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GNU GRUB manual
This is the documentation of GNU GRUB, the GRand Unified Bootloader, a
flexible and powerful boot loader program for a wide range of
   This edition documents version 1.98+20100804-14+squeeze2.
   This manual is for GNU GRUB (version 1.98+20100804-14+squeeze2,
2 August 2010).
   Copyright (C) 1999,2000,2001,2002,2004,2006,2008,2009,2010 Free
Software Foundation, Inc.
     Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.2 or any later version published by the Free Software
     Foundation; with no Invariant Sections.
* 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
* Vendor power-on keys::        Changing GRUB behaviour on vendor power-on keys
* Images::                      GRUB image files
* Filesystem::                  Filesystem syntax and semantics
* Interface::                   The menu and the command-line
* Commands::                    The list of available builtin commands
* Security::                    Authentication and authorisation
* Troubleshooting::             Error messages produced by GRUB
* Invoking grub-install::       How to use the GRUB installer
* Invoking grub-mkconfig::      Generate a GRUB configuration file
* Invoking grub-mkpasswd-pbkdf2::
                                Generate GRUB password hashes
* 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
* Copying This Manual::         Copying This Manual
* Index::
File:,  Node: Introduction,  Next: Naming convention,  Prev: Top,  Up: Top
1 Introduction to GRUB
* Menu:
* Overview::                    What exactly GRUB is and how to use it
* History::                     From maggot to house fly
* Features::                    GRUB features
* Changes from GRUB Legacy::    Differences from previous versions
* Role of a boot loader::       The role of a boot loader
File:,  Node: Overview,  Next: History,  Up: Introduction
1.1 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.
File:,  Node: History,  Next: Features,  Prev: Overview,  Up: Introduction
1.2 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.
   Over the next few years, GRUB was extended to meet many needs, but it
quickly became clear that its design was not keeping up with the
extensions being made to it, and we reached the point where it was very
difficult to make any further changes without breaking existing
features.  Around 2002, Yoshinori K. Okuji started work on PUPA
(Preliminary Universal Programming Architecture for GNU GRUB), aiming
to rewrite the core of GRUB to make it cleaner, safer, more robust, and
more powerful.  PUPA was eventually renamed to GRUB 2, and the original
version of GRUB was renamed to GRUB Legacy.  Small amounts of
maintenance continued to be done on GRUB Legacy, but the last release
(0.97) was made in 2005 and at the time of writing it seems unlikely
that there will be another.
   By around 2007, GNU/Linux distributions started to use GRUB 2 to
limited extents, and by the end of 2009 multiple major distributions
were installing it by default.
File:,  Node: Features,  Next: Changes from GRUB Legacy,  Prev: History,  Up: Introduction
1.4 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
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 "Amiga Fast FileSystem (AFFS)", "AtheOS fs", "BeFS",
     "cpio", "Linux ext2/ext3/ext4", "DOS FAT12/FAT16/FAT32", "HFS",
     "HFS+", "ISO9660", "JFS", "Minix fs", "nilfs2", "NTFS",
     "ReiserFS", "Amiga Smart FileSystem (SFS)", "tar", "UDF", "BSD
     UFS/UFS2", and "XFS". *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
     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
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"
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:,  Node: Changes from GRUB Legacy,  Next: Role of a boot loader,  Prev: Features,  Up: Introduction
1.3 Differences from previous versions
GRUB 2 is a rewrite of GRUB (*note History::), although it shares many
characteristics with the previous version, now known as GRUB Legacy.
Users of GRUB Legacy may need some guidance to find their way around
this new version.
   * The configuration file has a new name (`grub.cfg' rather than
     `menu.lst' or `grub.conf'), new syntax (*note Configuration::) and
     many new commands (*note Commands::).  Configuration cannot be
     copied over directly, although most GRUB Legacy users should not
     find the syntax too surprising.
   * `grub.cfg' is typically automatically generated by `grub-mkconfig'
     (*note Simple configuration::).  This makes it easier to handle
     versioned kernel upgrades.
   * Partition numbers in GRUB device names now start at 1, not 0
     (*note Naming convention::).
   * The configuration file is now written in something closer to a full
     scripting language: variables, conditionals, and loops are
   * A small amount of persistent storage is available across reboots,
     using the `save_env' and `load_env' commands in GRUB and the
     `grub-editenv' utility.
   * GRUB 2 has more reliable ways to find its own files and those of
     target kernels on multiple-disk systems, and has commands (*note
     search::) to find devices using file system labels or Universally
     Unique Identifiers (UUIDs).
   * GRUB 2 is available for several other types of system in addition
     to the PC BIOS systems supported by GRUB Legacy: PC EFI, PC
     coreboot, PowerPC, SPARC, and MIPS Lemote Yeeloong are all
   * Many more file systems are supported, including but not limited to
     ext4, HFS+, and NTFS.
   * GRUB 2 can read files directly from LVM and RAID devices.
   * A graphical terminal and a graphical menu system are available.
   * GRUB 2's interface can be translated, including menu entry names.
   * The image files (*note Images::) that make up GRUB have been
     reorganised; Stage 1, Stage 1.5, and Stage 2 are no more.
   * GRUB 2 puts many facilities in dynamically loaded modules,
     allowing the core image to be smaller, and allowing the core image
     to be built in more flexible ways.
File:,  Node: Role of a boot loader,  Prev: Changes from GRUB Legacy,  Up: Introduction
1.5 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:,  Node: Naming convention,  Next: Installation,  Prev: Introduction,  Up: Top
2 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:
   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.
   Here, `hd' means it is a hard disk drive. The first integer `0'
indicates the drive number, that is, the first hard disk, the string
`msdos' indicates the partition scheme, while the second integer, `2',
indicates the partition number (or the PC slice number in the BSD
terminology). The partition numbers are counted from _one_, not from
zero (as was the case in previous versions of GRUB). 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.
   This specifies the first "extended partition" of the first hard disk
drive. Note that the partition numbers for extended partitions are
counted from `5', regardless of the actual number of primary partitions
on your hard disk.
   This means the BSD `a' partition on first PC slice number of the
second hard disk.
   Of course, to actually access the disks or partitions with GRUB, you
need to use the device specification in a command, like `set
root=(fd0)' or `parttool (hd0,msdos3) hidden-'. 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
     set 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
   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
   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:,  Node: Installation,  Next: Booting,  Prev: Naming convention,  Up: Top
3 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
   GRUB comes with boot images, which are normally put in the directory
`/usr/lib/grub/i386-pc'. 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:
* Installing GRUB using grub-install::
* Making a GRUB bootable CD-ROM::
* Device map::
File:,  Node: Installing GRUB using grub-install,  Next: Making a GRUB bootable CD-ROM,  Up: Installation
3.1 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 `grub-mkimage' and `grub-setup'.  Therefore, you
may run those commands 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:,  Node: Making a GRUB bootable CD-ROM,  Next: Device map,  Prev: Installing GRUB using grub-install,  Up: Installation
3.2 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
`grub.cfg'. 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 `grub.cfg' 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:,  Node: Device map,  Prev: Making a GRUB bootable CD-ROM,  Up: Installation
3.3 The map between BIOS drives and OS devices
The `grub-mkdevicemap' program can be used to create the "device map
file".  It is often run automatically by tools such as `grub-install'
if the device map file does not already exist.  The file name
`/boot/grub/' is preferred.
   If the device map file exists, the GRUB utilities (`grub-probe',
`grub-setup', etc.) read it to map BIOS drives to OS devices.  This
file consists of lines like this:
   DEVICE is a drive specified in the GRUB syntax (*note Device
syntax::), and FILE is an OS file, which is normally a device file.
   Historically, the device map file was used because GRUB device names
had to be used in the configuration file, and they were derived from
BIOS drive numbers.  The map between BIOS drives and OS devices cannot
always be guessed correctly: for example, GRUB will get the order wrong
if you exchange the boot sequence between IDE and SCSI in your BIOS.
   Unfortunately, even OS device names are not always stable.  Modern
versions of the Linux kernel may probe drives in a different order from
boot to boot, and the prefix (`/dev/hd*' versus `/dev/sd*') may change
depending on the driver subsystem in use.  As a result, the device map
file required frequent editing on some systems.
   GRUB avoids this problem nowadays by using UUIDs or file system
labels when generating `grub.cfg', and we advise that you do the same
for any custom menu entries you write.  If the device map file does not
exist, then the GRUB utilities will assume a temporary device map on
the fly.  This is often good enough, particularly in the common case of
single-disk systems.
   However, the device map file is not entirely obsolete yet, and there
are still some situations that require it to exist.  If necessary, you
may edit the file if `grub-mkdevicemap' makes a mistake.  You can put
any comments in the file if needed, as the GRUB utilities assume that a
line is just a comment if the first character is `#'.
File:,  Node: Booting,  Next: Configuration,  Prev: Installation,  Up: Top
4 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
File:,  Node: General boot methods,  Next: OS-specific notes,  Up: Booting
4.1 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:,  Node: Loading an operating system directly,  Next: Chain-loading,  Up: General boot methods
4.1.1 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
   FIXME: this section is incomplete.
  1. 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
File:,  Node: Chain-loading,  Prev: Loading an operating system directly,  Up: General boot methods
4.1.2 Chain-loading an OS
Operating systems that do not support Multiboot and do not have specific
support in GRUB (specific support is available for Linux, FreeBSD,
NetBSD and OpenBSD) must be chain-loaded, which involves loading
another boot loader and jumping to it in real mode.
   The `chainloader' command (*note chainloader::) is used to set this
up.  It is normally also necessary to load some GRUB modules and set the
appropriate root device.  Putting this together, we get something like
this, for a Windows system on the first partition of the first hard
menuentry "Windows" {
	insmod chain
	insmod ntfs
	set root=(hd0,1)
	chainloader +1
   On systems with multiple hard disks, an additional workaround may be
required.  *Note DOS/Windows::.
   Chain-loading is only supported on PC BIOS and EFI platforms.
File:,  Node: OS-specific notes,  Prev: General boot methods,  Up: Booting
4.2 Some caveats on OS-specific issues
Here, we describe some caveats on several operating systems.
* Menu:
* GNU/Hurd::
* GNU/Linux::
* DOS/Windows::
File:,  Node: GNU/Hurd,  Next: GNU/Linux,  Up: OS-specific notes
4.2.1 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.
   FIXME: this section is incomplete.
  1. Run the command `boot' (*note boot::).
File:,  Node: GNU/Linux,  Next: DOS/Windows,  Prev: GNU/Hurd,  Up: OS-specific notes
4.2.2 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.  The
     command `search --file --set /vmlinuz' or similar may help you
     (*note search::).
