Subversion Repositories planix.SVN

.TH 9BOOT 8

.SH NAME

9boot, 9bootpbs, 9load, 9loadusb, pbs \- PC bootstrap programs

.SH SYNOPSIS

.I none

.SH DESCRIPTION

.I 9boot

is a specialized Plan 9 kernel loaded by

the PXE download (BOOTP/DHCP followed by TFTP)

found in any reasonable Ethernet card's BIOS; it bootstraps Plan 9 by using

PXE to load another

.B 386

or

.B amd64

kernel and start it.

.PP

.IR 9bootpbs ,

.I 9load

and

.I 9loadusb

are less-commonly-used variants

that reside in a FAT file system under the name

.L 9load

and bootstrap Plan 9.

.I 9bootpbs

is like

.I 9boot

but it can be started by a partition boot sector (PBS),

as can

.I 9load

and

.IR 9loadusb .

It is intended to PXE boot older machines without working PXE ROMs.

.I 9load

and

.I 9loadusb

read FAT file systems.

.I 9loadusb

will use only the BIOS's device drivers,

and thus can load from FAT file systems on USB devices.

In contrast,

.I 9load

will

.I not

use BIOS device drivers and cannot read USB devices.

.PP

This profusion of loaders is unfortunate, but at least they

are compiled from the same source.

The division into separate programs is dictated by the need to fit

within the first 640K of memory

and the need to avoid intermixing BIOS and non-BIOS disk access.

.PP

These programs are run automatically by the boot procedures described below;

they cannot be run directly by hand.

There are two bootstrap sequences:

.IP \- 3

PXE BIOS,

.IR 9boot ,

kernel

.IP \-

BIOS, MBR, disk partition PBS,

.IR 9load ,

kernel

.\" .IP \-

.\" BIOS, floppy PBS,

.\" .IR 9load ,

.\" kernel

.PP

In summary,

Plan 9 is usually booted on a PC

by using a PXE-capable BIOS to boot

.I 9boot

directly over the ethernet.

File servers that must be able to boot when other machines are down

boot directly from a Plan 9 disk partition

.\" or boot floppy

prepared using

.B format

to install the appropriate files and bootstrap sectors

(see

.IR prep (8)).

.PP

Details follow.

.SS Kernel loading

.I 9boot

is a bootstrap program that loads and starts a program,

typically the kernel, on a PC.

It is run by the PXE boot ROM of a PC,

which loads

.I 9boot

at physical address

.B 0x7C00

(31K).

When it starts running,

it switches to 32-bit mode.

It then double maps the first 16Mb of physical memory to

virtual addresses

.B 0

and

.BR 0x80000000 .

Only devices which can be automatically configured,

e.g. most PCI ethernet adapters,

will be recognised.

If the file

.BI /cfg/pxe/ ether

can be located via a DHCP server,

where

.I ether

is the lower-case MAC address of a recognised ethernet adapter,

the contents are obtained by TFTP and used as a

.IR plan9.ini (8).

.I 9boot

then loads the

.I bootfile

named within via TFTP,

trying each ethernet in sequence,

at the entry address specified by the kernel executable's header,

usually virtual

.BR 0xF0100020 .

After loading,

.I 9boot

creates a Gnu Multiboot header in low memory for

the benefit of the loaded kernel

and

control is passed to the entry location

in 32-bit protected mode, even for 64-bit kernels.

So far, only

.B amd64

kernels expect Multiboot headers.

.PP

Some options in

.B plan9.ini

are used by

.IR 9boot :

.TF bootfile=manual

.TP

.B console

.TP

.B baud

Specifies the console device and baud rate if not a display.

.TP

.BI ether n

Ethernet interfaces. These can be used to load the

.I bootfile

over a network.

.TP

.BI bootfile= bootfile

Specifies the

.IR bootfile .

.ig

.TP

.B bootfile=auto

Default.

.TP

.B bootfile=local

Like

.IR auto ,

but do not attempt to load over the network.

..

.TP

.B bootfile=manual

After determining which devices are available for loading from,

enter prompt mode.

.PD

.PP

.I 9load

is a similar bootstrap program,

loaded by the PC partition boot sector program (PBS),

which usually resides in the first

sector of the active disk partition.

