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@c -*-texinfo-*-
@c %**start of header
@include version.texi
@settitle GNU GRUB Manual @value{VERSION}
@c Unify all our little indices for now.
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@syncodeindex vr cp
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@footnotestyle separate
@paragraphindent 3
This manual is for GNU GRUB (version @value{VERSION},
Copyright @copyright{} 1999,2000,2001,2002,2004,2006,2008,2009,2010,2011,2012,2013 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.
@end quotation
@end copying
@dircategory Kernel
* 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-mkrelpath: (grub)Invoking grub-mkrelpath.
* grub-mkrescue: (grub)Invoking grub-mkrescue. Make a GRUB rescue image
* grub-mount: (grub)Invoking grub-mount. Mount a file system using GRUB
* grub-probe: (grub)Invoking grub-probe. Probe device information
* grub-script-check: (grub)Invoking grub-script-check.
@end direntry
@setchapternewpage odd
@sp 10
@title the GNU GRUB manual
@subtitle The GRand Unified Bootloader, version @value{VERSION}, @value{UPDATED}.
@author Gordon Matzigkeit
@author Yoshinori K. Okuji
@author Colin Watson
@author Colin D. Bennett
@c The following two commands start the copyright page.
@vskip 0pt plus 1filll
@end titlepage
@c Output the table of contents at the beginning.
@headings double
@node Top
@top GNU GRUB manual
This is the documentation of GNU GRUB, the GRand Unified Bootloader,
a flexible and powerful boot loader program for a wide range of
This edition documents version @value{VERSION}.
@end ifnottex
* Introduction:: Capturing the spirit of GRUB
* Naming convention:: Names of your drives in GRUB
* OS-specific notes about grub tools::
Some notes about OS-specific behaviour of 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
* Core image size limitation:: GRUB image files size limitations
* 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, authorisation, and signatures
* 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-mkrelpath:: Make system path relative to its root
* Invoking grub-mkrescue:: Make a GRUB rescue image
* Invoking grub-mount:: Mount a file system using GRUB
* Invoking grub-probe:: Probe device information for GRUB
* Invoking grub-script-check:: Check GRUB script file for syntax errors
* 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::
@end menu
@node Introduction
@chapter Introduction to GRUB
* 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
@end menu
@node Overview
@section Overview
Briefly, a @dfn{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 @dfn{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@footnote{@dfn{chain-load} is the mechanism for loading
unsupported operating systems by loading another boot loader. It is
typically used for loading DOS or Windows.}. 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
(@pxref{Command-line interface}), or a menu interface (@pxref{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
(@pxref{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 (@pxref{Naming convention}) to GRUB, how to
install GRUB on your drive (@pxref{Installation}), and how to boot your
OSes (@pxref{Booting}), step by step.
@node History
@section History of GRUB
GRUB originated in 1995 when Erich Boleyn was trying to boot the GNU
Hurd with the University of Utah's Mach 4 microkernel (now known as GNU
Mach). Erich and Brian Ford designed the Multiboot Specification
(@pxref{Top, Multiboot Specification, Motivation, multiboot, The Multiboot
Specification}), because they were determined not to add to the large
number of mutually-incompatible PC boot methods.
Erich then began modifying the FreeBSD boot loader so that it would
understand Multiboot. He soon realized that it would be a lot easier
to write his own boot loader from scratch than to keep working on the
FreeBSD boot loader, and so GRUB was born.
Erich added many features to GRUB, but other priorities prevented him
from keeping up with the demands of its quickly-expanding user base. In
1999, Gordon Matzigkeit and Yoshinori K. Okuji adopted GRUB as an
official GNU package, and opened its development by making the latest
sources available via anonymous CVS. @xref{Obtaining and Building
GRUB}, for more information.
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.
