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This is /home/phcoder/grub2/bzr/mainline/docs/grub.info, produced by
makeinfo version 4.13 from
/home/phcoder/grub2/bzr/mainline/docs/grub.texi.
This manual is for GNU GRUB (version 2.00, 23 June 2012).
Copyright (C) 1999,2000,2001,2002,2004,2006,2008,2009,2010,2011,2012
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.
INFO-DIR-SECTION Kernel
START-INFO-DIR-ENTRY
* GRUB: (grub). The GRand Unified Bootloader
* grub-install: (grub)Invoking grub-install. Install GRUB on your drive
* grub-mkconfig: (grub)Invoking grub-mkconfig. Generate GRUB configuration
* grub-mkpasswd-pbkdf2: (grub)Invoking grub-mkpasswd-pbkdf2.
* grub-mkrescue: (grub)Invoking grub-mkrescue. Make a GRUB rescue image
* grub-probe: (grub)Invoking grub-probe. Probe device information
END-INFO-DIR-ENTRY

File: grub.info, Node: Top, Next: Introduction, Up: (dir)
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
architectures.
This edition documents version 2.00.
This manual is for GNU GRUB (version 2.00, 23 June 2012).
Copyright (C) 1999,2000,2001,2002,2004,2006,2008,2009,2010,2011,2012
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
* Theme file format:: Format of GRUB theme files
* 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
* Environment:: GRUB environment variables
* Commands:: The list of available builtin commands
* Internationalisation:: Topics relating to language support
* Security:: Authentication and authorisation
* Platform limitations:: The list of platform-specific limitations
* Platform-specific operations:: Platform-specific operations
* Supported kernels:: The list of supported kernels
* 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
* Invoking grub-mkrescue:: Make a GRUB rescue image
* Invoking grub-probe:: Probe device information for GRUB
* 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
* Copying This Manual:: Copying This Manual
* Index::

File: grub.info, 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
* Changes from GRUB Legacy:: Differences from previous versions
* Features:: GRUB features
* Role of a boot loader:: The role of a boot loader

File: grub.info, 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: grub.info, Node: Overview-Footnotes, Up: Overview
(1) "chain-load" is the mechanism for loading unsupported operating
systems by loading another boot loader. It is typically used for
loading DOS or Windows.

File: grub.info, Node: History, Next: Changes from GRUB Legacy, 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: grub.info, Node: Changes from GRUB Legacy, Next: Features, Prev: History, 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
available.
* 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. This is not available in all
configurations (*note Environment block::).
* 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
supported.
* 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: grub.info, Node: Features, Next: Role of a boot loader, Prev: Changes from GRUB Legacy, 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
hundred.
Have a flexible command-line interface
A fairly flexible command-line interface, accessible from the menu,
is available to edit any preset commands, or write a new boot
command set from scratch. If no configuration file is present,
GRUB drops to the command-line.
The list of commands (*note Commands::) are a subset of those
supported for configuration files. Editing commands closely
resembles the Bash command-line (*note Bash: (features)Command
Line Editing.), with <TAB>-completion of commands, devices,
partitions, and files in a directory depending on context.
Support multiple filesystem types
Support multiple filesystem types transparently, plus a useful
explicit blocklist notation. The currently supported filesystem
types are "Amiga Fast FileSystem (AFFS)", "AtheOS fs", "BeFS",
"BtrFS" (including raid0, raid1, raid10, gzip and lzo), "cpio"
(little- and big-endian bin, odc and newc variants), "Linux
ext2/ext3/ext4", "DOS FAT12/FAT16/FAT32", "exFAT", "HFS", "HFS+",
"ISO9660" (including Joliet, Rock-ridge and multi-chunk files),
"JFS", "Minix fs" (versions 1, 2 and 3), "nilfs2", "NTFS"
(including compression), "ReiserFS", "ROMFS", "Amiga Smart
FileSystem (SFS)", "Squash4", "tar", "UDF", "BSD UFS/UFS2", "XFS",
and "ZFS" (including lzjb, gzip, zle, mirror, stripe, raidz1/2/3
and encryption in AES-CCM and AES-GCM). *Note Filesystem::, for
more information.
Support automatic decompression
Can decompress files which were compressed by `gzip' or `xz'(1)
(*note Features-Footnote-1::). 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.(2) (*note Features-Footnote-2::)
It is conceivable that some kernel modules should be loaded in a
compressed state, so a different module-loading command can be
specified to avoid uncompressing the modules.
Access data on any installed device
Support reading data from any or all floppies or hard disk(s)
recognized by the BIOS, independent of the setting of the root
device.
Be independent of drive geometry translations
Unlike many other boot loaders, GRUB makes the particular drive
translation irrelevant. A drive installed and running with one
translation may be converted to another translation without any
adverse effects or changes in GRUB's configuration.
Detect all installed RAM
GRUB can generally find all the installed RAM on a PC-compatible
machine. It uses an advanced BIOS query technique for finding all
memory regions. As described on the Multiboot Specification (*note
Multiboot Specification: (multiboot)Top.), not all kernels make
use of this information, but GRUB provides it for those who do.
Support Logical Block Address mode
In traditional disk calls (called "CHS mode"), there is a geometry
translation problem, that is, the BIOS cannot access over 1024
cylinders, so the accessible space is limited to at least 508 MB
and to at most 8GB. GRUB can't universally solve this problem, as
there is no standard interface used in all machines. However,
several newer machines have the new interface, Logical Block
Address ("LBA") mode. GRUB automatically detects if LBA mode is
available and uses it if available. In LBA mode, GRUB can access
the entire disk.
Support network booting
GRUB is basically a disk-based boot loader but also has network
support. You can load OS images from a network by using the "TFTP"
protocol.
Support remote terminals
To support computers with no console, GRUB provides remote terminal
support, so that you can control GRUB from a remote host. Only
serial terminal support is implemented at the moment.

File: grub.info, Node: Features-Footnotes, Up: Features
(1) Only CRC32 data integrity check is supported (xz default is
CRC64 so one should use -check=crc32 option). LZMA BCJ filters are
supported.
(2) There are a few pathological cases where loading a very badly
organized ELF kernel might take longer, but in practice this never
happen.

File: grub.info, Node: Role of a boot loader, Prev: Features, Up: Introduction
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: grub.info, Node: Role of a boot loader-Footnotes, Up: Role of a boot loader
(1) The LInux LOader, a boot loader that everybody uses, but nobody
likes.

File: grub.info, Node: Naming convention, Next: Installation, Prev: Introduction, Up: Top
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:
(fd0)
First of all, GRUB requires that the device name be enclosed with
`(' and `)'. The `fd' part means that it is a floppy disk. The number
`0' is the drive number, which is counted from _zero_. This expression
means that GRUB will use the whole floppy disk.
(hd0,msdos2)
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.
(hd0,msdos5)
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.
(hd1,msdos1,bsd1)
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
syntax.
Note that GRUB does _not_ distinguish IDE from SCSI - it simply
counts the drive numbers from zero, regardless of their type. Normally,
any IDE drive number is less than any SCSI drive number, although that
is not true if you change the boot sequence by swapping IDE and SCSI
drives in your BIOS.
Now the question is, how to specify a file? Again, consider an
example:
(hd0,msdos1)/vmlinuz
This specifies the file named `vmlinuz', found on the first
partition of the first hard disk drive. Note that the argument
completion works with file names, too.
That was easy, admit it. Now read the next chapter, to find out how
to actually install GRUB on your drive.

File: grub.info, Node: Installation, Next: Booting, Prev: Naming convention, Up: Top
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) by using the utility `grub-install' (*note
Invoking grub-install::) on a UNIX-like OS.
GRUB comes with boot images, which are normally put in the directory
`/usr/lib/grub/<cpu>-<platform>' (for BIOS-based machines
`/usr/lib/grub/i386-pc'). Hereafter, the directory where GRUB images are
initially placed (normally `/usr/lib/grub/<cpu>-<platform>') will be
called the "image directory", and the directory where the boot loader
needs to find them (usually `/boot') will be called the "boot
directory".
* Menu:
* Installing GRUB using grub-install::
* Making a GRUB bootable CD-ROM::
* Device map::
* BIOS installation::

File: grub.info, Node: Installing GRUB using grub-install, Next: Making a GRUB bootable CD-ROM, Up: Installation
3.1 Installing GRUB using grub-install
======================================
For information on where GRUB should be installed on PC BIOS platforms,
*note BIOS installation::.
In order 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 has to be either a device file (like `/dev/hda'). 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
But all the above examples assume that GRUB should put images under
the `/boot' directory. If you want GRUB to put images under a directory
other than `/boot', you need to specify the option `--boot-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
# mkdir /mnt/boot
# grub-install --boot-directory=/mnt/boot /dev/fd0
# umount /mnt
Some BIOSes have a bug of exposing the first partition of a USB
drive as a floppy instead of exposing the USB drive as a hard disk
(they call it "USB-FDD" boot). In such cases, you need to install like
this:
# losetup /dev/loop0 /dev/sdb1
# mount /dev/loop0 /mnt/usb
# grub-install --boot-directory=/mnt/usb/bugbios --force --allow-floppy /dev/loop0
This install doesn't conflict with standard install as long as they
are in separate directories.
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: grub.info, 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 image called
`cdboot.img', which is concatenated with `core.img'. The `core.img'
used for this should be built with at least the `iso9660' and
`biosdisk' modules. Your bootable CD-ROM will usually also need to
include a configuration file `grub.cfg' and some other GRUB modules.
To make a simple generic GRUB rescue CD, you can use the
`grub-mkrescue' program (*note Invoking grub-mkrescue::):
$ grub-mkrescue -o grub.iso
You will often need to include other files in your image. To do
this, first make a top directory for the bootable image, say, `iso':
$ mkdir iso
Make a directory for GRUB:
$ mkdir -p 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 the image:
$ grub-mkrescue -o grub.iso iso
This produces a file named `grub.iso', which then can be burned into
a CD (or a DVD), or written to a USB mass storage device.
The root device will be set up appropriately on entering your
`grub.cfg' configuration file, so you can refer to file names on the CD
without needing to use an explicit device name. This makes it easier to
produce rescue images that will work on both optical drives and USB mass
storage devices.

File: grub.info, Node: Making a GRUB bootable CD-ROM-Footnotes, Up: Making a GRUB bootable CD-ROM
(1) El Torito is a specification for bootable CD using BIOS
functions.

File: grub.info, Node: Device map, Next: BIOS installation, Prev: Making a GRUB bootable CD-ROM, Up: Installation
3.3 The map between BIOS drives and OS devices
==============================================
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) FILE
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 it is
used for overriding when current environment is different from the one
on boot. Most common case is if you use a partition or logical volume
as a disk for virtual machine. 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: grub.info, Node: BIOS installation, Prev: Device map, Up: Installation
3.4 BIOS installation
=====================
MBR
===
The partition table format traditionally used on PC BIOS platforms is
called the Master Boot Record (MBR) format; this is the format that
allows up to four primary partitions and additional logical partitions.
With this partition table format, there are two ways to install GRUB:
it can be embedded in the area between the MBR and the first partition
(called by various names, such as the "boot track", "MBR gap", or
"embedding area", and which is usually at least 31 KiB), or the core
image can be installed in a file system and a list of the blocks that
make it up can be stored in the first sector of that partition.
Each of these has different problems. There is no way to reserve
space in the embedding area with complete safety, and some proprietary
software is known to use it to make it difficult for users to work
around licensing restrictions; and systems are sometimes partitioned
without leaving enough space before the first partition. On the other
hand, installing to a filesystem means that GRUB is vulnerable to its
blocks being moved around by filesystem features such as tail packing,
or even by aggressive fsck implementations, so this approach is quite
fragile; and this approach can only be used if the `/boot' filesystem
is on the same disk that the BIOS boots from, so that GRUB does not
have to rely on guessing BIOS drive numbers.
The GRUB development team generally recommends embedding GRUB before
the first partition, unless you have special requirements. You must
ensure that the first partition starts at least 31 KiB (63 sectors)
from the start of the disk; on modern disks, it is often a performance
advantage to align partitions on larger boundaries anyway, so the first
partition might start 1 MiB from the start of the disk.
GPT
===
Some newer systems use the GUID Partition Table (GPT) format. This was
specified as part of the Extensible Firmware Interface (EFI), but it can
also be used on BIOS platforms if system software supports it; for
example, GRUB and GNU/Linux can be used in this configuration. With
this format, it is possible to reserve a whole partition for GRUB,
called the BIOS Boot Partition. GRUB can then be embedded into that
partition without the risk of being overwritten by other software and
without being contained in a filesystem which might move its blocks
around.
When creating a BIOS Boot Partition on a GPT system, you should make
sure that it is at least 31 KiB in size. (GPT-formatted disks are not
usually particularly small, so we recommend that you make it larger
than the bare minimum, such as 1 MiB, to allow plenty of room for
growth.) You must also make sure that it has the proper partition
type. Using GNU Parted, you can set this using a command such as the
following:
# parted /dev/DISK set PARTITION-NUMBER bios_grub on
If you are using gdisk, set the partition type to `0xEF02'. With
partitioning programs that require setting the GUID directly, it should
be `21686148-6449-6e6f-744e656564454649'.
*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.

File: grub.info, 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
* Loopback booting:: Notes on booting from loopbacks
* OS-specific notes:: Notes on some operating systems

File: grub.info, Node: General boot methods, Next: Loopback booting, 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: grub.info, 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
Chain-loading::).
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
information.