  2. Load the kernel using the command `linux' (*note linux::):
          grub> linux /vmlinuz root=/dev/sda1
     If you need to specify some kernel parameters, just append them to
     the command.  For example, to set `acpi' to `off', do this:
          grub> linux /vmlinuz root=/dev/sda1 acpi=off
     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 `linux':
          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:,  Node: DOS/Windows,  Prev: GNU/Linux,  Up: OS-specific notes
4.2.3 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 `drivemap' (*note drivemap::), like this:
     drivemap -s (hd0) (hd1)
   This performs a "virtual" swap between your first and second hard
   *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 "hides" a DOS (or Windows) partition (*note parttool::), DOS
(or Windows) will ignore the partition. If GRUB "unhides" a DOS (or
Windows) partition, 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:
     parttool (hd0,1) hidden-
     parttool (hd0,2) hidden+
     set root=(hd0,1)
     chainloader +1
     parttool ${root} boot+
File:,  Node: Configuration,  Next: Network,  Prev: Booting,  Up: Top
5 Writing your own configuration file
GRUB is configured using `grub.cfg', usually located under
`/boot/grub'.  This file is quite flexible, but most users will not
need to write the whole thing by hand.
* Menu:
* Simple configuration::        Recommended for most users
* Shell-like scripting::        For power users and developers
* Embedded configuration::      Embedding a configuration file into GRUB
* Themes::                      Graphical menu themes
File:,  Node: Simple configuration,  Next: Shell-like scripting,  Up: Configuration
5.1 Simple configuration handling
The program `grub-mkconfig' (*note Invoking grub-mkconfig::) generates
`grub.cfg' files suitable for most cases.  It is suitable for use when
upgrading a distribution, and will discover available kernels and
attempt to generate menu entries for them.
   The file `/etc/default/grub' controls the operation of
`grub-mkconfig'.  It is sourced by a shell script, and so must be valid
POSIX shell input; normally, it will just be a sequence of `KEY=value'
lines, but if the value contains spaces or other special characters
then it must be quoted.  For example:
     GRUB_TERMINAL_INPUT="console serial"
   Valid keys in `/etc/default/grub' are as follows:
     The default menu entry.  This may be a number, in which case it
     identifies the Nth entry in the generated menu counted from zero,
     or the full name of a menu entry, or the special string `saved'.
     Using the full name may be useful if you want to set a menu entry
     as the default even though there may be a variable number of
     entries before it.
     If you set this to `saved', then the default menu entry will be
     that saved by `GRUB_SAVEDEFAULT', `grub-set-default', or
     The default is `0'.
     If this option is set to `true', then, when an entry is selected,
     save it as a new default entry for use by future runs of GRUB.
     This is only useful if `GRUB_DEFAULT=saved'; it is a separate
     option because `GRUB_DEFAULT=saved' is useful without this option,
     in conjunction with `grub-set-default' or `grub-reboot'.  Unset by
     Boot the default entry this many seconds after the menu is
     displayed, unless a key is pressed.  The default is `5'.  Set to
     `0' to boot immediately without displaying the menu, or to `-1' to
     wait indefinitely.
     Wait this many seconds for a key to be pressed before displaying
     the menu.  If no key is pressed during that time, boot
     immediately.  Unset by default.
     In conjunction with `GRUB_HIDDEN_TIMEOUT', set this to `true' to
     suppress the verbose countdown while waiting for a key to be
     pressed before displaying the menu.  Unset by default.
     Variants of the corresponding variables without the `_BUTTON'
     suffix, used to support vendor-specific power buttons.  *Note
     Vendor power-on keys::.
     Set by distributors of GRUB to their identifying name.  This is
     used to generate more informative menu entry titles.
     Select the terminal input device.  You may select multiple devices
     here, separated by spaces.
     Valid terminal input names depend on the platform, but may include
     `console' (PC BIOS and EFI consoles), `serial' (serial terminal),
     `ofconsole' (Open Firmware console), `at_keyboard' (PC AT
     keyboard, mainly useful with Coreboot), or `usb_keyboard' (USB
     keyboard using the HID Boot Protocol, for cases where the firmware
     does not handle this).
     The default is to use the platform's native terminal input.
     Select the terminal output device.  You may select multiple
     devices here, separated by spaces.
     Valid terminal output names depend on the platform, but may include
     `console' (PC BIOS and EFI consoles), `serial' (serial terminal),
     `gfxterm' (graphics-mode output), `ofconsole' (Open Firmware
     console), or `vga_text' (VGA text output, mainly useful with
     The default is to use the platform's native terminal output.
     If this option is set, it overrides both `GRUB_TERMINAL_INPUT' and
     `GRUB_TERMINAL_OUTPUT' to the same value.
     A command to configure the serial port when using the serial
     console.  *Note serial::.  Defaults to `serial'.
     Command-line arguments to add to menu entries for the Linux kernel.
     Unless `GRUB_DISABLE_LINUX_RECOVERY' is set to `true', two menu
     entries will be generated for each Linux kernel: one default entry
     and one entry for recovery mode.  This option lists command-line
     arguments to add only to the default menu entry, after those
     listed in `GRUB_CMDLINE_LINUX'.
     Linux and Xen.
     Normally, `grub-mkconfig' will generate menu entries that use
     universally-unique identifiers (UUIDs) to identify the root
     filesystem to the Linux kernel, using a `root=UUID=...' kernel
     parameter.  This is usually more reliable, but in some cases it
     may not be appropriate.  To disable the use of UUIDs, set this
     option to `true'.
     If this option is set to `true', disable the generation of recovery
     mode menu entries for Linux.
     If this option is set to `true', disable the generation of recovery
     mode menu entries for NetBSD.
     If graphical video support is required, either because the
     `gfxterm' graphical terminal is in use or because
     `GRUB_GFXPAYLOAD_LINUX' is set, then `grub-mkconfig' will normally
     load all available GRUB video drivers and use the one most
     appropriate for your hardware.  If you need to override this for
     some reason, then you can set this option.
     After `grub-install' has been run, the available video drivers are
     listed in `/boot/grub/video.lst'.
     Set the resolution used on the `gfxterm' graphical terminal.  Note
     that you can only use modes which your graphics card supports via
     VESA BIOS Extensions (VBE), so for example native LCD panel
     resolutions may not be available.  The default is `640x480'.
     Set a background image for use with the `gfxterm' graphical
     terminal.  The value of this option must be a file readable by
     GRUB at boot time, and it must end with `.png', `.tga', `.jpg', or
     `.jpeg'.  The image will be scaled if necessary to fit the screen.
     Set a theme for use with the `gfxterm' graphical terminal.  *Note
     Set to `text' to force the Linux kernel to boot in normal text
     mode, `keep' to preserve the graphics mode set using
     `GRUB_GFXMODE', `WIDTHxHEIGHT'[`xDEPTH'] to set a particular
     graphics mode, or a sequence of these separated by commas or
     semicolons to try several modes in sequence.
     Depending on your kernel, your distribution, your graphics card,
     and the phase of the moon, note that using this option may cause
     GNU/Linux to suffer from various display problems, particularly
     during the early part of the boot sequence.  If you have problems,
     set this option to `text' and GRUB will tell Linux to boot in
     normal text mode.
     Normally, `grub-mkconfig' will try to use the external `os-prober'
     program, if installed, to discover other operating systems
     installed on the same system and generate appropriate menu entries
     for them.  Set this option to `true' to disable this.
     Play a tune on the speaker when GRUB starts.  This is particularly
     useful for users unable to see the screen.  The value of this
     option is passed directly to *note play::.
     If this option is set, GRUB will issue a *note badram:: command to
     filter out specified regions of RAM.

   For more detailed customisation of `grub-mkconfig''s output, you may
edit the scripts in `/etc/grub.d' directly.  `/etc/grub.d/40_custom' is
particularly useful for adding entire custom menu entries; simply type
the menu entries you want to add at the end of that file, making sure
to leave at least the first two lines intact.
File:,  Node: Shell-like scripting,  Next: Embedded configuration,  Prev: Simple configuration,  Up: Configuration
5.2 Writing full configuration files directly
`grub.cfg' is written in GRUB's built-in scripting language, which has
a syntax quite similar to that of GNU Bash and other Bourne shell
A "word" is a sequence of characters considered as a single unit by
GRUB.  Words are separated by "metacharacters", which are the following
plus space, tab, and newline:
     { } | & $ ; < >
   Quoting may be used to include metacharacters in words; see below.
Reserved words
Reserved words have a special meaning to GRUB.  The following words are
recognised as reserved when unquoted and either the first word of a
simple command or the third word of a `for' command:
     ! [[ ]] { }
     case do done elif else esac fi for function
     if in menuentry select then time until while
   Not all of these reserved words have a useful purpose yet; some are
reserved for future expansion.
Quoting is used to remove the special meaning of certain characters or
words.  It can be used to treat metacharacters as part of a word, to
prevent reserved words from being recognised as such, and to prevent
variable expansion.
   There are three quoting mechanisms: the escape character, single
quotes, and double quotes.
   A non-quoted backslash (\) is the "escape character".  It preserves
the literal value of the next character that follows, with the
exception of newline.
   Enclosing characters in single quotes preserves the literal value of
each character within the quotes.  A single quote may not occur between
single quotes, even when preceded by a backslash.
   Enclosing characters in double quotes preserves the literal value of
all characters within the quotes, with the exception of `$' and `\'.
The `$' character retains its special meaning within double quotes.
The backslash retains its special meaning only when followed by one of
the following characters: `$', `"', `\', or newline.  A
backslash-newline pair is treated as a line continuation (that is, it is
removed from the input stream and effectively ignored).  A double quote
may be quoted within double quotes by preceding it with a backslash.
Variable expansion
The `$' character introduces variable expansion.  The variable name to
be expanded may be enclosed in braces, which are optional but serve to
protect the variable to be expanded from characters immediately
following it which could be interpreted as part of the name.
   Normal variable names begin with an alphabetic character, followed
by zero or more alphanumeric characters.
   Positional variable names consist of one or more digits.  These are
reserved for future expansion.
   The special variable name `?' expands to the exit status of the most
recently executed command.
A word beginning with `#' causes that word and all remaining characters
on that line to be ignored.
Simple commands
A "simple command" is a sequence of words separated by spaces or tabs
and terminated by a semicolon or a newline.  The first word specifies
the command to be executed.  The remaining words are passed as
arguments to the invoked command.
   The return value of a simple command is its exit status.
