.\"	$NetBSD: boot.8,v 1.9 1999/05/07 14:00:39 drochner Exp $
.\"
.\" Copyright (c) 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" This code is derived from software written and contributed
.\" to Berkeley by William Jolitz.
.\"
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.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
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.\"     @(#)boot_i386.8	8.2 (Berkeley) 4/19/94
.\"
.Dd March 13, 1997
.Dt BOOT 8 i386
.Os
.Sh NAME
.Nm boot
.Nd
system bootstrapping procedures
.Sh DESCRIPTION
.Sy Power fail and crash recovery.
Normally, the system will reboot itself at power-up or after crashes.
An automatic consistency check of the file systems will be performed,
and unless this fails, the system will resume multi-user operations.
.Pp
.Sy Cold starts.
The 386
.Tn "PC AT"
clones attempt to boot the floppy disk drive A (otherwise known as drive
0) first, and failing that, attempt to boot the hard disk C (otherwise
known as hard disk controller 1, drive 0).
The
.Nx
bootblocks are loaded and started either by the BIOS, or by
a boot selector program (such as OS-BS, BOOTEASY, the OS/2 Boot Menu or
.Nx 's
boot-selecting master boot record - see
.Xr mbr 8 ).
.Pp
Once running, a prompt similar to the following will appear.
.Bd -unfilled -offset indent
>> NetBSD BIOS Boot, revision 2.2
>> (user@buildhost, builddate)
>> Memory: 637/15360 k
Use hd1a:netbsd to boot sd0 when wd0 is also installed
Press return to boot now, any other key for boot menu
booting wd0a:netbsd - starting in 5
.Ed
.Pp
After a countdown the system image listed will be loaded. (In the
above example, it will be
.Dq Li wd0a:netbsd
which is the file
.Nm netbsd
on partition 
.Dq a
of the
.Nx
MBR partition of the first hard disk known to the BIOS [which is
appearently an IDE or similar device - see the
.Em BUGS
section].)
.Pp
The default disk will be set to the disk that the boot loader was
loaded from.
To boot from an alternate disk, the full name of the device should
be given at the prompt. Alternate system images can be loaded by
just specifying the name of the image.
.Pp
The following list of supported devices may vary from installation to
installation:
.Bd -unfilled -offset indent
sd	SCSI disks on a controller recognized by the BIOS. The unit
	number is the BIOS device number.
wd	ST506, IDE, ESDI, RLL disks on a WD100[2367] or
	lookalike controller(s), as numbered by the BIOS.
hd	Hard disks as numbered by the BIOS.
fd	Floppy drives as numbered by the BIOS.
.Ed
.Pp
The
.Op Fl s
flag to the boot loader will bring the system up in single-user mode.
The
.Op Fl a
flag instructs the system to prompt for the location of the root filesystem
and the system crash dump device.
The
.Op Fl r
flag instructs the system to use the compiled in value for the root
device, not the device the system image was loaded from.
The
.Op Fl d
flag to the boot loader will bring the system up in debug mode.
Here it waits for a kernel debugger connect; see
.Xr ddb 4 .
.Pp
In an emergency, the bootstrap methods described in the
.Nx
installation notes for the i386 architecture
can be used to boot from floppy.
.Sh FILES
.Bl -tag -width /usr/mdec/biosboot.sym -compact
.It Pa /netbsd
system code
.It Pa /usr/mdec/biosboot.sym
boot block (not installed)
.It Pa /boot
boot block (installed).
.El
.Sh SEE ALSO
.Xr boot_console 8 ,
.Xr ddb 4 ,
.Xr halt 8 ,
.Xr installboot 8 ,
.Xr reboot 8 ,
.Xr shutdown 8 ,
.Xr dosboot 8 ,
.Xr mbr 8
.Sh BUGS
Hard disks are always accessed by BIOS functions. Unit numbers are
BIOS device numbers which might differ from numbering in the
.Nx
kernel or physical parameters (eg SCSI slave numbers). The distiction
into
.Dq sd
and
.Dq wd
devices at the bootloader level is meaningless and exists for
historical reasons. (This is less a bug of the bootloader code than
a shortcoming of the PC architecture.)
The default disk device's name printed in the starting message
is derived from the
.Dq type
field of the
.Nx
disklabel (if it is a hard disk).