File: grub.info, 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
disk:
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: grub.info, Node: Loopback booting, Next: OS-specific notes, Prev: General boot methods, Up: Booting
4.2 Loopback booting
====================
GRUB is able to read from an image (be it one of CD or HDD) stored on
any of its accessible storages (refer to *note loopback:: command).
However the OS itself should be able to find its root. This usually
involves running a userspace program running before the real root is
discovered. This is achieved by GRUB loading a specially made small
image and passing it as ramdisk to the kernel. This is achieved by
commands `kfreebsd_module', `knetbsd_module_elf', `kopenbsd_ramdisk',
`initrd' (*note initrd::), `initrd16' (*note initrd::),
`multiboot_module', `multiboot2_module' or `xnu_ramdisk' depending on
the loader. Note that for knetbsd the image must be put inside
miniroot.kmod and the whole miniroot.kmod has to be loaded. In kopenbsd
payload this is disabled by default. Aditionally behaviour of initial
ramdisk depends on command line options. Several distributors provide
the image for this purpose or it's integrated in their standard ramdisk
and activated by special option. Consult your kernel and distribution
manual for more details. Other loaders like appleloader, chainloader
(BIOS, EFI, coreboot), freedos, ntldr and plan9 provide no possibility
of loading initial ramdisk and as far as author is aware the payloads
in question don't support either initial ramdisk or discovering
loopback boot in other way and as such not bootable this way. Please
consider alternative boot methods like copying all files from the image
to actual partition. Consult your OS documentation for more details

File: grub.info, Node: OS-specific notes, Prev: Loopback booting, Up: Booting
4.3 Some caveats on OS-specific issues
======================================
Here, we describe some caveats on several operating systems.
* Menu:
* GNU/Hurd::
* GNU/Linux::
* DOS/Windows::

File: grub.info, Node: GNU/Hurd, Next: GNU/Linux, Up: OS-specific notes
4.3.1 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.
1. Set GRUB's root device to the same drive as GNU/Hurd's. The
command `search --set=root --file /boot/gnumach.gz' or similar may
help you (*note search::).
2. Load the kernel and the modules, like this:
grub> multiboot /boot/gnumach.gz root=device:hd0s1
grub> module /hurd/ext2fs.static ext2fs --readonly \
--multiboot-command-line='${kernel-command-line}' \
--host-priv-port='${host-port}' \
--device-master-port='${device-port}' \
--exec-server-task='${exec-task}' -T typed '${root}' \
'$(task-create)' '$(task-resume)'
grub> module /lib/ld.so.1 exec /hurd/exec '$(exec-task=task-create)'
3. Finally, run the command `boot' (*note boot::).

File: grub.info, Node: GNU/Linux, Next: DOS/Windows, Prev: GNU/Hurd, Up: OS-specific notes
4.3.2 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 --set=root --file /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.
With `linux' GRUB uses 32-bit protocol. Some BIOS services like APM
or EDD aren't available with this protocol. In this case you need
to use `linux16'
grub> linux16 /vmlinuz root=/dev/sda1 acpi=off
3. If you use an initrd, execute the command `initrd' (*note initrd::)
after `linux':
grub> initrd /initrd
If you used `linux16' you need to use `initrd16':
grub> initrd16 /initrd
4. Finally, run the command `boot' (*note boot::).
*Caution:* If you use an initrd and specify the `mem=' option to the
kernel to let it use less than actual memory size, you will also have
to specify the same memory size to GRUB. To let GRUB know the size, run
the command `uppermem' _before_ loading the kernel. *Note uppermem::,
for more information.

File: grub.info, Node: DOS/Windows, Prev: GNU/Linux, Up: OS-specific notes
4.3.3 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
drive.
*Caution:* This is effective only if DOS (or Windows) uses BIOS to
access the swapped disks. If that OS uses a special driver for the
disks, this probably won't work.
Another problem arises if you installed more than one set of
DOS/Windows onto one disk, because they could be confused if there are
more than one primary partitions for DOS/Windows. Certainly you should
avoid doing this, but there is a solution if you do want to do so. Use
the partition hiding/unhiding technique.
If GRUB "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+
boot

File: grub.info, Node: Configuration, Next: Theme file format, 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
* Multi-boot manual config:: For non-standard multi-OS scenarios
* Embedded configuration:: Embedding a configuration file into GRUB

File: grub.info, 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.
`grub-mkconfig' does have some limitations. While adding extra
custom menu entries to the end of the list can be done by editing
`/etc/grub.d/40_custom' or creating `/boot/grub/custom.cfg', changing
the order of menu entries or changing their titles may require making
complex changes to shell scripts stored in `/etc/grub.d/'. This may be
improved in the future. In the meantime, those who feel that it would
be easier to write `grub.cfg' directly are encouraged to do so (*note
Booting::, and *note Shell-like scripting::), and to disable any system
provided by their distribution to automatically run `grub-mkconfig'.
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:
`GRUB_DEFAULT'
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 title of a menu entry, or the special string `saved'.
Using the title 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.
For example, if you have:
menuentry 'Example GNU/Linux distribution' --class gnu-linux {
...
}
then you can make this the default using:
GRUB_DEFAULT='Example GNU/Linux distribution'
If you set this to `saved', then the default menu entry will be
that saved by `GRUB_SAVEDEFAULT', `grub-set-default', or
`grub-reboot'.
The default is `0'.
`GRUB_SAVEDEFAULT'
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
default. This option relies on the environment block, which may
not be available in all situations (*note Environment block::).
`GRUB_TIMEOUT'
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.
`GRUB_HIDDEN_TIMEOUT'
Wait this many seconds for a key to be pressed before displaying
the menu. If no key is pressed during that time, display the menu
for the number of seconds specified in GRUB_TIMEOUT before booting
the default entry. We expect that most people who use
GRUB_HIDDEN_TIMEOUT will want to have GRUB_TIMEOUT set to `0' so
that the menu is not displayed at all unless a key is pressed.
Unset by default.
`GRUB_HIDDEN_TIMEOUT_QUIET'
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.
`GRUB_DEFAULT_BUTTON'
`GRUB_TIMEOUT_BUTTON'
`GRUB_HIDDEN_TIMEOUT_BUTTON'
`GRUB_BUTTON_CMOS_ADDRESS'
Variants of the corresponding variables without the `_BUTTON'
suffix, used to support vendor-specific power buttons. *Note
Vendor power-on keys::.
`GRUB_DISTRIBUTOR'
Set by distributors of GRUB to their identifying name. This is
used to generate more informative menu entry titles.
`GRUB_TERMINAL_INPUT'
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.
`GRUB_TERMINAL_OUTPUT'
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
Coreboot).
The default is to use the platform's native terminal output.
`GRUB_TERMINAL'
If this option is set, it overrides both `GRUB_TERMINAL_INPUT' and
`GRUB_TERMINAL_OUTPUT' to the same value.
`GRUB_SERIAL_COMMAND'
A command to configure the serial port when using the serial
console. *Note serial::. Defaults to `serial'.
`GRUB_CMDLINE_LINUX'
Command-line arguments to add to menu entries for the Linux kernel.
`GRUB_CMDLINE_LINUX_DEFAULT'
Unless `GRUB_DISABLE_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'.
`GRUB_CMDLINE_NETBSD'
`GRUB_CMDLINE_NETBSD_DEFAULT'
As `GRUB_CMDLINE_LINUX' and `GRUB_CMDLINE_LINUX_DEFAULT', but for
NetBSD.
`GRUB_CMDLINE_GNUMACH'
As `GRUB_CMDLINE_LINUX', but for GNU Mach.
`GRUB_CMDLINE_XEN'
`GRUB_CMDLINE_XEN_DEFAULT'
The values of these options are appended to the values of
`GRUB_CMDLINE_LINUX' and `GRUB_CMDLINE_LINUX_DEFAULT' for Linux
and Xen menu entries.
`GRUB_CMDLINE_LINUX_XEN_REPLACE'
`GRUB_CMDLINE_LINUX_XEN_REPLACE_DEFAULT'
The values of these options replace the values of
`GRUB_CMDLINE_LINUX' and `GRUB_CMDLINE_LINUX_DEFAULT' for Linux
and Xen menu entries.
`GRUB_DISABLE_LINUX_UUID'
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'.
`GRUB_DISABLE_RECOVERY'
If this option is set to `true', disable the generation of recovery
mode menu entries.
`GRUB_VIDEO_BACKEND'
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'.
`GRUB_GFXMODE'
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 `auto', which
tries to select a preferred resolution. *Note gfxmode::.
`GRUB_BACKGROUND'
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.
`GRUB_THEME'
Set a theme for use with the `gfxterm' graphical terminal.
`GRUB_GFXPAYLOAD_LINUX'
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. *Note gfxpayload::.
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.
`GRUB_DISABLE_OS_PROBER'
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.
`GRUB_INIT_TUNE'
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::.
`GRUB_BADRAM'
If this option is set, GRUB will issue a *note badram:: command to
filter out specified regions of RAM.
`GRUB_PRELOAD_MODULES'
This option may be set to a list of GRUB module names separated by
spaces. Each module will be loaded as early as possible, at the
start of `grub.cfg'.
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: grub.info, Node: Shell-like scripting, Next: Multi-boot manual config, 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
derivatives.
Words
=====
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
=======
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: `$', `"', `\', or newline. A
backslash-newline pair is treated as a line continuation (that is, it is
removed from the input stream and effectively ignored(1) (*note
Shell-like scripting-Footnote-1::)). A double quote may be quoted
within double quotes by preceding it with a backslash.
Variable expansion
==================
The `$' 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. These names refer to entries
in the GRUB environment (*note Environment::).
Positional variable names consist of one or more digits. They
represent parameters passed to function calls, with `$1' representing
the first parameter, and so on.
The special variable name `?' expands to the exit status of the most
recently executed command. When positional variable names are active,
other special variable names `@', `*' and `#' are defined and they
expand to all positional parameters with necessary quoting, positional
parameters without any quoting, and positional parameter count
respectively.
Comments
========
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. If the
reserved word `!' precedes the command, then the return value is
instead the logical negation of the command's 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'] [`--unrestricted'] [`--hotkey=key'] { COMMAND; ... }
*Note menuentry::.
Built-in Commands
=================
Some built-in commands are also provided by GRUB script to help script
writers perform actions that are otherwise not possible. For example,
these include commands to jump out of a loop without fully completing
it, etc.
break [`n']
Exit from within a `for', `while', or `until' loop. If `n' is
specified, break `n' levels. `n' must be greater than or equal to
1. If `n' is greater than the number of enclosing loops, all
enclosing loops are exited. The return value is 0 unless `n' is
not greater than or equal to 1.
continue [`n']
Resume the next iteration of the enclosing `for', `while' or
`until' loop. If `n' is specified, resume at the `n'th enclosing
loop. `n' must be greater than or equal to 1. If `n' is greater
than the number of enclosing loops, the last enclosing loop (the
"top-level" loop) is resumed. The return value is 0 unless `n' is
not greater than or equal to 1.
return [`n']
Causes a function to exit with the return value specified by `n'.
If `n' is omitted, the return status is that of the last command
executed in the function body. If used outside a function the
return status is false.
shift [`n']
The positional parameters from `n'+1 ... are renamed to `$1'....
Parameters represented by the numbers `$#' down to `$#'-`n'+1 are
unset. `n' must be a non-negative number less than or equal to
`$#'. If `n' is 0, no parameters are changed. If `n' is not
given, it is assumed to be 1. If `n' is greater than `$#', the
positional parameters are not changed. The return status is
greater than zero if `n' is greater than `$#' or less than zero;
otherwise 0.

File: grub.info, Node: Shell-like scripting-Footnotes, Up: Shell-like scripting
(1) Currently a backslash-newline pair within a variable name is not
handled properly, so use this feature with some care.

File: grub.info, Node: Multi-boot manual config, Next: Embedded configuration, Prev: Shell-like scripting, Up: Configuration
5.3 Multi-boot manual config
============================
Currently autogenerating config files for multi-boot environments
depends on os-prober and has several shortcomings. While fixing it is
scheduled for the next release, meanwhile you can make use of the power
of GRUB syntax and do it yourself. A possible configuration is detailed
here, feel free to adjust to your needs.
First create a separate GRUB partition, big enough to hold GRUB.
Some of the following entries show how to load OS installer images from
this same partition, for that you obviously need to make the partition
large enough to hold those images as well. Mount this partition
on/mnt/boot and disable GRUB in all OSes and manually install
self-compiled latest GRUB with:
`grub-install --boot-directory=/mnt/boot /dev/sda'
In all the OSes install GRUB tools but disable installing GRUB in
bootsector, so you'll have menu.lst and grub.cfg available for use.
Also disable os-prober use by setting:
`GRUB_DISABLE_OS_PROBER=true'
in /etc/default/grub
Then write a grub.cfg (/mnt/boot/grub/grub.cfg):
menuentry "OS using grub2" {
insmod xfs
search --set=root --label OS1 --hint hd0,msdos8
configfile /boot/grub/grub.cfg
}
menuentry "OS using grub2-legacy" {
insmod ext2
search --set=root --label OS2 --hint hd0,msdos6
legacy_configfile /boot/grub/menu.lst
}
menuentry "Windows XP" {
insmod ntfs
search --set=root --label WINDOWS_XP --hint hd0,msdos1
ntldr /ntldr
}
menuentry "Windows 7" {
insmod ntfs
search --set=root --label WINDOWS_7 --hint hd0,msdos2
ntldr /bootmgr
}
menuentry "FreeBSD" {
insmod zfs
search --set=root --label freepool --hint hd0,msdos7
kfreebsd /freebsd@/boot/kernel/kernel
kfreebsd_module_elf /freebsd@/boot/kernel/opensolaris.ko
kfreebsd_module_elf /freebsd@/boot/kernel/zfs.ko
kfreebsd_module /freebsd@/boot/zfs/zpool.cache type=/boot/zfs/zpool.cache
set kFreeBSD.vfs.root.mountfrom=zfs:freepool/freebsd
set kFreeBSD.hw.psm.synaptics_support=1
}
menuentry "experimental GRUB" {
search --set=root --label GRUB --hint hd0,msdos5
multiboot /experimental/grub/i386-pc/core.img
}
menuentry "Fedora 16 installer" {
search --set=root --label GRUB --hint hd0,msdos5
linux /fedora/vmlinuz lang=en_US keymap=sg resolution=1280x800
initrd /fedora/initrd.img
}
menuentry "Fedora rawhide installer" {
search --set=root --label GRUB --hint hd0,msdos5
linux /fedora/vmlinuz repo=ftp://mirror.switch.ch/mirror/fedora/linux/development/rawhide/x86_64 lang=en_US keymap=sg resolution=1280x800
initrd /fedora/initrd.img
}
menuentry "Debian sid installer" {
search --set=root --label GRUB --hint hd0,msdos5
linux /debian/dists/sid/main/installer-amd64/current/images/hd-media/vmlinuz
initrd /debian/dists/sid/main/installer-amd64/current/images/hd-media/initrd.gz
}
Notes:
* Argument to search after -label is FS LABEL. You can also use
UUIDs with -fs-uuid UUID instead of -label LABEL. You could also
use direct `root=hd0,msdosX' but this is not recommened due to
device name instability.