Compound commands
A "compound command" is one of the following:
for NAME in WORD ...; do LIST; done
     The list of words following `in' is expanded, generating a list of
     items.  The variable NAME is set to each element of this list in
     turn, and LIST is executed each time.  The return value is the
     exit status of the last command that executes.  If the expansion
     of the items following `in' results in an empty list, no commands
     are executed, and the return status is 0.
if LIST; then LIST; [elif LIST; then LIST;] ... [else LIST;] fi
     The `if' LIST is executed.  If its exit status is zero, the `then'
     LIST is executed.  Otherwise, each `elif' LIST is executed in
     turn, and if its exit status is zero, the corresponding `then'
     LIST is executed and the command completes.  Otherwise, the `else'
     LIST is executed, if present.  The exit status is the exit status
     of the last command executed, or zero if no condition tested true.
while COND; do LIST; done
until COND; do LIST; done
     The `while' command continuously executes the `do' LIST as long as
     the last command in COND returns an exit status of zero.  The
     `until' command is identical to the `while' command, except that
     the test is negated; the `do' LIST is executed as long as the last
     command in COND returns a non-zero exit status.  The exit status
     of the `while' and `until' commands is the exit status of the last
     `do' LIST command executed, or zero if none was executed.
function NAME { COMMAND; ... }
     This defines a function named NAME.  The "body" of the function is
     the list of commands within braces, each of which must be
     terminated with a semicolon or a newline.  This list of commands
     will be executed whenever NAME is specified as the name of a
     simple command.  Function definitions do not affect the exit
     status in `$?'.  When executed, the exit status of a function is
     the exit status of the last command executed in the body.
menuentry TITLE [`--class=class' ...] [`--users=users'] [`--hotkey=key'] { COMMAND; ... }
     *Note menuentry::.
File:,  Node: Embedded configuration,  Next: Themes,  Prev: Shell-like scripting,  Up: Configuration
5.3 Embedding a configuration file into GRUB
GRUB supports embedding a configuration file directly into the core
image, so that it is loaded before entering normal mode.  This is
useful, for example, when it is not straightforward to find the real
configuration file, or when you need to debug problems with loading
that file.  `grub-install' uses this feature when it is not using BIOS
disk functions or when installing to a different disk from the one
containing `/boot/grub', in which case it needs to use the `search'
command (*note search::) to find `/boot/grub'.
   To embed a configuration file, use the `-c' option to
`grub-mkimage'.  The file is copied into the core image, so it may
reside anywhere on the file system, and may be removed after running
   After the embedded configuration file (if any) is executed, GRUB
will load the `normal' module, which will then read the real
configuration file from `$prefix/grub.cfg'.  By this point, the `root'
variable will also have been set to the root device name.  For example,
`prefix' might be set to `(hd0,1)/boot/grub', and `root' might be set to
`hd0,1'.  Thus, in most cases, the embedded configuration file only
needs to set the `prefix' and `root' variables, and then drop through
to GRUB's normal processing.  A typical example of this might look like
     search.fs_uuid 01234567-89ab-cdef-0123-456789abcdef root
     set prefix=($root)/boot/grub
   (The `search_fs_uuid' module must be included in the core image for
this example to work.)
   In more complex cases, it may be useful to read other configuration
files directly from the embedded configuration file.  This allows such
things as reading files not called `grub.cfg', or reading files from a
directory other than that where GRUB's loadable modules are installed.
To do this, include the `configfile' and `normal' modules in the core
image, and embed a configuration file that uses the `configfile'
command to load another file.  The following example of this also
requires the `echo', `search_label', and `test' modules to be included
in the core image:
     search.fs_label grub root
     if [ -e /boot/grub/example/test1.cfg ]; then
         set prefix=($root)/boot/grub
         configfile /boot/grub/example/test1.cfg
         if [ -e /boot/grub/example/test2.cfg ]; then
             set prefix=($root)/boot/grub
             configfile /boot/grub/example/test2.cfg
             echo "Could not find an example configuration file!"
   The embedded configuration file may not contain menu entries
directly, but may only read them from elsewhere using `configfile'.
File:,  Node: Themes,  Prev: Embedded configuration,  Up: Configuration
5.4 Graphical menu themes
File:,  Node: Network,  Next: Serial terminal,  Prev: Configuration,  Up: Top
6 Booting GRUB from the network
The following instructions only work on PC BIOS systems where the
Preboot eXecution Environment (PXE) is available.
   To generate a PXE boot image, run:
     grub-mkimage --format=i386-pc --output=core.img --prefix='(pxe)/boot/grub' pxe pxecmd
     cat /boot/grub/pxeboot.img core.img >grub.pxe
   Copy `grub.pxe', `/boot/grub/*.mod', and `/boot/grub/*.lst' to the
PXE (TFTP) server, ensuring that `*.mod' and `*.lst' are accessible via
the `/boot/grub/' path from the TFTP server root.  Set the DHCP server
configuration to offer `grub.pxe' as the boot file (the `filename'
option in ISC dhcpd).
   After GRUB has started, files on the TFTP server will be accessible
via the `(pxe)' device.
   The server and gateway IP address can be controlled by changing the
`(pxe)' device name to `(pxe:SERVER-IP)' or
`(pxe:SERVER-IP:GATEWAY-IP)'.  Note that this should be changed both in
the prefix and in any references to the device name in the
configuration file.
   GRUB provides several environment variables which may be used to
inspect or change the behaviour of the PXE device:
     The IP address of this machine.  Read-only.
     The network interface's MAC address.  Read-only.
     The client host name provided by DHCP.  Read-only.
     The client domain name provided by DHCP.  Read-only.
     The path to the client's root disk provided by DHCP.  Read-only.
     The path to additional DHCP vendor extensions provided by DHCP.
     The boot file name provided by DHCP.  Read-only.
     The name of the DHCP server responsible for these boot parameters.
     The PXE transfer block size.  Read-write, defaults to 512.
     The default PXE server.  Read-write, although setting this is only
     useful before opening a PXE device.
     The default gateway to use when contacting the PXE server.
     Read-write, although setting this is only useful before opening a
     PXE device.
File:,  Node: Serial terminal,  Next: Vendor power-on keys,  Prev: Network,  Up: Top
7 Using GRUB via a serial line
This chapter describes how to use the serial terminal support in GRUB.
   If you have many computers or computers with no display/keyboard, it
could be very useful to control the computers through serial
communications. To connect one computer with another via a serial line,
you need to prepare a null-modem (cross) serial cable, and you may need
to have multiport serial boards, if your computer doesn't have extra
serial ports. In addition, a terminal emulator is also required, such as
minicom. Refer to a manual of your operating system, for more
   As for GRUB, the instruction to set up a serial terminal is quite
simple.  Here is an example:
     grub> serial --unit=0 --speed=9600
     grub> terminal_input serial; terminal_output serial
   The command `serial' initializes the serial unit 0 with the speed
9600bps. The serial unit 0 is usually called `COM1', so, if you want to
use COM2, you must specify `--unit=1' instead. This command accepts
many other options, so please refer to *note serial::, for more details.
   The commands `terminal_input' (*note terminal_input::) and
`terminal_output' (*note terminal_output::) choose which type of
terminal you want to use. In the case above, the terminal will be a
serial terminal, but you can also pass `console' to the command, as
`terminal serial console'. In this case, a terminal in which you press
any key will be selected as a GRUB terminal. In the example above, note
that you need to put both commands on the same command line, as you
will lose the ability to type commands on the console after the first
   However, note that GRUB assumes that your terminal emulator is
compatible with VT100 by default. This is true for most terminal
emulators nowadays, but you should pass the option `--dumb' to the
command if your terminal emulator is not VT100-compatible or implements
few VT100 escape sequences. If you specify this option then GRUB
provides you with an alternative menu interface, because the normal
menu requires several fancy features of your terminal.
File:,  Node: Vendor power-on keys,  Next: Images,  Prev: Serial terminal,  Up: Top
8 Using GRUB with vendor power-on keys
Some laptop vendors provide an additional power-on button which boots
another OS.  GRUB supports such buttons with the `GRUB_TIMEOUT_BUTTON',
`GRUB_BUTTON_CMOS_ADDRESS' variables in default/grub (*note Simple
`GRUB_HIDDEN_TIMEOUT_BUTTON' are used instead of the corresponding
variables without the `_BUTTON' suffix when powered on using the special
button.  `GRUB_BUTTON_CMOS_ADDRESS' is vendor-specific and partially
model-specific.  Values known to the GRUB team are:
<Dell XPS M1530>
<Asus EeePC 1005PE>
     84:1 (unconfirmed)
   To take full advantage of this function, install GRUB into the MBR
(*note Installing GRUB using grub-install::).
File:,  Node: Images,  Next: Filesystem,  Prev: Vendor power-on keys,  Up: Top
9 GRUB image files
GRUB consists of several images: a variety of bootstrap images for
starting GRUB in various ways, a kernel image, and a set of modules
which are combined with the kernel image to form a core image.  Here is
a short overview of them.
     On PC BIOS systems, this image is the first part of GRUB to start.
     It is written to a master boot record (MBR) or to the boot sector
     of a partition.  Because a PC boot sector is 512 bytes, the size
     of this image is exactly 512 bytes.
     The sole function of `boot.img' is to read the first sector of the
     core image from a local disk and jump to it.  Because of the size
     restriction, `boot.img' cannot understand any file system
     structure, so `grub-setup' hardcodes the location of the first
     sector of the core image into `boot.img' when installing GRUB.
     This image is used as the first sector of the core image when
     booting from a hard disk.  It reads the rest of the core image
     into memory and starts the kernel.  Since file system handling is
     not yet available, it encodes the location of the core image using
     a block list format.
     This image is used as the first sector of the core image when
     booting from a CD-ROM drive.  It performs a similar function to
     This image is used as the start of the core image when booting
     from the network using PXE.  *Note Network::.
     This image may be placed at the start of the core image in order
     to make GRUB look enough like a Linux kernel that it can be booted
     by LILO using an `image=' section.
     This image contains GRUB's basic run-time facilities: frameworks
     for device and file handling, environment variables, the rescue
     mode command-line parser, and so on.  It is rarely used directly,
     but is built into all core images.
     This is the core image of GRUB.  It is built dynamically from the
     kernel image and an arbitrary list of modules by the `grub-mkimage'
     program.  Usually, it contains enough modules to access
     `/boot/grub', and loads everything else (including menu handling,
     the ability to load target operating systems, and so on) from the
     file system at run-time.  The modular design allows the core image
     to be kept small, since the areas of disk where it must be
     installed are often as small as 32KB.
     On PC systems using the traditional MBR partition table format,
     the core image is usually installed in the "MBR gap" between the
     master boot record and the first partition, or sometimes it is
     installed in a file system and read directly from that.  The
     latter is not recommended because GRUB needs to encode the
     location of all the core image sectors in `diskboot.img', and if
     the file system ever moves the core image around (as it is entitled
     to do) then GRUB must be reinstalled; it also means that GRUB will
     not be able to reliably find the core image if it resides on a
     different disk than the one to which `boot.img' was installed.
