docs/user-ref.texi

@node Introduction
@chapter Introduction

This part documents the user-visible aspect of GRUB. If you are looking
for the information on the internals, see the Programmer Reference
Manual (@pxref{Hacking}).

@menu
* History::                     From maggot to house fly.
* Features::                    How GRUB is different.
* Role of a boot loader::       Judging a system by its boot loader.
@end menu


@node History
@section 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
(@pxref{Top, Multiboot Specification, Motivation, multiboot, The Multiboot
Specification}), 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 OKUJI Yoshinori adopted GRUB as an official
GNU package, and opened its development by making the latest sources
available via anonymous CVS. @xref{Obtaining and Building GRUB}, for
more information.


@node Features
@section GRUB features

The primary requirement for GRUB is that it be compliant with the
@dfn{Multiboot Specification}, which is described in @ref{Top, Multiboot
Specification, Motivation, multiboot, The Multiboot Specification}.

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

@itemize @bullet{}
@item
Basic functions must be straightforward for end-users.

@item
Rich functionality to support kernel experts and designers.

@item
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.
@end itemize

Except for specific compatibility modes (chain-loading and the Linux
@dfn{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):

@table @asis
@item Multiple Executable Formats
Supports many of the @dfn{a.out} variants plus @dfn{ELF}. Symbol
tables are also loaded.

@item Support Non-Multiboot Kernels
Supports 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.

@item Load Multiples Modules
GRUB fully supports the Multiboot feature of loading multiple modules.

@item Configuration File
Supports a human-readable text configuration file with preset boot
commands. The list of commands (@pxref{Command}) are a superset of
those supported on the command line. An example command file is provided
in @ref{Configuration}.

@item Menu Interface
A menu interface listing the 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.

@item 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 command file is present, GRUB drops to
the command line.

The list of commands (@pxref{Command}) are a subset of those supported
for command files. Editing commands closely resemble the Bash command
line (@pxref{Command Line Editing, Bash, Command Line Editing, features,
Bash Features}), with @key{TAB}-completion of commands, devices,
partitions, and files in a directory depending on context.

@item Multiple Filesystem Types
Supports multiple filesystem types transparently, plus a useful explicit
blocklist notation. The currently supported filesystem types are
@dfn{BSD FFS}, @dfn{DOS FAT16 and FAT32}, @dfn{Minix fs}, and
@dfn{Linux ext2fs}. @xref{Filesystem}, for more information.

@item Decompression Support
Can decompress files which were compressed by @command{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 file size and loading time, a particularly
major benefit for floppies.@footnote{There are a few pathological cases
where loading a very badly organized ELF kernel might take longer, but
in practice this never happens.}

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.

@item Access Data on Any Installed Device
Supports reading data from any or all floppy or hard disk(s) recognized
by the BIOS, independent of the setting of the root device.

@item Independent of Drive Geometry Translation
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.

@item Detect All Installed @sc{ram}
GRUB can generally find all the installed @sc{ram} on a PC-compatible
machine. It uses an advanced BIOS query technique for finding all
memory regions (@pxref{Memory detection}). As described on the Multiboot
Specification (@pxref{Top, Multiboot Specification, Motivation,
multiboot, The Multiboot Specification}), not all kernels make use of
this information, but GRUB provides it for those who do.

@item Support Logical Block Address Mode
In traditional disk calls (called @dfn{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, some newer machines
have the new interface, Logical Block Address (@dfn{LBA}) mode. GRUB
automatically detects if LBA mode is available and uses it if
available. In LBA mode, GRUB can access the entire disk.
@end table

Future directions might include an internal programming language for
supporting richer sets of boot options with control statements (which
would make GRUB its own kind of kernel). Support for non-PC hardware
architectures is also planned.@footnote{There is already a port to the
NEC PC-98xx series. See
@url{http://www.kuis.kyoto-u.ac.jp/~kmc/proj/linux98/arch/i386/boot/grub98/},
for more information.}


@node Role of a boot loader
@section The role of a boot loader

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

@quotation
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
@emph{boot loader} is the most important software of all. I used to
refer to the above systems as either ``LILO''@footnote{The LInux LOader,
a boot loader that everybody uses, but nobody likes.} 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@dots{} GRUB!
@end quotation

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.


@node Filesystem
@chapter Filesystem syntax and semantics

GRUB uses a special syntax for specifying disk drives which can be
accessed by BIOS. Because of BIOS limitations, GRUB cannot distinguish
between IDE, ESDI, SCSI, or others. You must know yourself which BIOS
device is equivalent to which OS device. Normally, that will be clear if
you see the files in a device or use the command @command{find}
(@pxref{Command}).

