Trouble Rescuing a System

[Brian Minard]

I am trying to use the Fixit shell from FreeBSD 6.1 STABLE to rescue a
system running 7.0 STABLE. The problem is that I can't make the root
partition (i.e., "/") for the hard disk writable. I can mount other
partitions on the hard disks as writable. The hard disks contain a
mirrored GEOM file system. In creating the GEOM mirror I mapped
/dev/da0 to /dev/mirror/gm0 and then mirrored gm0 on /dev/da1. (All of
the GEOM configuration was done under 6.1 and the system was recently
upgraded to 7.0).

The fstab I created in the Fixit shell contains the following lines:

/dev/da0s1a /mnt/root ufs ro 0
/dev/da0s1d /mnt/var ufs rw 0

Fixit# mount /mnt/root
Fixit# mount -u -w /mnt/root
mount: /dev/da0s1a: Operation not permitted.

Mounting the /var file system works as expected.

What can I do to make /mnt/root a writable file system?

Thanks,
Brian