Re: Partial success and strange partial failure -was [Re: Physically have install DVD set. Want ISO's from which they came.]

["Thomas Schmitt" <scdbackup@gmx.net>]

Hi,

i am the developer of xorriso, which created the image in question
under control of the debian-cd package.

Debian i386 images are ISO 9660 filesystems with El Torito Boot Record
to boot from CD/DVD/BD, and with Master Boot Record, which enables
them to boot from hard disk and USB stick.

If you put an ISO 9660 image onto the overall device file of an
USB stick (e.g. /dev/sdb) then it should be mountable by the
overall device file of the stick, too:

  dd if=debian-7.3.0-i386-netinst.iso of=/dev/sdb
  mkdir /mnt/my_debian_7_1
  mount -t iso9660 /dev/sdb /mnt/my_debian_7_1

To then see all its files, do

  find /mnt/my_debian_7_1


Some technical background:
  
El Torito and MBR are only present for pointing BIOS to the boot files
which it shall execute to bring up an operating system.
The MBR might have a confusing impact on programs which inspect
devices and try to be smart. A program which simply complies to
the specs of ISO 9660, El Torito, and MBR should have no problem.

The El Torito stuff already was shown here by the output of isoinfo.

The MBR can be made visible by a run of fdisk on the .iso file

  /sbin/fdisk -lu debian-7.3.0-i386-netinst.iso

or if already on USB stick /dev/sdb, by

  /sbin/fdisk -lu /dev/sdb

which should yield:

     Device Boot      Start         End      Blocks   Id  System
  /dev/sdb1   *          64      567295      283616   17  Hidden HPFS/NTFS

This means that there is a MBR partition 1 with some filesystem.
(The System type is prescribed by the ISOLINUX project.)
By a special preparation of the ISO image, it should be possible
to mount it as superuser by the partition device file, too:

  mount -t iso9660 /dev/sdb1 /mnt/my_debian_7_1

The reason why both device files /dev/sdb and /dev/sdb1 work for
mounting is that the ISO has two superblocks and directory trees.
One pair ready for mounting from /dev/sdb and for mounting from
CD/DVD/BD. The other pair is ready for mounting /dev/sdb1.
For details see:
  http://libburnia-project.org/wiki/PartitionOffset


Have a nice day :)

Thomas