xref: /illumos-gate/usr/src/grub/grub-0.97/docs/grub.info-1 (revision 1b8adde7)

This is grub.info, produced by makeinfo version 4.0 from grub.texi.

INFO-DIR-SECTION Kernel
START-INFO-DIR-ENTRY
* GRUB: (grub).                 The GRand Unified Bootloader
* grub-install: (grub)Invoking grub-install.    Install GRUB on your drive
* grub-md5-crypt: (grub)Invoking grub-md5-crypt.        Encrypt a password
                                                        in MD5 format
* grub-terminfo: (grub)Invoking grub-terminfo.  Generate a terminfo
                                                command from a
                                                terminfo name
* grub-set-default: (grub)Invoking grub-set-default.    Set a default boot
                                                        entry
* mbchk: (grub)Invoking mbchk.  Check for the format of a Multiboot kernel
END-INFO-DIR-ENTRY

   Copyright (C) 1999,2000,2001,2002,2004 Free Software Foundation, Inc.

   Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided also
that the entire resulting derived work is distributed under the terms
of a permission notice identical to this one.

   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions.


File: grub.info,  Node: Top,  Next: Introduction,  Up: (dir)

GRUB manual
***********

   This is the documentation of GNU GRUB, the GRand Unified Bootloader,
a flexible and powerful boot loader program for PCs.

   This edition documents version 0.95.

* Menu:

* Introduction::                Capturing the spirit of GRUB
* Naming convention::           Names of your drives in GRUB
* Installation::                Installing GRUB on your drive
* Booting::                     How to boot different operating systems
* Configuration::               Writing your own configuration file
* Network::                     Downloading OS images from a network
* Serial terminal::             Using GRUB via a serial line
* Preset Menu::                 Embedding a configuration file into GRUB
* Security::                    Improving the security
* Images::                      GRUB image files
* Filesystem::                  Filesystem syntax and semantics
* Interface::                   The menu and the command-line
* Commands::                    The list of available builtin commands
* Troubleshooting::             Error messages produced by GRUB
* Invoking the grub shell::     How to use the grub shell
* Invoking grub-install::       How to use the GRUB installer
* Invoking grub-md5-crypt::     How to generate a cryptic password
* Invoking grub-terminfo::      How to generate a terminfo command
* Invoking grub-set-default::   How to set a default boot entry
* Invoking mbchk::              How to use the Multiboot checker
* Obtaining and Building GRUB:: How to obtain and build GRUB
* Reporting bugs::              Where you should send a bug report
* Future::                      Some future plans on GRUB
* Internals::                   Hacking GRUB
* Index::


File: grub.info,  Node: Introduction,  Next: Naming convention,  Prev: Top,  Up: Top

Introduction to GRUB
********************

* Menu:

* Overview::                    What exactly GRUB is and how to use it
* History::                     From maggot to house fly
* Features::                    GRUB features
* Role of a boot loader::       The role of a boot loader


File: grub.info,  Node: Overview,  Next: History,  Up: Introduction

Overview
========

   Briefly, a "boot loader" is the first software program that runs when
a computer starts.  It is responsible for loading and transferring
control to an operating system "kernel" software (such as Linux or GNU
Mach).  The kernel, in turn, initializes the rest of the operating
system (e.g. a GNU system).

   GNU GRUB is a very powerful boot loader, which can load a wide
variety of free operating systems, as well as proprietary operating
systems with chain-loading(1) (*note Overview-Footnote-1::). GRUB is
designed to address the complexity of booting a personal computer; both
the program and this manual are tightly bound to that computer platform,
although porting to other platforms may be addressed in the future.

   One of the important features in GRUB is flexibility; GRUB
understands filesystems and kernel executable formats, so you can load
an arbitrary operating system the way you like, without recording the
physical position of your kernel on the disk. Thus you can load the
kernel just by specifying its file name and the drive and partition
where the kernel resides.

   When booting with GRUB, you can use either a command-line interface
(*note Command-line interface::), or a menu interface (*note Menu
interface::). Using the command-line interface, you type the drive
specification and file name of the kernel manually. In the menu
interface, you just select an OS using the arrow keys. The menu is
based on a configuration file which you prepare beforehand (*note
Configuration::). While in the menu, you can switch to the command-line
mode, and vice-versa. You can even edit menu entries before using them.

   In the following chapters, you will learn how to specify a drive, a
partition, and a file name (*note Naming convention::) to GRUB, how to
install GRUB on your drive (*note Installation::), and how to boot your
OSes (*note Booting::), step by step.

   Besides the GRUB boot loader itself, there is a "grub shell" `grub'
(*note Invoking the grub shell::) which can be run when you are in your
operating system. It emulates the boot loader and can be used for
installing the boot loader.


File: grub.info,  Node: Overview-Footnotes,  Up: Overview

   (1) "chain-load" is the mechanism for loading unsupported operating
systems by loading another boot loader. It is typically used for
loading DOS or Windows.


File: grub.info,  Node: History,  Next: Features,  Prev: Overview,  Up: Introduction

History of GRUB
===============

   GRUB originated in 1995 when Erich Boleyn was trying to boot the GNU
Hurd with the University of Utah's Mach 4 microkernel (now known as GNU
Mach).  Erich and Brian Ford designed the Multiboot Specification
(*note Multiboot Specification: (multiboot)Top.), because they were
determined not to add to the large number of mutually-incompatible PC
boot methods.

   Erich then began modifying the FreeBSD boot loader so that it would
understand Multiboot. He soon realized that it would be a lot easier to
write his own boot loader from scratch than to keep working on the
FreeBSD boot loader, and so GRUB was born.