It is initially loaded at physical address

.BR 0x10000 (64K);

it begins execution at virtual address

.BR 0x80010000 .

In order to find configuration information,

.I 9load

searches all units on devices

.\" .BR fd

.\" and

.B sd?[0-9]*

(all

.B sd

devices),

for a file called

.\" .B plan9\eplan9.ini

.\" or

.B plan9.ini

(see

.IR plan9.ini (8))

on a FAT partition named

.B dos

or

.BR 9fat .

If one is found, searching stops and the file is read into memory

at physical address

.B 0x1200

where it can be found later by any loaded

.IR bootfile .

.PP

When the search for

.B plan9.ini

is done,

.I 9load

proceeds to determine which bootfile to load.

If there was no

.I bootfile

option,

.I 9load

searches

.B sd?[0-9]*

FAT partitions for a kernel

(any file named

.BR 9pc* ,

.B 9k8*

or

.BR 9k10* )

and if it finds exactly one kernel in a given FAT partition,

chooses it.

.I 9load

then attempts to load the

.IR bootfile .

.ig

unless

the

.B bootfile=manual

option was given, in which case prompt mode is entered immediately.

..

.ig

If the default device is

.BR fd ,

.I 9load

will prompt the user for input before proceeding with the

default bootfile load after 5 seconds;

this prompt is omitted if a

.I bootfile

option

was given.

..

.PP

.I 9load

prints the list of available

.IR device s

and

enters prompt mode on encountering any error

or if directed to do so by a

.B bootfile=manual

option.

In prompt mode, the user is required to type

a

.IB bootfile

in response to the

.L Boot

.L from:

prompt.

.br

.ne 4

.SS Bootfile

The

.I bootfile

can be specified to these programs as a

.B bootfile=

entry in

.IR plan9.ini ,

or if booting from the ethernet, by a BOOTP server

(see

.B Kernel

.B loading

below).

If loading with

.IR 9load ,

the

.I bootfile

may be a Plan 9 boot image compressed with

.IR gzip (1).

In all cases,

the uncompressed kernel must be in Plan 9 boot image, ELF or ELF64 format.

If the

.B plan9.ini

file contains multiple

.B bootfile=

entries,

these programs will present a numerical menu of the choices; type

the corresponding number to select an entry.

.PP

The format of the

.I bootfile

name is

.IB device ! file

or

.IB device ! partition ! file\f1.

If

.BI ! file

is omitted, the default for the particular

.I device

is used.

Supported

.I devices

are

.TF \fLethern

.PD

.TP

.BI ether n

Ethernet,

.I 9boot

only.

.I N

specifies the Ethernet device number.

If a

.I partition

is specified, it is taken to be the name of a host machine

from which to load the kernel.

.TP

.BI sd Cn

Normal disk,

.I 9load

only.

The device name format is described in

.IR sd (3).

A

.I partition

must be given and must normally

name a partition containing a FAT file system.

.\" The name

.\" .B dos

.\" refers to the first DOS partition on a given device.

It is common for Plan 9 partitions to contain a small

FAT file system for configuration.

By convention, this partition is called

.BR 9fat .

There is no default partition,

but if

.I file

is omitted,

.I 9load

will load a kernel directly from the named partition

without any interpretation of a file system.

.

.ig

.TP

.BI fd n

An MS-DOS floppy disk,

.I 9load

only.

.I N

specifies the floppy drive, either

The

.I bootfile

is the contents of the MS-DOS

.IR file .

There is no default file.

For compatibility with normal disks, a

.I partition

may be given, but only

.B dos

is recognized:

.BI fd0!dos! file\f1.

..

.

.TP

.BI bios n

USB or other BIOS device,

.IR 9loadusb

only.

.I 9load

loads from a FAT file system on

the first LBA device

in the BIOS's list of devices to try to boot from,

using the BIOS INT 13 calls also used by

.IR pbslba .

It does not understand any form of partition table;

see the

.B EXAMPLES

in

.IR prep (8)

for how to format such a device.

.TP

.BI sdB n

USB or other BIOS device's partition,

.IR 9loadusb

only.