     On PC systems using the more recent GUID Partition Table (GPT)
     format, the core image should be installed to a BIOS Boot
     Partition.  This may be created by GNU Parted using a command such
     as the following:
          # parted /dev/DISK set PARTITION-NUMBER bios_grub on
     *Caution:* Be very careful which partition you select!  When GRUB
     finds a BIOS Boot Partition during installation, it will
     automatically overwrite part of it.  Make sure that the partition
     does not contain any other data.
     Everything else in GRUB resides in dynamically loadable modules.
     These are often loaded automatically, or built into the core image
     if they are essential, but may also be loaded manually using the
     `insmod' command (*note insmod::).
For GRUB Legacy users
GRUB 2 has a different design from GRUB Legacy, and so correspondences
with the images it used cannot be exact.  Nevertheless, GRUB Legacy
users often ask questions in the terms they are familiar with, and so
here is a brief guide to how GRUB 2's images relate to that.
     Stage 1 from GRUB Legacy was very similar to `boot.img' in GRUB 2,
     and they serve the same function.
     In GRUB Legacy, Stage 1.5's function was to include enough
     filesystem code to allow the much larger Stage 2 to be read from
     an ordinary filesystem.  In this respect, its function was similar
     to `core.img' in GRUB 2.  However, `core.img' is much more capable
     than Stage 1.5 was; since it offers a rescue shell, it is
     sometimes possible to recover manually in the event that it is
     unable to load any other modules, for example if partition numbers
     have changed.  `core.img' is built in a more flexible way,
     allowing GRUB 2 to support reading modules from advanced disk
     types such as LVM and RAID.
     GRUB Legacy could run with only Stage 1 and Stage 2 in some limited
     configurations, while GRUB 2 requires `core.img' and cannot work
     without it.
     GRUB 2 has no single Stage 2 image.  Instead, it loads modules from
     `/boot/grub' at run-time.
     In GRUB 2, images for booting from CD-ROM drives are now
     constructed using `cdboot.img' and `core.img', making sure that
     the core image contains the `iso9660' module.  It is usually best
     to use the `grub-mkrescue' program for this.
     There is as yet no equivalent for `nbgrub' in GRUB 2; it was used
     by Etherboot and some other network boot loaders.
     In GRUB 2, images for PXE network booting are now constructed using
     `pxeboot.img' and `core.img', making sure that the core image
     contains the `pxe' and `pxecmd' modules.  *Note Network::.
File:,  Node: Filesystem,  Next: Interface,  Prev: Images,  Up: Top
10 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 `search' (*note
* Menu:
* Device syntax::               How to specify devices
* File name syntax::            How to specify files
* Block list syntax::           How to specify block lists
File:,  Node: Device syntax,  Next: File name syntax,  Up: Filesystem
10.1 How to specify devices
The device syntax is like this:
   `[]' means the parameter is optional. DEVICE should be either `fd'
or `hd' followed by a digit, like `fd0'.  But you can also set DEVICE
to a hexadecimal or a decimal number which is a BIOS drive number, so
the following are equivalent:
   PART-NUM represents the partition number of DEVICE, starting from
one for primary partitions and from five for extended partitions, and
BSD-SUBPART-LETTER represents the BSD disklabel subpartition, such as
`a' or `e'.
   A shortcut for specifying BSD subpartitions is
`(DEVICE,BSD-SUBPART-LETTER)', in this case, GRUB searches for the
first PC partition containing a BSD disklabel, then finds the
subpartition BSD-SUBPART-LETTER. Here is an example:
   The syntax `(hd0)' represents using the entire disk (or the MBR when
installing GRUB), while the syntax `(hd0,1)' represents using the first
partition of the disk (or the boot sector of the partition when
installing GRUB).
   If you enabled the network support, the special drive `(pxe)' is
also available. Before using the network drive, you must initialize the
network. *Note Network::, for more information.
   If you boot GRUB from a CD-ROM, `(cd)' is available. *Note Making a
GRUB bootable CD-ROM::, for details.
File:,  Node: File name syntax,  Next: Block list syntax,  Prev: Device syntax,  Up: Filesystem
10.2 How to specify files
There are two ways to specify files, by "absolute file name" and by
"block list".
   An absolute file name resembles a Unix absolute file name, using `/'
for the directory separator (not `\' as in DOS). One example is
`(hd0,1)/boot/grub/grub.cfg'. This means the file `/boot/grub/grub.cfg'
in the first partition of the first hard disk. If you omit the device
name in an absolute file name, GRUB uses GRUB's "root device"
implicitly. So if you set the root device to, say, `(hd1,1)' by the
command `set root=(hd1,1)' (*note set::), then `/boot/kernel' is the
same as `(hd1,1)/boot/kernel'.
File:,  Node: Block list syntax,  Prev: File name syntax,  Up: Filesystem
10.3 How to specify block lists
A block list is used for specifying a file that doesn't appear in the
filesystem, like a chainloader. The syntax is
`[OFFSET]+LENGTH[,[OFFSET]+LENGTH]...'.  Here is an example:
   This represents that GRUB should read blocks 0 through 99, block 200,
and blocks 300 through 599. If you omit an offset, then GRUB assumes
the offset is zero.
   Like the file name syntax (*note File name syntax::), if a blocklist
does not contain a device name, then GRUB uses GRUB's "root device". So
`(hd0,2)+1' is the same as `+1' when the root device is `(hd0,2)'.
File:,  Node: Interface,  Next: Commands,  Prev: Filesystem,  Up: Top
11 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 "command-line" menu
option, or if the configuration file was not found, then GRUB drops to
the command-line interface.
* Menu:
* Command-line interface::      The flexible command-line interface
* Menu interface::              The simple menu interface
* Menu entry editor::           Editing a menu entry
File:,  Node: Command-line interface,  Next: Menu interface,  Up: Interface
11.1 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(1) (*note Command-line
interface-Footnote-1::). The commands (*note Command-line and menu
entry commands::) 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:
<PC right key>
     Move forward one character.
<PC left key>
     Move back one character.
     Move to the start of the line.
     Move the the end of the line.
     Delete the character underneath the cursor.
     Delete the character to the left of the cursor.
     Kill the text from the current cursor position to the end of the
     Kill backward from the cursor to the beginning of the line.
     Yank the killed text back into the buffer at the cursor.
<PC up key>
     Move up through the history list.
<PC down key>
     Move down through the history list.
   When typing commands interactively, if the cursor is within or before
the first word in the command-line, pressing the <TAB> key (or <C-i>)
will display a listing of the available commands, and if the cursor is
after the first word, the `<TAB>' will provide a completion listing of
disks, partitions, and file names depending on the context. Note that
to obtain a list of drives, one must open a parenthesis, as `root ('.
   Note that you cannot use the completion functionality in the TFTP
filesystem. This is because TFTP doesn't support file name listing for
the security.
File:,  Node: Menu interface,  Next: Menu entry editor,  Prev: Command-line interface,  Up: Interface
11.2 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 "boot entries" to
the user to choose from. Use the arrow keys to select the entry of
choice, then press <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 <c>
(which operates exactly like the non-config-file version of GRUB, but
allows one to return to the menu if desired by pressing <ESC>) or to
edit any of the "boot entries" by pressing <e>.
   If you protect the menu interface with a password (*note Security::),
all you can do is choose an entry by pressing <RET>, or press <p> to
enter the password.
File:,  Node: Menu entry editor,  Prev: Menu interface,  Up: Interface
11.3 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 <ESC> is pressed in the editor, it aborts all the changes made
to the configuration entry and returns to the main menu interface.
   Each line in the menu entry can be edited freely, and you can add
new lines by pressing <RET> at the end of a line.  To boot the edited
entry, press <Ctrl-x>.
   Although GRUB unfortunately does not support "undo", you can do
almost the same thing by just returning to the main menu using <ESC>.
File:,  Node: Commands,  Next: Security,  Prev: Interface,  Up: Top
12 The list of available commands
In this chapter, we list all commands that are available in GRUB.
   Commands belong to different groups. A few can only be used in the
global section of the configuration file (or "menu"); most of them can
be entered on the command-line and can be used either anywhere in the
menu or specifically in the menu entries.
   In rescue mode, only the `insmod' (*note insmod::), `ls' (*note
ls::), `set' (*note set::), and `unset' (*note unset::) commands are
normally available.
* Menu:
* Menu-specific commands::
* General commands::
* Command-line and menu entry commands::
File:,  Node: Menu-specific commands,  Next: General commands,  Up: Commands
12.1 The list of commands for the menu only
The semantics used in parsing the configuration file are the following:
   * The menu-specific commands have to be used before any others.
   * The files _must_ be in plain-text format.
   * `#' at the beginning of a line in a configuration file means it is
     only a comment.
   * Options are separated by spaces.
   * All numbers can be either decimal or hexadecimal. A hexadecimal
     number must be preceded by `0x', and is case-insensitive.
   * Extra options or text at the end of the line are ignored unless
     otherwise specified.
   * Unrecognized commands are added to the current entry, except
     before entries start, where they are ignored.
   These commands can only be used in the menu:
* Menu:
* menuentry::                   Start a menu entry
File:,  Node: menuentry,  Up: Menu-specific commands
12.1.1 menuentry
 -- Command: menuentry TITLE [`--class=class' ...] [`--users=users']
          [`--hotkey=key'] { COMMAND; ... }
     This defines a GRUB menu entry named TITLE.  When this entry is
     selected from the menu, GRUB will set the CHOSEN environment
     variable to TITLE, execute the list of commands given within
     braces, and if the last command in the list returned successfully
     and a kernel was loaded it will execute the `boot' command.
     The `--class' option may be used any number of times to group menu
     entries into classes.  Menu themes may display different classes
     using different styles.
     The `--users' option grants specific users access to specific menu
     entries.  *Note Security::.
     The `--hotkey' option associates a hotkey with a menu entry.  KEY
     may be a single letter, or one of the aliases `backspace', `tab',
     or `delete'.
File:,  Node: General commands,  Next: Command-line and menu entry commands,  Prev: Menu-specific commands,  Up: Commands
12.2 The list of general commands
Commands usable anywhere in the menu and in the command-line.
* Menu:
* serial::                      Set up a serial device
* terminal_input::              Manage input terminals
* terminal_output::             Manage output terminals
* terminfo::                    Define terminal type
File:,  Node: serial,  Next: terminal_input,  Up: General commands
12.2.1 serial
 -- Command: serial [`--unit=unit'] [`--port=port'] [`--speed=speed']
          [`--word=word'] [`--parity=parity'] [`--stop=stop']
     Initialize a serial device. UNIT is a number in the range 0-3
     specifying which serial port to use; default is 0, which
     corresponds to the port often called COM1. PORT is the I/O port
     where the UART is to be found; if specified it takes precedence
     over UNIT.  SPEED is the transmission speed; default is 9600. WORD
     and STOP are the number of data bits and stop bits. Data bits must
     be in the range 5-8 and stop bits must be 1 or 2. Default is 8 data
     bits and one stop bit. PARITY is one of `no', `odd', `even' and
     defaults to `no'.
