*BSD Unix with MBR or moving to non-UEFI GPT?

[dchmelik]

If I install NetBSD, FreeBSD, maybe OpenBSD, and DragonFlyBSD (which I heard does best symmetric multiprocessing, SMP) Unixes on my PC, can any boot on MBR from extended/logical partitions, or can I redo my solid state drive (SSD) as non-UEFI GPT and then boot them from any partitions, with LILO or GRUB2?

These day's I'd probably only install a DOS (FreeDOS or even MS/Win9x/ME) on my classic PC for classic graphics/music demonstrations (demos) & games but not on my main desktop PC, so I may as well switch to GPT when Slackware GNU/Linux 15 is out, if it'll make installation & booting easier, right?

[jggimi]

I can answer for your "maybe" OpenBSD. It may be possible to boot from a logical MBR partition if the BIOS can do it, but the Project doesn't support it:

Originally Posted by the OpenBSD FAQ

Preferably use one of the four primary MBR partitions for booting OpenBSD. Extended partitions may not work.

For EFI multiboot, the Project states:

Originally Posted by the OpenBSD FAQ

rEFInd is reported to usually work. GRUB is reported to usually fail. In either case, you are completely on your own.

[shep]

There are 2 potential conflicts:
1 The need for a primary partition as @jggimi mentioned
2. The location and name of BOOTX64.EFI

/boot
/efi
/EFI
/BOOT
/BOOTX64.EFI
BOOTIA32.EFI

https://ackstorm.de/posts/uefi-openb...dual-boot.html

OpenBSD names and places BOOTX64.EFI exactly as Fedora/RHEL does and installing OpenBSD to free disk space in Fedora results in the next boot starting OpenBSD. The Fedora install is still there and can be recovered by re-installing Grub2 and configuring Grub. Debian Derivatives and Crux place the BOOTX64.EFI in a different location and are easy, via Grub2, to dual-boot with OpenBSD.

I think there is a keysum in OpenBSD's BOOTX64.EFI that is involved in kernel re-linking because re-linking will fail if OpenBSD's BOOTX64.EFI is moved and/or renamed. @jggimi walked me through debugging what probably is not really a bug but a conflict.

The generic NetBSD kernel does not re-link and actually uses lower case: bootx64.efi (may not matter in a case-insensitive msdos/vfat /boot/efi partition).
Appears to be amendable to gpt partition numbered greater than 4. I am using the 5th gpt partition for NetBSD swap.

If FreeBSD/Dragonfly do not kernel re-link and can install to gpt partitions >4, you may be able to get all 4 BSD's on one disk. I can think of 3 paths:

1. First install NetBSD/FreeBSD and then install Grub2 from the respective package repository.
https://wiki.netbsd.org/grub2/
https://forums.freebsd.org/threads/h...freebsd.28443/
2. Install a compatible Linux with Grub2
With the Grub2 option you can use /etc/grub.d/40_custom and 41_custom. I have not tried it but I believe that you can duplicate 4*_custom multiple times beyond 41.
3. Use reFIND - I have not used but believe that it is capable of finding and creating the additional boot options.

[dchmelik]

NON-UEFI GPT?

[jggimi]

If your hardware is UEFI-capable, then you're already using UEFI. So-called "Legacy Boot" to boot MBR uses a Compatibility Support Module (CSM) within UEFI firmware to simulate an x86 BIOS.

Some OSes have bootloaders which can read a GPT partition table on systems without UEFI. Wikipedia states "FreeBSD and most Linux distributions can boot from GPT partitions on systems with either the BIOS or the EFI firmware interface." https://en.wikipedia.org/wiki/GUID_Partition_Table

[Head_on_a_Stick]

Originally Posted by dchmelik

NON-UEFI GPT?

GRUB (Linux) needs a BIOS boot partition to hold the core.img on a GPT disk.

[dchmelik]

Originally Posted by Head_on_a_Stick

GRUB (Linux) needs a BIOS boot partition to hold the core.img on a GPT disk.

What about LILO or a *BSD bootloader?

[Head_on_a_Stick]

LILO has been dead since 2016[0]. I don't have any experience of it though so I would have to refer you to a search engine for details if you still want to use it. For example https://www.linuxquestions.org/quest...ns-4175560467/

In respect of BSD, I've only tried OpenBSD and for that I know that the installer will default to a UEFI system if it detects a GPT disk. I don't know if it's possible to force a non-UEFI installation to a GPT disk but I suspect not.

[jggimi]

Originally Posted by Head_on_a_Stick

I don't know if it's possible to force a non-UEFI installation to a GPT disk but I suspect not.

I've just tested this with vmm(4). A GPT drive is not bootable with the default SeaBIOS. It only becomes usable when you bypass the BIOS and load a kernel directly with vmctl(8)'s start -b option.

[shep]

I think Slackware is the only distribution using elilo. Crux linux used to but now recommends grub2-efi:
https://crux.nu/Main/Handbook3-6#ntoc11

The Slackware elilo documentation was updated 1/11/2021 but contains many dead links:
https://docs.slackware.com/howtos:sl...uefi_and_elilo

It also looks like the firmware of your system may impact your effort.

https://docs.slackware.com/howtos:sl...void_surprises

If you decide to try a Linux Distribution with grub2-efi, I would recommend either a Debian based distribution
that uses the following paths:
Debian installs grub-efi for its EFI bootloader, as:

For amd64 architecture:

/boot/efi/EFI/debian/grubx64.efi

or Crux

/boot/efi/EFI/grub/BOOTX64.EFI

Slackware uses:

/boot/efi/EFI/Slackware/elilo.efi

or in case of potential firmware constraints:

/boot/efi//EFI/boot/bootx64.efi

Not sure where it goes in Slackware if you use grub2

The OpenBSD path is hard coded into kernel re-linking. You can move it and
still boot but kernel re-linking will fail.

/boot/efi/BOOT/BOOTX64.EFI

NetBSD path is flexible

/boot/efi/bootx64.efi

or

/boot/efi/NBSD/bootx64.efi

Crux has some BSD features including /etc/rc.conf and a ports system that might be attractive to you. Using uefi gives you 128 partions while using MBR's 4 partition limit will need some workarounds for 4 BSD's + swap and boot partition.

As to whether FreeBSD or DragonFlyBSD can boot from higher partitions you will have to test. I did test NetBSD with /swap at gpt4 and / at gpt5 and it booted but had issues (panic) near the end while the kernel was setting up /swap for kernel dumping. Reversing the partitions; / at gpt4 and /swap at gpt5, made the issue go away.

[Sehnsucht94]

FreeBSD and NetBSD can indeed boot a GPT disk from a BIOS firmware. See gptboot(8) ("GPT bootcode for UFS on BIOS-based computers)" and gpt(8) biosboot respectively. Both man pages at the bottom contain an example of how to manually set up a GPT disk to boot *BSD on a BIOS system.