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Re: And yet another UEFI/BIOS question: Work on both.

On Sun 23 Sep 2018 at 10:58:54 (-0400), Wayne Sallee wrote:
> What do you recommend for setting up a system that will boot in either
> UEFI or BIOS mode, so if it is moved back and forth between UEFI and
> BIOS, it will boot every time?

I have no idea whether this would work as I haven't tried it. The only
EFI system I have access to needs a working W10 system at all times,
so I wasn't prepared to disturb it when I installed linux alongside.

I would start with a GPT disk, set up with the first partition
starting at sector 2048 (for 512-byte sectors), ie 1MB alignment.
Obviously it will need a protective MBR.

I would follow that with a ~8MB partition containing no filesystem,
and having the partition type EF02 (BIOS-Boot). This is where Grub
can put most of its boot code for BIOS booting.

Next would come a ~250MB partition with a type of EF00 for the ESP.

The rest of the partitions would have a type of 8300 except for the
swap partition which is 8200. I'd start with a perhaps ~500MB for
a separate /boot partition, and then would follow /home, swap and
(for me) a couple of ~30-40GB root partitions. (I like a spare OS.)
I don't normally separate /boot, but I think it might be wise to
try and limit damage to a "containment zone" while doing this

That gives you your playground, and here's where I leave my comfort
zone, as my linux system runs in BIOS mode. I would start by
installing in EFI mode so you get its ESP sorted out.

Then comes the bit where I have no idea if it will work and what
obstacles you will encounter. I'd boot in BIOS mode from a USB
stick and attempt to make Grub install itself in the MBR (using
the BIOS-Boot partition for the remainder of its boot code).
If you achieve that, you can now see whether either of the
booting methods still works, and let us know.

No doubt there'll be people ready to pick holes in all this, and I
welcome any feedback.


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