     The serial port is not used as a communication channel unless the
     `terminal_input' or `terminal_output' command is used (*note
     terminal_input::, *note terminal_output::).
     This command is only available if GRUB is compiled with serial
     support. See also *note Serial terminal::.
File:,  Node: terminal_input,  Next: terminal_output,  Prev: serial,  Up: General commands
12.2.2 terminal_input
 -- Command: terminal_input [`--append'|`--remove'] [terminal1]
          [terminal2] ...
     List or select an input terminal.
     With no arguments, list the active and available input terminals.
     With `--append', add the named terminals to the list of active
     input terminals; any of these may be used to provide input to GRUB.
     With `--remove', remove the named terminals from the active list.
     With no options but a list of terminal names, make only the listed
     terminal names active.
File:,  Node: terminal_output,  Next: terminfo,  Prev: terminal_input,  Up: General commands
12.2.3 terminal_output
 -- Command: terminal_output [`--append'|`--remove'] [terminal1]
          [terminal2] ...
     List or select an output terminal.
     With no arguments, list the active and available output terminals.
     With `--append', add the named terminals to the list of active
     output terminals; all of these will receive output from GRUB.
     With `--remove', remove the named terminals from the active list.
     With no options but a list of terminal names, make only the listed
     terminal names active.
File:,  Node: terminfo,  Prev: terminal_output,  Up: General commands
12.2.4 terminfo
 -- Command: terminfo [-a|-u|-v] [term]
     Define the capabilities of your terminal by giving the name of an
     entry in the terminfo database, which should correspond roughly to
     a `TERM' environment variable in Unix.
     The currently available terminal types are `vt100', `vt100-color',
     `ieee1275', and `dumb'.  If you need other terminal types, please
     contact us to discuss the best way to include support for these in
     The `-a' (`--ascii'), `-u' (`--utf8'), and `-v' (`--visual-utf8')
     options control how non-ASCII text is displayed.  `-a' specifies
     an ASCII-only terminal; `-u' specifies logically-ordered UTF-8;
     and `-v' specifies "visually-ordered UTF-8" (in other words,
     arranged such that a terminal emulator without bidirectional text
     support will display right-to-left text in the proper order; this
     is not really proper UTF-8, but a workaround).
     If no option or terminal type is specified, the current terminal
     type is printed.
File:,  Node: Command-line and menu entry commands,  Prev: General commands,  Up: Commands
12.3 The list of command-line and menu entry commands
These commands are usable in the command-line and in menu entries.  If
you forget a command, you can run the command `help' (*note help::).
* Menu:
* acpi::                        Load ACPI tables
* badram::                      Filter out bad regions of RAM
* blocklist::                   Print a block list
* boot::                        Start up your operating system
* cat::                         Show the contents of a file
* chainloader::                 Chain-load another boot loader
* cmp::                         Compare two files
* configfile::                  Load a configuration file
* cpuid::                       Check for CPU features
* crc::                         Calculate CRC32 checksums
* date::                        Display or set current date and time
* drivemap::                    Map a drive to another
* echo::                        Display a line of text
* export::                      Export an environment variable
* gettext::                     Translate a string
* gptsync::                     Fill an MBR based on GPT entries
* halt::                        Shut down your computer
* help::                        Show help messages
* initrd::                      Load a Linux initrd
* initrd16::                    Load a Linux initrd (16-bit mode)
* insmod::                      Insert a module
* keystatus::                   Check key modifier status
* linux::                       Load a Linux kernel
* linux16::                     Load a Linux kernel (16-bit mode)
* ls::                          List devices or files
* parttool::                    Modify partition table entries
* password::                    Set a clear-text password
* password_pbkdf2::             Set a hashed password
* play::                        Play a tune
* pxe_unload::                  Unload the PXE environment
* reboot::                      Reboot your computer
* search::                      Search devices by file, label, or UUID
* set::                         Set an environment variable
* unset::                       Unset an environment variable
* uppermem::                    Set the upper memory size
File:,  Node: acpi,  Next: badram,  Up: Command-line and menu entry commands
12.3.1 acpi
 -- Command: acpi [`-1'|`-2']
          [`--oemid=id'] [`--oemtable=table'] [`--oemtablerev=rev']
          [`--oemtablecreator=creator'] [`--oemtablecreatorrev=rev']
          [`--no-ebda'] filename ...
     Modern BIOS systems normally implement the Advanced Configuration
     and Power Interface (ACPI), and define various tables that
     describe the interface between an ACPI-compliant operating system
     and the firmware. In some cases, the tables provided by default
     only work well with certain operating systems, and it may be
     necessary to replace some of them.
     Normally, this command will replace the Root System Description
     Pointer (RSDP) in the Extended BIOS Data Area to point to the new
     tables. If the `--no-ebda' option is used, the new tables will be
     known only to GRUB, but may be used by GRUB's EFI emulation.
File:,  Node: badram,  Next: blocklist,  Prev: acpi,  Up: Command-line and menu entry commands
12.3.2 badram
 -- Command: badram addr,mask[,addr,mask...]
     Filter out bad RAM.
   This command notifies the memory manager that specified regions of
RAM ought to be filtered out (usually, because they're damaged).  This
remains in effect after a payload kernel has been loaded by GRUB, as
long as the loaded kernel obtains its memory map from GRUB.  Kernels
that support this include Linux, GNU Mach, the kernel of FreeBSD and
Multiboot kernels in general.
   Syntax is the same as provided by the Memtest86+ utility
( a list of address/mask pairs.  Given a
page-aligned address and a base address / mask pair, if all the bits of
the page-aligned address that are enabled by the mask match with the
base address, it means this page is to be filtered.  This syntax makes
it easy to represent patterns that are often result of memory damage,
due to physical distribution of memory cells.
File:,  Node: blocklist,  Next: boot,  Prev: badram,  Up: Command-line and menu entry commands
12.3.3 blocklist
 -- Command: blocklist file
     Print a block list (*note Block list syntax::) for FILE.
File:,  Node: boot,  Next: cat,  Prev: blocklist,  Up: Command-line and menu entry commands
12.3.4 boot
 -- Command: boot
     Boot the OS or chain-loader which has been loaded. Only necessary
     if running the fully interactive command-line (it is implicit at
     the end of a menu entry).
File:,  Node: cat,  Next: chainloader,  Prev: boot,  Up: Command-line and menu entry commands
12.3.5 cat
 -- Command: cat [`--dos'] file
     Display the contents of the file FILE. This command may be useful
     to remind you of your OS's root partition:
          grub> cat /etc/fstab
     If the `--dos' option is used, then carriage return / new line
     pairs will be displayed as a simple new line.  Otherwise, the
     carriage return will be displayed as a control character (`<d>')
     to make it easier to see when boot problems are caused by a file
     formatted using DOS-style line endings.
File:,  Node: chainloader,  Next: cmp,  Prev: cat,  Up: Command-line and menu entry commands
12.3.6 chainloader
 -- Command: chainloader [`--force'] file
     Load FILE as a chain-loader. Like any other file loaded by the
     filesystem code, it can use the blocklist notation (*note Block
     list syntax::) to grab the first sector of the current partition
     with `+1'.  If you specify the option `--force', then load FILE
     forcibly, whether it has a correct signature or not. This is
     required when you want to load a defective boot loader, such as
     SCO UnixWare 7.1.
File:,  Node: cmp,  Next: configfile,  Prev: chainloader,  Up: Command-line and menu entry commands
12.3.7 cmp
 -- Command: cmp file1 file2
     Compare the file FILE1 with the file FILE2. If they differ in
     size, print the sizes like this:
          Differ in size: 0x1234 [foo], 0x4321 [bar]
     If the sizes are equal but the bytes at an offset differ, then
     print the bytes like this:
          Differ at the offset 777: 0xbe [foo], 0xef [bar]
     If they are completely identical, nothing will be printed.
File:,  Node: configfile,  Next: cpuid,  Prev: cmp,  Up: Command-line and menu entry commands
12.3.8 configfile
 -- Command: configfile file
     Load FILE as a configuration file.  If FILE defines any menu
     entries, then show a menu containing them immediately.
File:,  Node: cpuid,  Next: crc,  Prev: configfile,  Up: Command-line and menu entry commands
12.3.9 cpuid
 -- Command: cpuid [-l]
     Check for CPU features.  This command is only available on x86
     With the `-l' option, return true if the CPU supports long mode
     If invoked without options, this command currently behaves as if
     it had been invoked with `-l'.  This may change in the future.
File:,  Node: crc,  Next: date,  Prev: cpuid,  Up: Command-line and menu entry commands
12.3.10 crc
 -- Command: crc file
     Display the CRC32 checksum of FILE.
File:,  Node: date,  Next: drivemap,  Prev: crc,  Up: Command-line and menu entry commands
12.3.11 date
 -- Command: date [[year-]month-day] [hour:minute[:second]]
     With no arguments, print the current date and time.
     Otherwise, take the current date and time, change any elements
     specified as arguments, and set the result as the new date and
     time.  For example, `date 01-01' will set the current month and
     day to January 1, but leave the year, hour, minute, and second
File:,  Node: drivemap,  Next: echo,  Prev: date,  Up: Command-line and menu entry commands
12.3.12 drivemap
 -- Command: drivemap `-l'|`-r'|[`-s'] from_drive to_drive
     Without options, map the drive FROM_DRIVE to the drive 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.  For
     convenience, any partition suffix on the drive is ignored, so you
     can safely use ${root} as a drive specification.
     With the `-s' option, perform the reverse mapping as well, swapping
     the two drives.
     With the `-l' option, list the current mappings.
     With the `-r' option, reset all mappings to the default values.
     For example:
          drivemap -s (hd0) (hd1)
File:,  Node: echo,  Next: export,  Prev: drivemap,  Up: Command-line and menu entry commands
12.3.13 echo
 -- Command: echo [`-n'] [`-e'] string ...
     Display the requested text and, unless the `-n' option is used, a
     trailing new line.  If there is more than one string, they are
     separated by spaces in the output.  As usual in GRUB commands,
     variables may be substituted using `${var}'.
     The `-e' option enables interpretation of backslash escapes.  The
     following sequences are recognised:
          alert (BEL)
          suppress trailing new line
          form feed
          new line
          carriage return
          horizontal tab
          vertical tab
     When interpreting backslash escapes, backslash followed by any
     other character will print that character.