@menu
* Device syntax::               How to specify devices
* Filename syntax::             How to specify files
* Blocklist syntax::            How to specify blocklists
@end menu


@node Device syntax
@section How to specify devices

The device syntax is like this:

@example
@code{(@var{bios-device}[,@var{part-num}][,@var{bsd-subpart-letter}])}
@end example

@samp{[]} means the parameter is optional. @var{bios-device} should be
either @samp{fd} or @samp{hd} followed by a digit, like @samp{fd0}.
But you can also set @var{bios-device} to a hexadecimal or a decimal,
which is a BIOS drive number, so the following are equivalent:

@example
(hd0)
(0x80)
(128)
@end example

@var{part-num} represents the partition number of @var{bios-device},
starting from zero for primary partitions and from four for extened
partitions, and @var{bsd-subpart-letter} represents the BSD disklabel
subpartition, such as @samp{a} or @samp{e}.

A shortcut for specifying BSD subpartitions is
@code{(@var{bios-device},@var{bsd-subpart-letter})}, in this case, GRUB
searches for the first PC partition containing a BSD disklabel, then
finds the subpartition @var{bsd-subpart-letter}. Here is an example:

@example
(hd0,a)
@end example

The syntax like @samp{(hd0)} represents using the entire disk (or the
MBR when installing GRUB), while the syntax like @samp{(hd0,0)}
represents using the partition of the disk (or the boot sector of the
partition when installing GRUB).


@node Filename syntax
@section How to specify files

There are two ways to specify files, by @dfn{absolute filename} and by
@dfn{blocklist}.

An absolute filename resembles a Unix absolute filename, using @samp{/}
for the directory separator (not @samp{\} as in DOS). One example is
@samp{(hd0,0)/boot/grub/menu.lst}. This means the file
@file{/boot/grub/menu.lst} in the first partition of the first hard
disk. If you omit the device name in an absolute filename, GRUB uses
GRUB's @dfn{root device} implicitly. So if you set the root device to,
say, @samp{(hd1,0)} by the command @command{root}, then
@code{/boot/kernel} is the same as @code{(hd1,0)/boot/kernel}.


@node Blocklist syntax
@section How to specify blocklists

A blocklist is used for specifying a file that doesn't appear in the
filesystem, like a chainloader. The syntax is
@code{[@var{offset}]+@var{length}[,[@var{offset}]+@var{length}]@dots{}}.
Here is an example:

@example
@code{0+100,200+1,300+300}
@end example

This represents that GRUB should read blocks 0 through 99, block 200,
and blocks 300 through 600. If you omit an offset, then GRUB assumes
the offset is zero.

Like the filename syntax (@pxref{Filename syntax}), if a blocklist does
not contain a device name, then GRUB uses GRUB's @dfn{root device}. So
@code{(hd0,1)+1} is the same as @code{+1} when the root device is
@samp{(hd0,1)}.


@node Interface
@chapter GRUB's user interface

GRUB has both a simple menu interface for choosing preset entries from a
configuration file, and a highly flexible command line for performing
any desired combination of boot commands.

GRUB looks for its configuration file as soon as it is loaded. If one
is found, then the full menu interface is activated using whatever
entries were found in the file. If you choose the @dfn{command line} menu
option, or if the configuration file was not found, then GRUB drops to
the command line interface.

@menu
* Command line::                The flexible command line interface.
* Menu::                        The simple menu interface.
* Menu entry editor::           Editing a menu entry.
@end menu


@node Command line
@section The flexible command line interface

The command line interface provides a prompt and after it an editable
text area much like a command line in Unix or DOS. Each command is
immediately executed after it is entered @footnote{However, this
behavior will be changed in the future version, in a user-invisible
way.}. The commands (@pxref{Command}) are a subset of those available in
the configuration file, used with exactly the same syntax.

Cursor movement and editing of the text on the line can be done via a
subset of the functions available in the Bash shell:

@table @key
@item C-f
@itemx PC right key
Move forward one character.

@item C-b
@itemx PC left key
Move back one character.

@item C-a
@itemx HOME
Move to the start of the line.

@item C-e
@itemx END
Move the the end of the line.

@item C-d
@itemx DEL
Delete the character underneath the cursor.

@item C-h
@itemx BS
Delete the character to the left of the cursor.

@item C-k
Kill the text from the current cursor position to the end of the line.

