Re: GRUB2 chainloading GPT NetBSD partition

[mlelstv%serpens.de@localhost (Michael van Elst)]

beaker%sdf.org@localhost (beaker) writes:

> gpt biosboot [-A] [-c bootcode] [-b startsec] [-i index] [-L label]

>for a gpt partitioned disk or is this relatively recent addition
>just an alternative of convenience?


It's a bit complicated.


A regular BIOS (not UEFI) loads the MBR from block 0 of a disk.
The boot program in the MBR checks the embedded partition table
and then continues to load a PBR from the first block of the
active partition. The PBR is then executed and continues with
the boot process.

MBR = master boot record
PBR = partition boot record

We maintain the regular MBR (and the partition table) with
the fdisk program (and the PBR with the installboot program).


If you use a GPT, there is only a "protective MBR" for compatibility.
But it's still possible to include a boot program in that "protective MBR"
that understands a GPT. This allows to use BIOS to boot from a
GPT formatted disk.

We maintain the GPT with the gpt program and 'gpt biosboot'
stores such a special boot program.


In your case however, you provide your own MBR (with grub)
and 'gpt biosboot' would just overwrite grub with our boot
program.