@node Changes from GRUB Legacy
@section Differences from previous versions
GRUB 2 is a rewrite of GRUB (@pxref{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
@itemize @bullet
The configuration file has a new name (@file{grub.cfg} rather than
@file{menu.lst} or @file{grub.conf}), new syntax (@pxref{Configuration}) and
many new commands (@pxref{Commands}). Configuration cannot be copied over
directly, although most GRUB Legacy users should not find the syntax too
@file{grub.cfg} is typically automatically generated by
@command{grub-mkconfig} (@pxref{Simple configuration}). This makes it
easier to handle versioned kernel upgrades.
Partition numbers in GRUB device names now start at 1, not 0 (@pxref{Naming
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
@command{save_env} and @command{load_env} commands in GRUB and the
@command{grub-editenv} utility. This is not available in all configurations
(@pxref{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 (@pxref{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 (@pxref{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.
@end itemize
@node Features
@section GRUB features
The primary requirement for GRUB is that it be compliant with the
@dfn{Multiboot Specification}, which is described in @ref{Top, Multiboot
Specification, Motivation, multiboot, The Multiboot Specification}.
The other goals, listed in approximate order of importance, are:
@itemize @bullet{}
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.
@end itemize
Except for specific compatibility modes (chain-loading and the Linux
@dfn{piggyback} format), all kernels will be started in much the same
state as in the Multiboot Specification. Only kernels loaded at 1 megabyte
or above are presently supported. Any attempt to load below that
boundary will simply result in immediate failure and an error message
reporting the problem.
In addition to the requirements above, GRUB has the following features
(note that the Multiboot Specification doesn't require all the features
that GRUB supports):
@table @asis
@item Recognize multiple executable formats
Support many of the @dfn{a.out} variants plus @dfn{ELF}. Symbol
tables are also loaded.
@item Support non-Multiboot kernels
Support many of the various free 32-bit kernels that lack Multiboot
compliance (primarily FreeBSD, NetBSD@footnote{The NetBSD/i386 kernel
is Multiboot-compliant, but lacks support for Multiboot modules.},
OpenBSD, and Linux). Chain-loading of other boot loaders is also
@item Load multiples modules
Fully support the Multiboot feature of loading multiple modules.
@item 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 (@pxref{Commands}) are a superset of those supported on the
command-line. An example configuration file is provided in
@item 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.
@item 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 (@pxref{Commands}) are a subset of those supported
for configuration files. Editing commands closely resembles the Bash
command-line (@pxref{Command Line Editing, Bash, Command Line Editing,
features, Bash Features}), with @key{TAB}-completion of commands,
devices, partitions, and files in a directory depending on context.
@item Support multiple filesystem types
Support multiple filesystem types transparently, plus a useful explicit
blocklist notation. The currently supported filesystem types are @dfn{Amiga
Fast FileSystem (AFFS)}, @dfn{AtheOS fs}, @dfn{BeFS},
@dfn{BtrFS} (including raid0, raid1, raid10, gzip and lzo),
@dfn{cpio} (little- and big-endian bin, odc and newc variants),
@dfn{Linux ext2/ext3/ext4}, @dfn{DOS FAT12/FAT16/FAT32}, @dfn{exFAT}, @dfn{HFS},
@dfn{HFS+}, @dfn{ISO9660} (including Joliet, Rock-ridge and multi-chunk files),
@dfn{JFS}, @dfn{Minix fs} (versions 1, 2 and 3), @dfn{nilfs2},
@dfn{NTFS} (including compression), @dfn{ReiserFS}, @dfn{ROMFS},
@dfn{Amiga Smart FileSystem (SFS)}, @dfn{Squash4}, @dfn{tar}, @dfn{UDF},
@dfn{BSD UFS/UFS2}, @dfn{XFS}, and @dfn{ZFS} (including lzjb, gzip,
zle, mirror, stripe, raidz1/2/3 and encryption in AES-CCM and AES-GCM).
@xref{Filesystem}, for more information.