File:,  Node: export,  Next: gettext,  Prev: echo,  Up: Command-line and menu entry commands
12.3.14 export
 -- Command: export envvar
     Export the environment variable ENVVAR. Exported variables are
     visible to subsidiary configuration files loaded using
File:,  Node: gettext,  Next: gptsync,  Prev: export,  Up: Command-line and menu entry commands
12.3.15 gettext
 -- Command: gettext string
     Translate STRING into the current language.
     The current language code is stored in the `lang' variable in
     GRUB's environment.  Translation files in MO format are read from
     `locale_dir', usually `/boot/grub/locale'.
File:,  Node: gptsync,  Next: halt,  Prev: gettext,  Up: Command-line and menu entry commands
12.3.16 gptsync
 -- Command: gptsync device [partition[+/-[type]]] ...
     Disks using the GUID Partition Table (GPT) also have a legacy
     Master Boot Record (MBR) partition table for compatibility with
     the BIOS and with older operating systems.  The legacy MBR can
     only represent a limited subset of GPT partition entries.
     This command populates the legacy MBR with the specified PARTITION
     entries on DEVICE.  Up to three partitions may be used.
     TYPE is an MBR partition type code; prefix with `0x' if you want
     to enter this in hexadecimal.  The separator between PARTITION and
     TYPE may be `+' to make the partition active, or `-' to make it
     inactive; only one partition may be active.  If both the separator
     and type are omitted, then the partition will be inactive.
File:,  Node: halt,  Next: help,  Prev: gptsync,  Up: Command-line and menu entry commands
12.3.17 halt
 -- Command: halt `--no-apm'
     The command halts the computer. If the `--no-apm' option is
     specified, no APM BIOS call is performed. Otherwise, the computer
     is shut down using APM.
File:,  Node: help,  Next: initrd,  Prev: halt,  Up: Command-line and menu entry commands
12.3.18 help
 -- Command: help [pattern ...]
     Display helpful information about builtin commands. If you do not
     specify PATTERN, this command shows short descriptions of all
     available commands.
     If you specify any PATTERNS, it displays longer information about
     each of the commands whose names begin with those PATTERNS.
File:,  Node: initrd,  Next: initrd16,  Prev: help,  Up: Command-line and menu entry commands
12.3.19 initrd
 -- Command: initrd file
     Load an initial ramdisk for a Linux kernel image, and set the
     appropriate parameters in the Linux setup area in memory.  This
     may only be used after the `linux' command (*note linux::) has
     been run.  See also *note GNU/Linux::.
File:,  Node: initrd16,  Next: insmod,  Prev: initrd,  Up: Command-line and menu entry commands
12.3.20 initrd16
 -- Command: initrd16 file
     Load an initial ramdisk for a Linux kernel image to be booted in
     16-bit mode, and set the appropriate parameters in the Linux setup
     area in memory.  This may only be used after the `linux16' command
     (*note linux16::) has been run.  See also *note GNU/Linux::.
     This command is only available on x86 systems.
File:,  Node: insmod,  Next: keystatus,  Prev: initrd16,  Up: Command-line and menu entry commands
12.3.21 insmod
 -- Command: insmod module
     Insert the dynamic GRUB module called MODULE.
File:,  Node: keystatus,  Next: linux,  Prev: insmod,  Up: Command-line and menu entry commands
12.3.22 keystatus
 -- Command: keystatus [`--shift'] [`--ctrl'] [`--alt']
     Return true if the Shift, Control, or Alt modifier keys are held
     down, as requested by options. This is useful in scripting, to
     allow some user control over behaviour without having to wait for
     a keypress.
     Checking key modifier status is only supported on some platforms.
     If invoked without any options, the `keystatus' command returns
     true if and only if checking key modifier status is supported.
File:,  Node: linux,  Next: linux16,  Prev: keystatus,  Up: Command-line and menu entry commands
12.3.23 linux
 -- Command: linux file ...
     Load a Linux kernel image from FILE.  The rest of the line is
     passed verbatim as the "kernel command-line".  Any initrd must be
     reloaded after using this command (*note initrd::).
     On x86 systems, the kernel will be booted using the 32-bit boot
     protocol.  Note that this means that the `vga=' boot option will
     not work; if you want to set a special video mode, you will need
     to use GRUB commands such as `set gfxpayload=1024x768' or `set
     gfxpayload=keep' (to keep the same mode as used in GRUB) instead.
     GRUB can automatically detect some uses of `vga=' and translate
     them to appropriate settings of `gfxpayload'.  The `linux16'
     command (*note linux16::) avoids this restriction.
File:,  Node: linux16,  Next: ls,  Prev: linux,  Up: Command-line and menu entry commands
12.3.24 linux16
 -- Command: linux16 file ...
     Load a Linux kernel image from FILE in 16-bit mode.  The rest of
     the line is passed verbatim as the "kernel command-line".  Any
     initrd must be reloaded after using this command (*note
     The kernel will be booted using the traditional 16-bit boot
     protocol.  As well as bypassing problems with `vga=' described in
     *note linux::, this permits booting some other programs that
     implement the Linux boot protocol for the sake of convenience.
     This command is only available on x86 systems.
File:,  Node: ls,  Next: parttool,  Prev: linux16,  Up: Command-line and menu entry commands
12.3.25 ls
 -- Command: ls [arg]
     List devices or files.
     With no arguments, print all devices known to GRUB.
     If the argument is a device name enclosed in parentheses (*note
     Device syntax::), then list all files at the root directory of
     that device.
     If the argument is a directory given as an absolute file name
     (*note File name syntax::), then list the contents of that
File:,  Node: parttool,  Next: password,  Prev: ls,  Up: Command-line and menu entry commands
12.3.26 parttool
 -- Command: parttool partition commands
     Make various modifications to partition table entries.
     Each COMMAND is either a boolean option, in which case it must be
     followed with `+' or `-' (with no intervening space) to enable or
     disable that option, or else it takes a value in the form
     Currently, `parttool' is only useful on DOS partition tables (also
     known as Master Boot Record, or MBR).  On these partition tables,
     the following commands are available:
    `boot' (boolean)
          When enabled, this makes the selected partition be the active
          (bootable) partition on its disk, clearing the active flag on
          all other partitions.  This command is limited to _primary_
    `type' (value)
          Change the type of an existing partition.  The value must be
          a number in the range 0-0xFF (prefix with `0x' to enter it in
    `hidden' (boolean)
          When enabled, this hides the selected partition by setting
          the "hidden" bit in its partition type code; when disabled,
          unhides the selected partition by clearing this bit.  This is
          useful only when booting DOS or Wwindows and multiple primary
          FAT partitions exist in one disk.  See also *note
File:,  Node: password,  Next: password_pbkdf2,  Prev: parttool,  Up: Command-line and menu entry commands
12.3.27 password
 -- Command: password user clear-password
     Define a user named USER with password CLEAR-PASSWORD.  *Note
File:,  Node: password_pbkdf2,  Next: play,  Prev: password,  Up: Command-line and menu entry commands
12.3.28 password_pbkdf2
 -- Command: password_pbkdf2 user hashed-password
     Define a user named USER with password hash HASHED-PASSWORD.  Use
     `grub-mkpasswd-pbkdf2' (*note Invoking grub-mkpasswd-pbkdf2::) to
     generate password hashes.  *Note Security::.
File:,  Node: play,  Next: pxe_unload,  Prev: password_pbkdf2,  Up: Command-line and menu entry commands
12.3.29 play
 -- Command: play file | tempo [pitch1 duration1] [pitch2 duration2] ...
     Plays a tune
     If the argument is a file name (*note File name syntax::), play
     the tune recorded in it.  The file format is first the tempo as an
     unsigned 32bit little-endian number, then pairs of unsigned 16bit
     little-endian numbers for pitch and duration pairs.
     If the arguments are a series of numbers, play the inline tune.
     The tempo is the base for all note durations. 60 gives a 1-second
     base, 120 gives a half-second base, etc.  Pitches are Hz.  Set
     pitch to 0 to produce a rest.
File:,  Node: pxe_unload,  Next: reboot,  Prev: play,  Up: Command-line and menu entry commands
12.3.30 pxe_unload
 -- Command: pxe_unload
     Unload the PXE environment (*note Network::).
     This command is only available on PC BIOS systems.
File:,  Node: reboot,  Next: search,  Prev: pxe_unload,  Up: Command-line and menu entry commands
12.3.31 reboot
 -- Command: reboot
     Reboot the computer.
File:,  Node: search,  Next: set,  Prev: reboot,  Up: Command-line and menu entry commands
12.3.32 search
 -- Command: search [`--file'|`--label'|`--fs-uuid'] [`--set' [var]]
          [`--no-floppy'] name
     Search devices by file (`-f', `--file'), filesystem label (`-l',
     `--label'), or filesystem UUID (`-u', `--fs-uuid').
     If the `--set' option is used, the first device found is set as the
     value of environment variable VAR.  The default variable is `root'.
     The `--no-floppy' option prevents searching floppy devices, which
     can be slow.
     The `search.file', `search.fs_label', and `search.fs_uuid'
     commands are aliases for `search --file', `search --label', and
     `search --fs-uuid' respectively.
File:,  Node: set,  Next: unset,  Prev: search,  Up: Command-line and menu entry commands
12.3.33 set
 -- Command: set [envvar=value]
     Set the environment variable ENVVAR to VALUE. If invoked with no
     arguments, print all environment variables with their values.
File:,  Node: unset,  Next: uppermem,  Prev: set,  Up: Command-line and menu entry commands
12.3.34 unset
 -- Command: unset envvar
     Unset the environment variable ENVVAR.
File:,  Node: uppermem,  Prev: unset,  Up: Command-line and menu entry commands
12.3.35 uppermem
This command is not yet implemented for GRUB 2, although it is planned.
File:,  Node: Security,  Next: Troubleshooting,  Prev: Commands,  Up: Top
13 Authentication and authorisation
By default, the boot loader interface is accessible to anyone with
physical access to the console: anyone can select and edit any menu
entry, and anyone can get direct access to a GRUB shell prompt.  For
most systems, this is reasonable since anyone with direct physical
access has a variety of other ways to gain full access, and requiring
authentication at the boot loader level would only serve to make it
difficult to recover broken systems.
   However, in some environments, such as kiosks, it may be appropriate
to lock down the boot loader to require authentication before
performing certain operations.
   The `password' (*note password::) and `password_pbkdf2' (*note
password_pbkdf2::) commands can be used to define users, each of which
has an associated password.  `password' sets the password in plain
text, requiring `grub.cfg' to be secure; `password_pbkdf2' sets the
password hashed using the Password-Based Key Derivation Function (RFC
2898), requiring the use of `grub-mkpasswd-pbkdf2' (*note Invoking
grub-mkpasswd-pbkdf2::) to generate password hashes.
