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From: mconst@soda.CSUA.Berkeley.EDU (Michael Constant)
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: undoing dangerous dedication
Date: 2 Dec 1995 06:47:41 GMT
Organization: Society for the Prevention of Cruelty to Vegetables, UC Berkeley
Lines: 34
Message-ID: <49osqd$7ma@agate.berkeley.edu>
NNTP-Posting-Host: soda.csua.berkeley.edu
The "dangerously dedicated" option in the FreeBSD install isn't so
dangerous! I installed one of the 2.1.0 SNAPs on my old 486/25, with
the dangerously dedicated disk option. I never really used the computer
much, though (my real computer is a much better FreeBSD platform), and
finally the time came when I needed to use it as a DOS box (don't ask,
you don't want to know).
So, with a shudder, I got out my old DOS disks and started installing
MS-DOS. When I booted into DOS, though, the BIOS gave me a "no bootable
partition" error. I assumed this was caused by the dangerous dedication
I had chosen in the FreeBSD install. I tried manually repartitioning
the disk and making sure the DOS partition was marked active. It didn't
help.
Then I sat down and thought. The FreeBSD install didn't do anything to
physically make it impossible to partition the disk again -- it just
stored data in some areas of the disk that are noramlly reserved for
system files. But I'd already refreshed the partition table. What else
was it using? The master boot record, of course! I ran "fdisk /mbr" to
refresh my boot record, and now DOS works fine (well, inasmuch as DOS
works in the first place).
For those who haven't seen it, "fdisk /mbr" is an undocumented DOS
command which rewrites the master boot record on drive C: with a generic
DOS boot program. I believe this will work to recover the ability to
use partitions on a disk that has been dangerously dedicated to FreeBSD.
It worked for me at least :-)
Of course, there are very few times when you would *want* to recover
the ability to use partitions on a disk that has been dedicated to
FreeBSD :-) But for those times when it is necessary, I hope this will
be helpful.
--
Michael Constant (mconst@soda.csua.berkeley.edu)