@item Support automatic decompression
Can decompress files which were compressed by @command{gzip} or
@command{xz}@footnote{Only CRC32 data integrity check is supported (xz default
is CRC64 so one should use --check=crc32 option). LZMA BCJ filters are
supported.}. 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.@footnote{There are a few
pathological cases where loading a very badly organized ELF kernel might
take longer, but in practice this never happen.}
It is conceivable that some kernel modules should be loaded in a
compressed state, so a different module-loading command can be specified
to avoid uncompressing the modules.
@item Access data on any installed device
Support reading data from any or all floppies or hard disk(s) recognized
by the BIOS, independent of the setting of the root device.
@item 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.
@item Detect all installed @sc{ram}
GRUB can generally find all the installed @sc{ram} on a PC-compatible
machine. It uses an advanced BIOS query technique for finding all
memory regions. As described on the Multiboot Specification (@pxref{Top,
Multiboot Specification, Motivation, multiboot, The Multiboot
Specification}), not all kernels make use of this information, but GRUB
provides it for those who do.
@item Support Logical Block Address mode
In traditional disk calls (called @dfn{CHS mode}), there is a geometry
translation problem, that is, the BIOS cannot access over 1024
cylinders, so the accessible space is limited to at least 508 MB and to
at most 8GB. GRUB can't universally solve this problem, as there is no
standard interface used in all machines. However, several newer machines
have the new interface, Logical Block Address (@dfn{LBA}) mode. GRUB
automatically detects if LBA mode is available and uses it if
available. In LBA mode, GRUB can access the entire disk.
@item 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 @dfn{TFTP}
@item 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.
@end table
@node Role of a boot loader
@section 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
@emph{boot loader} is the most important software of all. I used to
refer to the above systems as either ``LILO''@footnote{The LInux LOader,
a boot loader that everybody uses, but nobody likes.} or ``GRUB''
Unfortunately, nobody ever understood what I was talking about; now I
just use the word ``GNU'' as a pseudonym for GRUB.
So, if you ever hear people talking about their alleged ``GNU'' systems,
remember that they are actually paying homage to the best boot loader
around@dots{} GRUB!
@end quotation
We, the GRUB maintainers, do not (usually) encourage Gordon's level of
fanaticism, but it helps to remember that boot loaders deserve
recognition. We hope that you enjoy using GNU GRUB as much as we did
writing it.
@node Naming convention
@chapter 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:
@end example
First of all, GRUB requires that the device name be enclosed with
@samp{(} and @samp{)}. The @samp{fd} part means that it is a floppy
disk. The number @samp{0} is the drive number, which is counted from
@emph{zero}. This expression means that GRUB will use the whole floppy
@end example
Here, @samp{hd} means it is a hard disk drive. The first integer
@samp{0} indicates the drive number, that is, the first hard disk,
the string @samp{msdos} indicates the partition scheme, while
the second integer, @samp{2}, indicates the partition number (or the
@sc{pc} slice number in the BSD terminology). The partition numbers are
counted from @emph{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.
@end example
This specifies the first @dfn{extended partition} of the first hard disk
drive. Note that the partition numbers for extended partitions are
counted from @samp{5}, regardless of the actual number of primary
partitions on your hard disk.
@end example
This means the BSD @samp{a} partition on first @sc{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 @samp{set
root=(fd0)} or @samp{parttool (hd0,msdos3) hidden-}. To help you find out
which number specifies a partition you want, the GRUB command-line
(@pxref{Command-line interface}) options have argument
completion. This means that, for example, you only need to type
set root=(
@end example
followed by a @key{TAB}, and GRUB will display the list of drives,
partitions, or file names. So it should be quite easy to determine the
name of your target partition, even with minimal knowledge of the
Note that GRUB does @emph{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
@end example
This specifies the file named @samp{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.