@item C-u
Kill backward from the cursor to the beginning of the line.

@item C-y
Yank the killed text back into the buffer at the cursor.

@item C-p
@itemx PC up key
Move up through the history list.

@item C-n
@itemx PC down key
Move down through the history list.
@end table

When typing commands interactively, if the cursor is within or before
the first word in the command-line, pressing the @key{TAB} key (or
@key{C-i}) will display a listing of the available commands, and if the
cursor is after the first word, the @kbd{@key{TAB}} will provide a
completion listing of disks, partitions, and filenames depending on the
context.


@node Menu
@section The simple menu interface

The menu interface is quite easy to use. Its commands are both
reasonably intuitive and described on screen.

Basically, the menu interface provides a list of @dfn{boot entries} to
the user to choose from. Use the arrow keys to select the entry of
choice, then press @key{RET} to run it.  An optional timeout is
available to boot the default entry (the first one if not set), which is
aborted by pressing any key.

Commands are available to enter a bare command line by pressing @key{c}
(which operates exactly like the non-config-file version of GRUB, but
allows one to return to the menu if desired by pressing @key{ESC}) or to
edit any of the @dfn{boot entries} by pressing @key{e}.


@node Menu entry editor
@section Editing a menu entry

The menu entry editor looks much like the main menu interface, but the
lines in the menu are individual commands in the selected entry instead
of entry names.

If an @key{ESC} is pressed in the editor, it aborts all the changes made
to the configuration entry and returns to the main menu interface.

When a particular line is selected, the editor places the user at a
special version of the GRUB command line to edit that line.  When the
user hits @key{RET}, GRUB replaces the line in question in the boot
entry with the changes (unless it was aborted via @key{ESC},
in which case the changes are thrown away).

If you want to add a new line to the menu entry, press @key{o} if adding
a line after the current line or press @key{O} if before the current
line.

To delete a line, hit the key @key{d}. Although GRUB does not support
@dfn{undo} unfortunately, you can do almost the same thing by just
returning to the main menu.


@node Command
@chapter The list of available commands

In this chapter, we list the available commands, both in the
configuration file and in the command line.

@menu
* Menu-specific commands::
* General commands::
* Command-line-specific commands::
@end menu


@node Menu-specific commands
@section The list of commands for the menu only

The semantics are as follows:

@itemize @bullet
@item
The menu-specific commands have to be used before any others.

@item
The files @emph{must} be in plain-text format.

@item
@samp{#} at the beginning of a line in a configuration file means it is
only a comment.

@item
Options are separated by spaces.

@item
All numbers can be either decimal or hexadecimal. A hexadecimal number
must be preceded by @samp{0x}, and is case-insensitive.

@item
Extra options or text at the end of the line is ignored unless otherwise
specified.

@item
Bad commands are added to the current entry, except before entries
start, where they are ignored.
@end itemize

Commands usable in the menu only.

@deffn Command default num
Set the default entry to the entry number @var{num} (if not specified,
it is 0, the first entry).
@end deffn

@deffn Command fallback num
Go into unattended boot mode: if the default boot entry has any errors,
instead of waiting for the user to do anything, it immediately starts
over using the @var{num} entry (same numbering as the @code{default}
command). This obviously won't help if the machine was rebooted by a
kernel that GRUB loaded.
@end deffn

@deffn Command password passwd new-config-file
Disable all interactive editing control (menu entry editor and
command line). If the password @var{passwd} is entered, it loads the
@var{new-config-file} as a new config file and restarts the GRUB Stage
2.
@end deffn

@deffn Command timeout sec
Set a timeout, in @var{sec} seconds, before automatically booting the
default entry (normally the first entry defined).
@end deffn

@deffn Command title name @dots{}
Start a new boot entry, and set its name to the contents of the rest of
the line, starting with the first non-space character.
@end deffn


@node General commands
@section The list of general commands

Commands usable both in the menu and in the command line.

@deffn Command color normal [highlight]
Change the menu colors. The color @var{normal} is used for most
lines in the menu, and the color @var{highlight} is used to highlight the
line where the cursor points. If you omit @var{highlight}, then the
inverted color of @var{normal} is used for the highlighted line. 
The format of a color is
@code{@var{foreground}/@var{background}}. @var{foreground} and
@var{background} are symbolic color names. A symbolic color name must be
one of these:

@itemize @bullet
@item
black

@item
blue

@item
green

@item
cyan

@item
red

@item
magenta

@item
brown

@item
light-gray

@strong{These below can be specified only for the foreground.}

@item
dark-gray

@item
light-blue

@item
light-green

@item
light-cyan

@item
light-red

@item
light-magenta

@item
yellow

@item
white
@end itemize

But only the first eight names can be used for @var{background}. You can
prefix @code{blink-} to @var{foreground} if you want a blinking
foreground color.