   Erich added many features to GRUB, but other priorities prevented him
from keeping up with the demands of its quickly-expanding user base. In
1999, Gordon Matzigkeit and Yoshinori K. Okuji adopted GRUB as an
official GNU package, and opened its development by making the latest
sources available via anonymous CVS. *Note Obtaining and Building
GRUB::, for more information.


File: grub.info,  Node: Features,  Next: Role of a boot loader,  Prev: History,  Up: Introduction

GRUB features
=============

   The primary requirement for GRUB is that it be compliant with the
"Multiboot Specification", which is described in *Note Multiboot
Specification: (multiboot)Top.

   The other goals, listed in approximate order of importance, are:

   * Basic functions must be straightforward for end-users.

   * Rich functionality to support kernel experts and designers.

   * Backward compatibility for booting FreeBSD, NetBSD, OpenBSD, and
     Linux. Proprietary kernels (such as DOS, Windows NT, and OS/2) are
     supported via a chain-loading function.

   Except for specific compatibility modes (chain-loading and the Linux
"piggyback" format), all kernels will be started in much the same state
as in the Multiboot Specification. Only kernels loaded at 1 megabyte or
above are presently supported. Any attempt to load below that boundary
will simply result in immediate failure and an error message reporting
the problem.

   In addition to the requirements above, GRUB has the following
features (note that the Multiboot Specification doesn't require all the
features that GRUB supports):

Recognize multiple executable formats
     Support many of the "a.out" variants plus "ELF". Symbol tables are
     also loaded.

Support non-Multiboot kernels
     Support many of the various free 32-bit kernels that lack Multiboot
     compliance (primarily FreeBSD, NetBSD, OpenBSD, and Linux).
     Chain-loading of other boot loaders is also supported.

Load multiples modules
     Fully support the Multiboot feature of loading multiple modules.

Load a configuration file
     Support a human-readable text configuration file with preset boot
     commands. You can also load another configuration file dynamically
     and embed a preset configuration file in a GRUB image file. The
     list of commands (*note Commands::) are a superset of those
     supported on the command-line. An example configuration file is
     provided in *Note Configuration::.

Provide a menu interface
     A menu interface listing preset boot commands, with a programmable
     timeout, is available. There is no fixed limit on the number of
     boot entries, and the current implementation has space for several
     hundred.

Have a flexible command-line interface
     A fairly flexible command-line interface, accessible from the menu,
     is available to edit any preset commands, or write a new boot
     command set from scratch. If no configuration file is present,
     GRUB drops to the command-line.

     The list of commands (*note Commands::) are a subset of those
     supported for configuration files. Editing commands closely
     resembles the Bash command-line (*note Bash: (features)Command
     Line Editing.), with <TAB>-completion of commands, devices,
     partitions, and files in a directory depending on context.

Support multiple filesystem types
     Support multiple filesystem types transparently, plus a useful
     explicit blocklist notation. The currently supported filesystem
     types are "BSD FFS", "DOS FAT16 and FAT32", "Minix fs", "Linux
     ext2fs", "ReiserFS", "JFS", "XFS", and "VSTa fs". *Note
     Filesystem::, for more information.

Support automatic decompression
     Can decompress files which were compressed by `gzip'. This
     function is both automatic and transparent to the user (i.e. all
     functions operate upon the uncompressed contents of the specified
     files). This greatly reduces a file size and loading time, a
     particularly great benefit for floppies.(1) (*note
     Features-Footnote-1::)

     It is conceivable that some kernel modules should be loaded in a
     compressed state, so a different module-loading command can be
     specified to avoid uncompressing the modules.

Access data on any installed device
     Support reading data from any or all floppies or hard disk(s)
     recognized by the BIOS, independent of the setting of the root
     device.

Be independent of drive geometry translations
     Unlike many other boot loaders, GRUB makes the particular drive
     translation irrelevant. A drive installed and running with one
     translation may be converted to another translation without any
     adverse effects or changes in GRUB's configuration.

Detect all installed RAM
     GRUB can generally find all the installed RAM on a PC-compatible
     machine. It uses an advanced BIOS query technique for finding all
     memory regions. As described on the Multiboot Specification (*note
     Multiboot Specification: (multiboot)Top.), not all kernels make
     use of this information, but GRUB provides it for those who do.

Support Logical Block Address mode
     In traditional disk calls (called "CHS mode"), there is a geometry
     translation problem, that is, the BIOS cannot access over 1024
     cylinders, so the accessible space is limited to at least 508 MB
     and to at most 8GB. GRUB can't universally solve this problem, as
     there is no standard interface used in all machines. However,
     several newer machines have the new interface, Logical Block
     Address ("LBA") mode. GRUB automatically detects if LBA mode is
     available and uses it if available. In LBA mode, GRUB can access
     the entire disk.

Support network booting
     GRUB is basically a disk-based boot loader but also has network
     support. You can load OS images from a network by using the "TFTP"
     protocol.

Support remote terminals
     To support computers with no console, GRUB provides remote terminal
     support, so that you can control GRUB from a remote host. Only
     serial terminal support is implemented at the moment.


File: grub.info,  Node: Features-Footnotes,  Up: Features

   (1) There are a few pathological cases where loading a very badly
organized ELF kernel might take longer, but in practice this never
happen.


File: grub.info,  Node: Role of a boot loader,  Prev: Features,  Up: Introduction

The role of a boot loader
=========================

   The following is a quotation from Gordon Matzigkeit, a GRUB fanatic:

     Some people like to acknowledge both the operating system and
     kernel when they talk about their computers, so they might say
     they use "GNU/Linux" or "GNU/Hurd".  Other people seem to think
     that the kernel is the most important part of the system, so they
     like to call their GNU operating systems "Linux systems."