@node OS-specific notes about grub tools
@chapter OS-specific notes about grub tools
On OS which have device nodes similar to Unix-like OS GRUB tools use the
OS name. E.g. for GNU/Linux:
# @kbd{grub-install /dev/sda}
@end example
On AROS we use another syntax. For volumes:
//:<volume name>
@end example
@end example
For disks we use syntax:
//:<driver name>/unit/flags
@end example
# @kbd{grub-install //:ata.device/0/0}
@end example
On Windows we use UNC path. For volumes it's typically
\\?\<drive letter>:
@end example
@end example
For disks it's
@end example
# @kbd{grub-install \\?\PhysicalDrive0}
@end example
Beware that you may need to further escape the backslashes depending on your
When compiled with cygwin support then cygwin drive names are automatically
when needed. E.g.
# @kbd{grub-install /dev/sda}
@end example
@node Installation
@chapter 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 (@pxref{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
@command{grub-install} (@pxref{Invoking grub-install}) on a UNIX-like OS.
GRUB comes with boot images, which are normally put in the directory
@file{/usr/lib/grub/<cpu>-<platform>} (for BIOS-based machines
@file{/usr/lib/grub/i386-pc}). Hereafter, the directory where GRUB images are
initially placed (normally @file{/usr/lib/grub/<cpu>-<platform>}) will be
called the @dfn{image directory}, and the directory where the boot
loader needs to find them (usually @file{/boot}) will be called
the @dfn{boot directory}.
* Installing GRUB using grub-install::
* Making a GRUB bootable CD-ROM::
* Device map::
* BIOS installation::
@end menu
@node Installing GRUB using grub-install
@section Installing GRUB using grub-install
For information on where GRUB should be installed on PC BIOS platforms,
@pxref{BIOS installation}.
In order to install GRUB under a UNIX-like OS (such
as @sc{gnu}), invoke the program @command{grub-install} (@pxref{Invoking
grub-install}) as the superuser (@dfn{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 @samp{/dev/hda}).
For example, under Linux the following will install GRUB into the MBR
of the first IDE disk:
# @kbd{grub-install /dev/sda}
@end example
Likewise, under GNU/Hurd, this has the same effect:
# @kbd{grub-install /dev/hd0}
@end example
But all the above examples assume that GRUB should put images under
the @file{/boot} directory. If you want GRUB to put images under a directory
other than @file{/boot}, you need to specify the option
@option{--boot-directory}. The typical usage is that you create a GRUB
boot floppy with a filesystem. Here is an example:
# @kbd{mke2fs /dev/fd0}
# @kbd{mount -t ext2 /dev/fd0 /mnt}
# @kbd{mkdir /mnt/boot}
# @kbd{grub-install --boot-directory=/mnt/boot /dev/fd0}
# @kbd{umount /mnt}
@end group
@end example
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:
# @kbd{losetup /dev/loop0 /dev/sdb1}
# @kbd{mount /dev/loop0 /mnt/usb}
# @kbd{grub-install --boot-directory=/mnt/usb/bugbios --force --allow-floppy /dev/loop0}
@end example
This install doesn't conflict with standard install as long as they are in
separate directories.
Note that @command{grub-install} is actually just a shell script and the
real task is done by other tools such as @command{grub-mkimage}. Therefore,
you may run those commands directly to install GRUB, without using
@command{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.
On EFI systems for fixed disk install you have to mount EFI System Partition.
If you mount it at @file{/boot/efi} then you don't need any special arguments:
# @kbd{grub-install}
@end example
Otherwise you need to specify where your EFI System partition is mounted:
# @kbd{grub-install --efi-directory=/mnt/efi}
@end example
For removable installs you have to use @option{--removable} and specify both
@option{--boot-directory} and @option{--efi-directory}:
# @kbd{grub-install --efi-directory=/mnt/usb --boot-directory=/mnt/usb/boot --removable}
@end example
@node Making a GRUB bootable CD-ROM
@section Making a GRUB bootable CD-ROM
GRUB supports the @dfn{no emulation mode} in the El Torito
specification@footnote{El Torito is a specification for bootable CD
using BIOS functions.}. 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
@file{cdboot.img}, which is concatenated with @file{core.img}. The
@file{core.img} used for this should be built with at least the
@samp{iso9660} and @samp{biosdisk} modules. Your bootable CD-ROM will
usually also need to include a configuration file @file{grub.cfg} and some
other GRUB modules.
