Multi-boot Linux + FreeBSD

[Damien Fleuriot]

While no expert, I would advise against running the kernel directly.

The loader allows you to boot in single user which may come handy at times.


On 24 Nov 2012, at 18:08, "Lucas B. Cohen" <lbc at bnrlabs.com> wrote:

> Hi Ralf,
> 
> On 2012.11.24 17:06, Ralf Mardorf wrote:
>> Perhaps later today I'll install 9.0 amd64. If possible I'll keep my
>> Linux GRUB legacy. Can I use my menu.lst [1] and add a chainloader or
>> something similar to boot FreeBSD from /dev/sda1?
> I don't know if GRUB v1 allows that, on a multiboot system I use GRUB 2
> to either load FreeBSD's loader(8) :
> 
> menuentry "FreeBSD (Loader)" {
>        insmod part_bsd
>        set root='hd0,msdos2,bsd1'
>        echo "Loading FreeBSD loader"
>        kfreebsd /boot/loader
>        echo "Starting FreeBSD loader"
> }
> 
> or to run its kernel directly, after having passed it optional device hints:
> 
> menuentry "FreeBSD (Direct Boot)" {
>        insmod ufs2
>        set root='hd0,msdos2,bsd1'
>        echo "Loading FreeBSD kernel"
>        kfreebsd /boot/kernel/kernel
>        echo "Loading FreeBSD environment"
>        kfreebsd_loadenv /boot/device.hints
>        set kfreebsd.vfs.root.mountfrom=ufs:/dev/ada0s2
>        echo "Booting FreeBSD"
> }
> 
> I'm not saying it's impossible, but I'm unable to chainload to the
> loader code on my system with this:
> menuentry "FreeBSD (Chainload)" {
>        insmod chain
>        set root='hd0,msdos2'
>        chainloader +1
> }
> 
> 
> 
>> FWIW I made backups of my HDD's MBRs.
>> I wonder if the installer will overwrite the MBR?
> Always a good thing to have backups. From what I've experienced and
> read, 9.0-RELEASE's installer is not always predictable in that regard,
> it's probably safer to assume it'll won't do what you want, and just
> restore your MBR after the installation, to go back to using GRUB for
> dual-booting.
> 
> Here's the pitfall, though: the MBR also holds the partition table. So
> make a fresh backup after you've created/reorganized the primary
> partitions (slices) on your disk using a tool you're familiar with.
> (Logical partitions and BSD partitions are stored differently, so they
> will survive an MBR restore, provided it doesn't modify the primary
> partition they're contained in.)
> 
>> I also would like to know, if there's a way to recover the partition
>> table, including a primary FreeBSD partition/slice, if this ever should
>> get broken and there should be no backup of the partition table be
>> available.
> The partition table is held alongside the MBR, in the first logical
> sector of your disk. Restoring one will restore the other.
> For extra safety, you can save the output of partitioning tools like
> fdisk or GNU parted expressed in sectors.
> 
> Hope this helps,
> 
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