winxp freebsd dual boot with freebsd on second HD

Matthew Seaman m.seaman at
Sun Sep 19 05:09:36 PDT 2004

On Sat, Sep 18, 2004 at 05:20:35PM -0700, Abe Olson wrote:
> The instructions say:
> "Other operating systems, in particular Windows® 95, have been known to 
> overwrite an existing MBR with their own. If this happens to you, or you 
> want to replace your existing MBR with the FreeBSD MBR then use the 
> following command:
> # fdisk -B -b /boot/boot0 device
> Where device is the device that you boot from . . ."

You have to do that to all bootable drives in your machine -- so
assuming your Windows disk is ad0 and your FreeBSD disk is ad2, you'ld

    # fdisk -B -b /boot/boot0 ad0
    # fdisk -B -b /boot/boot0 ad2

In either case, you shouldn't need to rewrite the partition table.

See also boot0cfg(8) for a tool that lets you configure exactly how
the boot blocks work.  Indeed, you can use boot0cfg(8) instead of
fdisk(8) to achieve your ends:

    # boot0cfg -B -b /boot/boot0 ad0
    # boot0cfg -B -b /boot/boot0 ad2

boot0cfg only ever affects the boot blocks; unlike fdisk it doesn't do
anything with partition tables, other than allow you to choose which
slices to boot from.

Note that the boot0 boot block is very minimal -- it fits into a
single 512 byte sector -- and that many people prefer 3rd party boot
managers like GAG: which, while quite a
bit bigger, have a much friendlier user interface.



Dr Matthew J Seaman MA, D.Phil.                       26 The Paddocks
                                                      Savill Way
PGP:         Marlow
Tel: +44 1628 476614                                  Bucks., SL7 1TH UK
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