Re: Is --protective-msdos-label incompatible with -isohybrid-mbr?

[Thomas Schmitt]

Hi,

Martin Whitaker wrote:
> On booting from a USB stick, I get [at boot time] the error message:
>  isolinux.bin missing or corrupt.

Yes. --protective-msdos-label prevents the adjustment of the MBR template
isohdpfx.bin so that it knows where the El Torito boot image isolinux.bin
is. The message text stems from this MBR code when it wakes up and feels
lonely.

The option --protective-msdos-label was introduced on request of GRUB
development. It is obviously very unusual that this option is combined
with -isohybrid-mbr.
-isohybrid-mbr strives for a mountable ISO 9660 partition, which thus
to start at block 0 (if not -partition_offset 16 is used).
--protective-msdos-label strives for a first partition which begins at
block 1 and thus is not mountable. As said, a wish from GRUB development.

The two options override each other. The last one in the list of program
arguments is the winner.
  -isohybrid-mbr /dvdbuffer/debian-8.1.0-amd64-netinst.mbr \
  --protective-msdos-label \
produces a GRUB-ish partition table
  --protective-msdos-label \
  -isohybrid-mbr /dvdbuffer/debian-8.1.0-amd64-netinst.mbr \
produces isohybrid.

So my advise is to simply omit --protective-msdos-label unless you switch
to GRUB as BIOS boot loader. And even then i deem the result suboptimal.

In my eyes the most versatile and widely bootable pure GRUB layout is
what Ubuntu is using since release 20.10:
  ...
  -partition_offset 16 \
  --grub2-mbr ...path.to.grub.mbr.on.hard.disk... \
  -mbr-force-bootable \
  -append_partition 2 0xEF ...path.to.EFI.image.on.hard.disk... \
  -appended_part_as_gpt \
  -c /boot.catalog \
  -b ..path.to.file..."eltorito.img"...in.the.ISO... \
     -no-emul-boot -boot-load-size 4 -boot-info-table --grub2-boot-info \
  eltorito-alt-boot \
  -e '--interval:appended_partition_2:all::' \
    -no-emul-boot \
  ...


Have a nice day :)

Thomas