this works for me from a script;

    partition_id=169 
    disk=sd0 
    ...
    eval `fdisk -S $disk`
    echo "Writing the sector-0 partition table"
    fdisk -f -i -b ${DLCYL}/${DLHEAD}/${DLSEC} ${disk}
    echo "Configuring partition-4 of sector-0 partition table"
    fdisk -3 -afu -s ${partition_id}/0/${DLSIZE} ${disk}


Wolfgang Rupprecht writes:
 > 
 > The fdisk man page mentions a 'fdisk -b cyl/heads/sects' for writing
 > the bios geometry in the MBR.  (I hope I've got this weird dos
 > terminology right.)
 > 
 > As far as I can tell 'fdisk -f -b 1023/15/63 wd0' does nothing.
 > Running a subsequent 'fdisk wd0' give me the same BIOS geometry.
 > 
 >     NetBSD disklabel disk geometry:
 >     cylinders: 13424 heads: 15 sectors/track: 63 (945 sectors/cylinder)
 > 
 >     BIOS disk geometry:
 >     cylinders: 527 heads: 255 sectors/track: 63 (16065 sectors/cylinder)
 > 
 >     Partition table:
 >     0: <UNUSED>
 >     1: <UNUSED>
 >     2: <UNUSED>
 >     3: <UNUSED>
 > 
 > Am I reading the man page wrong or is fdisk broke? 
 > 
 > I'd really like the align the number of heads in the bios and netbsd
 > geometries so that I can set the netbsd partition to start on cylinder
 > 1 from both netbsd's and the bios's standpoint.  Some of my computers
 > won't boot from a partition that isn't on a bios cylinder boundary.
 > I'd like to write a universal "build this disk" script that clears
 > everything and rebuilds from scratch.
 > 
 > -wolfgang
 > -- 
 >        Wolfgang Rupprecht <wolfgang+gnus@dailyplanet.wsrcc.com>
 > 		    http://www.wsrcc.com/wolfgang/
 > Coming soon: GPS mapping tools for Open Systems. http://www.gnomad-mapping.com/

-- 
Rex McMaster