.\"	$NetBSD: boot.8,v 1.19 2000/10/01 13:45:46 bjh21 Exp $
.\"
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.\" This code is derived from software written and contributed
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.\"     @(#)boot_i386.8	8.2 (Berkeley) 4/19/94
.\"
.Dd August 31, 2000
.Dt BOOT 8 i386
.Os
.Sh NAME
.Nm boot
.Nd
system bootstrapping procedures
.Sh DESCRIPTION
.Ss 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
.Ss 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 No 's
.No boot-selecting
master boot record - see
.Xr mbr 8 ).
.Pp
.Ss Normal Operation
Once running, a banner 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
apparently an IDE or similar device - see the
.Em BUGS
section].) Pressing a key within the time limit will enter
interactive mode.
.Pp
.Ss Interactive mode
In interactive mode, the boot loader will present a prompt, allowing
input of these commands:
.\" NOTE: much of this text is duplicated in dosboot.8; please try to
.\" keep both files synchronized.
.Bl -tag -width 04n -offset 04n
.It Xo Ic boot
.Op Va device : Ns
.Op Va filename
.Op Fl adqsv
.Xc
The default
.Va device
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.
.Va device
is of the form
.Xo Va xd 
.Op Va N Ns Op Va x
.Xc
where
.Va xd
is the device from which to boot,
.Va N
is the unit number, and
.Va x
is the partition letter.
.Pp
The following list of supported devices may vary from installation to
installation:
.Pp
.Bl -hang -compact
.It sd
SCSI disks on a controller recognized by the BIOS. The 
unit number is the BIOS device number.
.It wd
ST506, IDE, ESDI, RLL disks on a WD100[2367] or
lookalike controller(s), as numbered by the BIOS.
.It hd
Hard disks as numbered by the BIOS.
.It fd
Floppy drives as numbered by the BIOS.
.El
.Pp
The default 
.Va filename
is 
.Pa netbsd ;
if the boot loader fails to successfully
open that image, it then tries
.Pa netbsd.gz
(expected to be a kernel image compressed by gzip), followed by
.Pa netbsd.old ,
.Pa netbsd.old.gz ,
.Pa onetbsd ,
and finally
.Pa onetbsd.gz .
Alternate system images can be loaded by just specifying the name of the image.
.Pp
Options are:
.Bl -tag -width xxx
.It Fl a
Prompt for the location of the root filesystem and the system crash
dump device.
.It Fl d
Bring the system up in debug mode.  Here it waits for a kernel
debugger connect; see
.Xr ddb 4 .
.It Fl q
Boot the system in quiet mode.
.It Fl s
Bring the system up in single-user mode.
.It Fl v
Boot the system in verbose mode.
.El
.It Ic consdev Va dev
Immediately switch the console to the specified device
.Va dev
and reprint the banner.
.Va dev
must be one of
.\" .Bl -item -width com[0123]kbd -offset indent -compact
.Ar pc , com0 , com1 , com2 ,
.Ar com3 , com0kbd , com1kbd , com2kbd ,
.Ar com3kbd ,
or
.Ar auto .
See
.Sx Console Selection Policy
in
.Xr boot_console 8 .
.It Ic dev Op Va device
Set the default drive and partition for subsequent filesystem
operations. Without an argument, print the current setting.
.Va device
is of the form specified in
.Cm boot .
.It Ic help
Print an overview about commands and arguments.
.It Ic ls Op Pa path
Print a directory listing of
.Pa path ,
containing inode number, filename and file type.
.Pa path
can contain a device specification.
.It Ic quit
Reboot the system.
.El
.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 /netbsd.gz
gzip-compressed system code
.It Pa /usr/mdec/biosboot.sym
boot block (read by installboot)
.It Pa /usr/mdec/biosboot_com0.sym
boot block with output redirected to serial console at com0.
.It Pa /usr/mdec/biosboot_ps2.sym
boot block for MCA PS/2 machines, see
.Xr mca 4 .
.It Pa /usr/mdec/biosboot_resetvideo.sym
boot block for machines that need their video boards reset on bootup (e.g. iOpeners).
.It Pa /boot
boot block (written by 
.Xr installboot 8 ).
.El
.Sh SEE ALSO
.Xr ddb 4 ,
.Xr boot_console 8 ,
.Xr dosboot 8 ,
.Xr halt 8 ,
.Xr installboot 8 ,
.Xr mbr 8 ,
.Xr reboot 8 ,
.Xr shutdown 8
.Sh BUGS
This manual page documents the
.Pa biosboot
interface, which is used by ports other than
.Nx Ns /i386 .
.Pp
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 distinction
between
.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).
.Pp
Any
.Ar filename
specified after the boot options, e.g.:
.Bd -unfilled -offset indent -compact
.Cm boot -d netbsd.test
.Ed
is ignored, and the default kernel is booted.