     I, personally, believe that this is a grave injustice, because the
     _boot loader_ is the most important software of all. I used to
     refer to the above systems as either "LILO"(1) (*note Role of a
     boot loader-Footnote-1::) or "GRUB" systems.

     Unfortunately, nobody ever understood what I was talking about;
     now I just use the word "GNU" as a pseudonym for GRUB.

     So, if you ever hear people talking about their alleged "GNU"
     systems, remember that they are actually paying homage to the best
     boot loader around... GRUB!

   We, the GRUB maintainers, do not (usually) encourage Gordon's level
of fanaticism, but it helps to remember that boot loaders deserve
recognition.  We hope that you enjoy using GNU GRUB as much as we did
writing it.


File: grub.info,  Node: Role of a boot loader-Footnotes,  Up: Role of a boot loader

   (1) The LInux LOader, a boot loader that everybody uses, but nobody
likes.


File: grub.info,  Node: Naming convention,  Next: Installation,  Prev: Introduction,  Up: Top

Naming convention
*****************

   The device syntax used in GRUB is a wee bit different from what you
may have seen before in your operating system(s), and you need to know
it so that you can specify a drive/partition.

   Look at the following examples and explanations:

     (fd0)

   First of all, GRUB requires that the device name be enclosed with
`(' and `)'. The `fd' part means that it is a floppy disk. The number
`0' is the drive number, which is counted from _zero_. This expression
means that GRUB will use the whole floppy disk.

     (hd0,1)

   Here, `hd' means it is a hard disk drive. The first integer `0'
indicates the drive number, that is, the first hard disk, while the
second integer, `1', indicates the partition number (or the PC slice
number in the BSD terminology). Once again, please note that the
partition numbers are counted from _zero_, not from one. This
expression means the second partition of the first hard disk drive. In
this case, GRUB uses one partition of the disk, instead of the whole
disk.

     (hd0,4)

   This specifies the first "extended partition" of the first hard disk
drive. Note that the partition numbers for extended partitions are
counted from `4', regardless of the actual number of primary partitions
on your hard disk.

     (hd1,a)

   This means the BSD `a' partition of the second hard disk. If you
need to specify which PC slice number should be used, use something
like this: `(hd1,0,a)'. If the PC slice number is omitted, GRUB
searches for the first PC slice which has a BSD `a' partition.

   Of course, to actually access the disks or partitions with GRUB, you
need to use the device specification in a command, like `root (fd0)' or
`unhide (hd0,2)'. To help you find out which number specifies a
partition you want, the GRUB command-line (*note Command-line
interface::) options have argument completion. This means that, for
example, you only need to type

     root (

   followed by a <TAB>, and GRUB will display the list of drives,
partitions, or file names. So it should be quite easy to determine the
name of your target partition, even with minimal knowledge of the
syntax.

   Note that GRUB does _not_ distinguish IDE from SCSI - it simply
counts the drive numbers from zero, regardless of their type. Normally,
any IDE drive number is less than any SCSI drive number, although that
is not true if you change the boot sequence by swapping IDE and SCSI
drives in your BIOS.

   Now the question is, how to specify a file? Again, consider an
example:

     (hd0,0)/vmlinuz

   This specifies the file named `vmlinuz', found on the first
partition of the first hard disk drive. Note that the argument
completion works with file names, too.

   That was easy, admit it. Now read the next chapter, to find out how
to actually install GRUB on your drive.


File: grub.info,  Node: Installation,  Next: Booting,  Prev: Naming convention,  Up: Top

Installation
************

   In order to install GRUB as your boot loader, you need to first
install the GRUB system and utilities under your UNIX-like operating
system (*note Obtaining and Building GRUB::). You can do this either
from the source tarball, or as a package for your OS.

   After you have done that, you need to install the boot loader on a
drive (floppy or hard disk). There are two ways of doing that - either
using the utility `grub-install' (*note Invoking grub-install::) on a
UNIX-like OS, or by running GRUB itself from a floppy. These are quite
similar, however the utility might probe a wrong BIOS drive, so you
should be careful.

   Also, if you install GRUB on a UNIX-like OS, please make sure that
you have an emergency boot disk ready, so that you can rescue your
computer if, by any chance, your hard drive becomes unusable
(unbootable).

   GRUB comes with boot images, which are normally put in the directory
`/usr/lib/grub/i386-pc'. If you do not use grub-install, then you need
to copy the files `stage1', `stage2', and `*stage1_5' to the directory
`/boot/grub', and run the `grub-set-default' (*note Invoking
grub-set-default::) if you intend to use `default saved' (*note
default::) in your configuration file. Hereafter, the directory where
GRUB images are initially placed (normally `/usr/lib/grub/i386-pc')
will be called the "image directory", and the directory where the boot
loader needs to find them (usually `/boot/grub') will be called the
"boot directory".

* Menu:

* Creating a GRUB boot floppy::
* Installing GRUB natively::
* Installing GRUB using grub-install::
* Making a GRUB bootable CD-ROM::


File: grub.info,  Node: Creating a GRUB boot floppy,  Next: Installing GRUB natively,  Up: Installation

Creating a GRUB boot floppy
===========================

   To create a GRUB boot floppy, you need to take the files `stage1'
and `stage2' from the image directory, and write them to the first and
the second block of the floppy disk, respectively.

   *Caution:* This procedure will destroy any data currently stored on
the floppy.

   On a UNIX-like operating system, that is done with the following
commands:

     # cd /usr/lib/grub/i386-pc
     # dd if=stage1 of=/dev/fd0 bs=512 count=1
     1+0 records in
     1+0 records out
     # dd if=stage2 of=/dev/fd0 bs=512 seek=1
     153+1 records in
     153+1 records out
     #

   The device file name may be different. Consult the manual for your
OS.


