man/yaboot.8

.\" Hey Emacs! This file is -*- nroff -*- source.
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.TH YABOOT 8 "28 April 2001" "GNU/Linux PowerPC" "System Manager's Manual"
.SH NAME
.B yaboot
\- PowerMac OpenFirmware boot loader
.SH SYNOPSIS
.B Yaboot
is an OpenFirmware ELF executable that bootstraps the Linux kernel.
.SH DESCRIPTION
This manual page explains the \fByaboot\fR OpenFirmware boot loader. 

.B yaboot
is \fInot\fR a Linux or MacOS executable file.  Attempting to execute
\fByaboot\fR from a Linux shell will only result in a Segmentation
Fault. \fByaboot\fR is meant to be executed only by OpenFirmware.

.B yaboot
is executed from OpenFirmare in the following manner:
.I boot hd:2,yaboot
where \fIhd:\fR is the OpenFirmware path for the hard disk, and the
\fI2\fR is the partition number \fByaboot\fR is located on.  In this
example, the hard disk path is actually an OpenFirmware alias which is
present on all NewWorld powermacs.  It usually points to the internal
ATA hard disk.  If you have a SCSI disk, then you might execute
\fByaboot\fR with this command:
.I boot /pci@80000000/pci-bridge@d/ADPT,2930CU@2/@1:2,yaboot
This path will vary depending on what kind of SCSI host adapter you
have. For a more detailed explanation of OpenFirmware's [disgusting]
paths, see man \fBbootstrap\fR(8).  On IBM hardware \fByaboot\fR is
directly copied to the \fBbootstrap\fR(8) partition raw, without any
filesystem.  OpenFirmare will boot from a type 0x41 PReP Boot parition
marked bootable, this must contain \fByaboot\fR.  On IBM hardware the
config file is read directly from the root filesystem.  On PowerMac
hardware it must be present on the \fBbootstrap\fR(8) partition but
.BR ybin (8)
will take care of that.

Fortunately you do not normally have to execute \fByaboot\fR manually.
If you have partitioned your disk with a \fBbootstrap\fR(8) partition
and used \fBybin\fR(8) to install \fByaboot\fR then you will not have
to execute \fByaboot\fR yourself.  (If this does not work you can also
set the \fIboot-device\fR variable in OpenFirmware to have it boot
automatically, see man \fBbootstrap\fR(8).)

Once \fByaboot\fR has been executed by OpenFirmware it will display a
\fIboot:\fR prompt where you may enter a label for a kernel image
defined in \fByaboot.conf\fR(5).  If there is no kernel image defined
in \fByaboot.conf\fR(5) you can still boot an arbitrary image by
specifying its absolute OpenFirmware path, similar to the above
commands for executing \fByaboot\fR itself.  Simply omit the \fIboot\fR
command and enter only the pathname.  (See EXAMPLES below)

When booting an image (either as a predefined label or absolute path)
any arguments are passed to the image.  For example:
.I boot: linux root=/dev/hda3
which would pass the argument \fIroot=/dev/hda3\fR to the kernel.

.B yaboot
should preferably be installed on a dedicated \fBbootstrap\fR(8)
partition (type Apple_Bootstrap for PowerMacs, type 0x41 PReP Boot for
IBM hardware).  This allows the partition to be modified in such a way
that OpenFirmare will load \fByaboot\fR or a boot menu automatically
with a default OF configuration. If \fByaboot\fR cannot be installed
on a \fBbootstrap\fR(8) partition it can be installed on the root of a
MacOS boot partition instead.  \fByaboot\fR however should not be
installed in a subdirectory of the MacOS filesystem as this is less
reliable and more difficult to execute from OpenFirmware.  See the
\fBybin\fR(8) man page for more details on installing \fByaboot\fR
(\fBybin\fR(8) is a utility for installing \fByaboot\fR with minimal
difficulty).

The \fByaboot.conf\fR(5) file must be next to the yaboot executable on
the \fBbootstrap\fR(8) partition.  \fBybin\fR(8) will take care of this.

OpenFirmware may be accessed by holding down the \fIcommand, option,
o, f\fR keys immediately upon power-up.

OpenFirmware's settings may be reset to default values by holding down
the \fIcommand, option, p, r\fR keys while cold booting.

If you have G4 hardware then your OpenFirmware may already have a
graphical boot selector built in.  This selector can be accessed by
holding down the option key when booting the machine.  You should see
a screen with buttons for each bootable partition.  The current
version (included with \fBybin\fR(8) 0.13) of ofboot includes a
badge icon, the button with a penguin icon is your \fBbootstrap\fR(8)
partition.  Thanks to Nicholas Humfrey for creating the Badge icon.

The \fBbootstrap\fR(8) need not and
.B should not
be mounted anywhere on your filesystem, especially not on top of /boot.  \fBYaboot\fR is able
to load the kernels from the ext2fs root partition so that is where
they should be kept.
.SH EXAMPLES
boot \fByaboot\fR from internal ATA disk, partition 2:

.I boot hd:2,yaboot 

boot \fByaboot\fR from partition 2 of a disk with SCSI ID 2 attached to a
Adaptec 2930 SCSI Host adapter (this is on a rev1 blue G3, it may vary
on other models): 

.I boot /pci@80000000/pci-bridge@d/ADPT,2930CU@2/@2:2,yaboot

boot a kernel image located on partition number 3 of internal ATA
disk (from \fByaboot's\fR \fIboot:\fR prompt):

.I hd:3,/boot/vmlinux

boot a kernel image located on partition 3 of SCSI disk ID 2 on a
Adaptec 2930 Host adapter (from \fByaboot's\fR \fIboot:\fR prompt):

.I /pci@80000000/pci-bridge@d/ADPT,2930CU@2/@2:3,/vmlinux
.SH FILES
.nf
/etc/yaboot.conf \- boot loader configuration file
.fi
.SH BUGS
OpenFirmware
.SH AUTHORS
This man page was written by Ethan Benson <erbenson@alaska.net>.
.P
.B yaboot
was written by Benjamin Herrenschmidt <benh@kernel.crashing.org>.
.SH REPORTING BUGS
Bugs in \fByaboot\fR should be reported to Benjamin Herrenschmidt
<benh@kernel.crashing.org>.
.SH SEE ALSO
.BR bootstrap (8),
.BR yaboot.conf (5),
.BR ybin (8).