File: grub.info, Node: Embedded configuration, Prev: Multi-boot manual config, Up: Configuration
5.4 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
`grub-mkimage'.
After the embedded configuration file (if any) is executed, GRUB
will load the `normal' module (*note normal::), which will then read
the real configuration file from `$prefix/grub.cfg'. By this point, the
`root' variable will also have been set to the root device name. For
example, `prefix' might be set to `(hd0,1)/boot/grub', and `root' might
be set to `hd0,1'. Thus, in most cases, the embedded configuration
file only needs to set the `prefix' and `root' variables, and then drop
through to GRUB's normal processing. A typical example of this might
look like this:
search.fs_uuid 01234567-89ab-cdef-0123-456789abcdef root
set prefix=($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=($root)/boot/grub
configfile /boot/grub/example/test1.cfg
else
if [ -e /boot/grub/example/test2.cfg ]; then
set prefix=($root)/boot/grub
configfile /boot/grub/example/test2.cfg
else
echo "Could not find an example configuration file!"
fi
fi
The embedded configuration file may not contain menu entries
directly, but may only read them from elsewhere using `configfile'.

File: grub.info, Node: Theme file format, Next: Network, Prev: Configuration, Up: Top
6 Theme file format
*******************
6.1 Introduction
================
The GRUB graphical menu supports themes that can customize the layout
and appearance of the GRUB boot menu. The theme is configured through
a plain text file that specifies the layout of the various GUI
components (including the boot menu, timeout progress bar, and text
messages) as well as the appearance using colors, fonts, and images.
Example is available in docs/example_theme.txt
6.2 Theme Elements
==================
6.2.1 Colors
------------
Colors can be specified in several ways:
* HTML-style "#RRGGBB" or "#RGB" format, where *R*, *G*, and *B* are
hexadecimal digits (e.g., "#8899FF")
* as comma-separated decimal RGB values (e.g., "128, 128, 255")
* with "SVG 1.0 color names" (e.g., "cornflowerblue") which must be
specified in lowercase.
6.2.2 Fonts
-----------
The fonts GRUB uses "PFF2 font format" bitmap fonts. Fonts are
specified with full font names. Currently there is no provision for a
preference list of fonts, or deriving one font from another. Fonts are
loaded with the "loadfont" command in GRUB. To see the list of loaded
fonts, execute the "lsfonts" command. If there are too many fonts to
fit on screen, do "set pager=1" before executing "lsfonts".
6.2.3 Progress Bar
------------------
Figure 6.1
Figure 6.2
Progress bars are used to display the remaining time before GRUB
boots the default menu entry. To create a progress bar that will
display the remaining time before automatic boot, simply create a
"progress_bar" component with the id "__timeout__". This indicates to
GRUB that the progress bar should be updated as time passes, and it
should be made invisible if the countdown to automatic boot is
interrupted by the user.
Progress bars may optionally have text displayed on them. This text
is controlled by variable "text" which contains a printf template with
the only argument %d is the number of seconds remaining. Additionally
special values "@TIMEOUT_NOTIFICATION_SHORT@",
"@TIMEOUT_NOTIFICATION_MIDDLE@", "@TIMEOUT_NOTIFICATION_LONG@" are
replaced with standard and translated templates.
6.2.4 Circular Progress Indicator
---------------------------------
The circular progress indicator functions similarly to the progress
bar. When given an id of "__timeout__", GRUB updates the circular
progress indicator's value to indicate the time remaining. For the
circular progress indicator, there are two images used to render it:
the *center* image, and the *tick* image. The center image is rendered
in the center of the component, while the tick image is used to render
each mark along the circumference of the indicator.
6.2.5 Labels
------------
Text labels can be placed on the boot screen. The font, color, and
horizontal alignment can be specified for labels. If a label is given
the id "__timeout__", then the "text" property for that label is also
updated with a message informing the user of the number of seconds
remaining until automatic boot. This is useful in case you want the
text displayed somewhere else instead of directly on the progress bar.
6.2.6 Boot Menu
---------------
The boot menu where GRUB displays the menu entries from the "grub.cfg"
file. It is a list of items, where each item has a title and an
optional icon. The icon is selected based on the *classes* specified
for the menu entry. If there is a PNG file named "myclass.png" in the
"grub/themes/icons" directory, it will be displayed for items which
have the class *myclass*. The boot menu can be customized in several
ways, such as the font and color used for the menu entry title, and by
specifying styled boxes for the menu itself and for the selected item
highlight.
6.2.7 Styled Boxes
------------------
One of the most important features for customizing the layout is the
use of *styled boxes*. A styled box is composed of 9 rectangular (and
potentially empty) regions, which are used to seamlessly draw the
styled box on screen:
Northwest (nw) North (n) Northeast (ne)
West (w) Center (c) East (e)
Southwest (sw) South (s) Southeast (se)
To support any size of box on screen, the center slice and the
slices for the top, bottom, and sides are all scaled to the correct
size for the component on screen, using the following rules:
1. The edge slices (north, south, east, and west) are scaled in the
direction of the edge they are adjacent to. For instance, the
west slice is scaled vertically.
2. The corner slices (northwest, northeast, southeast, and southwest)
are not scaled.
3. The center slice is scaled to fill the remaining space in the
middle.
As an example of how an image might be sliced up, consider the
styled box used for a terminal view.
Figure 6.3
6.2.8 Creating Styled Box Images
--------------------------------
The Inkscape_ scalable vector graphics editor is a very useful tool for
creating styled box images. One process that works well for slicing a
drawing into the necessary image slices is:
1. Create or open the drawing you'd like use.
2. Create a new layer on the top of the layer stack. Make it
visible. Select this layer as the current layer.
3. Draw 9 rectangles on your drawing where you'd like the slices to
be. Clear the fill option, and set the stroke to 1 pixel wide
solid stroke. The corners of the slices must meet precisely; if
it is off by a single pixel, it will probably be evident when the
styled box is rendered in the GRUB menu. You should probably go
to File | Document Properties | Grids and enable a grid or create
a guide (click on one of the rulers next to the drawing and drag
over the drawing; release the mouse button to place the guide) to
help place the rectangles precisely.
4. Right click on the center slice rectangle and choose Object
Properties. Change the "Id" to "slice_c" and click Set. Repeat
this for the remaining 8 rectangles, giving them Id values of
"slice_n", "slice_ne", "slice_e", and so on according to the
location.
5. Save the drawing.
6. Select all the slice rectangles. With the slice layer selected,
you can simply press Ctrl+A to select all rectangles. The status
bar should indicate that 9 rectangles are selected.
7. Click the layer hide icon for the slice layer in the layer
palette. The rectangles will remain selected, even though they
are hidden.
8. Choose File | Export Bitmap and check the *Batch export 9 selected
objects* box. Make sure that *Hide all except selected* is
unchecked. click *Export*. This will create PNG files in the same
directory as the drawing, named after the slices. These can now
be used for a styled box in a GRUB theme.
6.3 Theme File Manual
=====================
The theme file is a plain text file. Lines that begin with "#" are
ignored and considered comments. (Note: This may not be the case if
the previous line ended where a value was expected.)
The theme file contains two types of statements:
1. Global properties.
2. Component construction.
6.3.1 Global Properties
-----------------------
6.3.2 Format
------------
Global properties are specified with the simple format:
* name1: value1
* name2: "value which may contain spaces"
* name3: #88F
In this example, name3 is assigned a color value.
6.3.3 Global Property List
--------------------------
title-text Specifies the text to display at the top
center of the screen as a title.
title-font Defines the font used for the title
message at the top of the screen.
title-color Defines the color of the title message.
message-font Defines the font used for messages, such
as when GRUB is unable to automatically
boot an entry.
message-color Defines the color of the message text.
message-bg-color Defines the background color of the
message text area.
desktop-image Specifies the image to use as the
background. It will be scaled to fit the
screen size.
desktop-color Specifies the color for the background if
*desktop-image* is not specified.
terminal-box Specifies the file name pattern for the
styled box slices used for the command
line terminal window. For example,
"terminal-box: terminal_*.png" will use
the images "terminal_c.png" as the center
area, "terminal_n.png" as the north (top)
edge, "terminal_nw.png" as the northwest
(upper left) corner, and so on. If the
image for any slice is not found, it will
simply be left empty.
6.3.4 Component Construction
----------------------------
Greater customizability comes is provided by components. A tree of
components forms the user interface. *Containers* are components that
can contain other components, and there is always a single root
component which is an instance of a *canvas* container.
Components are created in the theme file by prefixing the type of
component with a '+' sign:
` + label { text="GRUB" font="aqui 11" color="#8FF" } '
properties of a component are specified as "name = value" (whitespace
surrounding tokens is optional and is ignored) where *value* may be:
* a single word (e.g., "align = center", "color = #FF8080"),
* a quoted string (e.g., "text = "Hello, World!""), or
* a tuple (e.g., "preferred_size = (120, 80)").
6.3.5 Component List
--------------------
The following is a list of the components and the properties they
support.
* label A label displays a line of text.
Properties:
text The text to display.
font The font to use for text display.
color The color of the text.
align The horizontal alignment of the text within
the component. Options are "left", "center",
and "right".
* image A component that displays an image. The image is scaled
to fit the component, although the preferred size defaults to
the image's original size unless the "preferred_size" property
is explicitly set.
Properties:
file The full path to the image file to load.
* progress_bar Displays a horizontally oriented progress bar. It
can be rendered using simple solid filled rectangles, or using
a pair of pixmap styled boxes.
Properties:
fg_color The foreground color for plain solid color
rendering.
bg_color The background color for plain solid color
rendering.
border_color The border color for plain solid color
rendering.
text_color The text color.
show_text Boolean value indicating whether or not text
should be displayed on the progress bar. If
set to *false*, then no text will be displayed
on the bar. If set to any other value, text
will be displayed on the bar.
bar_style The styled box specification for the frame of
the progress bar. Example:
"progress_frame_*.png"
highlight_styleThe styled box specification for the
highlighted region of the progress bar. This
box will be used to paint just the highlighted
region of the bar, and will be increased in
size as the bar nears completion. Example:
"progress_hl_*.png".
text The text to display on the progress bar. If
the progress bar's ID is set to "__timeout__",
then GRUB will updated this property with an
informative message as the timeout approaches.
value The progress bar current value. Normally not
set manually.
start The progress bar start value. Normally not
set manually.
end The progress bar end value. Normally not set
manually.
* circular_progress Displays a circular progress indicator. The
appearance of this component is determined by two images: the
*center* image and the *tick* image. The center image is
generally larger and will be drawn in the center of the
component. Around the circumference of a circle within the
component, the tick image will be drawn a certain number of
times, depending on the properties of the component.
Properties:
center_bitmap The file name of the image to draw in
the center of the component.
tick_bitmap The file name of the image to draw for
the tick marks.
num_ticks The number of ticks that make up a full
circle.
ticks_disappear Boolean value indicating whether tick
marks should progressively appear,
or progressively disappear as *value*
approaches *end*. Specify "true"
or "false".
value The progress indicator current value.
Normally not set manually.
start The progress indicator start value.
Normally not set manually.
end The progress indicator end value.
Normally not set manually.
* boot_menu Displays the GRUB boot menu. It allows selecting
items and executing them.
Properties:
item_font The font to use for the menu item
titles.
selected_item_font The font to use for the selected
menu item, or "inherit" (the
default) to use "item_font"
for the selected menu item as
well.
item_color The color to use for the menu
item titles.
selected_item_color The color to use for the selected
menu item, or "inherit" (the
default) to use
"item_color" for the selected
menu item as well.
icon_width The width of menu item icons.
Icons are scaled to the specified
size.
icon_height The height of menu item icons.
item_height The height of each menu item in
pixels.
item_padding The amount of space in pixels to
leave on each side of the menu
item contents.
item_icon_space The space between an item's icon
and the title text, in pixels.
item_spacing The amount of space to leave
between menu items, in pixels.
menu_pixmap_style The image file pattern for the
menu frame styled box.
Example: "menu_*.png" (this will
use images such as "menu_c.png",
"menu_w.png", `menu_nw.png",
etc.)
selected_item_pixmap_style The image file pattern for the
selected item highlight styled
box.
scrollbar Boolean value indicating whether
the scroll bar should be drawn if
the frame and thumb styled
boxes are configured.
scrollbar_frame The image file pattern for the
entire scroll bar.
Example: "scrollbar_*.png"
scrollbar_thumb The image file pattern for the
scroll bar thumb (the part of the
scroll bar that moves as
scrolling occurs).
Example: "scrollbar_thumb_*.png"
max_items_shown The maximum number of items to
show on the menu. If there are
more than *max_items_shown*
items in the menu, the list will
scroll to make all items
accessible.
* canvas Canvas is a container that allows manual placement of
components within it. It does not alter the positions of its
child components. It assigns all child components their
preferred sizes.
* hbox The *hbox* container lays out its children from left to
right, giving each one its preferred width. The height of each
child is set to the maximum of the preferred heights of all
children.
* vbox The *vbox* container lays out its children from top to
bottom, giving each one its preferred height. The width of
each child is set to the maximum of the preferred widths of all
children.
6.3.6 Common properties
-----------------------
The following properties are supported by all components:
`left'
The distance from the left border of container to left border of
the object in either of three formats:
x Value in pixels
p% Percentage
p%+x mixture of both
`top'
The distance from the left border of container to left border of
the object in same format.
`width'
The width of object in same format.
`height'
The height of object in same format.
`id'
The identifier for the component. This can be any arbitrary
string. The ID can be used by scripts to refer to various
components in the GUI component tree. Currently, there is one
special ID value that GRUB recognizes:
"__timeout__" Any component with this ID will have its
*text*, *start*, *end*, *value*, and *visible*
properties set by GRUB when it is counting
down to an automatic boot of the default menu
entry.