File: grub.info,  Node: Installing GRUB natively,  Next: Installing GRUB using grub-install,  Prev: Creating a GRUB boot floppy,  Up: Installation

Installing GRUB natively
========================

   *Caution:* Installing GRUB's stage1 in this manner will erase the
normal boot-sector used by an OS.

   GRUB can currently boot GNU Mach, Linux, FreeBSD, NetBSD, and OpenBSD
directly, so using it on a boot sector (the first sector of a
partition) should be okay. But generally, it would be a good idea to
back up the first sector of the partition on which you are installing
GRUB's stage1. This isn't as important if you are installing GRUB on
the first sector of a hard disk, since it's easy to reinitialize it
(e.g. by running `FDISK /MBR' from DOS).

   If you decide to install GRUB in the native environment, which is
definitely desirable, you'll need to create a GRUB boot disk, and
reboot your computer with it. Otherwise, see *Note Installing GRUB
using grub-install::.

   Once started, GRUB will show the command-line interface (*note
Command-line interface::). First, set the GRUB's "root device"(1)
(*note Installing GRUB natively-Footnote-1::) to the partition
containing the boot directory, like this:

     grub> root (hd0,0)

   If you are not sure which partition actually holds this directory,
use the command `find' (*note find::), like this:

     grub> find /boot/grub/stage1

   This will search for the file name `/boot/grub/stage1' and show the
devices which contain the file.

   Once you've set the root device correctly, run the command `setup'
(*note setup::):

     grub> setup (hd0)

   This command will install the GRUB boot loader on the Master Boot
Record (MBR) of the first drive. If you want to put GRUB into the boot
sector of a partition instead of putting it in the MBR, specify the
partition into which you want to install GRUB:

     grub> setup (hd0,0)

   If you install GRUB into a partition or a drive other than the first
one, you must chain-load GRUB from another boot loader. Refer to the
manual for the boot loader to know how to chain-load GRUB.

   After using the setup command, you will boot into GRUB without the
GRUB floppy. See the chapter *Note Booting:: to find out how to boot
your operating systems from GRUB.


File: grub.info,  Node: Installing GRUB natively-Footnotes,  Up: Installing GRUB natively

   (1) Note that GRUB's root device doesn't necessarily mean your OS's
root partition; if you need to specify a root partition for your OS,
add the argument into the command `kernel'.


File: grub.info,  Node: Installing GRUB using grub-install,  Next: Making a GRUB bootable CD-ROM,  Prev: Installing GRUB natively,  Up: Installation

Installing GRUB using grub-install
==================================

   *Caution:* This procedure is definitely less safe, because there are
several ways in which your computer can become unbootable. For example,
most operating systems don't tell GRUB how to map BIOS drives to OS
devices correctly--GRUB merely "guesses" the mapping. This will succeed
in most cases, but not always. Therefore, GRUB provides you with a map
file called the "device map", which you must fix if it is wrong. *Note
Device map::, for more details.

   If you still do want to install GRUB under a UNIX-like OS (such as
GNU), invoke the program `grub-install' (*note Invoking grub-install::)
as the superuser ("root").

   The usage is basically very simple. You only need to specify one
argument to the program, namely, where to install the boot loader. The
argument can be either a device file (like `/dev/hda') or a partition
specified in GRUB's notation. For example, under Linux the following
will install GRUB into the MBR of the first IDE disk:

     # grub-install /dev/hda

   Likewise, under GNU/Hurd, this has the same effect:

     # grub-install /dev/hd0

   If it is the first BIOS drive, this is the same as well:

     # grub-install '(hd0)'

   Or you can omit the parentheses:

     # grub-install hd0

   But all the above examples assume that GRUB should use images under
the root directory. If you want GRUB to use images under a directory
other than the root directory, you need to specify the option
`--root-directory'. The typical usage is that you create a GRUB boot
floppy with a filesystem. Here is an example:

     # mke2fs /dev/fd0
     # mount -t ext2 /dev/fd0 /mnt
     # grub-install --root-directory=/mnt fd0
     # umount /mnt

   Another example is when you have a separate boot partition which is
mounted at `/boot'. Since GRUB is a boot loader, it doesn't know
anything about mountpoints at all. Thus, you need to run `grub-install'
like this:

     # grub-install --root-directory=/boot /dev/hda

   By the way, as noted above, it is quite difficult to guess BIOS
drives correctly under a UNIX-like OS. Thus, `grub-install' will prompt
you to check if it could really guess the correct mappings, after the
installation. The format is defined in *Note Device map::. Please be
quite careful. If the output is wrong, it is unlikely that your
computer will be able to boot with no problem.

   Note that `grub-install' is actually just a shell script and the
real task is done by the grub shell `grub' (*note Invoking the grub
shell::). Therefore, you may run `grub' directly to install GRUB,
without using `grub-install'. Don't do that, however, unless you are
very familiar with the internals of GRUB. Installing a boot loader on a
running OS may be extremely dangerous.


File: grub.info,  Node: Making a GRUB bootable CD-ROM,  Prev: Installing GRUB using grub-install,  Up: Installation

Making a GRUB bootable CD-ROM
=============================

   GRUB supports the "no emulation mode" in the El Torito
specification(1) (*note Making a GRUB bootable CD-ROM-Footnote-1::).
This means that you can use the whole CD-ROM from GRUB and you don't
have to make a floppy or hard disk image file, which can cause
compatibility problems.

   For booting from a CD-ROM, GRUB uses a special Stage 2 called
`stage2_eltorito'. The only GRUB files you need to have in your
bootable CD-ROM are this `stage2_eltorito' and optionally a config file
`menu.lst'. You don't need to use `stage1' or `stage2', because El
Torito is quite different from the standard boot process.

