Re: ISO installer image: GPT versus MBR partitions

["pelzflorian (Florian Pelz)" <pelzflorian@pelzflorian.de>]

On Tue, Apr 23, 2019 at 10:18:10PM +0200, Thomas Schmitt wrote:
> Florian Pelz wrote:
> > florian@florianmacbook ~ [env]$ grub-mkrescue -o output.iso minimal
> > --xorriso=./grub-mkrescue-sed.sh
> > grub-mkrescue: warning: Your xorriso doesn't support `--grub2-boot-info'.
> > Some features are disabled. Please use xorriso 1.2.9 or later..
> >
> > and yields no output.iso for me.  Note that xorriso actually has
> > version 1.5.0.
> 
> Does the script offer x-permission ?
> (Shame on me for not thinking of this in my download instructions.)
> 

This was the error.  It works after `chmod +x grub-mkrescue-sed.sh`.


On Tue, Apr 23, 2019 at 08:14:48PM +0200, Thomas Schmitt wrote:
> It would be interesting to learn about EFIs which fail without MBR
> signature.
> […]
> - Put the resulting output.iso on USB stick and offer it to your firmware
>   at boot time.
>   Is it not found by the EFI boot manager ?
>   If you let it boot, does the machine not show a GRUB prompt in the end ?
> 

It shows up twice in the boot selection screen as “GRUB 2.02” and “EFI
Boot” just like the Guix USB drive before.  It is bootable and shows a
GRUB prompt on my Macbook.



> - Negative results with other mode settings in MKRESCUE_SED_MODE would be
>   interesting, too.
> 

I can try tomorrow.

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.  I wonder if we could get that machine to boot Guix
(at least it currently cannot boot
guixsd-install-0.15.0.i686-linux.iso), but that may well be a waste of
time.  It might just not be feasible to please every EFI system.



> I wrote:
> > > So programs like /sbin/isosize can tell the image size even when the
> > > ISO has already been copied to USB stick.
> 
> > Sounds like this could be used to get a checksum or maybe GPG
> > verification of a USB drive that supposedly contains the iso.
> 
> That's what this property is advised for in Debian's CD FAQ.
> One can read trailing garbage not only from USB sticks but also from
> most DVD types.
> (The layout with nested partitions obsoletes the cleanliness
>  considerations about partition start at LBA 0.)
>

So… GPT is wrong for some optical media too?

Regards,
Florian