File: grub.info, Node: Network, Next: Serial terminal, Prev: Theme file format, Up: Top
7 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-pxe --output=grub.pxe --prefix='(pxe)/boot/grub' pxe pxecmd
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).
You can also use the `grub-mknetdir' utility to generate an image
and a GRUB directory tree, rather than copying files around manually.
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:
`net_pxe_ip'
The IP address of this machine. Read-only.
`net_pxe_mac'
The network interface's MAC address. Read-only.
`net_pxe_hostname'
The client host name provided by DHCP. Read-only.
`net_pxe_domain'
The client domain name provided by DHCP. Read-only.
`net_pxe_rootpath'
The path to the client's root disk provided by DHCP. Read-only.
`net_pxe_extensionspath'
The path to additional DHCP vendor extensions provided by DHCP.
Read-only.
`net_pxe_boot_file'
The boot file name provided by DHCP. Read-only.
`net_pxe_dhcp_server_name'
The name of the DHCP server responsible for these boot parameters.
Read-only.
`net_default_server'
The default server. Read-write, although setting this is only
useful before opening a network device.

File: grub.info, Node: Serial terminal, Next: Vendor power-on keys, Prev: Network, Up: Top
8 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
information.
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_input 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
command.
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: grub.info, Node: Vendor power-on keys, Next: Images, Prev: Serial terminal, Up: Top
9 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_DEFAULT_BUTTON', `GRUB_HIDDEN_TIMEOUT_BUTTON' and
`GRUB_BUTTON_CMOS_ADDRESS' variables in default/grub (*note Simple
configuration::). `GRUB_TIMEOUT_BUTTON', `GRUB_DEFAULT_BUTTON' and
`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>
85:3
<Asus EeePC 1005PE>
84:1 (unconfirmed)
To take full advantage of this function, install GRUB into the MBR
(*note Installing GRUB using grub-install::).
If you have a laptop which has a similar feature and not in the
above list could you figure your address and contribute? To discover
the address do the following:
* boot normally
* sudo modprobe nvram
sudo cat /dev/nvram | xxd > normal_button.txt
* boot using vendor button
* sudo modprobe nvram
sudo cat /dev/nvram | xxd > normal_vendor.txt
Then compare these text files and find where a bit was toggled. E.g.
in case of Dell XPS it was:
byte 0x47: 20 --> 28
It's a bit number 3 as seen from following table:
0 01
1 02
2 04
3 08
4 10
5 20
6 40
7 80
0x47 is decimal 71. Linux nvram implementation cuts first 14 bytes of
CMOS. So the real byte address in CMOS is 71+14=85 So complete address
is 85:3

File: grub.info, Node: Images, Next: Filesystem, Prev: Vendor power-on keys, Up: Top
10 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.
`boot.img'
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.
`diskboot.img'
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.
`cdboot.img'
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
`diskboot.img'.
`pxeboot.img'
This image is used as the start of the core image when booting
from the network using PXE. *Note Network::.
`lnxboot.img'
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.
`kernel.img'
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.
`core.img'
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.
*Note BIOS installation::, for details on where the core image can
be installed on PC systems.
`*.mod'
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.
`stage1'
Stage 1 from GRUB Legacy was very similar to `boot.img' in GRUB 2,
and they serve the same function.
`*_stage1_5'
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.
`stage2'
GRUB 2 has no single Stage 2 image. Instead, it loads modules from
`/boot/grub' at run-time.
`stage2_eltorito'
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.
`nbgrub'
There is as yet no equivalent for `nbgrub' in GRUB 2; it was used
by Etherboot and some other network boot loaders.
`pxegrub'
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: grub.info, Node: Filesystem, Next: Interface, Prev: Images, Up: Top
11 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
search::).
* Menu:
* Device syntax:: How to specify devices
* File name syntax:: How to specify files
* Block list syntax:: How to specify block lists

File: grub.info, Node: Device syntax, Next: File name syntax, Up: Filesystem
11.1 How to specify devices
===========================
The device syntax is like this:
`(DEVICE[,PARTMAP-NAME1PART-NUM1[,PARTMAP-NAME2PART-NUM2[,...]]])'
`[]' means the parameter is optional. DEVICE depends on the disk
driver in use. BIOS and EFI disks use either `fd' or `hd' followed by a
digit, like `fd0', or `cd'. AHCI, PATA (ata), crypto, USB use the name
of driver followed by a number. Memdisk and host are limited to one
disk and so it's refered just by driver name. RAID (md), ofdisk
(ieee1275 and nand), LVM (lv), LDM and arcdisk (arc) use intrinsic name
of disk prefixed by driver name. Additionally just "nand" refers to the
disk aliased as "nand". Conflicts are solved by suffixing a number if
necessarry. Commas need to be escaped. Loopback uses whatever name
specified to `loopback' command. Hostdisk uses names specified in
device.map as long as it's of the form [fhc]d[0-9]* or hostdisk/<OS
DEVICE>. For crypto and RAID (md) additionally you can use the syntax
<driver name>uuid/<uuid>.
(fd0)
(hd0)
(cd)
(ahci0)
(ata0)
(crypto0)
(usb0)
(cryptouuid/123456789abcdef0123456789abcdef0)
(mduuid/123456789abcdef0123456789abcdef0)
(lv/system-root)
(md/myraid)
(md/0)
(ieee1275/disk2)
(ieee1275//pci@1f\,0/ide@d/disk@2)
(nand)
(memdisk)
(host)
(myloop)
(hostdisk//dev/sda)
PART-NUM represents the partition number of DEVICE, starting from
one. PARTNAME is optional but is recommended since disk may have
several top-level partmaps. Specifying third and later component you
can access to subpartitions.
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).
(hd0,msdos1)
(hd0,msdos1,msdos5)
(hd0,msdos1,bsd3)
(hd0,netbsd1)
(hd0,gpt1)
(hd0,1,3)
If you enabled the network support, the special drives `(tftp)',
`(http)' and so on ars 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: grub.info, Node: File name syntax, Next: Block list syntax, Prev: Device syntax, Up: Filesystem
11.2 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: grub.info, Node: Block list syntax, Prev: File name syntax, Up: Filesystem
11.3 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:
`0+100,200+1,300+300'
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: grub.info, Node: Interface, Next: Environment, Prev: Filesystem, Up: Top
12 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: grub.info, Node: Command-line interface, Next: Menu interface, Up: Interface
12.1 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:
<C-f>
<PC right key>
Move forward one character.
<C-b>
<PC left key>
Move back one character.
<C-a>
<HOME>
Move to the start of the line.
<C-e>
<END>
Move the the end of the line.
<C-d>
<DEL>
Delete the character underneath the cursor.
<C-h>
<BS>
Delete the character to the left of the cursor.
<C-k>
Kill the text from the current cursor position to the end of the
line.
<C-u>
Kill backward from the cursor to the beginning of the line.
<C-y>
Yank the killed text back into the buffer at the cursor.
<C-p>
<PC up key>
Move up through the history list.
<C-n>
<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: grub.info, Node: Command-line interface-Footnotes, Up: Command-line interface
(1) However, this behavior will be changed in the future version, in
a user-invisible way.

File: grub.info, Node: Menu interface, Next: Menu entry editor, Prev: Command-line interface, Up: Interface
12.2 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: grub.info, Node: Menu entry editor, Prev: Menu interface, Up: Interface
12.3 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: grub.info, Node: Environment, Next: Commands, Prev: Interface, Up: Top
13 GRUB environment variables
*****************************
GRUB supports environment variables which are rather like those offered
by all Unix-like systems. Environment variables have a name, which is
unique and is usually a short identifier, and a value, which is an
arbitrary string of characters. They may be set (*note set::), unset
(*note unset::), or looked up (*note Shell-like scripting::) by name.
A number of environment variables have special meanings to various
parts of GRUB. Others may be used freely in GRUB configuration files.
* Menu:
* Special environment variables::
* Environment block::

File: grub.info, Node: Special environment variables, Next: Environment block, Up: Environment
13.1 Special environment variables
==================================
These variables have special meaning to GRUB.
* Menu:
* biosnum::
* chosen::
* color_highlight::
* color_normal::
* debug::
* default::
* fallback::
* gfxmode::
* gfxpayload::
* gfxterm_font::
* icondir::
* lang::
* locale_dir::
* menu_color_highlight::
* menu_color_normal::
* net_pxe_boot_file::
* net_pxe_dhcp_server_name::
* net_pxe_domain::
* net_pxe_extensionspath::
* net_pxe_hostname::
* net_pxe_ip::
* net_pxe_mac::
* net_pxe_rootpath::
* pager::
* prefix::
* pxe_blksize::
* pxe_default_gateway::
* pxe_default_server::
* root::
* superusers::
* theme::
* timeout::

File: grub.info, Node: biosnum, Next: chosen, Up: Special environment variables
13.1.1 biosnum
--------------
When chain-loading another boot loader (*note Chain-loading::), GRUB may
need to know what BIOS drive number corresponds to the root device
(*note root::) so that it can set up registers properly. If the
BIOSNUM variable is set, it overrides GRUB's own means of guessing this.
For an alternative approach which also changes BIOS drive mappings
for the chain-loaded system, *note drivemap::.

File: grub.info, Node: chosen, Next: color_highlight, Prev: biosnum, Up: Special environment variables
13.1.2 chosen
-------------
When executing a menu entry, GRUB sets the CHOSEN variable to the title
of the entry being executed.
If the menu entry is in one or more submenus, then CHOSEN is set to
the titles of each of the submenus starting from the top level followed
by the title of the menu entry itself, separated by `>'.

File: grub.info, Node: color_highlight, Next: color_normal, Prev: chosen, Up: Special environment variables
13.1.3 color_highlight
----------------------
This variable contains the "highlight" foreground and background
terminal colors, separated by a slash (`/'). Setting this variable
changes those colors. For the available color names, *note
color_normal::.
The default is `black/white'.

File: grub.info, Node: color_normal, Next: debug, Prev: color_highlight, Up: Special environment variables
13.1.4 color_normal
-------------------
This variable contains the "normal" foreground and background terminal
colors, separated by a slash (`/'). Setting this variable changes
those colors. Each color must be a name from the following list:
* black
* blue
* green
* cyan
* red
* magenta
* brown
* light-gray
* dark-gray
* light-blue
* light-green
* light-cyan
* light-red
* light-magenta
* yellow
* white
The default is `white/black'.

File: grub.info, Node: debug, Next: default, Prev: color_normal, Up: Special environment variables
13.1.5 debug
------------
This variable may be set to enable debugging output from various
components of GRUB. The value is a list of debug facility names
separated by whitespace or `,', or `all' to enable all available
debugging output.

File: grub.info, Node: default, Next: fallback, Prev: debug, Up: Special environment variables
13.1.6 default
--------------
If this variable is set, it identifies a menu entry that should be
selected by default, possibly after a timeout (*note timeout::). The
entry may be identified by number or by title.
If the entry is in a submenu, then it must be identified using the
titles of each of the submenus starting from the top level followed by
the number or title of the menu entry itself, separated by `>'. For
example, take the following menu structure:
Submenu 1
Menu Entry 1
Menu Entry 2
Submenu 2
Submenu 3
Menu Entry 3
Menu Entry 4
Menu Entry 5
"Menu Entry 3" would then be identified as `Submenu 2>Submenu 3>Menu
Entry 3'.
This variable is often set by `GRUB_DEFAULT' (*note Simple
configuration::), `grub-set-default', or `grub-reboot'.

File: grub.info, Node: fallback, Next: gfxmode, Prev: default, Up: Special environment variables
13.1.7 fallback
---------------
If this variable is set, it identifies a menu entry that should be
selected if the default menu entry fails to boot. Entries are
identified in the same way as for `default' (*note default::).

File: grub.info, Node: gfxmode, Next: gfxpayload, Prev: fallback, Up: Special environment variables
13.1.8 gfxmode
--------------
If this variable is set, it sets 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
`auto', which selects a platform-specific default that should look
reasonable.
The resolution may be specified as a sequence of one or more modes,
separated by commas (`,') or semicolons (`;'); each will be tried in
turn until one is found. Each mode should be either `auto',
`WIDTHxHEIGHT', or `WIDTHxHEIGHTxDEPTH'.

File: grub.info, Node: gfxpayload, Next: gfxterm_font, Prev: gfxmode, Up: Special environment variables
13.1.9 gfxpayload
-----------------
If this variable is set, it controls the video mode in which the Linux
kernel starts up, replacing the `vga=' boot option (*note linux::). It
may be set to `text' to force the Linux kernel to boot in normal text
mode, `keep' to preserve the graphics mode set using `gfxmode', or any
of the permitted values for `gfxmode' to set a particular graphics mode
(*note gfxmode::).
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 variable to
`text' and GRUB will tell Linux to boot in normal text mode.
The default is platform-specific. On platforms with a native text
mode (such as PC BIOS platforms), the default is `text'. Otherwise the
default may be `auto' or a specific video mode.
This variable is often set by `GRUB_GFXPAYLOAD_LINUX' (*note Simple
configuration::).

