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Re: [Bug-xorriso] ISO installer image: GPT versus MBR partitions

From: Thomas Schmitt
Subject: Re: [Bug-xorriso] ISO installer image: GPT versus MBR partitions
Date: Wed, 24 Apr 2019 08:56:57 +0200


i wrote:
> > > > So programs like /sbin/isosize can tell the image size

> > (The [Debian] layout with nested partitions obsoletes the cleanliness
> >  considerations about partition start at LBA 0.)

Florian Pelz wrote
> So… GPT is wrong for some optical media too?

Not in this aspect. GPT partitions must not start at block 0.
So the overall ISO superblock is not mountable as partition and thus
free to claim the full image size as filesystem size.

The problem of restriction to partition size arises with MBR and
start block 0 of partition 1, when the nested partition mess of
"isohybrid -u" is untangled.

> By the way, someone I know has a most peculiar machine called Lenovo
> Ideapad 100S which does not boot Guix, but apparently is very picky in
> general (cf. <https://forums.linuxmint.com/viewtopic.php?t=216476>).
> Its CPU is claimed to support 64-bit, but its boot firmware rejects
> most 64-bit isos.

If Guix does not show up in the boot manager, try a plain grub-mkrescue
image that was made when GRUB was configured for both EFI variations:
32 bit x86 and 64 x86.
My experiments are made when it is configured for those two plus PC-BIOS.
The EFI partition then has bootx64.efi and bootia32.efi in /efi/boot/.

> It might just not be feasible to please every EFI system.

Let's see how far we get. This research not only helps Guix but also
GRUB. (And it has a tendency to reveal my bugs in xorriso.)

Have a nice day :)


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