.\"	$OpenBSD: biosboot.8,v 1.17 2003/06/06 21:45:33 jmc Exp $
.\"
.\" Copyright (c) 1997 Michael Shalayeff
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF MIND, USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.Dd September 1, 1997
.Dt BIOSBOOT 8 i386
.Os
.Sh NAME
.Nm biosboot
.Nd
i386-specific first-stage system bootstrap
.Sh DESCRIPTION
This small program (roughly 512 bytes of code) is responsible for
loading the second stage
.Xr boot 8
program, which in turn will load the kernel.
It takes no input or options directly.
.Pp
In order for
.Nm
to load the second-stage bootstrap, it has a table inside it which
describes
.Xr boot 8 's
location.
.Nm
must be installed by, and have its block table filled in by, the
.Xr installboot 8
program.
As this data is BIOS dependent, you must re-run
.Xr installboot 8
each time you reinstall
.Xr boot 8
or move your disk or software between machines and/or controllers.
.Pp
When
.Nm
receives control from either the BIOS or the MBR it will print the message:
.Pp
.Dl loading /boot
.Pp
followed by a dot for every successfully loaded block,
and then put the cursor on the next line right before switching into
protected mode and transferring control to the just loaded /boot program.
.Sh DIAGNOSTICS
Diagnostics consist of two error messages:
.Bl -tag -width read_error_
.It Er Read error
Some kind of error returned by the BIOS read call.
This might be any media error, including bad sectors (common on floppy disks),
and invalid sectors (can occur with messed up geometry translations).
.It Er Bad magic
The just loaded /boot image contains a bad magic in its header.
This might indicate some kind of hardware problem, the
.Ar boot
argument to the
.Xr installboot 8
command was not a valid /boot program, or /boot has been moved or
changed.
.El
.Pp
Other common reasons for these errors to appear is that a wrong BIOS geometry
has been used in
.Xr installboot 8
for the device you are booting from.
.Sh NOTES
The practice of making
.Ox
use the whole disk (ie: having
.Nm
as the MBR) has been deprecated, and will not work on certain BIOS versions.
There is a lot of strange behaviour with different BIOSes; one well
known lobotomy case is that the BIOS does not pass the right boot drive
number to the
.Nm
program.
This is one of the main reasons that having
.Nm
as the MBR has been deprecated.
.Sh FILES
.Bl -tag -width /usr/mdec/biosbootxx -compact
.It Pa /usr/mdec/mbr
Master Boot Record block
.It Pa /usr/mdec/biosboot
primary bootstrap
.It Pa /boot
secondary bootstrap
.It Pa /bsd
system code
.El
.Sh SEE ALSO
.Xr boot 8 ,
.Xr boot_i386 8 ,
.Xr fdisk 8 ,
.Xr installboot 8
.Sh HISTORY
This program was written by Michael Shalayeff for
.Ox 2.1 .
However it's based on bootstrap code from older versions of this
operating system, other operating systems, other programs, and
other people's work.
.Sh BUGS
It should do a checksum over the loaded /boot image, and check that against
a value that
.Xr installboot 8
has precomputed.
.Pp
There is no BIOS error number reported nor is the location of the error
reported.
.Pp
You can pick your motherboard, and you can pick your BIOS,
but you can't pick your motherboard's BIOS.