File: grub.info, Node: gfxterm_font, Next: icondir, Prev: gfxpayload, Up: Special environment variables
13.1.10 gfxterm_font
--------------------
If this variable is set, it names a font to use for text on the
`gfxterm' graphical terminal. Otherwise, `gfxterm' may use any
available font.

File: grub.info, Node: icondir, Next: lang, Prev: gfxterm_font, Up: Special environment variables
13.1.11 icondir
---------------
If this variable is set, it names a directory in which the GRUB
graphical menu should look for icons after looking in the theme's
`icons' directory. *Note Theme file format::.

File: grub.info, Node: lang, Next: locale_dir, Prev: icondir, Up: Special environment variables
13.1.12 lang
------------
If this variable is set, it names the language code that the `gettext'
command (*note gettext::) uses to translate strings. For example,
French would be named as `fr', and Simplified Chinese as `zh_CN'.
`grub-mkconfig' (*note Simple configuration::) will try to set a
reasonable default for this variable based on the system locale.

File: grub.info, Node: locale_dir, Next: menu_color_highlight, Prev: lang, Up: Special environment variables
13.1.13 locale_dir
------------------
If this variable is set, it names the directory where translation files
may be found (*note gettext::), usually `/boot/grub/locale'. Otherwise,
internationalization is disabled.
`grub-mkconfig' (*note Simple configuration::) will set a reasonable
default for this variable if internationalization is needed and any
translation files are available.

File: grub.info, Node: menu_color_highlight, Next: menu_color_normal, Prev: locale_dir, Up: Special environment variables
13.1.14 menu_color_highlight
----------------------------
This variable contains the foreground and background colors to be used
for the highlighted menu entry, separated by a slash (`/'). Setting
this variable changes those colors. For the available color names,
*note color_normal::.
The default is the value of `color_highlight' (*note
color_highlight::).

File: grub.info, Node: menu_color_normal, Next: net_pxe_boot_file, Prev: menu_color_highlight, Up: Special environment variables
13.1.15 menu_color_normal
-------------------------
This variable contains the foreground and background colors to be used
for non-highlighted menu entries, separated by a slash (`/'). Setting
this variable changes those colors. For the available color names,
*note color_normal::.
The default is the value of `color_normal' (*note color_normal::).

File: grub.info, Node: net_pxe_boot_file, Next: net_pxe_dhcp_server_name, Prev: menu_color_normal, Up: Special environment variables
13.1.16 net_pxe_boot_file
-------------------------
*Note Network::.

File: grub.info, Node: net_pxe_dhcp_server_name, Next: net_pxe_domain, Prev: net_pxe_boot_file, Up: Special environment variables
13.1.17 net_pxe_dhcp_server_name
--------------------------------
*Note Network::.

File: grub.info, Node: net_pxe_domain, Next: net_pxe_extensionspath, Prev: net_pxe_dhcp_server_name, Up: Special environment variables
13.1.18 net_pxe_domain
----------------------
*Note Network::.

File: grub.info, Node: net_pxe_extensionspath, Next: net_pxe_hostname, Prev: net_pxe_domain, Up: Special environment variables
13.1.19 net_pxe_extensionspath
------------------------------
*Note Network::.

File: grub.info, Node: net_pxe_hostname, Next: net_pxe_ip, Prev: net_pxe_extensionspath, Up: Special environment variables
13.1.20 net_pxe_hostname
------------------------
*Note Network::.

File: grub.info, Node: net_pxe_ip, Next: net_pxe_mac, Prev: net_pxe_hostname, Up: Special environment variables
13.1.21 net_pxe_ip
------------------
*Note Network::.

File: grub.info, Node: net_pxe_mac, Next: net_pxe_rootpath, Prev: net_pxe_ip, Up: Special environment variables
13.1.22 net_pxe_mac
-------------------
*Note Network::.

File: grub.info, Node: net_pxe_rootpath, Next: pager, Prev: net_pxe_mac, Up: Special environment variables
13.1.23 net_pxe_rootpath
------------------------
*Note Network::.

File: grub.info, Node: pager, Next: prefix, Prev: net_pxe_rootpath, Up: Special environment variables
13.1.24 pager
-------------
If set to `1', pause output after each screenful and wait for keyboard
input. The default is not to pause output.

File: grub.info, Node: prefix, Next: pxe_blksize, Prev: pager, Up: Special environment variables
13.1.25 prefix
--------------
The location of the `/boot/grub' directory as an absolute file name
(*note File name syntax::). This is normally set by GRUB at startup
based on information provided by `grub-install'. GRUB modules are
dynamically loaded from this directory, so it must be set correctly in
order for many parts of GRUB to work.

File: grub.info, Node: pxe_blksize, Next: pxe_default_gateway, Prev: prefix, Up: Special environment variables
13.1.26 pxe_blksize
-------------------
*Note Network::.

File: grub.info, Node: pxe_default_gateway, Next: pxe_default_server, Prev: pxe_blksize, Up: Special environment variables
13.1.27 pxe_default_gateway
---------------------------
*Note Network::.

File: grub.info, Node: pxe_default_server, Next: root, Prev: pxe_default_gateway, Up: Special environment variables
13.1.28 pxe_default_server
--------------------------
*Note Network::.

File: grub.info, Node: root, Next: superusers, Prev: pxe_default_server, Up: Special environment variables
13.1.29 root
------------
The root device name (*note Device syntax::). Any file names that do
not specify an explicit device name are read from this device. The
default is normally set by GRUB at startup based on the value of
`prefix' (*note prefix::).
For example, if GRUB was installed to the first partition of the
first hard disk, then `prefix' might be set to `(hd0,msdos1)/boot/grub'
and `root' to `hd0,msdos1'.

File: grub.info, Node: superusers, Next: theme, Prev: root, Up: Special environment variables
13.1.30 superusers
------------------
This variable may be set to a list of superuser names to enable
authentication support. *Note Security::.

File: grub.info, Node: theme, Next: timeout, Prev: superusers, Up: Special environment variables
13.1.31 theme
-------------
This variable may be set to a directory containing a GRUB graphical menu
theme. *Note Theme file format::.
This variable is often set by `GRUB_THEME' (*note Simple
configuration::).

File: grub.info, Node: timeout, Prev: theme, Up: Special environment variables
13.1.32 timeout
---------------
If this variable is set, it specifies the time in seconds to wait for
keyboard input before booting the default menu entry. A timeout of `0'
means to boot the default entry immediately without displaying the
menu; a timeout of `-1' (or unset) means to wait indefinitely.
This variable is often set by `GRUB_TIMEOUT' or
`GRUB_HIDDEN_TIMEOUT' (*note Simple configuration::).

File: grub.info, Node: Environment block, Prev: Special environment variables, Up: Environment
13.2 The GRUB environment block
===============================
It is often useful to be able to remember a small amount of information
from one boot to the next. For example, you might want to set the
default menu entry based on what was selected the last time. GRUB
deliberately does not implement support for writing files in order to
minimise the possibility of the boot loader being responsible for file
system corruption, so a GRUB configuration file cannot just create a
file in the ordinary way. However, GRUB provides an "environment
block" which can be used to save a small amount of state.
The environment block is a preallocated 1024-byte file, which
normally lives in `/boot/grub/grubenv' (although you should not assume
this). At boot time, the `load_env' command (*note load_env::) loads
environment variables from it, and the `save_env' (*note save_env::)
command saves environment variables to it. From a running system, the
`grub-editenv' utility can be used to edit the environment block.
For safety reasons, this storage is only available when installed on
a plain disk (no LVM or RAID), using a non-checksumming filesystem (no
ZFS), and using BIOS or EFI functions (no ATA, USB or IEEE1275).
`grub-mkconfig' uses this facility to implement `GRUB_SAVEDEFAULT'
(*note Simple configuration::).

File: grub.info, Node: Commands, Next: Internationalisation, Prev: Environment, Up: Top
14 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. If you end up in rescue mode and do not know what
to do, then *note GRUB only offers a rescue shell::.
* Menu:
* Menu-specific commands::
* General commands::
* Command-line and menu entry commands::

File: grub.info, Node: Menu-specific commands, Next: General commands, Up: Commands
14.1 The list of commands for the menu only
===========================================
The semantics used in parsing the configuration file are the following:
* 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.
These commands can only be used in the menu:
* Menu:
* menuentry:: Start a menu entry
* submenu:: Group menu entries

File: grub.info, Node: menuentry, Next: submenu, Up: Menu-specific commands
14.1.1 menuentry
----------------
-- Command: menuentry TITLE [`--class=class' ...] [`--users=users']
[`--unrestricted'] [`--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 `--unrestricted' option grants all 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: grub.info, Node: submenu, Prev: menuentry, Up: Menu-specific commands
14.1.2 submenu
--------------
-- Command: submenu TITLE [`--class=class' ...] [`--users=users']
[`--unrestricted'] [`--hotkey=key'] { MENU ENTRIES ... }
This defines a submenu. An entry called TITLE will be added to the
menu; when that entry is selected, a new menu will be displayed
showing all the entries within this submenu.
All options are the same as in the `menuentry' command (*note
menuentry::).

File: grub.info, Node: General commands, Next: Command-line and menu entry commands, Prev: Menu-specific commands, Up: Commands
14.2 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: grub.info, Node: serial, Next: terminal_input, Up: General commands
14.2.1 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::).
See also *note Serial terminal::.

File: grub.info, Node: terminal_input, Next: terminal_output, Prev: serial, Up: General commands
14.2.2 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: grub.info, Node: terminal_output, Next: terminfo, Prev: terminal_input, Up: General commands
14.2.3 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: grub.info, Node: terminfo, Prev: terminal_output, Up: General commands
14.2.4 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
GRUB.
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: grub.info, Node: Command-line and menu entry commands, Prev: General commands, Up: Commands
14.3 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
* false:: Do nothing, unsuccessfully
* 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)
* list_env:: List variables in environment block
* load_env:: Load variables from environment block
* loopback:: Make a device from a filesystem image
* ls:: List devices or files
* normal:: Enter normal mode
* normal_exit:: Exit from normal mode
* 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
* read:: Read user input
* reboot:: Reboot your computer
* save_env:: Save variables to environment block
* search:: Search devices by file, label, or UUID
* sendkey:: Emulate keystrokes
* set:: Set an environment variable
* true:: Do nothing, successfully
* unset:: Unset an environment variable
* uppermem:: Set the upper memory size

File: grub.info, Node: acpi, Next: badram, Up: Command-line and menu entry commands
14.3.1 acpi
-----------
-- Command: acpi [`-1'|`-2']
[`--exclude=table1,...'|`--load-only=table1,...']
[`--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: grub.info, Node: badram, Next: blocklist, Prev: acpi, Up: Command-line and menu entry commands
14.3.2 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
(http://www.memtest.org/): 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: grub.info, Node: blocklist, Next: boot, Prev: badram, Up: Command-line and menu entry commands
14.3.3 blocklist
----------------
-- Command: blocklist file
Print a block list (*note Block list syntax::) for FILE.

File: grub.info, Node: boot, Next: cat, Prev: blocklist, Up: Command-line and menu entry commands
14.3.4 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: grub.info, Node: cat, Next: chainloader, Prev: boot, Up: Command-line and menu entry commands
14.3.5 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: grub.info, Node: chainloader, Next: cmp, Prev: cat, Up: Command-line and menu entry commands
14.3.6 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: grub.info, Node: cmp, Next: configfile, Prev: chainloader, Up: Command-line and menu entry commands
14.3.7 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: grub.info, Node: configfile, Next: cpuid, Prev: cmp, Up: Command-line and menu entry commands
14.3.8 configfile
-----------------
-- Command: configfile file
Load FILE as a configuration file. If FILE defines any menu
entries, then show a menu containing them immediately.

File: grub.info, Node: cpuid, Next: crc, Prev: configfile, Up: Command-line and menu entry commands
14.3.9 cpuid
------------
-- Command: cpuid [-l]
Check for CPU features. This command is only available on x86
systems.
With the `-l' option, return true if the CPU supports long mode
(64-bit).
If invoked without options, this command currently behaves as if
it had been invoked with `-l'. This may change in the future.

File: grub.info, Node: crc, Next: date, Prev: cpuid, Up: Command-line and menu entry commands
14.3.10 crc
-----------
-- Command: crc file
Display the CRC32 checksum of FILE.

File: grub.info, Node: date, Next: drivemap, Prev: crc, Up: Command-line and menu entry commands
14.3.11 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
unchanged.

File: grub.info, Node: drivemap, Next: echo, Prev: date, Up: Command-line and menu entry commands
14.3.12 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: grub.info, Node: echo, Next: export, Prev: drivemap, Up: Command-line and menu entry commands
14.3.13 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:
`\\'
backslash
`\a'
alert (BEL)
`\c'
suppress trailing new line
`\f'
form feed
`\n'
new line
`\r'
carriage return
`\t'
horizontal tab
`\v'
vertical tab
When interpreting backslash escapes, backslash followed by any
other character will print that character.

File: grub.info, Node: export, Next: false, Prev: echo, Up: Command-line and menu entry commands
14.3.14 export
--------------
-- Command: export envvar
Export the environment variable ENVVAR. Exported variables are
visible to subsidiary configuration files loaded using
`configfile'.

File: grub.info, Node: false, Next: gettext, Prev: export, Up: Command-line and menu entry commands
14.3.15 false
-------------
-- Command: false
Do nothing, unsuccessfully. This is mainly useful in control
constructs such as `if' and `while' (*note Shell-like scripting::).

File: grub.info, Node: gettext, Next: gptsync, Prev: false, Up: Command-line and menu entry commands
14.3.16 gettext
---------------
-- Command: gettext string
Translate STRING into the current language.
The current language code is stored in the `lang' variable in
GRUB's environment (*note lang::). Translation files in MO format
are read from `locale_dir' (*note locale_dir::), usually
`/boot/grub/locale'.

