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BOOT(8) OpenBSD System Manager's Manual (I386 Architecture) BOOT(8)
boot - second-stage bootstrap
The main purpose of this program is to load the system kernel, dealing
with the downfalls of the PC BIOS architecture.
As described in boot_i386(8) this program is loaded by the biosboot(8)
primary bootstrap loader and provides a convenient way to load the ker-
nel. This program acts as an enhanced boot monitor for PC systems, pro-
viding common interface for the kernel to start from.
Basic operations include:
- Detecting and switching between multiple consoles.
- Loading kernels from any device supported by your system BIOS.
- Loading kernels compressed by gzip(1).
- Passing system parameters queried from the BIOS to the kernel.
- Providing an interactive command line.
The sequence of its operation is as follows: initialization, parsing the
configuration file, then an interactive command line. While at the com-
mand line you have 5 seconds to type any commands, if needed. If time ex-
pires, the kernel will be loaded according to the current variable set-
tings (See the set command). Each time a kernel load fails, the timeout
is increased by one second. The sequence of boot operations is as fol-
1. Set up a protected mode environment which catches and reports pro-
cessor exceptions, and provides a simple protected-mode BIOS inter-
2. Probe for console devices, which includes the (default) PC VGA+Key-
board console (pc0) and up to four serial consoles (com0 through
com3) connected to the serial ports. Display messages to the default
console about the devices found.
3. Detect memory. Conventional memory is detected by quering the BIOS.
Extended memory is detected by probing page-by-page through the ad-
dress space, rather than asking the BIOS; many BIOS cannot report
larger than 64M of memory. All the memory found is reported to the
default console device.
4. Probe for APM support in the BIOS. Message printed if support is
5. If the file /etc/boot.conf exists on the filesystem boot was loaded
from, open and parse it. This file may contain any commands boot ac-
cepts at the interactive prompt. Though default settings usually
suffice, they can be changed here.
6. The header line
OpenBSD BOOT [x.xx]
is displayed to the active console, where x.xx is a version number
of the boot program, followed by the
prompt, which means you are in the interactive mode and may enter
commands. If you do not, boot will proceed loading kernel with the
current parameters after the timeout period has expired.
The following commands are accepted at the boot prompt:
boot [image [-abcds]] Boots kernel image specified by the image with
options if any. Image specification consists
of a pair device: filename, either of each
maybe omitted (':' is not needed if both), in
which case values from boot variables will be
echo [args] Displays args on the console device.
help Prints a list of available commands and ma-
chine dependant commands, if any.
machine [subcommand] Issues machine-dependant commands. These are
defined for i386 architecture:
cnvmem Prints/sets the amount of conven-
diskinfo Prints list of hard disks installed
on your system including: BIOS de-
vice number, and the BIOS geometry.
extmem Prints/sets the amount of extended
memory Prints physical memory map.
regs Prints contents of processor regis-
ters if compiled with DEBUG.
ls [directory] Prints contents of the specified directory in
long format including: attributes and file
type, owner, group, size, filename.
reboot Reboots machine by initiating a warm boot pro-
set [varname [value]] If invoked without arguments, prints a list of
variables and their values. If only varname
is specified, displays contents of that vari-
able. If varname and value are both speci-
fied, sets that variable to the given value.
addr Address at wich to load the kernel.
howto Options to pass to the loaded kernel.
debug Debug flag if boot was compiled with
device Boot device name (ie fd0a, sd0a).
tty Active console device name.
image File name containing the kernel im-
stty [device [baudrate]] Displays or sets the baudrate for a console
device. If changing speed for the currently
active console, gives you five seconds of
pause before changing the baud rate to allow
you to change your terminal's speed to match.
If changing speed not for the active console,
sets the baudrate value to be used the next
time you switch to a serial console. The bau-
drate value is not used for the pc0 console.
The default baudrate if not specifically set
is 9600 baud.
time Displays system time and date.
/usr/mdec/biosboot first stage bootstrap
/boot system bootstrap
/etc/boot.conf system bootstrap's startup file
/bsd kernel image
boot_i386(8), fdisk(8), installboot(8), gzip(1).
RFC 1950 describes the zlib library interface.
The official home page for the version of zlib used in this operating
system see http://quest.jpl.nasa.gov/zlib/ .
Well, nobody is perfect.
This program was written by Michael Shalayeff for OpenBSD 2.1.
OpenBSD 2.3 September 1, 1997 3
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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