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Re: hybrid BIOS/UEFI images for cloud

Hello Chris,

Sorry for the very late response.

On 5/27/21 9:25 PM, Chris Murphy wrote:
> Hi,
> Fedora Cloud SIG have a couple of related issues, create images using
> GPT [1] and create images supporting UEFI boot [2]. What we'd like to
> do is create a single set of images that are UEFI and BIOS bootable,
> out of the box. And I'm wondering if this is possible in Anaconda now,
> or if it could easily be enhanced to make it possible via kickstart?

I don't think is possible with the Anaconda UI but it's certainly via
kickstart. And that is exactly what RHEL/CentOS does for cloud images:


> If the image creation environment is BIOS, grub2-install will populate
> LBA 0 and BIOS Boot partitions correctly. But I'm uncertain whether
> anaconda will create and mount /boot/efi, i.e. if the kickstart
> manually creates an ESP mounting it at /boot/efi, will anaconda resist
> due to the environment being BIOS? The installation of grub2-efi-*
> RPMs should work though. We probably don't need efibootmgr to run, we
> can just expect BOOTX64.EFI fallback to discover there isn't an nvram
> entry, and add one. And due to Fedora 34 unified grub feature, a
> single /boot/grub2/grub.cfg should work whether UEFI or BIOS boot.

Yes, relying on the default EFI boot behavior is completely reasonable.

> If the image creation environment is UEFI, grub2-install doesn't work,
> it'll detect UEFI and it'll fail. And thus no BIOS bootloader can be
> installed. Maybe we could do a UEFI installation, additionally
> creating BIOS Boot partition, and run a post install script that does
> `grub2-install --target=i386-pc` to  add the BIOS bootloader?
> Thoughts?

You could do it either way with a custom quickstart, doing a BIOS install
and add the EFI bits on top or do an EFI install and add the BIOS bits.

I *think* the CentOS-Stream-9-kvm-x86_64.ks shared above could work for
either case.
> [1]
> https://pagure.io/cloud-sig/issue/330
> [2]
> https://pagure.io/cloud-sig/issue/309

Best regards,
Javier Martinez Canillas
Software Engineer
New Platform Technologies Enablement team
RHEL Engineering

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