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BIOSBOOT(8) OpenBSD System Manager's Manual (I386 Architecture) BIOSBOOT(8)
biosboot - first-stage system bootstrap
This small program (roughly 256 bytes of code) is responsible for loading
the second stage boot(8) program, which in turn, will load the kernel.
It takes no input or options directly.
In order for biosboot to load the second-stage bootstrap, it has a table
inside it which describes boot(8)'s location. biosboot must be in-
stalled by, and have its block table filled in by, the installboot(8)
program. As this data is BIOS dependant, you must re-run installboot(8)
each time you reinstall boot(8) or move your disk or software between ma-
chines and/or controllers.
When biosboot receives control from either the BIOS or the MBR it will
print the message:
followed by a dot for every successfully loaded block, and then put cur-
sor on the next line right before switching into protected mode and
transferring control to the just loaded /boot program.
Diagnostics consist of two error messages:
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
Bad magic The just loaded /boot image contains a bad magic in it's
header. This might indicate some kind of hardware problem,
the boot argument to the installboot(8) command was not a
valid /boot program, or /boot or has been moved or changed.
Other common reasons for these errors to appear is that a wrong BIOS ge-
ometry has been used in installboot(8) for the device you are booting
The practice of making OpenBSD use the whole disk (ie: having biosboot as
the MBR) has been depreciated, and will not work on certain BIOS ver-
sions. There is a lot of strange behaviour with different BIOS's, one of
well known lobotomy cases is that the BIOS does not pass the right boot
drive number to the biosboot program. This is one of the main reasons
that having biosboot as the MBR has been depreciated.
/usr/mdec/mbr Master Boot Record block
/usr/mdec/biosboot primary bootstrap
/boot secondary bootstrap
/bsd system code
boot_i386(8), fdisk(8), installboot(8), boot(8).
It contains a fake partition table and associated things that it should
It should do a checksum over the loaded /boot image, and check that
against a value that installboot(8) has precomputed.
There is no BIOS error number reported nor is the location of the error
You can pick your motherboard, and you can pick your BIOS, but you can't
pick your motherboard's BIOS.
This program was written by Michael Shalayeff for OpenBSD 2.1. However
it's based on bootstrap code from older versions of this operating sys-
tem, other operating systems, other programs, and other people's work.
OpenBSD 2.1 September 1, 1997 2
Source: OpenBSD 2.6 man pages. Copyright: Portions are copyrighted by BERKELEY
SOFTWARE DESIGN, INC., The Regents of the University of California, Massachusetts
Institute of Technology, Free Software Foundation, FreeBSD Inc., and others.
(Corrections, notes, and links courtesy of RocketAware.com)
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