   Here is an example of procedures to make a bootable CD-ROM image.
First, make a top directory for the bootable image, say, `iso':

     $ mkdir iso

   Make a directory for GRUB:

     $ mkdir -p iso/boot/grub

   Copy the file `stage2_eltorito':

     $ cp /usr/lib/grub/i386-pc/stage2_eltorito iso/boot/grub

   If desired, make the config file `menu.lst' under `iso/boot/grub'
(*note Configuration::), and copy any files and directories for the
disc to the directory `iso/'.

   Finally, make a ISO9660 image file like this:

     $ mkisofs -R -b boot/grub/stage2_eltorito -no-emul-boot \
         -boot-load-size 4 -boot-info-table -o grub.iso iso

   This produces a file named `grub.iso', which then can be burned into
a CD (or a DVD).  `mkisofs' has already set up the disc to boot from
the `boot/grub/stage2_eltorito' file, so there is no need to setup GRUB
on the disc.  (Note that the `-boot-load-size 4' bit is required for
compatibility with the BIOS on many older machines.)

   You can use the device `(cd)' to access a CD-ROM in your config
file. This is not required; GRUB automatically sets the root device to
`(cd)' when booted from a CD-ROM. It is only necessary to refer to
`(cd)' if you want to access other drives as well.


File: grub.info,  Node: Making a GRUB bootable CD-ROM-Footnotes,  Up: Making a GRUB bootable CD-ROM

   (1) El Torito is a specification for bootable CD using BIOS
functions.


File: grub.info,  Node: Booting,  Next: Configuration,  Prev: Installation,  Up: Top

Booting
*******

   GRUB can load Multiboot-compliant kernels in a consistent way, but
for some free operating systems you need to use some OS-specific magic.

* Menu:

* General boot methods::        How to boot OSes with GRUB generally
* OS-specific notes::           Notes on some operating systems
* Making your system robust::   How to make your system robust


File: grub.info,  Node: General boot methods,  Next: OS-specific notes,  Up: Booting

How to boot operating systems
=============================

   GRUB has two distinct boot methods. One of the two is to load an
operating system directly, and the other is to chain-load another boot
loader which then will load an operating system actually. Generally
speaking, the former is more desirable, because you don't need to
install or maintain other boot loaders and GRUB is flexible enough to
load an operating system from an arbitrary disk/partition. However, the
latter is sometimes required, since GRUB doesn't support all the
existing operating systems natively.

* Menu:

* Loading an operating system directly::
* Chain-loading::


File: grub.info,  Node: Loading an operating system directly,  Next: Chain-loading,  Up: General boot methods

How to boot an OS directly with GRUB
------------------------------------

   Multiboot (*note Multiboot Specification: (multiboot)Top.) is the
native format supported by GRUB.  For the sake of convenience, there is
also support for Linux, FreeBSD, NetBSD and OpenBSD. If you want to
boot other operating systems, you will have to chain-load them (*note
Chain-loading::).

   Generally, GRUB can boot any Multiboot-compliant OS in the following
steps:

  1. Set GRUB's root device to the drive where the OS images are stored
     with the command `root' (*note root::).

  2. Load the kernel image with the command `kernel' (*note kernel::).

  3. If you need modules, load them with the command `module' (*note
     module::) or `modulenounzip' (*note modulenounzip::).

  4. Run the command `boot' (*note boot::).

   Linux, FreeBSD, NetBSD and OpenBSD can be booted in a similar
manner. You load a kernel image with the command `kernel' and then run
the command `boot'. If the kernel requires some parameters, just append
the parameters to `kernel', after the file name of the kernel. Also,
please refer to *Note OS-specific notes::, for information on your
OS-specific issues.


File: grub.info,  Node: Chain-loading,  Prev: Loading an operating system directly,  Up: General boot methods

Load another boot loader to boot unsupported operating systems
--------------------------------------------------------------

   If you want to boot an unsupported operating system (e.g. Windows
95), chain-load a boot loader for the operating system. Normally, the
boot loader is embedded in the "boot sector" of the partition on which
the operating system is installed.

  1. Set GRUB's root device to the partition by the command
     `rootnoverify' (*note rootnoverify::):

          grub> rootnoverify (hd0,0)

  2. Set the "active" flag in the partition using the command
     `makeactive'(1) (*note Chain-loading-Footnote-1::) (*note
     makeactive::):

          grub> makeactive

  3. Load the boot loader with the command `chainloader' (*note
     chainloader::):

          grub> chainloader +1

     `+1' indicates that GRUB should read one sector from the start of
     the partition. The complete description about this syntax can be
     found in *Note Block list syntax::.

  4. Run the command `boot' (*note boot::).

   However, DOS and Windows have some deficiencies, so you might have to
use more complicated instructions. *Note DOS/Windows::, for more
information.


File: grub.info,  Node: Chain-loading-Footnotes,  Up: Chain-loading

   (1) This is not necessary for most of the modern operating systems.


File: grub.info,  Node: OS-specific notes,  Next: Making your system robust,  Prev: General boot methods,  Up: Booting

Some caveats on OS-specific issues
==================================

   Here, we describe some caveats on several operating systems.

* Menu:

* GNU/Hurd::
* GNU/Linux::
* FreeBSD::
* NetBSD::
* OpenBSD::
* DOS/Windows::
* SCO UnixWare::
* QNX::


File: grub.info,  Node: GNU/Hurd,  Next: GNU/Linux,  Up: OS-specific notes

GNU/Hurd
--------

   Since GNU/Hurd is Multiboot-compliant, it is easy to boot it; there
is nothing special about it. But do not forget that you have to specify
a root partition to the kernel.