File: grub.info, Node: gptsync, Next: halt, Prev: gettext, Up: Command-line and menu entry commands
14.3.17 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: grub.info, Node: halt, Next: help, Prev: gptsync, Up: Command-line and menu entry commands
14.3.18 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: grub.info, Node: help, Next: initrd, Prev: halt, Up: Command-line and menu entry commands
14.3.19 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: grub.info, Node: initrd, Next: initrd16, Prev: help, Up: Command-line and menu entry commands
14.3.20 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: grub.info, Node: initrd16, Next: insmod, Prev: initrd, Up: Command-line and menu entry commands
14.3.21 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: grub.info, Node: insmod, Next: keystatus, Prev: initrd16, Up: Command-line and menu entry commands
14.3.22 insmod
--------------
-- Command: insmod module
Insert the dynamic GRUB module called MODULE.

File: grub.info, Node: keystatus, Next: linux, Prev: insmod, Up: Command-line and menu entry commands
14.3.23 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: grub.info, Node: linux, Next: linux16, Prev: keystatus, Up: Command-line and menu entry commands
14.3.24 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: grub.info, Node: linux16, Next: list_env, Prev: linux, Up: Command-line and menu entry commands
14.3.25 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
initrd16::).
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: grub.info, Node: list_env, Next: load_env, Prev: linux16, Up: Command-line and menu entry commands
14.3.26 list_env
----------------
-- Command: list_env [`-f' file]
List all variables in the environment block file. *Note
Environment block::.
The `-f' option overrides the default location of the environment
block.

File: grub.info, Node: load_env, Next: loopback, Prev: list_env, Up: Command-line and menu entry commands
14.3.27 load_env
----------------
-- Command: load_env [`-f' file]
Load all variables from the environment block file into the
environment. *Note Environment block::.
The `-f' option overrides the default location of the environment
block.

File: grub.info, Node: loopback, Next: ls, Prev: load_env, Up: Command-line and menu entry commands
14.3.28 loopback
----------------
-- Command: loopback [`-d'] device file
Make the device named DEVICE correspond to the contents of the
filesystem image in FILE. For example:
loopback loop0 /path/to/image
ls (loop0)/
With the `-d' option, delete a device previously created using this
command.

File: grub.info, Node: ls, Next: normal, Prev: loopback, Up: Command-line and menu entry commands
14.3.29 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
directory.

File: grub.info, Node: normal, Next: normal_exit, Prev: ls, Up: Command-line and menu entry commands
14.3.30 normal
--------------
-- Command: normal [file]
Enter normal mode and display the GRUB menu.
In normal mode, commands, filesystem modules, and cryptography
modules are automatically loaded, and the full GRUB script parser
is available. Other modules may be explicitly loaded using
`insmod' (*note insmod::).
If a FILE is given, then commands will be read from that file.
Otherwise, they will be read from `$prefix/grub.cfg' if it exists.
`normal' may be called from within normal mode, creating a nested
environment. It is more usual to use `configfile' (*note
configfile::) for this.

File: grub.info, Node: normal_exit, Next: parttool, Prev: normal, Up: Command-line and menu entry commands
14.3.31 normal_exit
-------------------
-- Command: normal_exit
Exit normal mode (*note normal::). If this instance of normal
mode was not nested within another one, then return to rescue mode.

File: grub.info, Node: parttool, Next: password, Prev: normal_exit, Up: Command-line and menu entry commands
14.3.32 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
`COMMAND=VALUE'.
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_
partitions.
`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
hexadecimal).
`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
DOS/Windows::.

File: grub.info, Node: password, Next: password_pbkdf2, Prev: parttool, Up: Command-line and menu entry commands
14.3.33 password
----------------
-- Command: password user clear-password
Define a user named USER with password CLEAR-PASSWORD. *Note
Security::.

File: grub.info, Node: password_pbkdf2, Next: play, Prev: password, Up: Command-line and menu entry commands
14.3.34 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: grub.info, Node: play, Next: pxe_unload, Prev: password_pbkdf2, Up: Command-line and menu entry commands
14.3.35 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: grub.info, Node: pxe_unload, Next: read, Prev: play, Up: Command-line and menu entry commands
14.3.36 pxe_unload
------------------
-- Command: pxe_unload
Unload the PXE environment (*note Network::).
This command is only available on PC BIOS systems.

File: grub.info, Node: read, Next: reboot, Prev: pxe_unload, Up: Command-line and menu entry commands
14.3.37 read
------------
-- Command: read [var]
Read a line of input from the user. If an environment variable
VAR is given, set that environment variable to the line of input
that was read, with no terminating newline.

File: grub.info, Node: reboot, Next: save_env, Prev: read, Up: Command-line and menu entry commands
14.3.38 reboot
--------------
-- Command: reboot
Reboot the computer.

File: grub.info, Node: save_env, Next: search, Prev: reboot, Up: Command-line and menu entry commands
14.3.39 save_env
----------------
-- Command: save_env [`-f' file] var ...
Save the named variables from the environment to the environment
block file. *Note Environment block::.
The `-f' option overrides the default location of the environment
block.

File: grub.info, Node: search, Next: sendkey, Prev: save_env, Up: Command-line and menu entry commands
14.3.40 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: grub.info, Node: sendkey, Next: set, Prev: search, Up: Command-line and menu entry commands
14.3.41 sendkey
---------------
-- Command: sendkey [`--num'|`--caps'|`--scroll'|`--insert'|
`--pause'|`--left-shift'|`--right-shift'|
`--sysrq'|`--numkey'|`--capskey'|`--scrollkey'|
`--insertkey'|`--left-alt'|`--right-alt'|
`--left-ctrl'|`--right-ctrl' `on'|`off']... [`no-led']
keystroke
Insert keystrokes into the keyboard buffer when booting.
Sometimes an operating system or chainloaded boot loader requires
particular keys to be pressed: for example, one might need to
press a particular key to enter "safe mode", or when chainloading
another boot loader one might send keystrokes to it to navigate
its menu.
You may provide up to 16 keystrokes (the length of the BIOS
keyboard buffer). Keystroke names may be upper-case or lower-case
letters, digits, or taken from the following table:
Name Key
---------------------------------------------------------------
escape Escape
exclam !
at @
numbersign #
dollar $
percent %
caret ^
ampersand &
asterisk *
parenleft (
parenright )
minus -
underscore _
equal =
plus +
backspace Backspace
tab Tab
bracketleft [
braceleft {
bracketright ]
braceright }
enter Enter
control press and release Control
semicolon ;
colon :
quote '
doublequote "
backquote `
tilde ~
shift press and release left Shift
backslash \
bar |
comma ,
less <
period .
greater >
slash /
question ?
rshift press and release right Shift
alt press and release Alt
space space bar
capslock Caps Lock
F1 F1
F2 F2
F3 F3
F4 F4
F5 F5
F6 F6
F7 F7
F8 F8
F9 F9
F10 F10
F11 F11
F12 F12
num1 1 (numeric keypad)
num2 2 (numeric keypad)
num3 3 (numeric keypad)
num4 4 (numeric keypad)
num5 5 (numeric keypad)
num6 6 (numeric keypad)
num7 7 (numeric keypad)
num8 8 (numeric keypad)
num9 9 (numeric keypad)
num0 0 (numeric keypad)
numperiod . (numeric keypad)
numend End (numeric keypad)
numdown Down (numeric keypad)
numpgdown Page Down (numeric keypad)
numleft Left (numeric keypad)
numcenter 5 with Num Lock inactive (numeric
keypad)
numright Right (numeric keypad)
numhome Home (numeric keypad)
numup Up (numeric keypad)
numpgup Page Up (numeric keypad)
numinsert Insert (numeric keypad)
numdelete Delete (numeric keypad)
numasterisk * (numeric keypad)
numminus - (numeric keypad)
numplus + (numeric keypad)
numslash / (numeric keypad)
numenter Enter (numeric keypad)
delete Delete
insert Insert
home Home
end End
pgdown Page Down
pgup Page Up
down Down
up Up
left Left
right Right
As well as keystrokes, the `sendkey' command takes various options
that affect the BIOS keyboard status flags. These options take an
`on' or `off' parameter, specifying that the corresponding status
flag be set or unset; omitting the option for a given status flag
will leave that flag at its initial state at boot. The `--num',
`--caps', `--scroll', and `--insert' options emulate setting the
corresponding mode, while the `--numkey', `--capskey',
`--scrollkey', and `--insertkey' options emulate pressing and
holding the corresponding key. The other status flag options are
self-explanatory.
If the `--no-led' option is given, the status flag options will
have no effect on keyboard LEDs.
If the `sendkey' command is given multiple times, then only the
last invocation has any effect.
Since `sendkey' manipulates the BIOS keyboard buffer, it may cause
hangs, reboots, or other misbehaviour on some systems. If the
operating system or boot loader that runs after GRUB uses its own
keyboard driver rather than the BIOS keyboard functions, then
`sendkey' will have no effect.
This command is only available on PC BIOS systems.

File: grub.info, Node: set, Next: true, Prev: sendkey, Up: Command-line and menu entry commands
14.3.42 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: grub.info, Node: true, Next: unset, Prev: set, Up: Command-line and menu entry commands
14.3.43 true
------------
-- Command: true
Do nothing, successfully. This is mainly useful in control
constructs such as `if' and `while' (*note Shell-like scripting::).

File: grub.info, Node: unset, Next: uppermem, Prev: true, Up: Command-line and menu entry commands
14.3.44 unset
-------------
-- Command: unset envvar
Unset the environment variable ENVVAR.

File: grub.info, Node: uppermem, Prev: unset, Up: Command-line and menu entry commands
14.3.45 uppermem
----------------
This command is not yet implemented for GRUB 2, although it is planned.

File: grub.info, Node: Internationalisation, Next: Security, Prev: Commands, Up: Top
15 Charset
**********
GRUB uses UTF-8 internally other than in rendering where some
GRUB-specific appropriate representation is used. All text files
(including config) are assumed to be encoded in UTF-8.
16 Filesystems
**************
NTFS, JFS, UDF, HFS+, exFAT, long filenames in FAT, Joliet part of
ISO9660 are treated as UTF-16 as per specification. AFS and BFS are read
as UTF-8, again according to specification. BtrFS, cpio, tar, squash4,
minix, minix2, minix3, ROMFS, ReiserFS, XFS, ext2, ext3, ext4, FAT
(short names), RockRidge part of ISO9660, nilfs2, UFS1, UFS2 and ZFS
are assumed to be UTF-8. This might be false on systems configured with
legacy charset but as long as the charset used is superset of ASCII you
should be able to access ASCII-named files. And it's recommended to
configure your system to use UTF-8 to access the filesystem, convmv may
help with migration. ISO9660 (plain) filenames are specified as being
ASCII or being described with unspecified escape sequences. GRUB
assumes that the ISO9660 names are UTF-8 (since any ASCII is valid
UTF-8). There are some old CD-ROMs which use CP437 in non-compliant
way. You're still able to access files with names containing only ASCII
characters on such filesystems though. You're also able to access any
file if the filesystem contains valid Joliet (UTF-16) or RockRidge
(UTF-8). AFFS, SFS and HFS never use unicode and GRUB assumes them to
be in Latin1, Latin1 and MacRoman respectively. GRUB handles filesystem
case-insensitivity however no attempt is performed at case conversion
of international characters so e.g. a file named lowercase greek alpha
is treated as different from the one named as uppercase alpha. The
filesystems in questions are NTFS (except POSIX namespace), HFS+
(configurable at mkfs time, default insensitive), SFS (configurable at
mkfs time, default insensitive), JFS (configurable at mkfs time,
default sensitive), HFS, AFFS, FAT, exFAT and ZFS (configurable on
per-subvolume basis by property "casesensitivity", default sensitive).
On ZFS subvolumes marked as case insensitive files containing lowercase
international characters are inaccessible. Also like all supported
filesystems except HFS+ and ZFS (configurable on per-subvolume basis by
property "normalization", default none) GRUB makes no attempt at check
of canonical equivalence so a file name u-diaresis is treated as
distinct from u+combining diaresis. This however means that in order to
access file on HFS+ its name must be specified in normalisation form D.
On normalized ZFS subvolumes filenames out of normalisation are
inaccessible.
17 Output terminal
******************
Firmware output console "console" on ARC and IEEE1275 are limited to
ASCII. BIOS firmware console and VGA text are limited to ASCII and
some pseudographics. None of above mentioned is appropriate for
displaying international and any unsupported character is replaced with
question mark except pseudographics which we attempt to approximate
with ASCII. EFI console on the other hand nominally supports UTF-16 but
actual language coverage depends on firmware and may be very limited.
The encoding used on serial can be chosen with `terminfo' as either
ASCII, UTF-8 or "visual UTF-8". Last one is against the specification
but results in correct rendering of right-to-left on some readers which
don't have own bidi implementation. When using gfxterm or gfxmenu GRUB
itself is responsible for rendering the text. In this case GRUB is
limited by loaded fonts. If fonts contain all required characters then
bidirectional text, cursive variants and combining marks other than
enclosing, half (e.g. left half tilde or combining overline) and double
ones. Ligatures aren't supported though. This should cover European,
Middle Eastern (if you don't mind lack of lam-alif ligature in Arabic)
and East Asian scripts. Notable unsupported scripts are Brahmic family
and derived as well as Mongolian, Tifinagh, Korean Jamo (precomposed
characters have no problem) and tonal writing (2e5-2e9). GRUB also
ignores deprecated (as specified in Unicode) characters (e.g. tags).
GRUB also doesn't handle so called "annotation characters" If you can
complete either of two lists or, better, propose a patch to improve
rendering, please contact developper team.
18 Input terminal
*****************
Firmware console on BIOS, IEEE1275 and ARC doesn't allow you to enter
non-ASCII characters. EFI specification allows for such but author is
unaware of any actual implementations. Serial input is currently
limited for latin1 (unlikely to change). Own keyboard implementations
(at_keyboard and usb_keyboard) supports any key but work on
one-char-per-keystroke. So no dead keys or advanced input method. Also
there is no keymap change hotkey. In practice it makes difficult to
enter any text using non-Latin alphabet. Moreover all current input
consumers are limited to ASCII.
19 Gettext
**********
GRUB supports being translated. For this you need to have language *.mo
files in $prefix/locale, load gettext module and set "lang" variable.
20 Regexp
*********
Regexps work on unicode characters, however no attempt at checking
cannonical equivalence has been made. Moreover the classes like
[:alpha:] match only ASCII subset.
21 Other
********
Currently GRUB always uses YEAR-MONTH-DAY HOUR:MINUTE:SECOND [WEEKDAY]
24-hour datetime format but weekdays are translated. GRUB always uses
the decimal number format with [0-9] as digits and . as descimal
separator and no group separator. IEEE1275 aliases are matched
case-insensitively except non-ASCII which is matched as binary. Similar
behaviour is for matching OSBundleRequired. Since IEEE1275 aliases and
OSBundleRequired don't contain any non-ASCII it should never be a
problem in practice. Case-sensitive identifiers are matched as raw
strings, no canonical equivalence check is performed. Case-insenstive
identifiers are matched as RAW but additionally [a-z] is equivalent to
[A-Z]. GRUB-defined identifiers use only ASCII and so should
user-defined ones. Identifiers containing non-ASCII may work but
aren't supported. Only the ASCII space characters (space U+0020, tab
U+000b, CR U+000d and LF U+000a) are recognised. Other unicode space
characters aren't a valid field separator. `test' tests <, >, <=, >=,
-pgt and -plt compare the strings in the lexicographical order of
unicode codepoints, replicating the behaviour of test from coreutils.
environment variables and commands are listed in the same order.

