problems....just
> wondering is there wierd magic I could do to make it work.
> 
> Kate


Use gpart to find the partition offsets:

An example:

Say you have a 32MB disk image with a given geometry,
the following (non obvious) gpart command shows the
appropriate info:

gpart -vgd -C 31,32,63 sentinel.img

This will print info like:

Primary partition(1)
    type: 131(0x83)(Linux ext2 filesystem)
    size: 2mb #s(4576) s(32-4607)
    chs:  (0/1/1)-(8/15/32)d (0/0/33)-(2/9/9)r
    hex:  00 01 01 00 83 0F 20 08 20 00 00 00 E0 11 00 00

Primary partition(2)
    type: 131(0x83)(Linux ext2 filesystem)
    size: 28mb #s(58368) s(4608-62975)
    chs:  (9/0/1)-(122/15/32)d (2/9/10)-(31/7/39)r
    hex:  00 00 01 09 83 0F 20 7A 00 12 00 00 00 E4 00 00

The pertinent info here is s(32-4607) and s(4608-62975).
This means that partition 1 starts @ block 32 and partition 2
@ block 4608. The blocks are 512 bytes so the offset in bytes
for partitions 1 & 2 is: 16384 & 2359296.

These are the 2 bits of info required for the mount command,
so to mount the image you would do:

mkdir par1 par2
mount -t ext2 -o loop,offset=16384,ro sentinel.img par1
mount -t ext2 -o loop,offset=2359296,ro sentinel.img par2

Padraig.