MultiBoot OpenBSD/Debian

[Head_on_a_Stick]

Originally Posted by shep

I renamed BOOTX64.EFI from OpenBSD to BSD_BOOTX64.EFI and copied it over to Debian /boot/efi/.

You can keep OpenBSD's BOOTX64.EFI loader in the original location and use this instead:

menuentry 'OpenBSD' {
   set root='hd0,gpt1'
   chainloader EFI/BOOT/BOOTX64.EFI
}

^ If that is saved as /boot/grub/custom.cfg then there is no need to run `update-grub` afterwards, it will be sourced automatically by Debian's standard grub.cfg

The only caveat here is that some defective UEFI implementations will boot $ESP/EFI/BOOT/BOOTX64.EFI automatically even if Debian's GRUB creates NVRAM entries instructing the motherboard to do otherwise, in that case moving BOOTX64.EFI will be necessary to load GRUB's menu.

I find the insmod commands unnecessary, GRUB loads the modules automatically.

Note that OpenBSD will default to a UEFI installation if a GPT disk is used and will install a non-UEFI system to an msdos disk.

[shep]

Originally Posted by Head_on_a_Stick

The only caveat here is that some defective UEFI implementations will boot $ESP/EFI/BOOT/BOOTX64.EFI automatically even if Debian's GRUB creates NVRAM entries instructing the motherboard to do otherwise, in that case moving BOOTX64.EFI will be necessary to load GRUB's menu.

On my install Debian produced a $ESP/EFI/BOOT/bootx64.efi. I had read that EFI partitions were msdos and I was concerned that bootx64.efi would not be distinguished from BOOTX64.EFI. Hence I renamed it and placed it in a location specified in 40_custom. This was in part based on a post in the OpenBSD mailing list where BOOTX64.EFI was renamed.

Debian 10 is rolling out a secure boot that needs the linux boot kernel placed in /boot. I have not ventured into this as far as secure Dual booting with OpenBSD.

https://wiki.debian.org/SecureBoot

https://wiki.debian.org/SecureBoot/Discussion

[Head_on_a_Stick]

Originally Posted by shep

On my install Debian produced a $ESP/EFI/BOOT/bootx64.efi

Ah, I see. I haven't installed Debian on a UEFI computer since stretch, I think that used $ESP/grub/debian/grubx64.efi and made an NVRAM entry to set that as the loader.

I will have to try the buster installer on a UEFI laptop.

I had read that EFI partitions were msdos and I was concerned that bootx64.efi would not be distinguished from BOOTX64.EFI.

The FAT filesystem is case-insensitive but because the names are longer than 8 characters they should have an LFN extension which will distinguish between the two.

[hrsetrdr]

Originally Posted by shep

This is still relevant for MBR bootloaders. In the interim GPT/UEFI bootloading has become a newer option for supported hardware. I'm presently running Debian 10(Buster) and OpenBSD 6.4 with a GPT bootloader and this entry in Debian /etc/grub.d/40_custom

Thanks, good to know. MBR will be the route I'll be going with this particular machine(AMD Phenom II x4 965).