File: grub.info, Node: Security, Next: Platform limitations, Prev: Internationalisation, Up: Top
22 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 `--unrestricted'
option is used for a menu entry, then that entry is unrestricted. If
the `--users' option is not used for a menu entry, then that only
superusers are able to use it.
Putting this together, a typical `grub.cfg' fragment might look like
this:
set superusers="root"
password_pbkdf2 root grub.pbkdf2.sha512.10000.biglongstring
password user1 insecure
menuentry "May be run by any user" --unrestricted {
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: grub.info, Node: Platform limitations, Next: Platform-specific operations, Prev: Security, Up: Top
23 Platform limitations
***********************
GRUB2 is designed to be portable and is actually ported across
platforms. We try to keep all platforms at the level. Unfortunately
some platforms are better supported than others. This is detailed in
current and 2 following sections.
ARC platform is unable to change datetime (firmware doesn't seem to
provide a function for it). EMU has similar limitation.
ARC platform no serial port is available. EMU has similar
limitation.
Console charset refers only to firmware-assisted console. gfxterm is
always Unicode (see Internationalisation section for its limitations).
Serial is configurable to UTF-8 or ASCII (see Internationalisation). In
case of qemu and coreboot ports the refered console is vga_text.
Loongson always uses gfxterm.
Most limited one is ASCII. CP437 provides additionally
pseudographics. GRUB2 doesn't use any language characters from CP437
as often CP437 is replaced by national encoding compatible only in
pseudographics. Unicode is the most versatile charset which supports
many languages. However the actual console may be much more limited
depending on firmware
On BIOS network is supported only if the image is loaded through
network. On sparc64 GRUB is unable to determine which server it was
booted from.
On platforms not having direct serial support (as indicated in the
line serial) you can still redirect firmware console to serial if it
allows so.
Direct ATA/AHCI support allows to circumvent various firmware
limitations but isn't needed for normal operation except on baremetal
ports.
AT keyboard support allows keyboard layout remapping and support for
keys not available through firmware. It isn't needed for normal
operation except baremetal ports.
USB support provides benefits similar to ATA (for USB disks) or AT
(for USB keyboards). In addition it allows USBserial.
Chainloading refers to the ability to load another bootloader
through the same protocol
Hints allow faster disk discovery by already knowing in advance
which is the disk in question. On some platforms hints are correct
unless you move the disk between boots. On other platforms it's just
an educated guess. Note that hint failure results in just reduced
performance, not a failure
BadRAM is the ability to mark some of the RAM as "bad". Note: due to
protocol limitations mips-loongson (with Linux protocol) and
mips-qemu_mips can use only memory up to first hole.
BIOS Coreboot Multiboot Qemu
video yes yes yes yes
console CP437 CP437 CP437 CP437
charset
network yes (*) no no no
ATA/AHCI yes yes yes yes
AT keyboard yes yes yes yes
USB yes yes yes yes
chainloader local yes yes no
cpuid partial partial partial partial
hints guess guess guess guess
PCI yes yes yes yes
badram yes yes yes yes
compression always pointless no no
exit yes no no no
ia32 EFI amd64 EFI ia32 IEEE1275 Itanium
video yes yes no no
console Unicode Unicode ASCII Unicode
charset
network yes yes yes yes
ATA/AHCI yes yes yes no
AT keyboard yes yes yes no
USB yes yes yes no
chainloader local local no local
cpuid partial partial partial no
hints guess guess good guess
PCI yes yes yes no
badram yes yes no yes
compression no no no no
exit yes yes yes yes
Loongson sparc64 Powerpc ARC
video yes no yes no
console N/A ASCII ASCII ASCII
charset
network no yes (*) yes no
ATA/AHCI yes no no no
AT keyboard yes no no no
USB yes no no no
chainloader yes no no no
cpuid no no no no
hints good good good no
PCI yes no no no
badram yes (*) no no no
compression configurable no no configurable
exit no yes yes yes
MIPS qemu emu
video no yes
console CP437 ASCII
charset
network no yes
ATA/AHCI yes no
AT keyboard yes no
USB N/A yes
chainloader yes no
cpuid no no
hints guess no
PCI no no
badram yes (*) no
compression configurable no
exit no yes

File: grub.info, Node: Platform-specific operations, Next: Supported kernels, Prev: Platform limitations, Up: Top
24 Outline
**********
Some platforms have features which allows to implement some commands
useless or not implementable on others.
Quick summary:
Information retrieval:
* mipsel-loongson: lsspd
* mips-arc: lsdev
* efi: lsefisystab, lssal, lsefimmap
* i386-pc: lsapm
* acpi-enabled (i386-pc, i386-coreboot, i386-multiboot, *-efi):
lsacpi
Workarounds for platform-specific issues:
* i386-efi/x86_64-efi: loadbios, fixvideo
* acpi-enabled (i386-pc, i386-coreboot, i386-multiboot, *-efi):
acpi (override ACPI tables)
* i386-pc: drivemap
* i386-pc: sendkey
Advanced operations for power users:
* x86: iorw (direct access to I/O ports)
Miscelaneous:
* cmos (x86-*, ieee1275, mips-qemu_mips, mips-loongson): cmostest
(used on some laptops to check for special power-on key)
* i386-pc: play

File: grub.info, Node: Supported kernels, Next: Troubleshooting, Prev: Platform-specific operations, Up: Top
25 Supported boot targets
*************************
X86 support is summarised in the following table. "Yes" means that the
kernel works on the given platform, "crashes" means an early kernel
crash which we hope will be fixed by concerned kernel developers. "no"
means GRUB doesn't load the given kernel on a given platform.
"headless" means that the kernel works but lacks console drivers (you
can still use serial or network console). In case of "no" and
"crashes" the reason is given in footnote.
BIOS Coreboot
BIOS chainloading yes no (1)
NTLDR yes no (1)
Plan9 yes no (1)
Freedos yes no (1)
FreeBSD bootloader yes crashes (1)
32-bit kFreeBSD yes crashes (2,6)
64-bit kFreeBSD yes crashes (2,6)
32-bit kNetBSD yes crashes (1)
64-bit kNetBSD yes crashes (2)
32-bit kOpenBSD yes yes
64-bit kOpenBSD yes yes
Multiboot yes yes
Multiboot2 yes yes
32-bit Linux (legacy protocol) yes no (1)
64-bit Linux (legacy protocol) yes no (1)
32-bit Linux (modern protocol) yes yes
64-bit Linux (modern protocol) yes yes
32-bit XNU yes ?
64-bit XNU yes ?
32-bit EFI chainloader no (3) no (3)
64-bit EFI chainloader no (3) no (3)
Appleloader no (3) no (3)
Multiboot Qemu
BIOS chainloading no (1) no (1)
NTLDR no (1) no (1)
Plan9 no (1) no (1)
FreeDOS no (1) no (1)
FreeBSD bootloader crashes (1) crashes (1)
32-bit kFreeBSD crashes (6) crashes (6)
64-bit kFreeBSD crashes (6) crashes (6)
32-bit kNetBSD crashes (1) crashes (1)
64-bit kNetBSD yes yes
32-bit kOpenBSD yes yes
64-bit kOpenBSD yes yes
Multiboot yes yes
Multiboot2 yes yes
32-bit Linux (legacy protocol) no (1) no (1)
64-bit Linux (legacy protocol) no (1) no (1)
32-bit Linux (modern protocol) yes yes
64-bit Linux (modern protocol) yes yes
32-bit XNU ? ?
64-bit XNU ? ?
32-bit EFI chainloader no (3) no (3)
64-bit EFI chainloader no (3) no (3)
Appleloader no (3) no (3)
ia32 EFI amd64 EFI
BIOS chainloading no (1) no (1)
NTLDR no (1) no (1)
Plan9 no (1) no (1)
FreeDOS no (1) no (1)
FreeBSD bootloader crashes (1) crashes (1)
32-bit kFreeBSD headless headless
64-bit kFreeBSD headless headless
32-bit kNetBSD crashes (1) crashes (1)
64-bit kNetBSD yes yes
32-bit kOpenBSD headless headless
64-bit kOpenBSD headless headless
Multiboot yes yes
Multiboot2 yes yes
32-bit Linux (legacy protocol) no (1) no (1)
64-bit Linux (legacy protocol) no (1) no (1)
32-bit Linux (modern protocol) yes yes
64-bit Linux (modern protocol) yes yes
32-bit XNU yes yes
64-bit XNU yes (5) yes
32-bit EFI chainloader yes no (4)
64-bit EFI chainloader no (4) yes
Appleloader yes yes
ia32 IEEE1275
BIOS chainloading no (1)
NTLDR no (1)
Plan9 no (1)
FreeDOS no (1)
FreeBSD bootloader crashes (1)
32-bit kFreeBSD crashes (6)
64-bit kFreeBSD crashes (6)
32-bit kNetBSD crashes (1)
64-bit kNetBSD ?
32-bit kOpenBSD ?
64-bit kOpenBSD ?
Multiboot ?
Multiboot2 ?
32-bit Linux (legacy protocol) no (1)
64-bit Linux (legacy protocol) no (1)
32-bit Linux (modern protocol) ?
64-bit Linux (modern protocol) ?
32-bit XNU ?
64-bit XNU ?
32-bit EFI chainloader no (3)
64-bit EFI chainloader no (3)
Appleloader no (3)
1. Requires BIOS
2. Crashes because the memory at 0x0-0x1000 isn't available
3. EFI only
4. 32-bit and 64-bit EFI have different structures and work in
different CPU modes so it's not possible to chainload 32-bit
bootloader on 64-bit platform and vice-versa
5. Some modules may need to be disabled
6. Requires ACPI
PowerPC, IA64 and Sparc64 ports support only Linux. MIPS port
supports Linux and multiboot2.
26 Boot tests
*************
As you have seen in previous chapter the support matrix is pretty big
and some of the configurations are only rarely used. To ensure the
quality bootchecks are available for all x86 targets except EFI
chainloader, Appleloader and XNU. All x86 platforms have bootcheck
facility except ieee1275. Multiboot, multiboot2, BIOS chainloader,
ntldr and freebsd-bootloader boot targets are tested only with a fake
kernel images. Only Linux is tested among the payloads using Linux
protocols.
Following variables must be defined:
GRUB_PAYLOADS_DIR directory containing the required kernels
GRUB_CBFSTOOL cbfstoll from Coreboot package (for coreboot
platform only)
GRUB_COREBOOT_ROM empty Coreboot ROM
GRUB_QEMU_OPTS additional options to be supplied to QEMU
Required files are:
kfreebsd_env.i386 32-bit kFreeBSD device hints
kfreebsd.i386 32-bit FreeBSD kernel image
kfreebsd.x86_64, same from 64-bit kFreeBSD
kfreebsd_env.x86_64
knetbsd.i386 32-bit NetBSD kernel image
knetbsd.miniroot.i386 32-bit kNetBSD miniroot.kmod.
knetbsd.x86_64, same from 64-bit kNetBSD
knetbsd.miniroot.x86_64
kopenbsd.i386 32-bit OpenBSD kernel bsd.rd image
kopenbsd.x86_64 same from 64-bit kOpenBSD
linux.i386 32-bit Linux
linux.x86_64 64-bit Linux

File: grub.info, Node: Troubleshooting, Next: Invoking grub-install, Prev: Supported kernels, Up: Top
27 Error messages produced by GRUB
**********************************
* Menu:
* GRUB only offers a rescue shell::

File: grub.info, Node: GRUB only offers a rescue shell, Up: Troubleshooting
27.1 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
(*note normal::). 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
# Find out which devices are available:
ls
# Set to the correct value, which might be something like this:
set prefix=(hd0,1)/grub
set root=(hd0,1)
insmod normal
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
remember:
* 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. `device.map' (*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: grub.info, Node: Invoking grub-install, Next: Invoking grub-mkconfig, Prev: Troubleshooting, Up: Top
28 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
name.
`grub-install' accepts the following options:
`--help'
Print a summary of the command-line options and exit.
`--version'
Print the version number of GRUB and exit.
`--boot-directory=DIR'
Install GRUB images under the directory `DIR/grub/' This option is
useful when you want to install GRUB into a separate partition or
a removable disk. If this option is not specified then it
defaults to `/boot', so
grub-install /dev/sda
is equivalent to
grub-install --boot-directory=/boot/ /dev/sda
Here is an example in which you have a separate "boot" partition
which is mounted on `/mnt/boot':
grub-install --boot-directory=/mnt/boot /dev/sdb
`--recheck'
Recheck the device map, even if `/boot/grub/device.map' already
exists. You should use this option whenever you add/remove a disk
into/from your computer.