   In order to enable authentication support, the `superusers'
environment variable must be set to a list of usernames, separated by
any of spaces, commas, semicolons, pipes, or ampersands.  Superusers
are permitted to use the GRUB command line, edit menu entries, and
execute any menu entry.  If `superusers' is set, then use of the
command line is automatically restricted to superusers.
   Other users may be given access to specific menu entries by giving a
list of usernames (as above) using the `--users' option to the
`menuentry' command (*note menuentry::).  If the `--users' option is
not used for a menu entry, then that entry is unrestricted.
   Putting this together, a typical `grub.cfg' fragment might look like
     set superusers="root"
     password_pbkdf2 root grub.pbkdf2.sha512.10000.biglongstring
     password user1 insecure
     menuentry "May be run by any user" {
     	set root=(hd0,1)
     	linux /vmlinuz
     menuentry "Superusers only" --users "" {
     	set root=(hd0,1)
     	linux /vmlinuz single
     menuentry "May be run by user1 or a superuser" --users user1 {
     	set root=(hd0,2)
     	chainloader +1
   The `grub-mkconfig' program does not yet have built-in support for
generating configuration files with authentication.  You can use
`/etc/grub.d/40_custom' to add simple superuser authentication, by
adding `set superusers=' and `password' or `password_pbkdf2' commands.
File:,  Node: Troubleshooting,  Next: Invoking grub-install,  Prev: Security,  Up: Top
14 Error messages produced by GRUB
* Menu:
* GRUB only offers a rescue shell::
File:,  Node: GRUB only offers a rescue shell,  Up: Troubleshooting
14.1 GRUB only offers a rescue shell
GRUB's normal start-up procedure involves setting the `prefix'
environment variable to a value set in the core image by
`grub-install', setting the `root' variable to match, loading the
`normal' module from the prefix, and running the `normal' command.
This command is responsible for reading `/boot/grub/grub.cfg', running
the menu, and doing all the useful things GRUB is supposed to do.
   If, instead, you only get a rescue shell, this usually means that
GRUB failed to load the `normal' module for some reason.  It may be
possible to work around this temporarily: for instance, if the reason
for the failure is that `prefix' is wrong (perhaps it refers to the
wrong device, or perhaps the path to `/boot/grub' was not correctly
made relative to the device), then you can correct this and enter
normal mode manually:
     # Inspect the current prefix (and other preset variables):
     # Set to the correct value, which might be something like this:
     set prefix=(hd0,1)/grub
     set root=(hd0,1)
     insmod normal
   However, any problem that leaves you in the rescue shell probably
means that GRUB was not correctly installed.  It may be more useful to
try to reinstall it properly using `grub-install DEVICE' (*note
Invoking grub-install::).  When doing this, there are a few things to
   * Drive ordering in your operating system may not be the same as the
     boot drive ordering used by your firmware.  Do not assume that
     your first hard drive (e.g. `/dev/sda') is the one that your
     firmware will boot from.  `' (*note Device map::) can be
     used to override this, but it is usually better to use UUIDs or
     file system labels and avoid depending on drive ordering entirely.
   * At least on BIOS systems, if you tell `grub-install' to install
     GRUB to a partition but GRUB has already been installed in the
     master boot record, then the GRUB installation in the partition
     will be ignored.
   * If possible, it is generally best to avoid installing GRUB to a
     partition (unless it is a special partition for the use of GRUB
     alone, such as the BIOS Boot Partition used on GPT).  Doing this
     means that GRUB may stop being able to read its core image due to
     a file system moving blocks around, such as while defragmenting,
     running checks, or even during normal operation.  Installing to
     the whole disk device is normally more robust.
   * Check that GRUB actually knows how to read from the device and
     file system containing `/boot/grub'.  It will not be able to read
     from encrypted devices, nor from file systems for which support
     has not yet been added to GRUB.
File:,  Node: Invoking grub-install,  Next: Invoking grub-mkconfig,  Prev: Troubleshooting,  Up: Top
15 Invoking grub-install
The program `grub-install' installs GRUB on your drive using
`grub-mkimage' and (on some platforms) `grub-setup'.  You must specify
the device name on which you want to install GRUB, like this:
     grub-install INSTALL_DEVICE
   The device name INSTALL_DEVICE is an OS device name or a GRUB device
   `grub-install' accepts the following options:
     Print a summary of the command-line options and exit.
     Print the version number of GRUB and exit.
     Install GRUB images under the directory DIR instead of the root
     directory. This option is useful when you want to install GRUB
     into a separate partition or a removable disk. Here is an example
     in which you have a separate "boot" partition which is mounted on
          grub-install --root-directory=/boot hd0
     Recheck the device map, even if `/boot/grub/' already
     exists. You should use this option whenever you add/remove a disk
     into/from your computer.
File:,  Node: Invoking grub-mkconfig,  Next: Invoking grub-mkpasswd-pbkdf2,  Prev: Invoking grub-install,  Up: Top
16 Invoking grub-mkconfig
The program `grub-mkconfig' generates a configuration file for GRUB
(*note Simple configuration::).
     grub-mkconfig -o /boot/grub/grub.cfg
   `grub-mkconfig' accepts the following options:
     Print a summary of the command-line options and exit.
     Print the version number of GRUB and exit.
`-o FILE'
     Send the generated configuration file to FILE.  The default is to
     send it to standard output.
File:,  Node: Invoking grub-mkpasswd-pbkdf2,  Next: Obtaining and Building GRUB,  Prev: Invoking grub-mkconfig,  Up: Top
17 Invoking grub-mkpasswd-pbkdf2
The program `grub-mkpasswd-pbkdf2' generates password hashes for GRUB
(*note Security::).
   `grub-mkpasswd-pbkdf2' accepts the following options:
     Number of iterations of the underlying pseudo-random function.
     Defaults to 10000.
     Length of the generated hash.  Defaults to 64.
     Length of the salt.  Defaults to 64.
File:,  Node: Obtaining and Building GRUB,  Next: Reporting bugs,  Prev: Invoking grub-mkpasswd-pbkdf2,  Up: Top
Appendix A How to obtain and build GRUB
     *Caution:* GRUB requires binutils- or later because the
     GNU assembler has been changed so that it can produce real 16bits
     machine code between 2.9.1 and See
     `', to obtain information on
     how to get the latest version.
   GRUB is available from the GNU alpha archive site
`' or any of its mirrors. The file will be
named grub-version.tar.gz. The current version is
1.98+20100804-14+squeeze2, so the file you should grab is:
   To unbundle GRUB use the instruction:
     zcat grub-1.98+20100804-14+squeeze2.tar.gz | tar xvf -
   which will create a directory called
`grub-1.98+20100804-14+squeeze2' with all the sources. You can look at
the file `INSTALL' for detailed instructions on how to build and
install GRUB, but you should be able to just do:
     cd grub-1.98+20100804-14+squeeze2
     make install
   Also, the latest version is available using Bazaar. See
`' for more
File:,  Node: Reporting bugs,  Next: Future,  Prev: Obtaining and Building GRUB,  Up: Top
Appendix B Reporting bugs
These are the guideline for how to report bugs. Take a look at this
list below before you submit bugs:
  1. Before getting unsettled, read this manual through and through.
     Also, see the GNU GRUB FAQ
  2. Always mention the information on your GRUB. The version number
     and the configuration are quite important. If you build it
     yourself, write the options specified to the configure script and
     your operating system, including the versions of gcc and binutils.
  3. If you have trouble with the installation, inform us of how you
     installed GRUB. Don't omit error messages, if any. Just `GRUB hangs
     up when it boots' is not enough.
     The information on your hardware is also essential. These are
     especially important: the geometries and the partition tables of
     your hard disk drives and your BIOS.
  4. If GRUB cannot boot your operating system, write down _everything_
     you see on the screen. Don't paraphrase them, like `The foo OS
     crashes with GRUB, even though it can boot with the bar boot
     loader just fine'. Mention the commands you executed, the messages
     printed by them, and information on your operating system
     including the version number.
  5. Explain what you wanted to do. It is very useful to know your
     purpose and your wish, and how GRUB didn't satisfy you.
  6. If you can investigate the problem yourself, please do. That will
     give you and us much more information on the problem. Attaching a
     patch is even better.
     When you attach a patch, make the patch in unified diff format, and
     write ChangeLog entries. But, even when you make a patch, don't
     forget to explain the problem, so that we can understand what your
     patch is for.
  7. Write down anything that you think might be related. Please
     understand that we often need to reproduce the same problem you
     encounterred in our environment. So your information should be
     sufficient for us to do the same thing--Don't forget that we
     cannot see your computer directly. If you are not sure whether to
     state a fact or leave it out, state it!  Reporting too many things
     is much better than omitting something important.
   If you follow the guideline above, submit a report to the Bug
Tracking System (
Alternatively, you can submit a report via electronic mail to
<bug-grub AT>, but we strongly recommend that you use the Bug
Tracking System, because e-mail can be passed over easily.
   Once we get your report, we will try to fix the bugs.
File:,  Node: Future,  Next: Internals,  Prev: Reporting bugs,  Up: Top
Appendix C Where GRUB will go
We started the next generation of GRUB, GRUB 2. GRUB 2 includes
internationalization, dynamic module loading, real memory management,
multiple architecture support, a scripting language, and many other
nice features. If you are interested in the development of GRUB 2, take
a look at the homepage (
File:,  Node: Internals,  Next: Copying This Manual,  Prev: Future,  Up: Top
Appendix D Hacking GRUB
* Menu:
* Getting the source code::
* Finding your way around::
File:,  Node: Getting the source code,  Next: Finding your way around,  Up: Internals
D.1 Getting the source code
GRUB is maintained using the Bazaar revision control system
(  To fetch the primary development branch:
     bzr get
   The GRUB developers maintain several other branches with work in
progress.  Of these, the most interesting is the experimental branch,
which is a staging area for new code which we expect to eventually
merge into trunk but which is not yet ready:
     bzr get
   Once you have used `bzr get' to fetch an initial copy of a branch,
you can use `bzr pull' to keep it up to date.  If you have modified your
local version, you may need to resolve conflicts when pulling.
File:,  Node: Finding your way around,  Prev: Getting the source code,  Up: Internals
D.2 Finding your way around
Here is a brief map of the GRUB code base.
   GRUB uses Autoconf, but not (yet) Automake.  The top-level build
rules are in `', `', and `conf/*.rmk'.  Each
`conf/*.rmk' file represents a particular target configuration, and is
processed into GNU Make rules by `genmk.rb' (which you only need to
look at if you are extending the build system).  If you are adding a new
module which follows an existing pattern, such as a new command or a new
filesystem implementation, it is usually easiest to grep `conf/*.rmk'
for an existing example of that pattern to find out where it should be
   Low-level boot code, such as the MBR implementation on PC BIOS
systems, is in the `boot/' directory.
