Filesystems readable by grub

Posted Jul 27, 2024 20:43 UTC (Sat) by Wol (subscriber, #4433)
In reply to: Filesystems readable by grub by jem
Parent article: Giving bootloaders the boot with nmbl

> This has nothing to do with Windows. VFAT is the only file system UEFI understands, and the UEFI firmware expects to read executables from a VFAT formatted system partition at boot.

That is not, actually, true.

Witness Apple hardware, which afaik uses UEFI, but does not (unless we bugger about with it) have any VFAT partitions.

The specification states that UEFI *must* understand VFAT. It does not say that it's not allowed to understand anything else.

Which means if Grub is to boot linux on an Apple system it should/needs to understand Apple's disk formats. And who's to say Grub is running on a UEFI systsm anyway.

That's the point - Grub does not want to demand that there is a VFAT partition, because there is a quite possible scenario that it is the only software making that demand, and it doesn't want to be in that position. (And that position is - I believe - the case for all modern Apple systems.)

Cheers,
Wol

Filesystems readable by grub

Posted Jul 28, 2024 10:04 UTC (Sun) by jem (subscriber, #24231) [Link] (1 responses)

Ok, let's put it this way: the only thing UEFI firmware implementations have in common is that they can read from a VFAT file system. And that's typically the only file system UEFI firmware implementations know of. So if we are talking about the general case, i.e. how distro makers are going to set up booting so that it works on all UEFI machines, VFAT is the only choice. I admit that it may be possible for the kernel images to be placed on some other partition, if a boot loader is able to read from it. But the way UEFI normally works requires a VFAT partition anyway.

> Which means if Grub is to boot linux on an Apple system it should/needs to understand Apple's disk formats.

Not at all, my ca 2011 MacBook Air boots Linux the standard UEFI way, by loading systemd-boot and the kernel image from the EFI System Partition, which is a VFAT file system. Maybe macOS is started differently; I don't know and I don't care.

>And who's to say Grub is running on a UEFI systsm anyway.

True. I stopped using Grub about ten years ago, when I discovered that the kernel image can be loaded directly by UEFI. In this case, the over-engineered, hard to configure piece of software called Grub is relegated to being just a chooser application. There are better alternatives for this task, like systemd-boot.

Filesystems readable by grub

Posted Jul 28, 2024 13:42 UTC (Sun) by Wol (subscriber, #4433) [Link]

> There are better alternatives for this task, like systemd-boot.

: -)

Cheers,
Wol