This command can be used in the configuration file and on the command
line, so you may write something like this in your configuration file:

@example
# Set default colors.
color light-gray/blue black/light-gray

# Change the colors.
title OS-BS like
color magenta/blue black/magenta
@end example
@end deffn

@deffn Command device drive file
In the grub shell, specify the file @var{file} as the actual drive for a
@sc{bios} drive @var{drive}. You can use this command to create a disk
image and to fix the drives guessed by GRUB when GRUB fails to determine
them correctly, like this:

@example
grub> device (fd0) /floppy-image
grub> device (hd0) /dev/sd0
@end example

This command can be used only in the grub shell (@pxref{Invoking the
grub shell}).
@end deffn

@deffn Command hide partition
Hide @var{partition} by setting the @dfn{hidden} bit in its partition
type code. This is useful only for DOS or Windows when multiple primary
partitions exist in one disk.
@end deffn

@deffn Command unhide partition
Unhide @var{partition} by clearing the @dfn{hidden} bit in its partition
type code. This is useful only for DOS or Windows when multiple primary
partitions exist in one disk.
@end deffn


@node Command-line-specific commands
@section The list of commands in the command line

These commands are usable only in the command line and in menu entries.
If you forget some command, run the command @command{help}.

@deffn Command boot
This boots the OS/chain-loader which has been loaded. Only necessary if
running the fully interactive command line (it is implicit at the end of
a config-file entry).
@end deffn

@deffn Command cat file
Display the contents of the file @var{file}. This command may be useful
to remind you of your OS's root partition:

@example
grub> cat /etc/fstab
@end example
@end deffn

@deffn Command chainloader file
Load @var{file} as a chain-loader. Like any other file loaded by the
filesystem code, it can use the blocklist notation to grab the first
sector of the current partition with @samp{+1}.
@end deffn

@deffn Command configfile @var{file}
Load @var{file} as the configuration file.
@end deffn

@deffn Command embed stage1_5 device
Embed the Stage 1.5 @var{stage1_5} in the sectors after the MBR if
@var{device} is a drive, or in the @dfn{boot loader} area if @var{device}
is a FFS partition.@footnote{The latter feature has not been implemented
yet.} Print the number of sectors which @var{stage1_5} occupies if
successful.
@end deffn

@deffn Command displaymem
Display what GRUB thinks the system address space map of the machine is,
including all regions of physical @sc{ram} installed. GRUB's
@dfn{upper/lower memory} display uses the standard BIOS interface for
the available memory in the first megabyte, or @dfn{lower memory}, and a
synthesized number from various BIOS interfaces of the memory starting
at 1MB and going up to the first chipset hole for @dfn{upper memory}
(the standard PC @dfn{upper memory} interface is limited to reporting a
maximum of 64MB).
@end deffn

@deffn Command find filename
Search for the filename @var{filename} in all of partitions and print
the list of the devices which contain the file. The filename
@var{filename} should be an absolute filename like
@code{/boot/grub/stage1}.
@end deffn

@deffn Command fstest
Toggle filesystem test mode.

Filesystem test mode, when turned on, prints out data corresponding to
all the device reads and what values are being sent to the low-level
routines. The format is @samp{<@var{partition-offset-sector},
@var{byte-offset}, @var{byte-length}>} for high-level reads inside a
partition, and @samp{[@var{disk-offset-sector}]} for low-level sector
requests from the disk.

Filesystem test mode is turned off by any use of the @command{install}
or @command{testload} commands.
@end deffn

@deffn Command geometry drive [cylinder head sector [total_sector]]
Print the information for the drive @var{drive}. In the grub shell, you
can set the geometry of the drive arbitrarily. The number of the
cylinders, the one of the heads, the one of the sectors and the one of
the total sectors are set to CYLINDER, HEAD, SECTOR and TOTAL_SECTOR,
respectively. If you omit TOTAL_SECTOR, then it will be calculated
based on the C/H/S values automatically.
@end deffn

@deffn Command help [pattern @dots{}]
Display helpful information about builtin commands. If you do not
specify @var{pattern}, this command lists the short documents of all
available commands, and, if you specify one or more @var{pattern}s, it
displays long documents of the commands which match @var{pattern}.
@end deffn

