Bug 61605

Documentation for disk geometry (i386) is lacking.

As described in i386/61603, sysinstall doesn't always come up with a
usable disk geometry.

The Handbook documentation on sysinstall is a bit sparse. It should
mention that geometry may be guessed wrong, \\tools\\pfdisk.exe on the
CD-ROM can be used to pick up workable geometry numbers from within a
working DOS environment (but not a normally-running Windows XP, which
won't allow the necessary device access -- boot floppy created in XP
works, though).

http://www.freebsd.org/relnotes/4-STABLE/installation/i386/trouble.html #4.2.2
claims sysinstall will figure out geometry from a preexisting DOS partition,
but this didn't work for me -- perhaps because my DOS partition started at
sector #63??

I was able to boot FreeBSD from the 5.2 CD-ROM, after installing with
sysinstall's bad geometry values. It seems it should be possible to install
FreeBSD boot blocks at this point, without running through the whole
sysinstall process, but I was unable to find any pointers to how to do
so. I checked the FAQ (which says to reinstall from scratch), and the
manual pages for fdisk, sysinstall, boot0cfg, and disklabel (4.9) -- is
"bsdlabel -B ad0s2" the right way to go??

Fix: 

Mention sysinstall's good but imperfect geometry guessing in Handbook
(http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/install-pre.html 2.2.3) &
FAQ (http://www.freebsd.org/doc/en_US.ISO8859-1/books/faq/install.html#GEOMETRY).

Suggest disklabel/bsdlabel in Handbook & FAQ &
http://www.freebsd.org/relnotes/4-STABLE/installation/i386/trouble.html (4.2.2)
for fixing non-bootable systems installed with incorrect geometry.

Add bsdlabel/disklabel to SEE ALSO under boot0cfg.
How-To-Repeat: Search www.freebsd.org for "sysinstall geometry" seeking information on
getting a 5.2 system to bootstrap correctly. Bang head -- do not damage desk.