  1. Set GRUB's root device to the same drive as GNU/Hurd's. Probably
     the command `find /boot/gnumach' or similar can help you (*note
     find::).

  2. Load the kernel and the module, like this:

          grub> kernel /boot/gnumach root=hd0s1
          grub> module /boot/serverboot

  3. Run the command `boot' (*note boot::).


File: grub.info,  Node: GNU/Linux,  Next: FreeBSD,  Prev: GNU/Hurd,  Up: OS-specific notes

GNU/Linux
---------

   It is relatively easy to boot GNU/Linux from GRUB, because it
somewhat resembles to boot a Multiboot-compliant OS.

  1. Set GRUB's root device to the same drive as GNU/Linux's. Probably
     the command `find /vmlinuz' or similar can help you (*note find::).

  2. Load the kernel:

          grub> kernel /vmlinuz root=/dev/hda1

     If you need to specify some kernel parameters, just append them to
     the command. For example, to set `vga' to `ext', do this:

          grub> kernel /vmlinuz root=/dev/hda1 vga=ext

     See the documentation in the Linux source tree for complete
     information on the available options.

  3. If you use an initrd, execute the command `initrd' (*note
     initrd::) after `kernel':

          grub> initrd /initrd

  4. Finally, run the command `boot' (*note boot::).

   *Caution:* If you use an initrd and specify the `mem=' option to the
kernel to let it use less than actual memory size, you will also have
to specify the same memory size to GRUB. To let GRUB know the size, run
the command `uppermem' _before_ loading the kernel. *Note uppermem::,
for more information.


File: grub.info,  Node: FreeBSD,  Next: NetBSD,  Prev: GNU/Linux,  Up: OS-specific notes

FreeBSD
-------

   GRUB can load the kernel directly, either in ELF or a.out format. But
this is not recommended, since FreeBSD's bootstrap interface sometimes
changes heavily, so GRUB can't guarantee to pass kernel parameters
correctly.

   Thus, we'd recommend loading the very flexible loader `/boot/loader'
instead. See this example:

     grub> root (hd0,a)
     grub> kernel /boot/loader
     grub> boot


File: grub.info,  Node: NetBSD,  Next: OpenBSD,  Prev: FreeBSD,  Up: OS-specific notes

NetBSD
------

   GRUB can load NetBSD a.out and ELF directly, follow these steps:

  1. Set GRUB's root device with `root' (*note root::).

  2. Load the kernel with `kernel' (*note kernel::). You should append
     the ugly option `--type=netbsd', if you want to load an ELF
     kernel, like this:

          grub> kernel --type=netbsd /netbsd-elf

  3. Run `boot' (*note boot::).

   For now, however, GRUB doesn't allow you to pass kernel parameters,
so it may be better to chain-load it instead. For more information,
please see *Note Chain-loading::.


File: grub.info,  Node: OpenBSD,  Next: DOS/Windows,  Prev: NetBSD,  Up: OS-specific notes

OpenBSD
-------

   The booting instruction is exactly the same as for NetBSD (*note
NetBSD::).


File: grub.info,  Node: DOS/Windows,  Next: SCO UnixWare,  Prev: OpenBSD,  Up: OS-specific notes

DOS/Windows
-----------

   GRUB cannot boot DOS or Windows directly, so you must chain-load them
(*note Chain-loading::). However, their boot loaders have some critical
deficiencies, so it may not work to just chain-load them. To overcome
the problems, GRUB provides you with two helper functions.

   If you have installed DOS (or Windows) on a non-first hard disk, you
have to use the disk swapping technique, because that OS cannot boot
from any disks but the first one. The workaround used in GRUB is the
command `map' (*note map::), like this:

     grub> map (hd0) (hd1)
     grub> map (hd1) (hd0)

   This performs a "virtual" swap between your first and second hard
drive.

   *Caution:* This is effective only if DOS (or Windows) uses BIOS to
access the swapped disks. If that OS uses a special driver for the
disks, this probably won't work.

   Another problem arises if you installed more than one set of
DOS/Windows onto one disk, because they could be confused if there are
more than one primary partitions for DOS/Windows. Certainly you should
avoid doing this, but there is a solution if you do want to do so. Use
the partition hiding/unhiding technique.

   If GRUB "hide"s a DOS (or Windows) partition (*note hide::), DOS (or
Windows) will ignore the partition. If GRUB "unhide"s a DOS (or
Windows) partition (*note unhide::), DOS (or Windows) will detect the
partition. Thus, if you have installed DOS (or Windows) on the first
and the second partition of the first hard disk, and you want to boot
the copy on the first partition, do the following:

     grub> unhide (hd0,0)
     grub> hide (hd0,1)
     grub> rootnoverify (hd0,0)
     grub> chainloader +1
     grub> makeactive
     grub> boot


File: grub.info,  Node: SCO UnixWare,  Next: QNX,  Prev: DOS/Windows,  Up: OS-specific notes

SCO UnixWare
------------

   It is known that the signature in the boot loader for SCO UnixWare is
wrong, so you will have to specify the option `--force' to
`chainloader' (*note chainloader::), like this:

     grub> rootnoverify (hd1,0)
     grub> chainloader --force +1
     grub> makeactive
     grub> boot


File: grub.info,  Node: QNX,  Prev: SCO UnixWare,  Up: OS-specific notes

QNX
---

   QNX seems to use a bigger boot loader, so you need to boot it up,
like this:

     grub> rootnoverify (hd1,1)
     grub> chainloader +4
     grub> boot


File: grub.info,  Node: Making your system robust,  Prev: OS-specific notes,  Up: Booting

How to make your system robust
==============================

   When you test a new kernel or a new OS, it is important to make sure
that your computer can boot even if the new system is unbootable. This
is crucial especially if you maintain servers or remote systems. To
accomplish this goal, you need to set up two things:

  1. You must maintain a system which is always bootable. For instance,
     if you test a new kernel, you need to keep a working kernel in a
     different place. And, it would sometimes be very nice to even have
     a complete copy of a working system in a different partition or
     disk.