To make a simple generic GRUB rescue CD, you can use the
@command{grub-mkrescue} program (@pxref{Invoking grub-mkrescue}):
$ @kbd{grub-mkrescue -o grub.iso}
@end example
You will often need to include other files in your image. To do this, first
make a top directory for the bootable image, say, @samp{iso}:
$ @kbd{mkdir iso}
@end example
Make a directory for GRUB:
$ @kbd{mkdir -p iso/boot/grub}
@end example
If desired, make the config file @file{grub.cfg} under @file{iso/boot/grub}
(@pxref{Configuration}), and copy any files and directories for the disc to the
directory @file{iso/}.
Finally, make the image:
$ @kbd{grub-mkrescue -o grub.iso iso}
@end example
This produces a file named @file{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
@file{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.
@node Device map
@section The map between BIOS drives and OS devices
If the device map file exists, the GRUB utilities (@command{grub-probe},
etc.) read it to map BIOS drives to OS devices. This file consists of lines
like this:
(@var{device}) @var{file}
@end example
@var{device} is a drive specified in the GRUB syntax (@pxref{Device
syntax}), and @var{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 (@file{/dev/hd*} versus @file{/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 @file{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 @samp{#}.
@node BIOS installation
@section BIOS installation
@heading 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 @file{/boot} filesystem is on the same disk that the
BIOS boots from, so that GRUB does not have to rely on guessing BIOS drive
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.
@heading 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:
# @kbd{parted /dev/@var{disk} set @var{partition-number} bios_grub on}
@end example
If you are using gdisk, set the partition type to @samp{0xEF02}. With
partitioning programs that require setting the GUID directly, it should be
@strong{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.
@node Booting
@chapter Booting
GRUB can load Multiboot-compliant kernels in a consistent way,
but for some free operating systems you need to use some OS-specific
* 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
@end menu
@node General boot methods
@section 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.
* Loading an operating system directly::
* Chain-loading::
@end menu
@node Loading an operating system directly
@subsection How to boot an OS directly with GRUB
Multiboot (@pxref{Top, Multiboot Specification, Motivation, multiboot,
The Multiboot Specification}) 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 (@pxref{Chain-loading}).
FIXME: this section is incomplete.
Run the command @command{boot} (@pxref{boot}).
@end enumerate
However, DOS and Windows have some deficiencies, so you might have to
use more complicated instructions. @xref{DOS/Windows}, for more
@node Chain-loading
@subsection 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 @command{chainloader} command (@pxref{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
@end verbatim
@c FIXME: document UUIDs.
On systems with multiple hard disks, an additional workaround may be
required. @xref{DOS/Windows}.
Chain-loading is only supported on PC BIOS and EFI platforms.
@node Loopback booting
@section 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 @pxref{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 @command{kfreebsd_module}, @command{knetbsd_module_elf},
@command{kopenbsd_ramdisk}, @command{initrd} (@pxref{initrd}),
@command{initrd16} (@pxref{initrd}), @command{multiboot_module},
@command{multiboot2_module} or @command{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
@node OS-specific notes
@section Some caveats on OS-specific issues
Here, we describe some caveats on several operating systems.
* GNU/Hurd::
* GNU/Linux::
* NetBSD::
* DOS/Windows::
@end menu
@node GNU/Hurd
@subsection 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.
Set GRUB's root device to the same drive as GNU/Hurd's. The command
@code{search --set=root --file /boot/gnumach.gz} or similar may help you
Load the kernel and the modules, like this:
grub> @kbd{multiboot /boot/gnumach.gz root=device:hd0s1}
grub> @kbd{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)' '$(task-resume)'}
grub> @kbd{module /lib/ exec /hurd/exec '$(exec-task=task-create)'}
@end group
@end example
Finally, run the command @command{boot} (@pxref{boot}).
