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Re: Removing CSM compability from grub bootloader.

From: noone atall
Subject: Re: Removing CSM compability from grub bootloader.
Date: Sun, 9 Aug 2020 09:50:11 -0400

I was going to post this earlier but I wanted to make sure I understand
some concepts and that took quite some time.
First off I'm sorry for not explaining the problem properly beforehand. I
should have.

The said motherboard is a Gigabyte GA-990-XA-UD3.
It's using the weird Hybrid EFI firmware.
It does not have any option regarding CSM. I think the name hybrid is well
put because it's not really UEFI nor BIOS.
All it does regarding boot process is booting fallback EFI file
/EFI/boot/bootx64.efi .

efibootmgr has no control over it. So I think it creates EFI entries at
boot and it does not actually hold any memory regarding EFI entries.

When the drive is capable of booting both EFI and legacy it checks whether
the device is larger than 3 TB or not and boots legacy whenever possible.

More info here:

Destroying the boot sector did not work.
dd if=/dev/zero of=/dev/sdXY bs=446 count=1

So I concluded the motherboard does not like MBR/EFI configuration of
bootable ISOs.

As a last resort, I decided to try GPT/EFI, which worked out well.

But i'm still shocked at how hard it is to gather information regarding
bootloaders. Those websites out there make a good job of sounding like they
are actually on something but after a long read I look back and I see that
I got no new information. It's like a joke that goes on and on but the
punchline never comes.

They are all very confusing because authors don't actually have a clue what
they are talking about. It's worse than clickbait.

Btw if you don't mind one last question, why grub does not boot when I
don't flag fat32 EFI system partition as 'esp' and 'boot' from GParted?
What is a flag actually and where is it stored? Is it a signature like 55

Many thanks for your attention.

On Wed, Aug 5, 2020, 11:36 AM noone atall <> wrote:

> help-grub <> is a list
> for getting help for GRUB. Subscription to the list is not required to post
> a question
> Hi,
> I read this and i hoped it would be okay to ask a question.
> I have an old motherboard that is unable to boot usb devices in EFI mode.
> Which means it only boots hard drives and cd/dvd in efi mode. As i have
> encountered some issues with dvds and i don't like them in general i
> decided to use hard drives as installation media.
> However, the Manjaro linux iso is set to boot both modes. As it is based
> on grub i decided to try my luck asking help on grub forums, which
> apparently is not present so here i am.
> Long story short I would very much appreciate it if you could tell me
> which files and folders one needs to remove from grub bootloader to destroy
> it's capability to boot on legacy BIOS firmware.

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