  2. You must direct GRUB to boot a working system when the new system
     fails. This is possible with the "fallback" system in GRUB.

   The former requirement is very specific to each OS, so this
documentation does not cover that topic. It is better to consult some
backup tools.

   So let's see the GRUB part. There are two possibilities: one of them
is quite simple but not very robust, and the other is a bit complex to
set up but probably the best solution to make sure that your system can
start as long as GRUB itself is bootable.

* Menu:

* Booting once-only::
* Booting fallback systems::


File: grub.info,  Node: Booting once-only,  Next: Booting fallback systems,  Up: Making your system robust

Booting once-only
-----------------

   You can teach GRUB to boot an entry only at next boot time. Suppose
that your have an old kernel `old_kernel' and a new kernel
`new_kernel'. You know that `old_kernel' can boot your system
correctly, and you want to test `new_kernel'.

   To ensure that your system will go back to the old kernel even if the
new kernel fails (e.g. it panics), you can specify that GRUB should try
the new kernel only once and boot the old kernel after that.

   First, modify your configuration file. Here is an example:

     default saved        # This is important!!!
     timeout 10

     title the old kernel
     root (hd0,0)
     kernel /old_kernel
     savedefault

     title the new kernel
     root (hd0,0)
     kernel /new_kernel
     savedefault 0         # This is important!!!

   Note that this configuration file uses `default saved' (*note
default::) at the head and `savedefault 0' (*note savedefault::) in the
entry for the new kernel. This means that GRUB boots a saved entry by
default, and booting the entry for the new kernel saves `0' as the
saved entry.

   With this configuration file, after all, GRUB always tries to boot
the old kernel after it booted the new one, because `0' is the entry of
`the old kernel'.

   The next step is to tell GRUB to boot the new kernel at next boot
time. For this, execute `grub-set-default' (*note Invoking
grub-set-default::):

     # grub-set-default 1

   This command sets the saved entry to `1', that is, to the new kernel.

   This method is useful, but still not very robust, because GRUB stops
booting, if there is any error in the boot entry, such that the new
kernel has an invalid executable format. Thus, it it even better to use
the "fallback" mechanism of GRUB. Look at next subsection for this
feature.


File: grub.info,  Node: Booting fallback systems,  Prev: Booting once-only,  Up: Making your system robust

Booting fallback systems
------------------------

   GRUB supports a fallback mechanism of booting one or more other
entries if a default boot entry fails. You can specify multiple
fallback entries if you wish.

   Suppose that you have three systems, `A', `B' and `C'. `A' is a
system which you want to boot by default. `B' is a backup system which
is supposed to boot safely. `C' is another backup system which is used
in case where `B' is broken.

   Then you may want GRUB to boot the first system which is bootable
among `A', `B' and `C'. A configuration file can be written in this way:

     default saved        # This is important!!!
     timeout 10
     fallback 1 2         # This is important!!!

     title A
     root (hd0,0)
     kernel /kernel
     savedefault fallback # This is important!!!

     title B
     root (hd1,0)
     kernel /kernel
     savedefault fallback # This is important!!!

     title C
     root (hd2,0)
     kernel /kernel
     savedefault

   Note that `default saved' (*note default::), `fallback 1 2' and
`savedefault fallback' are used. GRUB will boot a saved entry by
default and save a fallback entry as next boot entry with this
configuration.

   When GRUB tries to boot `A', GRUB saves `1' as next boot entry,
because the command `fallback' specifies that `1' is the first fallback
entry. The entry `1' is `B', so GRUB will try to boot `B' at next boot
time.

   Likewise, when GRUB tries to boot `B', GRUB saves `2' as next boot
entry, because `fallback' specifies `2' as next fallback entry. This
makes sure that GRUB will boot `C' after booting `B'.

   It is noteworthy that GRUB uses fallback entries both when GRUB
itself fails in booting an entry and when `A' or `B' fails in starting
up your system. So this solution ensures that your system is started
even if GRUB cannot find your kernel or if your kernel panics.

   However, you need to run `grub-set-default' (*note Invoking
grub-set-default::) when `A' starts correctly or you fix `A' after it
crashes, since GRUB always sets next boot entry to a fallback entry.
You should run this command in a startup script such as `rc.local' to
boot `A' by default:

     # grub-set-default 0

   where `0' is the number of the boot entry for the system `A'.

   If you want to see what is current default entry, you can look at the
file `/boot/grub/default' (or `/grub/default' in some systems). Because
this file is plain-text, you can just `cat' this file. But it is
strongly recommended *not to modify this file directly*, because GRUB
may fail in saving a default entry in this file, if you change this
file in an unintended manner. Therefore, you should use
`grub-set-default' when you need to change the default entry.


File: grub.info,  Node: Configuration,  Next: Network,  Prev: Booting,  Up: Top

Configuration
*************

   You've probably noticed that you need to type several commands to
boot your OS. There's a solution to that - GRUB provides a menu
interface (*note Menu interface::) from which you can select an item
(using arrow keys) that will do everything to boot an OS.

   To enable the menu, you need a configuration file, `menu.lst' under
the boot directory. We'll analyze an example file.

   The file first contains some general settings, the menu interface
related options. You can put these commands (*note Menu-specific
commands::) before any of the items (starting with `title' (*note
title::)).