   The GRUB kernel is in `kern/'.  This contains core facilities such as
the device, disk, and file frameworks, environment variable handling,
list processing, and so on.  The kernel should contain enough to get up
to a rescue prompt.  Header files for kernel facilities, among others,
are in `include/'.
   Terminal implementations are in `term/'.
   Disk access code is spread across `disk/' (for accessing the disk
devices themselves), `partmap/' (for interpreting partition table
data), and `fs/' (for accessing filesystems).  Note that, with the odd
specialised exception, GRUB only contains code to _read_ from
filesystems and tries to avoid containing any code to _write_ to
filesystems; this lets us confidently assure users that GRUB cannot be
responsible for filesystem corruption.
   PCI and USB bus handling is in `bus/'.
   Video handling code is in `video/'.  The graphical menu system uses
this heavily, but is in a separate directory, `gfxmenu/'.
   Most commands are implemented by files in `commands/', with the
following exceptions:
   * A few core commands live in `kern/corecmd.c'.
   * Commands related to normal mode live under `normal/'.
   * Commands that load and boot kernels live under `loader/'.
   * The `loopback' command is really a disk device, and so lives in
   * The `gettext' command lives under `gettext/'.
   * The `loadfont' and `lsfonts' commands live under `font/'.
   * The `serial', `terminfo', and `background_image' commands live
     under `term/'.
   * The `efiemu_*' commands live under `efiemu/'.
   There are a few other special-purpose exceptions; grep for them if
they matter to you.
File:,  Node: Copying This Manual,  Next: Index,  Prev: Internals,  Up: Top
Appendix E Copying This Manual
* Menu:
* GNU Free Documentation License::  License for copying this manual.
File:,  Node: GNU Free Documentation License,  Up: Copying This Manual
E.1 GNU Free Documentation License
                      Version 1.2, November 2002
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     version of the Document.
     You may copy and distribute a Modified Version of the Document
     under the conditions of sections 2 and 3 above, provided that you
     release the Modified Version under precisely this License, with
     the Modified Version filling the role of the Document, thus
     licensing distribution and modification of the Modified Version to
     whoever possesses a copy of it.  In addition, you must do these
     things in the Modified Version:
       A. Use in the Title Page (and on the covers, if any) a title
          distinct from that of the Document, and from those of
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       B. List on the Title Page, as authors, one or more persons or
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          principal authors of the Document (all of its principal
          authors, if it has fewer than five), unless they release you
          from this requirement.
       C. State on the Title page the name of the publisher of the
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       D. Preserve all the copyright notices of the Document.
       E. Add an appropriate copyright notice for your modifications
          adjacent to the other copyright notices.
       F. Include, immediately after the copyright notices, a license
          notice giving the public permission to use the Modified
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       G. Preserve in that license notice the full lists of Invariant
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          license notice.
       H. Include an unaltered copy of this License.
       I. Preserve the section Entitled "History", Preserve its Title,
          and add to it an item stating at least the title, year, new
          authors, and publisher of the Modified Version as given on
          the Title Page.  If there is no section Entitled "History" in
          the Document, create one stating the title, year, authors,
          and publisher of the Document as given on its Title Page,
          then add an item describing the Modified Version as stated in
          the previous sentence.
       J. Preserve the network location, if any, given in the Document
          for public access to a Transparent copy of the Document, and
          likewise the network locations given in the Document for
          previous versions it was based on.  These may be placed in
          the "History" section.  You may omit a network location for a
          work that was published at least four years before the
          Document itself, or if the original publisher of the version
          it refers to gives permission.
       K. For any section Entitled "Acknowledgements" or "Dedications",
          Preserve the Title of the section, and preserve in the
          section all the substance and tone of each of the contributor
          acknowledgements and/or dedications given therein.
       L. Preserve all the Invariant Sections of the Document,
          unaltered in their text and in their titles.  Section numbers
          or the equivalent are not considered part of the section
       M. Delete any section Entitled "Endorsements".  Such a section
          may not be included in the Modified Version.
       N. Do not retitle any existing section to be Entitled
          "Endorsements" or to conflict in title with any Invariant
       O. Preserve any Warranty Disclaimers.
     If the Modified Version includes new front-matter sections or
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     other section titles.
     You may add a section Entitled "Endorsements", provided it contains
     nothing but endorsements of your Modified Version by various
     parties--for example, statements of peer review or that the text
     has been approved by an organization as the authoritative
     definition of a standard.
     You may add a passage of up to five words as a Front-Cover Text,
     and a passage of up to 25 words as a Back-Cover Text, to the end
     of the list of Cover Texts in the Modified Version.  Only one
     passage of Front-Cover Text and one of Back-Cover Text may be
     added by (or through arrangements made by) any one entity.  If the
     Document already includes a cover text for the same cover,
     previously added by you or by arrangement made by the same entity
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     The author(s) and publisher(s) of the Document do not by this
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     assert or imply endorsement of any Modified Version.
     You may combine the Document with other documents released under
     this License, under the terms defined in section 4 above for
     modified versions, provided that you include in the combination
     all of the Invariant Sections of all of the original documents,
     unmodified, and list them all as Invariant Sections of your
     combined work in its license notice, and that you preserve all
     their Warranty Disclaimers.
     The combined work need only contain one copy of this License, and
     multiple identical Invariant Sections may be replaced with a single
     copy.  If there are multiple Invariant Sections with the same name
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     original author or publisher of that section if known, or else a
     unique number.  Make the same adjustment to the section titles in
     the list of Invariant Sections in the license notice of the
     combined work.
     In the combination, you must combine any sections Entitled
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     "Acknowledgements", and any sections Entitled "Dedications".  You
     must delete all sections Entitled "Endorsements."
     You may make a collection consisting of the Document and other
     documents released under this License, and replace the individual
     copies of this License in the various documents with a single copy
     that is included in the collection, provided that you follow the
     rules of this License for verbatim copying of each of the
     documents in all other respects.
     You may extract a single document from such a collection, and
     distribute it individually under this License, provided you insert
     a copy of this License into the extracted document, and follow
     this License in all other respects regarding verbatim copying of
     that document.
     A compilation of the Document or its derivatives with other
     separate and independent documents or works, in or on a volume of
     a storage or distribution medium, is called an "aggregate" if the
     copyright resulting from the compilation is not used to limit the
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     works permit.  When the Document is included in an aggregate, this
     License does not apply to the other works in the aggregate which
     are not themselves derivative works of the Document.
     If the Cover Text requirement of section 3 is applicable to these
     copies of the Document, then if the Document is less than one half
     of the entire aggregate, the Document's Cover Texts may be placed
     on covers that bracket the Document within the aggregate, or the
     electronic equivalent of covers if the Document is in electronic
     form.  Otherwise they must appear on printed covers that bracket
     the whole aggregate.
     Translation is considered a kind of modification, so you may
     distribute translations of the Document under the terms of section
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     permission from their copyright holders, but you may include
     translations of some or all Invariant Sections in addition to the
     original versions of these Invariant Sections.  You may include a
     translation of this License, and all the license notices in the
     Document, and any Warranty Disclaimers, provided that you also
     include the original English version of this License and the
     original versions of those notices and disclaimers.  In case of a
     disagreement between the translation and the original version of
     this License or a notice or disclaimer, the original version will
     If a section in the Document is Entitled "Acknowledgements",
     "Dedications", or "History", the requirement (section 4) to
     Preserve its Title (section 1) will typically require changing the
     actual title.
     You may not copy, modify, sublicense, or distribute the Document
     except as expressly provided for under this License.  Any other
     attempt to copy, modify, sublicense or distribute the Document is
     void, and will automatically terminate your rights under this
     License.  However, parties who have received copies, or rights,
     from you under this License will not have their licenses
     terminated so long as such parties remain in full compliance.
     The Free Software Foundation may publish new, revised versions of
     the GNU Free Documentation License from time to time.  Such new
     versions will be similar in spirit to the present version, but may
     differ in detail to address new problems or concerns.  See
     Each version of the License is given a distinguishing version
     number.  If the Document specifies that a particular numbered
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     have the option of following the terms and conditions either of
     that specified version or of any later version that has been
     published (not as a draft) by the Free Software Foundation.  If
     the Document does not specify a version number of this License,
     you may choose any version ever published (not as a draft) by the
     Free Software Foundation.
E.1.1 ADDENDUM: How to use this License for your documents
To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:
       Copyright (C)  YEAR  YOUR NAME.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.2
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
       Texts.  A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.
   If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the "with...Texts." line with this:
         with the Invariant Sections being LIST THEIR TITLES, with
         the Front-Cover Texts being LIST, and with the Back-Cover Texts
         being LIST.
   If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
   If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License, to
permit their use in free software.
File:,  Node: Index,  Prev: Copying This Manual,  Up: Top
* Menu:
* acpi:                                  acpi.                 (line 11)
* badram:                                badram.               (line  7)
* blocklist:                             blocklist.            (line  7)
* boot:                                  boot.                 (line  7)
* cat:                                   cat.                  (line  7)
* chainloader:                           chainloader.          (line  7)
* cmp:                                   cmp.                  (line  7)
* configfile:                            configfile.           (line  7)
* cpuid:                                 cpuid.                (line  7)
* crc:                                   crc.                  (line  7)
* date:                                  date.                 (line  7)
* drivemap:                              drivemap.             (line  7)
* echo:                                  echo.                 (line  7)
* export:                                export.               (line  7)
* FDL, GNU Free Documentation License:   GNU Free Documentation License.
                                                               (line  6)
* gettext:                               gettext.              (line  7)
* gptsync:                               gptsync.              (line  7)
* halt:                                  halt.                 (line  7)
* help:                                  help.                 (line  7)
* initrd:                                initrd.               (line  7)
* initrd16:                              initrd16.             (line  7)
* insmod:                                insmod.               (line  7)
* keystatus:                             keystatus.            (line  7)
* linux:                                 linux.                (line  7)
* linux16:                               linux16.              (line  7)
* ls:                                    ls.                   (line  7)
* menuentry:                             menuentry.            (line  8)
* parttool:                              parttool.             (line  7)
* password:                              password.             (line  7)
* password_pbkdf2:                       password_pbkdf2.      (line  7)
* play:                                  play.                 (line  7)
* pxe_unload:                            pxe_unload.           (line  7)
* reboot:                                reboot.               (line  7)
* search:                                search.               (line  8)
* serial:                                serial.               (line  8)
* set:                                   set.                  (line  7)
* terminal_input:                        terminal_input.       (line  8)
* terminal_output:                       terminal_output.      (line  8)
* terminfo:                              terminfo.             (line  7)
* unset:                                 unset.                (line  7)