A special case of

.BI sd Cn

that uses

.BI bios n

to read from a FAT file system.

.SS Boot Sectors

A copy of the Plan 9 PBS is kept in

.BR /386/pbs ,

but due to the ``cylinder-head-sector'' (CHS) addressing mode of old BIOSes, it can only

operate up to 8.5GB into the disk.

Plan 9 partitions further into the disk

can only be booted using

.BR /386/pbslba ,

and then only if the machine's BIOS supports

linear block addressing (LBA) mode for disk transfers.

.PP

When booting from disk,

.\" or floppy,

the BIOS loads the

first sector of the medium at location

.BR 0x7C00 .

In the case of a disk, it is the master boot record (MBR).

.\" In the case of a floppy, this is the PBS.

The MBR copies itself to address

.BR 0x600 ,

finds the active partition and loads its PBS at address

.BR 0x7C00 .

A copy of the Plan 9 MBR is kept in

.BR /386/mbr ;

some commercial MBRs cannot read sectors

past 2GB.

The Plan 9 MBR can read sectors up to 8.5GB into

the disk, and further if the BIOS supports LBA.

The single file

.B /386/mbr

detects whether the BIOS supports LBA and

acts appropriately, defaulting to CHS mode

when LBA is not present.

The PBSs cannot do this due to code size limitations.

The Plan 9 MBR is suitable for booting non-Plan-9

operating systems,

and (modulo the large disk constraints just described)

non-Plan-9 MBRs are suitable for booting Plan 9.

.br

.ne 4

.SS Other facilities and caveats

.I 9load

parses the master boot record and Plan 9 partition tables

(see

.IR prep (8)),

leaving partitioning information appended to the

in-memory contents of

.I plan9.ini

for the

.IR bootfile .

This is used by

.IR sd (3)

to initialize partitions so that

may be read for NVRAM contents or

.IR fossil (4)

or

.IR kfs (4)

file systems can be mounted as the root file system.

On ISO 9660 CDs,

.I 9load

treats the contents of a file named

.B /bootdisk.img

as a 

.B 9fat

partition,

and it is assumed to contain the image of a FAT file system.

A more extensive partitioning is typically done by

.I fdisk

and

.I prep

as part of

.I termrc

or

.I cpurc

(see

.IR cpurc (8)).

.I 9boot

cannot parse partition tables,

as it lacks disk drivers, so add

.L readparts=

to the machine's

.B /cfg/pxe

file, per

.IR plan9.ini (8),

if needed.

.PP

A

control-P

character typed at any time on the console causes

.B 9boot

to perform a hardware reset

(Ctrl-Alt-Del can also be used on a PC keyboard).

.PP

.I 9load

must be contiguously allocated on

the disk.

See

.IR dossrv (4)

for information on ensuring this.

.SH FILES

.TF /cfg/pxe

.TP

.B /386

these programs reside here

.TP

.BI /cfg/pxe

directory of configuration

.RI ( plan9.ini )

files on your TFTP server

.PP

.IB "FAT-filesystem" :\e9load

.br

.IB "FAT-filesystem" :\eplan9.ini

.\" .br

.\" .IB "FAT-filesystem" :\eplan9\eplan9.ini

.SH SOURCE

.TF "/sys/src/9/^(pc port ip)"

.PD 0

.TP

.B /sys/src/boot/pc

first-stage disk boot sectors (MBR, PBS)

.TP

.B /sys/src/9/pcboot

PC-bootstrap-specific source

.TP

.B /sys/src/9/^(pc port ip)

common kernel source

.PD

.SH "SEE ALSO"

.IR 8l (1),

.IR cons (3),

.IR booting (8),

.IR dhcpd (8),

.IR fshalt (8),

.IR mkusbboot (8),

.IR plan9.ini (8),

.IR prep (8)

.SH BUGS

Some of the work done by

.I 9boot

is duplicated by the loaded kernel,

but usually by the same source code.

.PP

.B bios

and

.B sdB

usually only work on the first LBA device in the BIOS's list of boot devices,

if they work at all.

.PP

USB keyboards will only work with

.I 9boot

if the BIOS emulates a PS/2 keyboard (and that is enabled).