File: grub.info, Node: Invoking grub-mkconfig, Next: Invoking grub-mkpasswd-pbkdf2, Prev: Invoking grub-install, Up: Top
29 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:
`--help'
Print a summary of the command-line options and exit.
`--version'
Print the version number of GRUB and exit.
`-o FILE'
`--output=FILE'
Send the generated configuration file to FILE. The default is to
send it to standard output.

File: grub.info, Node: Invoking grub-mkpasswd-pbkdf2, Next: Invoking grub-mkrescue, Prev: Invoking grub-mkconfig, Up: Top
30 Invoking grub-mkpasswd-pbkdf2
********************************
The program `grub-mkpasswd-pbkdf2' generates password hashes for GRUB
(*note Security::).
grub-mkpasswd-pbkdf2
`grub-mkpasswd-pbkdf2' accepts the following options:
`-c NUMBER'
`--iteration-count=NUMBER'
Number of iterations of the underlying pseudo-random function.
Defaults to 10000.
`-l NUMBER'
`--buflen=NUMBER'
Length of the generated hash. Defaults to 64.
`-s NUMBER'
`--salt=NUMBER'
Length of the salt. Defaults to 64.

File: grub.info, Node: Invoking grub-mkrescue, Next: Invoking grub-probe, Prev: Invoking grub-mkpasswd-pbkdf2, Up: Top
31 Invoking grub-mkrescue
*************************
The program `grub-mkrescue' generates a bootable GRUB rescue image
(*note Making a GRUB bootable CD-ROM::).
grub-mkrescue -o grub.iso
All arguments not explicitly listed as `grub-mkrescue' options are
passed on directly to `xorriso' in `mkisofs' emulation mode. Options
passed to `xorriso' will normally be interpreted as `mkisofs' options;
if the option `--' is used, then anything after that will be
interpreted as native `xorriso' options.
Non-option arguments specify additional source directories. This is
commonly used to add extra files to the image:
mkdir -p disk/boot/grub
(add extra files to `disk/boot/grub')
grub-mkrescue -o grub.iso disk
`grub-mkrescue' accepts the following options:
`--help'
Print a summary of the command-line options and exit.
`--version'
Print the version number of GRUB and exit.
`-o FILE'
`--output=FILE'
Save output in FILE. This "option" is required.
`--modules=MODULES'
Pre-load the named GRUB modules in the image. Multiple entries in
MODULES should be separated by whitespace (so you will probably
need to quote this for your shell).
`--rom-directory=DIR'
If generating images for the QEMU or Coreboot platforms, copy the
resulting `qemu.img' or `coreboot.elf' files respectively to the
DIR directory as well as including them in the image.
`--xorriso=FILE'
Use FILE as the `xorriso' program, rather than the built-in
default.
`--grub-mkimage=FILE'
Use FILE as the `grub-mkimage' program, rather than the built-in
default.

File: grub.info, Node: Invoking grub-probe, Next: Obtaining and Building GRUB, Prev: Invoking grub-mkrescue, Up: Top
32 Invoking grub-probe
**********************
The program `grub-probe' probes device information for a given path or
device.
grub-probe --target=fs /boot/grub
grub-probe --target=drive --device /dev/sda1
`grub-probe' must be given a path or device as a non-option
argument, and also accepts the following options:
`--help'
Print a summary of the command-line options and exit.
`--version'
Print the version number of GRUB and exit.
`-d'
`--device'
If this option is given, then the non-option argument is a system
device name (such as `/dev/sda1'), and `grub-probe' will print
information about that device. If it is not given, then the
non-option argument is a filesystem path (such as `/boot/grub'),
and `grub-probe' will print information about the device
containing that part of the filesystem.
`-m FILE'
`--device-map=FILE'
Use FILE as the device map (*note Device map::) rather than the
default, usually `/boot/grub/device.map'.
`-t TARGET'
`--target=TARGET'
Print information about the given path or device as defined by
TARGET. The available targets and their meanings are:
`fs'
GRUB filesystem module.
`fs_uuid'
Filesystem Universally Unique Identifier (UUID).
`fs_label'
Filesystem label.
`drive'
GRUB device name.
`device'
System device name.
`partmap'
GRUB partition map module.
`abstraction'
GRUB abstraction module (e.g. `lvm').
`cryptodisk_uuid'
Crypto device UUID.
`msdos_parttype'
MBR partition type code (two hexadecimal digits).
`hints_string'
A string of platform search hints suitable for passing to the
`search' command (*note search::).
`bios_hints'
Search hints for the PC BIOS platform.
`ieee1275_hints'
Search hints for the IEEE1275 platform.
`baremetal_hints'
Search hints for platforms where disks are addressed directly
rather than via firmware.
`efi_hints'
Search hints for the EFI platform.
`arc_hints'
Search hints for the ARC platform.
`compatibility_hint'
A guess at a reasonable GRUB drive name for this device,
which may be used as a fallback if the `search' command fails.
`disk'
System device name for the whole disk.
`-v'
`--verbose'
Print verbose messages.

File: grub.info, Node: Obtaining and Building GRUB, Next: Reporting bugs, Prev: Invoking grub-probe, Up: Top
Appendix A How to obtain and build GRUB
***************************************
*Caution:* GRUB requires binutils-2.9.1.0.23 or later because the
GNU assembler has been changed so that it can produce real 16bits
machine code between 2.9.1 and 2.9.1.0.x. See
`http://sources.redhat.com/binutils/', to obtain information on
how to get the latest version.
GRUB is available from the GNU alpha archive site
`ftp://ftp.gnu.org/gnu/grub' or any of its mirrors. The file will be
named grub-version.tar.gz. The current version is 2.00, so the file you
should grab is:
`ftp://ftp.gnu.org/gnu/grub/grub-2.00.tar.gz'
To unbundle GRUB use the instruction:
zcat grub-2.00.tar.gz | tar xvf -
which will create a directory called `grub-2.00' 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-2.00
./configure
make install
Also, the latest version is available using Bazaar. See
`http://www.gnu.org/software/grub/grub-download.en.html' for more
information.

File: grub.info, 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
(http://www.gnu.org/software/grub/grub-faq.html).
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
encountered 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 (http://savannah.gnu.org/bugs/?group=grub).
Alternatively, you can submit a report via electronic mail to
<bug-grub@gnu.org>, 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: grub.info, Node: Future, Next: Copying This Manual, Prev: Reporting bugs, Up: Top
Appendix C Where GRUB will go
*****************************
GRUB 2 is now quite stable and used in many production systems. We are
currently working towards a 2.0 release.
If you are interested in the development of GRUB 2, take a look at
the homepage (http://www.gnu.org/software/grub/grub.html).

File: grub.info, Node: Copying This Manual, Next: Index, Prev: Future, Up: Top
Appendix D Copying This Manual
******************************
* Menu:
* GNU Free Documentation License:: License for copying this manual.

File: grub.info, Node: GNU Free Documentation License, Up: Copying This Manual
D.1 GNU Free Documentation License
==================================
Version 1.2, November 2002
Copyright (C) 2000,2001,2002 Free Software Foundation, Inc.
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
0. PREAMBLE
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D.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
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notices just after the title page:
Copyright (C) YEAR YOUR NAME.
Permission is granted to copy, distribute and/or modify this document
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If you have Invariant Sections without Cover Texts, or some other
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File: grub.info, Node: Index, Prev: Copying This Manual, Up: Top
Index
*****
�[index�]
* 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)
* false: false. (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)
* list_env: list_env. (line 7)
* load_env: load_env. (line 7)
* loopback: loopback. (line 7)
* ls: ls. (line 7)
* menuentry: menuentry. (line 8)
* normal: normal. (line 7)
* normal_exit: normal_exit. (line 7)
* parttool: parttool. (line 7)
* password: password. (line 7)
* password_pbkdf2: password_pbkdf2. (line 7)
* play: play. (line 7)
* pxe_unload: pxe_unload. (line 7)
* read: read. (line 7)
* reboot: reboot. (line 7)
* save_env: save_env. (line 7)
* search: search. (line 8)
* sendkey: sendkey. (line 12)
* serial: serial. (line 8)
* set: set. (line 7)
* submenu: submenu. (line 8)
* terminal_input: terminal_input. (line 8)
* terminal_output: terminal_output. (line 8)
* terminfo: terminfo. (line 7)
* true: true. (line 7)
* unset: unset. (line 7)

Tag Table:
Node: Top1043
Node: Introduction3645
Node: Overview4089
Node: Overview-Footnotes6073
Ref: Overview-Footnote-16134
Node: History6295
Node: Changes from GRUB Legacy8383
Node: Features10859
Node: Features-Footnotes17218
Ref: Features-Footnote-117279
Ref: Features-Footnote-217425
Node: Role of a boot loader17570
Node: Role of a boot loader-Footnotes18908
Ref: Role of a boot loader-Footnote-118995
Node: Naming convention19074
Node: Installation21949
Node: Installing GRUB using grub-install23052
Node: Making a GRUB bootable CD-ROM25223
Node: Making a GRUB bootable CD-ROM-Footnotes27077
Ref: Making a GRUB bootable CD-ROM-Footnote-127180
Node: Device map27255
Node: BIOS installation29236
Node: Booting32613
Node: General boot methods33069
Node: Loading an operating system directly33809
Node: Chain-loading34540
Node: Loopback booting35511
Node: OS-specific notes37174
Node: GNU/Hurd37452
Node: GNU/Linux38574
Node: DOS/Windows40202
Node: Configuration41975
Node: Simple configuration42585
Node: Shell-like scripting52699
Node: Shell-like scripting-Footnotes60630
Ref: Shell-like scripting-Footnote-160715
Node: Multi-boot manual config60842
Node: Embedded configuration64467
Node: Theme file format67304
Ref: Pixmap-styled progress bar68727
Ref: Plain progress bar68739
Ref: An example of the slices (in red) used for a terminal window. This drawing was created and sliced in Inkscape_72237
Node: Network86459
Node: Serial terminal88609
Node: Vendor power-on keys90836
Node: Images92666
Node: Filesystem97626
Node: Device syntax98313
Node: File name syntax100696
Node: Block list syntax101450
Node: Interface102183
Node: Command-line interface103005
Node: Command-line interface-Footnotes104946
Ref: Command-line interface-Footnote-1105035
Node: Menu interface105130
Node: Menu entry editor106140
Node: Environment106878
Node: Special environment variables107582
Node: biosnum108333
Node: chosen108847
Node: color_highlight109289
Node: color_normal109695
Node: debug110317
Node: default110664
Node: fallback111591
Node: gfxmode111922
Node: gfxpayload112655
Node: gfxterm_font113807
Node: icondir114106
Node: lang114422
Node: locale_dir114891
Node: menu_color_highlight115400
Node: menu_color_normal115896
Node: net_pxe_boot_file116389
Node: net_pxe_dhcp_server_name116600
Node: net_pxe_domain116822
Node: net_pxe_extensionspath117029
Node: net_pxe_hostname117244
Node: net_pxe_ip117443
Node: net_pxe_mac117619
Node: net_pxe_rootpath117797
Node: pager117980
Node: prefix118234
Node: pxe_blksize118683
Node: pxe_default_gateway118860
Node: pxe_default_server119065
Node: root119261
Node: superusers119802
Node: theme120050
Node: timeout120371
Node: Environment block120868
Node: Commands122300
Node: Menu-specific commands123145
Node: menuentry123872
Node: submenu125006
Node: General commands125533
Node: serial126029
Node: terminal_input127074
Node: terminal_output127740
Node: terminfo128407
Node: Command-line and menu entry commands129542
Node: acpi132513
Node: badram133552
Node: blocklist134594
Node: boot134828
Node: cat135149
Node: chainloader135784
Node: cmp136406
Node: configfile136957
Node: cpuid137257
Node: crc137722
Node: date137912
Node: drivemap138451
Node: echo139254
Node: export140191
Node: false140501
Node: gettext140797
Node: gptsync141244
Node: halt142189
Node: help142515
Node: initrd142978
Node: initrd16143390
Node: insmod143895
Node: keystatus144117
Node: linux144755
Node: linux16145658
Node: list_env146372
Node: load_env146726
Node: loopback147104
Node: ls147552
Node: normal148097
Node: normal_exit148856
Node: parttool149178
Node: password150683
Node: password_pbkdf2150965
Node: play151373
Node: pxe_unload152125
Node: read152404
Node: reboot152753
Node: save_env152938
Node: search153324
Node: sendkey154102
Node: set160376
Node: true160674
Node: unset160959
Node: uppermem161165
Node: Internationalisation161366
Node: Security167965
Node: Platform limitations170787
Node: Platform-specific operations177174
Node: Supported kernels178160
Node: Troubleshooting186151
Node: GRUB only offers a rescue shell186377
Node: Invoking grub-install189303
Node: Invoking grub-mkconfig190681
Node: Invoking grub-mkpasswd-pbkdf2191318
Node: Invoking grub-mkrescue191976
Node: Invoking grub-probe193731
Node: Obtaining and Building GRUB196327
Node: Reporting bugs197564
Node: Future200367
Node: Copying This Manual200767
Node: GNU Free Documentation License200995
Node: Index223403

End Tag Table