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\# -*- coding: utf-8 -*-
.\" bootstrap - Description of the disk boot process for Powermacs
.TH bootstrap 8 "16 March 1997" "" "PowerMac/Linux"
.SH NAME
bootstrap \- Disk boot process for PowerMac/Linux
.SH DESCRIPTION
The process of booting PowerMac/Linux from a disk starts with Open
Firmware loading the boot block from the first bootable partition of
the boot disk into memory. The user specifies which device is to be
the boot disk by setting the \fBboot\-device\fR environment variable to
the Open Firmware name of the boot disk, or by giving it as an
explicit argument to the Open Firmware \fBboot\fR command.
.PP
Open Firmware then transfers control to the first\-stage bootstrap
(\fBfirst.b\fR), located at the beginning of the boot block. The boot
block also contains the list of block numbers for the second\-stage
bootstrap. \fBFirst.b\fR reads these blocks into memory, thus loading
the second\-stage bootstrap.
.PP
The task of the second\-stage bootstrap (\fBsecond.b\fR) is to load the
Linux kernel into memory and pass it any arguments given by the user.
\fBSecond.b\fR can also be used for loading other programs, such as
diagnostic programs or other operating systems, as long as they are
present as an ELF binary in an ext2 filesystem.
.PP
\fBSecond.b\fR gets two string values from Open Firmware,
called \fIbootpath\fR and \fIbootargs\fR. \fIBootpath\fR is the Open
Firmware name of the boot disk (i.e., the device that the first\-stage
bootstrap was loaded from). If Open Firmware auto\-booted, or if the
\fBboot\fR command was given without arguments, then \fIbootpath\fR
and \fIbootargs\fR are set to the values of the \fBboot\-device\fR and
\fBboot\-file\fR variables, respectively. If the \fBboot\fR command
was given with arguments, the first argument becomes \fIbootpath\fR
and any subsequent arguments are saved in \fIbootargs\fR.
.PP
\fBSecond.b\fR uses the Open Firmware input and output devices for
communicating with the user. By default, the modem port is used for
both, but this can be changed by setting the Open Firmware
\fBinput\-device\fR and \fBoutput\-device\fR variables.
.PP
\fBSecond.b\fR starts by printing a message to indicate
that it has started, and then reads the configuration file. By
default, the configuration file is \fB/etc/quik.conf\fR on the same
partition as the boot block, but this can be overridden with quik(1).
The configuration file must be on the same disk as the boot block.
The format of the configuration file is described in quik.conf(5).
.PP
Then \fBsecond.b\fR prints its \fBboot:\fR prompt and waits for the
user to type a command line. Normally the configuration file
specifies a timeout, and if the user does not type anything within
that period of time, \fBsecond.b\fR proceeds using the \fIbootargs\fR
value as the command line. If the timeout value is 0, \fBsecond.b\fR
will always use the \fIbootargs\fR value, ignoring anything the user
types. This can be useful when a modem is connected to the
modem port.
.PP
Having obtained a command line, \fBsecond.b\fR takes the first word
(whitespace\-separated) as the name of the program to load. Any
remaining words on the line become arguments to be passed to the
program when it is loaded. If the command line is empty,
\fBsecond.b\fR uses the value of the \fBdefault\fR keyword in the
configuration file, or failing that, the first program specified in
the configuration file.
.PP
The configuration file can specify several alternative programs to
load (referred to as \fIimages\fR in the configuration file syntax),
along with shorthand labels for them and extra arguments to be
prepended to those specified by the user. The program name given in
the command line can be either an explicit path name or a shorthand
label. If it is a shorthand label, the configuration file gives the
corresponding path name.
.PP
Path names are of the form
.PP
.RS
.RI [ device\fB: ][ partno ]\fB/ filepath
.RE
.PP
where \fIdevice\fR is the Open Firmware name of the disk, \fIpartno\fR
is the (decimal) number of the partition on that disk, and
\fIfilepath\fR is the path to the file in the ext2 filesystem on that
partition. The default for \fIdevice\fR is \fIbootpath\fR, and the
default for \fIpartno\fR is the first bootable partition on
\fIdevice\fR. Alternatively, the \fB/\fIfilepath\fR section can be
replaced by a span of 512\-byte blocks to load using the syntax
.BI [ start \- end ]
where \fIstart\fR and \fIend\fR are decimal block numbers.
.PP
\fBSecond.b\fR will attempt to open the file identified by the path
name and load it into memory as an ELF binary. If the file cannot be
found, or if it is not an ELF binary, \fBsecond.b\fR will print an
error message and print its \fBboot:\fR prompt again. In this case
there is no timeout and \fBsecond.b\fR does not use the \fIbootargs\fR
value.
.PP
Once \fBsecond.b\fR has loaded the program into memory, it transfers
control to it, passing it the list of arguments.
.PP
.SH SEE ALSO
.I quik(8), quik.conf(5)
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