Set up Grub2 to boot Freebsd using either Ubuntu tools or LiveUSB to find what partitions?

Question

I currently have Windows7 and Ubuntu 11.04 (Natty) installed on my computer. I also made a FreeBSD liveUSB (or installer, not sure; just dded their .img to the USB stick) and installed it without installing a bootloader (because I didn't want to mess up Grub2, and I thought Grub2 should be able to boot most anything). FreeBSD has it's own partition and inside that it has Freebsd partitions (maybe they are called slices?) as automatically allocated by the installer. I already tried running update-grub -- it said it was an Unknown Linux and didn't add an entry for it.

So, two questions:

1. How can I find what partition to tell Grub using either Ubuntu tools or the USB installer stick I have?
2. Once I find the partition, what would I put in /etc/grub.d/40_custom?

Answer 1

You have three choices: you can have Grub treat FreeBSD as some unknown OS and chainload FreeBSD's stage 1 bootloader, or you can have Grub load FreeBSD's stage 2 bootloader, or you can have Grub load the FreeBSD kernel.

Chainloading

This is the simplest and most reliable method. All you need is to install the FreeBSD bootloader on its own slice (what *BSD calls a slice is what Linux and Windows call a partition). Then Grub should find it automatically (via /etc/grub.d/30_os-prober) when you run update-grub. The entry in /boot/grub/grub.cfg would look like this (if FreeBSD is on /dev/sda2 a.k.a. /dev/wd0s2):

menuentry "FreeBSD" {
    set root=(hd0,2)
    chainloader +1
}

Loading a FreeBSD bootloader or kernel

Grub2 currently supports all major BSD kernels (assuming your computer boots from BIOS). The installation scripts don't (at least the ones shipped with Ubuntu 10.04, I haven't checked 11.04), so if you choose this route, you'll have to add your own entries via /etc/grub.d/40_Custom.

Here are sample entries from David Marec on the FreeBSD forums. I haven't tested them but they look plausible. The best method seems to be to load the FreeBSD stage 2 bootloader. You can specify the location of the FreeBSD installation as a disk number, slice number and partition a:

menuentry "FreeBSD (/boot/loader)" {
    insmod ufs2
    set root=(hd0,1,a)
    kfreebsd /boot/loader
}

or by searching a filesystem with a certain UUID, file or label:

menuentry "FreeBSD (/boot/loader)" {
    insmod ufs2
    search --no-floppy --file /boot/loader
    kfreebsd /boot/loader
}

Answer 2

Have you considered running update-grub? This will automatically update the GRUB system and its list of items for you.

Answer 3

Searching a filesystem with a certain UUID, file or label:

menuentry "FreeBSD (/boot/loader)" {
    insmod ufs2
    search --no-floppy --file --set=root /boot/loader
    kfreebsd /boot/loader
}

or:

menuentry "FreeBSD (/boot/loader)" {
    insmod ufs2
    search --no-floppy --file /boot/loader --set=root /boot/loader
    kfreebsd /boot/loader
}