Re: GRUB2 chainloading GPT NetBSD partition

[<tlaronde%kergis.com@localhost>]

On Tue, Jul 08, 2025 at 07:11:05AM +0000, RVP wrote:
> On Sun, 6 Jul 2025, beaker wrote:
> 
> > Thanks but my system isn't UEFI so I think this won't work but I'll
> > squirrel this away for future reference.
> > 
> 
> So, you want BIOS + GPT? Hmm, this'll be a bit tricky, I think.
> 
> On Mon, 7 Jul 2025, beaker wrote:
> 
> > # determine which wedge to install primary bootstrap to:
> > $ sudo dkctl wd0 listwedges
> > /dev/rwd0: 6 wedges:
> > dk5: e8b85d79-899f-4cd6-964e-af3db098e992, 2048 blocks at 2048, type:
> > dk0: Boot, 1046528 blocks at 4096, type: msdos
> > dk1: Debian, 268435456 blocks at 1050624, type: ext2fs
> > dk2: NetBSD, 125829120 blocks at 269486080, type: msdos  # <<<
> > 
> 
> This should be type `ffs', but, no matter because, ...
> 
> > # reboot and attempt GRUB 'chainloader (hd0,gpt3)+1':
> > => ERROR NO SLICE
> > 
> 
> I don't think bootxx_ffsv2 understands GPT. Here, I think it finds only the
> Protective MBR (and no NetBSD-type primary partition) and throws this error.
> 
> Try creating an Hybrid MBR with an NetBSD-type MBR entry with start and size
> corresponding to that of `dk2' (gdisk(8) on Linux).
> 

The caveat being that this sort of mixing is illegal concerning GPT
and that the GPT will not be manageable under some systems or with
some tools (the MBR is a "protected" one int GPT/UEFI scheme, i.e. it
must not be tampered with) so some systems / some tools will not see
the partitions anymore.

And the problem is that this is a multiboot disk so NetBSD could
then be bootable, while some other systems will not anymore depending
on the way others accept or not the tampered GPT.

In every case, do backup the GPT before changing anything...

FWIW...
-- 
        Thierry Laronde <tlaronde +AT+ kergis +dot+ com>
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