@deffn Command impsprobe
Probe the Intel Multiprocessor Specification 1.1 or 1.4 configuration
table and boot the various CPUs which are found into a tight loop. This
command can be used only in the Stage 2.
@end deffn

@deffn Command initrd file @dots{}
Load an initial ramdisk for a Linux format boot image and set the
appropriate parameters in the Linux setup area in memory.
@end deffn

@deffn Command install stage1_file [@option{d}] dest_dev file [addr] [@option{p}] [config_file]
This command is fairly complex, and you should not use this command
unless you are familiar with GRUB. In short, it will perform a full
install presuming the Stage 2 or Stage 1.5@footnote{They're loaded the
same way, so we will refer to the Stage 1.5 as a Stage 2 from now on.}
is in its final install location.

In slightly more detail, it will load @var{stage1_file}, validate that
it is a GRUB Stage 1 of the right version number, install a blocklist for
loading @var{file} as a Stage 2. If the option @option{d} is present, the
Stage 1 will always look for the actual disk @var{file} was installed on,
rather than using the booting drive. The Stage 2 will be loaded at
address @var{addr}, which must be @samp{0x8000} for a true Stage 2, and
@samp{0x2000} for a Stage 1.5. If @var{addr} is not present, GRUB will
determine the address automatically. It then writes the completed Stage 1
to the first block of the device @var{dest_dev}. If the options @option{p}
or @var{config_file} are present, then it reads the first block of
stage2, modifies it with the values of the partition @var{file} was
found on (for @option{p}) or places the string @var{config_file} into the
area telling the stage2 where to look for a configuration file at boot
time. This command preserves the DOS BPB (and for hard disks, the
partition table) of the sector the Stage 1 is to be installed into.
@end deffn

@deffn Command kernel file @dots{}
Attempt to load the primary boot image (Multiboot a.out or @sc{elf},
Linux zImage or bzImage, FreeBSD a.out, NetBSD a.out, etc.) from
@var{file}. The rest of the line is passed verbatim as the @dfn{kernel
command line}. Any modules must be reloaded after using this command.
@end deffn

@deffn Command makeactive
Set the active partition on the root disk to GRUB's root device.
This command is limited to @emph{primary} PC partitions on a hard disk.
@end deffn

@deffn Command map to_drive from_drive
Map the drive @var{from_drive} to the drive @var{to_drive}. This is
necessary when you chain-load some operating systems, such as DOS, if
such an OS resides at a non-first drive. Here is an example:

@example
grub> map (hd0) (hd1)
grub> map (hd1) (hd0)
@end example

The example exchanges the order between the first hard disk and the
second hard disk.
@end deffn

@deffn Command module file @dots{}
Load a boot module @var{file} for a Multiboot format boot image (no
interpretation of the file contents are made, so that user of this
command must know what the kernel in question expects). The rest of the
line is passed as the @dfn{module command line}, like the
@command{kernel} command. You must load a Multiboot kernel image before
loading any module.
@end deffn

@deffn Command modulenounzip file @dots{}
The same as @command{module}, except that automatic decompression is
disabled.
@end deffn

@deffn Command pause message @dots{}
Print the @var{message}, then wait until a key is pressed. Note that
placing @key{^G} (ASCII code 7) in the message will cause the speaker to
emit the standard beep sound, which is useful when prompting the user to
change floppies.
@end deffn

@deffn Command quit
Exit from the GRUB shell @command{grub} (@pxref{Invoking the grub
shell}). This command can be used only in the grub shell.
@end deffn

@deffn Command read addr
Read a 32-bit value from memory at address @var{addr} and display it in
hex format.
@end deffn

@deffn Command root device [hdbias]
Set the current @dfn{root device} to the device @var{device}, then
attempt to mount it to get the partition size (for passing the partition
descriptor in @code{ES:ESI}, used by some chain-loaded boot loaders), the
BSD drive-type (for booting BSD kernels using their native boot format),
and correctly determine the PC partition where a BSD sub-partition is
located. The optional @var{hdbias} parameter is a number to tell a BSD
kernel how many BIOS drive numbers are on controllers before the current
one. For example, if there is an IDE disk and a SCSI disk, and your
FreeBSD root partition is on the SCSI disk, then use a @samp{1} for
@var{hdbias}.
@end deffn

@deffn Command rootnoverify device [hdbias]
Similar to @command{root}, but don't attempt to mount the
partition. This is useful for when an OS is outside of the area of the
disk that GRUB can read, but setting the correct root device is still
desired. Note that the items mentioned in @command{root} above which
derived from attempting the mount will @emph{not} work correctly.
@end deffn

