'\"macro stdmacro
.if n .pH g8.boot @(#)boot	40.9 of 10/10/89
.\" Copyright 1989 AT&T
'\"macro stdmacro
.nr X
.if \nX=0 .ds x} boot 8 "" "\&"
.if \nX=1 .ds x} boot 8 ""
.if \nX=2 .ds x} boot 8 "" "\&"
.if \nX=3 .ds x} boot "" "" "\&"
.TH \*(x}
'\" tc
.SH NAME
\f4boot\f1 \- bootstrap procedures
.SH DESCRIPTION
Bootstrapping is the process of loading and executing a standalone program.
For the purpose of this discussion,
bootstrapping means the process of loading and executing the
bootable operating system, but any standalone program can be booted
instead.
The diagnostic monitor for a machine is a good example of a standalone
program other than the operating system that can be booted.
.P
The bootstrap procedure on most machines consists of the following
basic phases.
.P
First, the machine is either turned on, or brought down to firmware mode in
any of a number of ways (hardware reset button, a \f4shutdown\f1 or
\f4init\f1 command, etc.).
On powerup, the boot process is generally begun automatically:  a small
firmware program is loaded and executed, and the process
moves into the second phase.
.P
From firmware mode, however, the boot process is not automatic and
the user can request the running of a firmware
command, a standalone program (such as the bootable operating system),
or the reconfiguration of the operating system.
See \f4firmware\f1(8) for more information on firmware operations.
For the purposes of this discussion, assume that an operating system boot
is requested from firmware;  a small
firmware program is loaded and executed, and the process
moves into the second phase.
.P
Second, the firmware boot program loads and executes a larger
micro-boot program;  the sole purpose of this program is to
load and execute a larger boot program.
.P
Third, the boot program loads and executes the bootable operating system.
It is at this point that the UNIX System is started, necessary file systems are
mounted [see \f4vfstab\f1(4)], and \f4init\f1 is run to bring
the system to the \f4initdefault\f1 state specified in \f4/sbin/inittab\f1
[see \f4inittab\f1(4)].
.P
For the AT&T 3B2 Computers, the micro-boot program is called \f4mboot\f1
and the boot program is called \f4boot\f1.
These programs are taken from the \f4boot\f1 partition on disk, and
loaded and executed at boot time.
Copies of these programs exist in the directory \f4/usr/lib\f1, for the
purpose of copying them to another hard disk using the \f4newboot\f1
command.
.P
The bootable operating system file is \f4/stand/unix\f1.
.SH NOTES
The boot program isn't smart enough to know which
files can be used as bootable programs.
If the booting of a file that is not bootable is requested from firmware,
the boot program loads it and branches to it.
What happens after that is unpredictable.
.SH SEE ALSO
\f4init\fP(1M),
\f4newboot\fP(1M),
\f4shutdown\fP(1M),
\f4inittab\fP(4),
\f4vfstab\fP(4),
\f4firmware\fP(8)
.P
The ``Machine'' chapter in the \f2System Administrator's Guide\f1
.Ee