     #
     # Sample boot menu configuration file
     #

   As you may have guessed, these lines are comments. Lines starting
with a hash character (`#'), and blank lines, are ignored by GRUB.

     # By default, boot the first entry.
     default 0

   The first entry (here, counting starts with number zero, not one!)
will be the default choice.

     # Boot automatically after 30 secs.
     timeout 30

   As the comment says, GRUB will boot automatically in 30 seconds,
unless interrupted with a keypress.

     # Fallback to the second entry.
     fallback 1

   If, for any reason, the default entry doesn't work, fall back to the
second one (this is rarely used, for obvious reasons).

   Note that the complete descriptions of these commands, which are menu
interface specific, can be found in *Note Menu-specific commands::.
Other descriptions can be found in *Note Commands::.

   Now, on to the actual OS definitions. You will see that each entry
begins with a special command, `title' (*note title::), and the action
is described after it. Note that there is no command `boot' (*note
boot::) at the  end of each item. That is because GRUB automatically
executes `boot' if it loads other commands successfully.

   The argument for the command `title' is used to display a short
title/description of the entry in the menu. Since `title' displays the
argument as is, you can write basically anything there.

     # For booting GNU/Hurd
     title  GNU/Hurd
     root   (hd0,0)
     kernel /boot/gnumach.gz root=hd0s1
     module /boot/serverboot.gz

   This boots GNU/Hurd from the first hard disk.

     # For booting GNU/Linux
     title  GNU/Linux
     kernel (hd1,0)/vmlinuz root=/dev/hdb1

   This boots GNU/Linux, but from the second hard disk.

     # For booting Mach (getting kernel from floppy)
     title  Utah Mach4 multiboot
     root   (hd0,2)
     pause  Insert the diskette now^G!!
     kernel (fd0)/boot/kernel root=hd0s3
     module (fd0)/boot/bootstrap

   This boots Mach with a kernel on a floppy, but the root filesystem at
hd0s3. It also contains a `pause' line (*note pause::), which will
cause GRUB to display a prompt and delay, before actually executing the
rest of the commands and booting.

     # For booting FreeBSD
     title  FreeBSD
     root   (hd0,2,a)
     kernel /boot/loader

   This item will boot FreeBSD kernel loaded from the `a' partition of
the third PC slice of the first hard disk.

     # For booting OS/2
     title OS/2
     root  (hd0,1)
     makeactive
     # chainload OS/2 bootloader from the first sector
     chainloader +1
     # This is similar to "chainload", but loads a specific file
     #chainloader /boot/chain.os2

   This will boot OS/2, using a chain-loader (*note Chain-loading::).

     # For booting Windows NT or Windows95
     title Windows NT / Windows 95 boot menu
     root        (hd0,0)
     makeactive
     chainloader +1
     # For loading DOS if Windows NT is installed
     # chainload /bootsect.dos

   The same as the above, but for Windows.

     # For installing GRUB into the hard disk
     title Install GRUB into the hard disk
     root    (hd0,0)
     setup   (hd0)

   This will just (re)install GRUB onto the hard disk.

     # Change the colors.
     title Change the colors
     color light-green/brown blink-red/blue

   In the last entry, the command `color' is used (*note color::), to
change the menu colors (try it!). This command is somewhat special,
because it can be used both in the command-line and in the menu. GRUB
has several such commands, see *Note General commands::.

   We hope that you now understand how to use the basic features of
GRUB. To learn more about GRUB, see the following chapters.


File: grub.info,  Node: Network,  Next: Serial terminal,  Prev: Configuration,  Up: Top

Downloading OS images from a network
************************************

   Although GRUB is a disk-based boot loader, it does provide network
support. To use the network support, you need to enable at least one
network driver in the GRUB build process. For more information please
see `netboot/README.netboot' in the source distribution.

* Menu:

* General usage of network support::
* Diskless::


File: grub.info,  Node: General usage of network support,  Next: Diskless,  Up: Network

How to set up your network
==========================

   GRUB requires a file server and optionally a server that will assign
an IP address to the machine on which GRUB is running. For the former,
only TFTP is supported at the moment. The latter is either BOOTP, DHCP
or a RARP server(1) (*note General usage of network
support-Footnote-1::). It is not necessary to run both the servers on
one computer. How to configure these servers is beyond the scope of this
document, so please refer to the manuals specific to those
protocols/servers.

   If you decided to use a server to assign an IP address, set up the
server and run `bootp' (*note bootp::), `dhcp' (*note dhcp::) or `rarp'
(*note rarp::) for BOOTP, DHCP or RARP, respectively. Each command will
show an assigned IP address, a netmask, an IP address for your TFTP
server and a gateway. If any of the addresses is wrong or it causes an
error, probably the configuration of your servers isn't set up properly.

   Otherwise, run `ifconfig', like this:

     grub> ifconfig --address=192.168.110.23 --server=192.168.110.14

   You can also use `ifconfig' in conjuction with `bootp', `dhcp' or
`rarp' (e.g. to reassign the server address manually). *Note
ifconfig::, for more details.

   Finally, download your OS images from your network. The network can
be accessed using the network drive `(nd)'. Everything else is very
similar to the normal instructions (*note Booting::).

   Here is an example:

     grub> bootp
     Probing... [NE*000]
     NE2000 base ...
     Address: 192.168.110.23    Netmask: 255.255.255.0
     Server: 192.168.110.14     Gateway: 192.168.110.1

     grub> root (nd)
     grub> kernel /tftproot/gnumach.gz root=sd0s1
     grub> module /tftproot/serverboot.gz
     grub> boot


File: grub.info,  Node: General usage of network support-Footnotes,  Up: General usage of network support

   (1) RARP is not advised, since it cannot serve much information