@deffn Command setup install_device [image_device]
Set up the installation of GRUB automatically. This command uses the
more flexible command @command{install} in the backend and installs GRUB
into the device @var{install_device}. If @var{image_device} is
specified, then find the GRUB images in the device @var{image_device},
otherwise use the current @dfn{root device}, which can be set by the
command @command{root}. If @var{install_dvice} is a hard disk, then
embed a Stage 1.5 in the disk if possible.
@end deffn

@deffn Command testload file
Read the entire contents of @var{file} in several different ways and
compares them, to test the filesystem code. The output is somewhat
cryptic , but if no errors are reported and the final @samp{i=@var{X},
filepos=@var{Y}} reading has @var{X} and @var{Y} equal, then it is
definitely consistent, and very likely works correctly subject to a
consistent offset error. If this test succeeds, then a good next step is
to try loading a kernel.
@end deffn

@deffn Command uppermem kbytes
Force GRUB to assume that only @var{kbytes} kilobytes of upper memory
are installed. Any system address range maps are discarded.

@strong{Caution:} This should be used with great caution, and should
only be necessary on some old machines. GRUB's BIOS probe can pick up
all @sc{ram} on all new machines the author has ever heard of. It can
also be used for debugging purposes to lie to an OS.
@end deffn


@node Troubleshooting
@chapter Error messages reported by GRUB

This chapter describes error messages reported by GRUB when you
encounter trouble. @xref{Invoking the grub shell}, if your problem is
specific to the grub shell.

@menu
* Stage1 errors::               Errors reported by the Stage 1
* Stage1.5 errors::             Errors reported by the Stage 1.5
* Stage2 errors::               Errors reported by the Stage 2
@end menu


@node Stage1 errors
@section Errors reported by the Stage 1

The general way that the Stage 1 handles errors is to print an error
string and then halt. Pressing @kbd{@key{CTRL}-@key{ALT}-@key{DEL}} will
reboot.

The following is a comprehensive list of error messages for the Stage 1:

@table @asis
@item Hard Disk Error
The stage2 or stage1.5 is being read from a hard disk, and the attempt
to determine the size and geometry of the hard disk failed.

@item Floppy Error
The stage2 or stage1.5 is being read from a floppy disk, and the attempt
to determine the size and geometry of the floppy disk failed. It's listed
as a separate error since the probe sequence is different than for hard
disks.

@item Read Error
A disk read error happened while trying to read the stage2 or stage1.5.

@item Geom Error
The location of the stage2 or stage1.5 is not in the portion of the disk
supported directly by the BIOS read calls.  This could occur because the
BIOS translated geometry has been changed by the user or the disk is
moved to another machine or controller after installation, or GRUB was
not installed using itself (if it was, the Stage 2 version of this error
would have been seen during that process and it would not have completed
the install).
@end table


@node Stage1.5 errors
@section Errors reported by the Stage 1.5

The general way that the Stage 1.5 handles errors is to print an error
number in the form @code{Error: @var{num}} and then halt. Pressing
@kbd{@key{CTRL}-@key{ALT}-@key{DEL}} will reboot.

The error numbers correspond to the @ref{Stage2 errors} in the listed
sequence.


@node Stage2 errors
@section Errors reported by the Stage 2

The general way that the Stage 2 handles errors is to abort the
operation in question, print an error string, then (if possible) either
continue based on the fact that an error occurred or wait for the user to
deal with the error.

The following is a comprehensive list of error messages for the Stage 2
(error numbers for the Stage 1.5 are listed before the colon in each
description):

@table @asis
@item 1 : Bad filename (must be absolute filename or blocklist)
This error is returned if a filename is requested which doesn't fit the
syntax/rules listed in the @ref{Filesystem}.

@item 2 : Bad file or directory type
This error is returned if a file requested is not a regular file, but
something like a symbolic link, directory, or FIFO.

@item 3 : Bad or corrupt data while decompressing file
This error is returned the run-length decompression code gets an
internal error. This is usually from a corrupt file.

@item 4 : Bad or incompatible header on compressed file
This error is returned if the file header for a supposedly compressed
file is bad.

@item 5 : Partition table invalid or corrupt
This error s returned if the sanity checks on the integrity of the
partition table fail. This is a bad sign.

