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From: Marcel Moolenaar <xcllnt@mac.com>
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Date: Wed, 11 Nov 2009 17:00:17 -0800
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References: <86tyx0mxjw.fsf@ds4.des.no>
To: =?iso-8859-1?Q?Dag-Erling_Sm=F8rgrav?= <des@des.no>
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Cc: current@freebsd.org
Subject: Re: How to confuse geom_part_mbr
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On Nov 11, 2009, at 3:49 PM, Dag-Erling Sm=F8rgrav wrote:

> While installing 8.0-RC2 via a netbooted 7.0-RELEASE:
>=20
> # fdisk -I -B ad0
> # bsdlabel -rw ad0 auto
> # bsdlabel -e ad0
> [hmm, that wasn't right!]
> # fdisk -I -B ad0
> # bsdlabel -rw ad0s1 auto
> # bsdlabel -e ad0s1
> # bsdlabel -B ad0s1a
> # newfs -U -L root ad0s1a
> # mount /dev/ufs/root /mnt
> [install to /mnt]
> # reboot
>=20
> The machine won't boot, even though you have a valid partition table =
on
> ad0 that points to a valid bsdlabel in ad0s1.

No, you don't have a valid partition table on ad0, because
you didn't remove the BSD disklabel in sector 2 on ad0.
You just overwrote sector 1 on ad0 and created a new BSD
disklabel in sector 64.

You still have a dangerously dedicated disk without partitions,
by virtue of the BSD label in sector 2.

--=20
Marcel Moolenaar
xcllnt@mac.com