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Re: How important is the MBR partition offset of grub-mkrescue ?

From: Thomas Schmitt
Subject: Re: How important is the MBR partition offset of grub-mkrescue ?
Date: Sun, 03 Nov 2013 16:21:55 +0100


> Isn't this HFS+ catalog sufficient for the problem at hand?

I see the misleading link to /dev/sdb1 with Debian 6
and with a Debian 7 based distro. Dunno which udev rule
first looks at /dev/sdb for an ISO PVD and then links
./by-label to the first partition of that device.

The filesystem itself is not necessarily mounted.
Actually, the /dev/sdb1 with start at LBA 1 cannot be mounted.
Neither as ISO nor as HFS+ (if that was present). An offset
of 512 bytes would spoil any address that works in an ISO image.

> Can we detect presence of this bug?

It is a bug of the perceiving system. Linux specific. Lifetime
at least for Debian 6 and 7, i'd say. 

Put a grub-mkrescue generated ISO on a USB stick (e.g. /dev/sdb),
replug, and see what your Linux has in /dev/disk/by-label.
(If it has such a directory, at all.)

> Additional problem you don't mention: consumption of space by additional
> headers. We use xorriso for making floppies as well (and it works).

The feature is easy to add by user arguments of grub-mkrescue
anyway. No need for action inside grub-mkrescue.
I am mainly fishing for experience with pure GRUB2 boot setups
and Linux. Most distros let BIOS boot ISOLINUX.

Is there a distro which produces its ISO images with grub-mkrescue
and uses all or most of the BIOS, UEFI, and Apple features ?

As soon as i have a working ISO image, i can play with it.
I never learned to build operating systems or boot loaders myself.
It would be helpful to have a copy of the grub-mkrescue script
which was used for image production. I understand it evolves.

> Another solution is to have a hybrid ISO + FAT or ISO + HFS+ + FAT layouts.

But will this help against udev madness ?

Whatever. If i remember correctly, we still have open plans
about adding FAT to the super-hybrid layout.
See the very end of

(I see that i did not yet document the --grub2-boot-info

Have a nice day :)


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