@item 6 : Bad or corrupt version of stage1/stage2
This error is returned if the install command is pointed to incompatible
or corrupt versions of the stage1 or stage2. It can't detect corruption
in general, but this is a sanity check on the version numbers, which
should be correct.

@item 7 : Loading below 1MB is not supported
This error is returned if the lowest address in a kernel is below the
1MB boundary. The Linux zImage format is a special case and can be
handled since it has a fixed loading address and maximum size.

@item 8 : Cannot boot without kernel loaded
This error is returned if GRUB is told to execute the boot sequence
without having a kernel to start.

@item 9 : Unknown boot failure
This error is returned if the boot attempt did not succeed for reasons
which are unknown.

@item 10 : Unsupported Multiboot features requested
This error is returned when the Multiboot features word in the Multiboot
header requires a feature that is not recognized. The point of this is
that the kernel requires special handling which GRUB is likely unable to
provide.

@item 11 : Device string unrecognizable
This error is returned if a device string was expected, and the string
encountered didn't fit the syntax/rules listed in the @ref{Filesystem}.

@item 12 : Invalid device requested
This error is returned if a device string is recognizable but does not
fall under the other device errors.

@item 13 : Invalid or unsupported executable format
This error is returned if the kernel image being loaded is not
recognized as Multiboot or one of the supported native formats (Linux
zImage or bzImage, FreeBSD, or NetBSD).

@item 14 : Filesystem compatibility error, can't read whole file
Some of the filesystem reading code in GRUB has limits on the length of
the files it can read. This error is returned when the user runs into
such a limit.

@item 15 : File not found
This error is returned if the specified filename cannot be found, but
everything else (like the disk/partition info) is OK.

@item 16 : Inconsistent filesystem structure
This error is returned by the filesystem code to denote an internal
error caused by the sanity checks of the filesystem structure on disk
not matching what it expects. This is usually caused by a corrupt
filesystem or bugs in the code handling it in GRUB.

@item 17 : Cannot mount selected partition
This error is returned if the partition requested exists, but the
filesystem type cannot be recognized by GRUB.

@item 18 : Selected cylinder exceeds maximum supported by BIOS
This error is returned when a read is attempted at a linear block
address beyond the end of the BIOS translated area. This generally
happens if your disk is larger than the BIOS can handle (512MB for
(E)IDE disks on older machines or larger than 8GB in general).

@item 19 : Must load Linux kernel before initrd
This error is returned if the initrd command is used before loading a
Linux kernel. Similar to the above error, it only makes sense in that
case anyway.

@item 20 : Must load Multiboot kernel before modules
This error is returned if the module load command is used before loading
a Multiboot kernel. It only makes sense in this case anyway, as GRUB has
no idea how to communicate the presence of location of such modules to a
non-Multiboot-aware kernel.

@item 21 : Selected disk does not exist
This error is returned if the device part of a device- or full filename
refers to a disk or BIOS device that is not present or not recognized by
the BIOS in the system.

@item 22 : No such partition
This error is returned if a partition is requested in the device part of
a device- or full filename which isn't on the selected disk.

@item 23 : Error while parsing number
This error is returned if GRUB was expecting to read a number and
encountered bad data.

@item 24 : Attempt to access block outside partition
This error is returned if a linear block address is outside of the disk
partition. This generally happens because of a corrupt filesystem on the
disk or a bug in the code handling it in GRUB (it's a great debugging
tool).

@item 25 : Disk read error
This error is returned if there is a disk read error when trying to
probe or read data from a particular disk.

@item 26 : Too many symbolic links
This error is returned if the link count is beyond the maximum
(currently 5), possibly the symbolic links are looped.

@item 27 : Unrecognized command
This error is returned if an unrecognized command is entered into the
command line or in a boot sequence section of a configuration file and
that entry is selected.

@item 28 : Selected item won't fit into memory
This error is returned if a kernel, module, or raw file load command is
either trying to load its data such that it won't fit into memory or it
is simply too big.

@item 29 : Disk write error
This error is returned if there is a disk write error when trying to
write to a particular disk. This would generally only occur during an
install of set active partition command.
@end table


@node Invoking the grub shell
@chapter Invoking the grub shell

This chapter documents the grub shell @command{grub}.

@menu
* Basic usage::                 How to use the grub shell
* Installation under UNIX::     How to install GRUB via @command{grub}
* Device map::                  The map between BIOS drives and OS devices
@end menu


@node Basic usage
@section Introduction into the grub shell

You can use the command @command{grub} for installing GRUB under your
operating systems and for a testbed when you add a new feature into GRUB
or when fix a bug. @command{grub} is almost the same as the Stage 2,
and, in fact, it shares the source code with the Stage 2 and you can use
the same commands (@pxref{Command}) in @command{grub}. It is emulated by
replacing BIOS calls with UNIX system calls and libc functions.

