Are Fedora CoreOS disk images hybrid BIOS+UEFI bootable?

As it says on the tin, I’m trying to find out if Fedora CoreOS disk images are hybridized to be able to boot properly on BIOS or UEFI systems (without a CSM).

I’m looking at potentially running Fedora CoreOS based systems in environments that are either UEFI-only or BIOS-only and I’d like to be able to use the same image for both environments, to reduce the strain on my sanity for managing images and debugging boot issues…

We provide a single metal image (actually that’s not true, we provide two to target disks with different sector sizes (512b and 4k)). The image(s) can be used for either BIOS (legacy) boot or UEFI boot. If you hit trouble please open an issue as that is the way it’s designed to work and we should fix any issues.

Edit: I’ve found that the 4k image doesn’t have the BIOS boot partition and that the hybrid BIOS/UEFI setup isn’t limited to our metal images. The statement above should read:

Our x86_64 images (including the metal image, like fedora-coreos-32.20200629.3.0-metal.x86_64.raw.xz) can be used for either BIOS (legacy) boot or UEFI boot. The exception to that is the metal4k 4k native image, which is targeted at disks with 4k sectors and does not have a BIOS boot partition because they are only supported with UEFI.

One aspect of FCOS is that our “default” partitioning is very simple (it’d be even simpler without the special temporary RHCOS <= 4.5 LUKS code), see the coreos-assembler - because all of the complexity for non-default setups lives in Ignition.

But we ship with BIOS/UEFI created by that script - Ignition handles reprovisioning just the filesystem with label=root if desired (see ).