Re: iso-hybrid is a syslinux feature
Hi,
i found this thread by googling. Please cc me if you think
i should know about any replies.
> > > iso-hybrid currently is only supported when using syslinux, not grub.
> > Why, why not with grub?
> The isohybrid program is a component of syslinux
True. isohybrid itself is a data add-on to ISO 9660 filesystems.
It is a Master Boot Record that gets written to the start of
the ISO image where the ISO specs reserve 32 KB for such purposes.
The data need to get equipped with a few block addresses within
the ISO 9660 image. The isohybrid programs (old and new) of
SYSLINUX produce the MBR from built-in templates and the
CD boot records (El Torito). My program xorriso can produce the
MBR together with the ISO image and its El Torito records.
Debian installation image production uses xorriso for that
purpose because it also generates Jigdo files in the same run.
> I have heard hybrid grub images can be made with xorriso, but this is as
> yet not implemented by debian-live.
Actually xorriso is used by the ISO image production script of
GRUB2: grub-mkrescue.
I understand it takes a prepared tree of operating system files,
adds the necessary files for GRUB2 booting, and determines the
xorriso options which bring the very early boot information
to El Torito and MBR. Then it runs xorriso by its mkisofs emulation
interface.
GRUB2 does not need an isohybrid program because it brings its
own MBR templates which additionally are smart enough to find
their boot time successor files in the ISO image by themselves.
No MBR patching is needed.
Both boot loaders move towards (U)EFI but will have to keep
the MBR stuff for BIOS booting from disk-like devices.
Some technical background stuff:
http://en.wikipedia.org/wiki/Master_boot_record
http://bazaar.launchpad.net/~libburnia-team/libisofs/scdbackup/view/head:/doc/boot_sectors.txt
Have a nice day :)
Thomas
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