The command @command{grub} accepts the following options:

@table @option
@item --help
Print a summary of the command line options and exit.

@item --version
Print the version number of GRUB and exit.

@item --verbose
Print some verbose messages for debugging purpose.

@item --device-map=@var{file}
Read the device map file instead of @file{/boot/grub/device.map}. The
format is described in @ref{Device map}.

@item --no-floppy
Do not probe any floppy drive. This option has no effect if there is the
device map file (@pxref{Device map}).

@item --probe-second-floppy
Probe the second floppy drive. If this option is not specified, the grub
shell does not probe it, as that sometimes takes a long time. If there
is the device map file (@pxref{Device map}), the grub shell just ignores
this option.

@item --config-file=@var{file}
Read the configuration file @var{file} instead of
@file{/boot/grub/menu.lst}. The format is the same as the normal GRUB
syntax. See @ref{Filesystem}, for more information.

@item --boot-drive=@var{drive}
Set the stage2 @var{boot_drive} to @var{drive}. This argument should be
an integer (decimal, octal or hexadecimal).

@item --install-partition=@var{par}
Set the stage2 @var{install_partition} to @var{par}. This argument
should be an integer (decimal, octal or hexadecimal).

@item --no-config-file
Do not use the configuration file even if it can be read.

@item --no-curses
Do not use the curses interface even if it is available.

@item --batch
This option has the same meaning as @samp{--no-config-file --no-curses}.

@item --read-only
Disable writing to any disk.

@item --hold
Wait until a debugger will attach. This option is useful when you want
to debug the startup code.
@end table


@node Installation under UNIX
@section How to install GRUB via @command{grub}

The installation procedure is the same as under the @dfn{native} Stage
2. @xref{Installation}, for more information. The command
@command{grub}-specific information is described here.

What you should be careful about is @dfn{buffer cache}. @command{grub}
makes use of raw devices instead of filesystems that your operating
systems serve, so there exists a potential problem that some cache
inconsistency may corrupt your filesystems. What we recommend is:

@itemize @bullet
@item
If you can unmount drives to which GRUB may write any amount of data,
unmount them before running @command{grub}.

@item
If a drive cannot be unmounted but can be mounted with the read-only
flag, mount it in read-only mode. That should be secure.

@item
If a drive must be mounted with the read-write flag, make sure that any
activity is not being done on it during running the command
@command{grub}.

@item
Reboot your operating system as soon as possible. Probably that is not
required if you follow these rules above, but reboot is the most secure
way.
@end itemize

In addition, enter the command @command{quit} when you finish the
installation. That is @emph{very important} because @command{quit} makes
the buffer cache consistent. Do not push @key{C-c}.

If you want to install GRUB non-interactively, specify @samp{--batch}
option in the command line. This is a simple example:

@example
#!/bin/sh

/sbin/grub --batch <<EOT 1>/dev/null 2>/dev/null
root (hd0,0)
setup (hd0)
quit
EOT
@end example


@node Device map
@section The map between BIOS drives and OS devices

The grub shell creates the @dfn{device map file} automatically unless it
already exists. The default location is
@file{/boot/grub/device.map}. @xref{Basic usage}, if you want to change
the filename.

If the device map file exists, the grub shell reads it to map BIOS
drives to OS devices. This file consists of lines like this:

@example
@var{device} @var{file}
@end example

@var{device} is a drive, which syntax is the same as the one in GRUB
(@pxref{Device syntax}), and @var{file} is an OS's file, which is
normally a device file.

The reason why the grub shell gives you the device map file is that it
cannot guess the map between BIOS drives and OS devices correctly in
some environments. For example, if you exchange the boot sequence
between IDE and SCSI in your BIOS, it mistakes the order.

Thus, edit the file if the grub shell makes a mistake. You can put any
comments in the file if needed, as the grub shell assumes that a line is
just a comment if the first character is @samp{#}.


@node Invoking mbchk
@chapter Invoking mbchk

The program @command{mbchk} checks for the format of a Multiboot
kernel. We recommend using this program before booting your own kernel
by GRUB.

@command{mbchk} accepts the following options:

@table @option
@item --help
Print a summary of the command line options and exit.

@item --version
Print the version number of GRUB and exit.

@item --quiet
Supress all normal output.
@end table