@end enumerate
@node GNU/Linux
@subsection GNU/Linux
It is relatively easy to boot GNU/Linux from GRUB, because it somewhat
resembles to boot a Multiboot-compliant OS.
Set GRUB's root device to the same drive as GNU/Linux's. The command
@code{search --set=root --file /vmlinuz} or similar may help you
Load the kernel using the command @command{linux} (@pxref{linux}):
grub> @kbd{linux /vmlinuz root=/dev/sda1}
@end example
If you need to specify some kernel parameters, just append them to the
command. For example, to set @option{acpi} to @samp{off}, do this:
grub> @kbd{linux /vmlinuz root=/dev/sda1 acpi=off}
@end example
See the documentation in the Linux source tree for complete information on
the available options.
With @command{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
grub> @kbd{linux16 /vmlinuz root=/dev/sda1 acpi=off}
@end example
If you use an initrd, execute the command @command{initrd} (@pxref{initrd})
after @command{linux}:
grub> @kbd{initrd /initrd}
@end example
If you used @command{linux16} you need to use @command{initrd16}:
grub> @kbd{initrd16 /initrd}
@end example
Finally, run the command @command{boot} (@pxref{boot}).
@end enumerate
@strong{Caution:} If you use an initrd and specify the @samp{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 @command{uppermem} @emph{before} loading the
kernel. @xref{uppermem}, for more information.
@node NetBSD
@subsection NetBSD
Booting a NetBSD kernel from GRUB is also relatively easy: first set
GRUB's root device, then load the kernel and the modules, and finally
run @command{boot}.
Set GRUB's root device to the partition holding the NetBSD root file
system. For a disk with a NetBSD disk label, this is usually the first
partition (a:). In that case, and assuming that the partition is on the
first hard disk, set GRUB's root device as follows:
grub> @kbd{insmod part_bsd}
grub> @kbd{set root=(hd0,netbsd1)}
@end example
For a disk with a GUID Partition Table (GPT), and assuming that the
NetBSD root partition is the third GPT partition, do this:
grub> @kbd{insmod part_gpt}
grub> @kbd{set root=(hd0,gpt3)}
@end example
Load the kernel using the command @command{knetbsd}:
grub> @kbd{knetbsd /netbsd}
@end example
Various options may be given to @command{knetbsd}. These options are,
for the most part, the same as in the NetBSD boot loader. For instance,
to boot the system in single-user mode and with verbose messages, do
grub> @kbd{knetbsd /netbsd -s -v}
@end example
If needed, load kernel modules with the command
@command{knetbsd_module_elf}. A typical example is the module for the
root file system:
grub> @kbd{knetbsd_module_elf /stand/amd64/6.0/modules/ffs/ffs.kmod}
@end example
Finally, run the command @command{boot} (@pxref{boot}).
@end enumerate
@node DOS/Windows
@subsection DOS/Windows
GRUB cannot boot DOS or Windows directly, so you must chain-load them
(@pxref{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 @command{drivemap} (@pxref{drivemap}), like this:
drivemap -s (hd0) (hd1)
@end example
This performs a @dfn{virtual} swap between your first and second hard
@strong{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 @dfn{hides} a DOS (or Windows) partition (@pxref{parttool}), DOS (or
Windows) will ignore the partition. If GRUB @dfn{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 @verb{'${root}'} boot+
@end group
@end example
@node Configuration
@chapter Writing your own configuration file
GRUB is configured using @file{grub.cfg}, usually located under
@file{/boot/grub}. This file is quite flexible, but most users will not
need to write the whole thing by hand.
* 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
@end menu
@node Simple configuration
@section Simple configuration handling
The program @command{grub-mkconfig} (@pxref{Invoking grub-mkconfig})
generates @file{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.
