index.md 7.3 KB
title: BSD operating systems x-toc-enable: true ...
Guide last updated on 16 November 2022.
NOTE: This guide pertains to x86 hosts, and does not cover supported CrOS/ARM chromebooks. For ARM targets, you should refer to u-boot documentation.
libreboot is capable of booting many BSD systems. This section mostly documents the peculiarities of libreboot as it pertains to BSD; you can otherwise refer to the official documentation for whatever BSD system you would like to use.
Kernel Mode Setting
Your BSD system must support Kernel Mode Setting for your graphics device (most of them do nowadays). The reasons will become apparent, as you read this article.
Boot BSD, using SeaBIOS
On x86 platforms, libreboot/libreboot both provide the choice of GNU GRUB and/or SeaBIOS payload. GRUB can technically boot BSD kernels, but the code is poorly maintained and unreliable for this use-case scenario; on BIOS systems, GRUB can chainload BSD bootloaders, but on bare metal (as coreboot payload), GRUB can only chainload other coreboot payloads or boot Linux/BSD kernels directly (but direct booting is only really reliable for Linux, in GRUB).
It is recommended that you boot in text mode, with SeaBIOS. You can literally just follow the official installation guides for your BSD system, whether it be FreeBSD, OpenBSD or others.
If you don't plan to set up Xorg/Wayland, then that's all you really need to do. For example, you might want to run a headless server, in which case you probably don't mind running in text mode all the time.
OpenBSD and corebootfb
It's still recommended to use SeaBIOS in text mode, but OpenBSD specifically
can work with SeaBIOS booting in a coreboot framebuffer, with SeaVGABIOS. In
Libreboot ROM images, this would be SeaBIOS images with corebootfb in the
file name.
Make sure to select MBR-style partitioning on the installer, and it will Just Work.
If you're using the GRUB payload but SeaBIOS is available in the boot menu, you can just select SeaBIOS at said menu, and OpenBSD will work fine.
FreeBSD and corebootfb
Assumed broken, so please ensure that you boot with SeaBIOS payload in text
mode (lbmk ROM images with txtmode in the file name, not corebootfb).
Warnings for X11 users
One important peculiarity of most libreboot and libreboot systems is: VGA mode support exists, if booting with corebootfb (coreboot's own framebuffer) and the SeaVGABIOS option ROM used in the SeaBIOS payload; however, the ability to switch modes is not present, which means you can't switch to text mode either.
Coreboot can start in framebuffer (corebootfb) or INT10H text mode, and it stays in whatever mode was set, unless KMS is used to change the mode. It should be noted that the coreboot framebuffer is not a VGA mode, but instead coreboot implements minimal drivers for hardware that it supports, providing a framebuffer directly in memory, which software (such as GRUB) can simply use.
The BSD bootloaders on x86, in BIOS systems, typically expect text mode startup. It is usually possible to set the console to higher VGA modes, on most systems, but not on most coreboot systems with native video initialisation used, due to the quirks already described. If you see any documentation (in BSD land) pertaining to VESA modes, ignore it entirely; unless you're using the proprietary VGA ROM for your device, it won't work, and libreboot/libreboot don't distribute these (instead, coreboot's own video initialisation is used where possible, or a headless SeaBIOS payload setup is provided, where you would either run it headless or install a graphics card).
Now, this would otherwise mean: no X11/Wayland. If you start in corebootfb mode with SeaVGABIOS, you won't get a display in BSD bootloaders, and if you boot in text mode, you can't set VESA modes from BSD. However, you're in luck:
At least OpenBSD and FreeBSD (possibly others) all have excellent KMS
support nowadays; short for Kernel Mode Setting. This avoids the inefficiency
of BIOS/UEFI methods, by having the kernel set modes directly. It is based on
KMS drivers that the BSD projects ported over from the Linux kernel. With this,
you can use X11/Wayland in FreeBSD (and just X11 in OpenBSD, for now).
For example: on FreeBSD, you can install graphics/drm-kmod as a package
or from ports, and (for Intel GPUs) do this:
sysrc kld_list+="i915kms"
This creates the following entry in /etc/rc.conf:
kld_list="i915kms"
On FreeBSD it is also recommended that you switch to KMS on the console/TTY;
add this to /boot/loader.conf so that you can still use the console after
terminating Xorg:
kern.vty=vt
You should not rely on the above instruction (for FreeBSD), because the exact step might change, and it does not go into full detail either. Refer to the documentation provided by your system, to know how KMS is configured.
ALWAYS READ THE MANUAL
All of the BSDs have excellent documentation; it's one of the defining characteristics, versus typical Linux distros.
Aside from this quirk in coreboot, regarding BIOS video modes, the BSDs otherwise work in exactly the same way as you would expect, and you can follow along to their official documentation without much fuss.
No specific or detailed guides will be provided here, because SeaBIOS is fairly self-explanatory; you can otherwise refer to the SeaBIOS documentation.
If you're flashing a ROM for a machine where seabios_withgrub
and seabios_grubfirst ROMs are available, choose seabios_withgrub.
DO NOT USE ROM IMAGES WITH seabios_grubfirst IN THE FILE NAME! These were
present in older Libreboot releases, and supported in previous revisions
of the build system, but they did not work for the intended purpose. More
info is written on the Libreboot installation guide. ROM
images with seabios_grubfirst in the filename will NOT be included in
future Libreboot releases.
Dubious mention: Tianocore
Tianocore is extremely bloated, and unauditable, so it is not included in libreboot or libreboot, but it is the reference UEFI implementation by Intel and contributors. It can boot most BSD systems very well.
More robust ways to provide UEFI services in Libreboot are to be investigated. Tianocore integration will not be provided officially, in any current or future releases of Libreboot.
Desktop users
Desktop users on libreboot/libreboot should just install a graphics card, and again boot with SeaBIOS in text mode; however, when you do this, SeaBIOS will execute the VGA option ROM on the card which will provide early video initialisation instead of coreboot's initialisation, and that VGA ROM will usually implement full INT10H modes, including the ability to set modes in the BIOS (using interrupts), in which case you don't need to worry about Kernel Mode Setting, but you should still use KMS anyway.
The reason to use KMS is because it's more efficient. The INT10H service can only be called in Real Mode or Virtual 8086 mode; v8086 is unavailable in long mode (x86_64) and switching into Real Mode just to set VGA modes is extremely expensive computationally speaking. This is why modern kernels (Linux and BSD one) do mode setting themselves.
You can learn more about INT10H text/VGA modes here: