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Re: Write iso/isohybrid on pendrive:problem


i would still like to see confirmation whether a non-zero
partition start indeed makes the USB stick acceptable for
Gparted again, after it was made unacceptable by program

antispammbox-debian wrote:
> Why an iso file is iso file, and a file  isohybrid is isohybrid?
> What is the difference between the two?

It is a hierarchy of specialization:
ISO 9660 image
  Bootable ISO image
    MBR equipped bootable ISO image
      ISOLINUX isohybrid MBR equipped bootable ISO image

A file with name ending ".iso" is supposed to be a disk image
that contains an ISO 9660 filesystem with data files in it.

ISO 9660 fileystems can additionally contain El Torito boot
information for booting via BIOS from CD, DVD, or BD media.
That's the traditional equipment of installation images and
Live CDs. Partitioning is not involved here.

BIOS boots from other media, e.g. from USB stick, by reading
a data structure called Master Boot Record (MBR) from the
first 512 bytes of the medium. These bytes get executed
as program code in order to start the boot procedure.
An MBR contains a partition table. This is were Gparted
gets involved.
ISO images have free space between bytes 0 and 32767. Thus
they may well contain an MBR.

Isohybrid is a feature of the ISOLINUX boot loader. The
program "isohybrid" writes an MBR into the start block of an
ISO image which already holds El Torito equipment of ISOLINUX.
The partition table of this MBR shows one partition spanning
from block 0 to the end of the ISO filesystem.

Debian installation ISOs for "i386" and "amd64" get produced
by program xorriso with options which insert an isohybrid MBR
into the emerging ISO image. So there is no need to apply
program "isohybrid" to them.
The images for architecture "i386" get prepared for MBR
partition start at 32 KB rather than 0. Last time i looked,
the images for "amd64" had an MBR with a partition that
starts at 0.

ISO 9660 images produced by the script grub-mkrescue of
bootloader GRUB2 contain El Torito and MBR, too.
It would be harmful for USB stick bootability if one would
apply ISOLINUX program "isohybrid" to them.
grub-mkrescue images have partition start at block 1, which
makes them unmountable.
(There is a problem with udev rules about /dev/disk/by-label.
See http://www.spinics.net/lists/hotplug/msg05814.html)

Have a nice day :)


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