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Re: FreeBSD Boot Details

From: Jordan Uggla
Subject: Re: FreeBSD Boot Details
Date: Wed, 20 Jun 2012 14:44:26 -0700

On Wed, Jun 20, 2012 at 1:31 PM, Werner Scheinast <address@hidden> wrote:
> Am Montag schrieb Jordan Uggla:
>> The problem is that you don't just have an absence of an embedding
>> area, with UFS it's not even clear that you have a reserved *boot
>> sector*.
>> You can see the mailing list discussion about this here
> In this thread they say "UFS file system" when they apparently mean the
> whole scheme of disk label and sub-partitions that is normally used in a
> *BSD slice. So I'm still not sure about this point ...

No, they mean exactly what they said, and exactly what I explicitly
stated earlier, this has everything to do with the UFS filesystem and
nothing to do with disk labels. If you were using an ext2 filesystem
with BSD slices then you would be able to install grub's boot sector
to the first sector of the slice (though it still wouldn't be
recommended as it would require blocklists pointing to blocks on an
active filesystem, which are unreliable).

>> There is a way to tell grub-install "Clobber the first sector of this
>> partition even though that might make the entire filesystem unusable,
>> or clobber something more subtle but also important" but it seems like
>> such a bad idea to do that that I'm reluctant to state how.
> :-)
>> You should either install grub's boot sector to the MBR or nowhere
>> (using "grub-install --grub-setup=/bin/true /dev/sda" and loading the
>> core.img from another bootloader using multiboot).
> With this command the core.img is installed behind the MBR but nothing is
> written to the MBR itself, right? That's an interesting variant, good for
> many nice tricks. ;-)

No, with --grub-setup=/bin/true nothing is written except to files on
the filesystem. This is useful if you want to load grub's core.img
from another filesystem aware bootloader via the multiboot protocol.

> Okay, I think I know enough for now,
> thanks for the details,

You're welcome.

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