Auto-install EFI / BIOS bootloader

Auto-install EFI / BIOS bootloader

[Pierre Neidhardt]

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The manual suggests the following:

--8<---------------cut here---------------start------------->8---
     Note: Unsure whether to use EFI- or BIOS-based GRUB? If the
     directory ‘/sys/firmware/efi’ exists in the installation image,
     then you should probably perform an EFI installation, using
     ‘grub-efi-bootloader’.  Otherwise you should use the BIOS-based
     GRUB, known as ‘grub-bootloader’.  *Note Bootloader
     Configuration::, for more info on bootloaders.
--8<---------------cut here---------------end--------------->8---

From there, why wouldn't Guix do that automatically for use?

For instance, would could have the following:

--8<---------------cut here---------------start------------->8---
    (bootloader (bootloader-configuration
                 (bootloader grub-auto-bootloader)
                 (target "/dev/sdX))
--8<---------------cut here---------------end--------------->8---

The "target" can be used as follows:

- If in BIOS mode, use /dev/sdX directly.
- If in EFI mode, pick the partition with the ESP flag and look up the
mount-point in the (file-systems ...).

What do you think?


Side question: I just tried installing GuixSD on a brandnew workstation
and the motherboard (Asus PRIME B450M-K) displays "UEFI" when I press F2
on start.  Now when I boot the Guix image, /sys/firmware/efi does not
exist, and indeed the Grub EFI installation fails (the BIOS one works).
I tried with another distribution, same thing.  The error is something
like:

--8<---------------cut here---------------start------------->8---
/gnu/store/...-grub-.../.../modinfo.sh doesn't exist, please specify
--target or --directory.
--8<---------------cut here---------------end--------------->8---

Is it possible that Linux fails to detect the UEFI?

--
Pierre Neidhardt
https://ambrevar.xyz/

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Re: Auto-install EFI / BIOS bootloader

[Pierre Neidhardt]

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> Is it possible that Linux fails to detect the UEFI?

Wait... Could that be because of the SecureBoot thing? :/

-- 
Pierre Neidhardt
https://ambrevar.xyz/

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Re: Auto-install EFI / BIOS bootloader

[Danny Milosavljevic]

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Hi Pierre,

> From there, why wouldn't Guix do that automatically for use?

In practise UEFI likes to fake a lot of stuff.  It can happen that
/sys/firmware/efi exists but the system cannot *boot* via EFI.

Likewise, /sys/firmware/efi can vanish just because you booted
from CD using UEFI's BIOS fallback.

There are lots of other "fun" situations--and also lots of bugs in EFI
implementations.

grub-hybrid is better:  It supports booting both via EFI and via BIOS.

In order to support it we would have to partition somewhat like this:

http://www.slivermetal.org/2016/09/18/how-to-create-an-hybrid-uefi-gpt-bios-gptmbr-boot-usb-disk/

In short:

* Have both GPT and MBR partition tables, with the same entries.
* Invoke grub-install twice:
** Once with --target=x86_64-efi and the vfat ESP partition as argument,
** Once with --target=i386-pc and the drive (or a partition, I guess) as argument

Now it always boots.

(Hybrid MBR/GPT are "dangerous" because they have to be updated in lock-step)

Also, if we want to convert people from Windows or similar other operating systems,
the user should have to explicitly confirm overwriting the bootloader.

> Side question: I just tried installing GuixSD on a brandnew workstation
> and the motherboard (Asus PRIME B450M-K) displays "UEFI" when I press F2
> on start.  Now when I boot the Guix image, /sys/firmware/efi does not
> exist, and indeed the Grub EFI installation fails (the BIOS one works).
> I tried with another distribution, same thing.

See?

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Re: Auto-install EFI / BIOS bootloader

[Danny Milosavljevic]

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> (Hybrid MBR/GPT are "dangerous" because they have to be updated in lock-step)

Oops, correction:

GPT always has a dummy MBR partition table which marks everything as "used".
So the MBR will not be updated further.

Grub2 will use GPT (if available) both in the EFI and in the non-EFI case.

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Re: Auto-install EFI / BIOS bootloader

[Pierre Neidhardt]

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Interesting, Danny, thanks for sharing!

-- 
Pierre Neidhardt
https://ambrevar.xyz/

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