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Re: A thread on grub-bug could need attention

From: Thomas Schmitt
Subject: Re: A thread on grub-bug could need attention
Date: Wed, 31 Jan 2018 22:37:59 +0100


it comes to me that possibly Michel's grub-mkrescue run was BIOS-only.
So Michel, take much care to come back in good shape. We have experiments
to do. :))


At least on Debian the boot equipment prepared by grub-mkrescue depends
on which grub-* Debian packages are installed.

"grub-pc" enables BIOS equipment. In the case of an USB stick, it's the
MBR x86 boot code which comes into effect. It knows the block address of
the El Torito boot image. So i assume it loads and executes that binary.

"grub-efi-amd64" causes grub-mkrescue to prepare an EFI System Partition
with binary /efi/boot/bootx64.efi . 

"grub-efi-ia32" causes an EFI System Partition with binary
/efi/boot/bootia32.efi .

All three can be combined.

So after a vanilla run with grub-mkrescue, it is essential to inspect
the partition tables and El Torito boot equipment by

  xorriso -indev output.iso \
          -report_el_torito plain -report_system_area plain

If no lines like
  GPT disk GUID      :      04a5adf35d1adb4382bf8300bebe08a1
  GPT start and size :   4  34132  600
are reported, then the ISO has no EFI System Partition.

In this case a run with will not make much sense.
First one will have to configure GRUB to enable at least one of the EFI
variants. I dimly remember that the machine was 64 bit, i.e. should run

Have a nice day :)


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