@command{grub-mkconfig} does have some limitations. While adding extra
custom menu entries to the end of the list can be done by editing
@file{/etc/grub.d/40_custom} or creating @file{/boot/grub/custom.cfg},
changing the order of menu entries or changing their titles may require
making complex changes to shell scripts stored in @file{/etc/grub.d/}. This
may be improved in the future. In the meantime, those who feel that it
would be easier to write @file{grub.cfg} directly are encouraged to do so
(@pxref{Booting}, and @ref{Shell-like scripting}), and to disable any system
provided by their distribution to automatically run @command{grub-mkconfig}.
The file @file{/etc/default/grub} controls the operation of
@command{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
@samp{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"
@end example
Valid keys in @file{/etc/default/grub} are as follows:
@table @samp
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 @samp{saved}. Using the id 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 --id example-gnu-linux {
@end verbatim
then you can make this the default using:
@end example
Previously it was documented the way to use entry title. While this still
works it's not recommended since titles often contain unstable device names
and may be translated
If you set this to @samp{saved}, then the default menu entry will be that
saved by @samp{GRUB_SAVEDEFAULT} or @command{grub-set-default}. This relies on
the environment block, which may not be available in all situations
(@pxref{Environment block}).
The default is @samp{0}.
If this option is set to @samp{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 @samp{GRUB_DEFAULT=saved}; it is a separate option because
@samp{GRUB_DEFAULT=saved} is useful without this option, in conjunction with
@command{grub-set-default}. Unset by default.
This option relies on the environment block, which may not be available in
all situations (@pxref{Environment block}).
Boot the default entry this many seconds after the menu is displayed, unless
a key is pressed. The default is @samp{5}. Set to @samp{0} to boot
immediately without displaying the menu, or to @samp{-1} to wait
If @samp{GRUB_TIMEOUT_STYLE} is set to @samp{countdown} or @samp{hidden},
the timeout is instead counted before the menu is displayed.
If this option is unset or set to @samp{menu}, then GRUB will display the
menu and then wait for the timeout set by @samp{GRUB_TIMEOUT} to expire
before booting the default entry. Pressing a key interrupts the timeout.
If this option is set to @samp{countdown} or @samp{hidden}, then, before
displaying the menu, GRUB will wait for the timeout set by
@samp{GRUB_TIMEOUT} to expire. If @key{ESC} is pressed during that time, it
will display the menu and wait for input. If a hotkey associated with a
menu entry is pressed, it will boot the associated menu entry immediately.
If the timeout expires before either of these happens, it will boot the
default entry. In the @samp{countdown} case, it will show a one-line
indication of the remaining time.
Variants of the corresponding variables without the @samp{_BUTTON} suffix,
used to support vendor-specific power buttons. @xref{Vendor power-on keys}.
Set by distributors of GRUB to their identifying name. This is used to
generate more informative menu entry titles.
Select the terminal input device. You may select multiple devices here,
separated by spaces.
Valid terminal input names depend on the platform, but may include
@samp{console} (native platform console), @samp{serial} (serial terminal),
@samp{serial_<port>} (serial terminal with explicit port selection),
@samp{at_keyboard} (PC AT keyboard), or @samp{usb_keyboard} (USB keyboard
using the HID Boot Protocol, for cases where the firmware does not handle
The default is to use the platform's native terminal input.
Select the terminal output device. You may select multiple devices here,
separated by spaces.
Valid terminal output names depend on the platform, but may include
@samp{console} (native platform console), @samp{serial} (serial terminal),
@samp{serial_<port>} (serial terminal with explicit port selection),
@samp{gfxterm} (graphics-mode output), @samp{vga_text} (VGA text output),
@samp{mda_text} (MDA text output), @samp{morse} (Morse-coding using system
beeper) or @samp{spkmodem} (simple data protocol using system speaker).
@samp{spkmodem} is useful when no serial port is available. Connect the output
of sending system (where GRUB is running) to line-in of receiving system
(usually developer machine).
On receiving system compile @samp{spkmodem-recv} from
@samp{util/spkmodem-recv.c} and run:
parecord --channels=1 --rate=48000 --format=s16le | ./spkmodem-recv
@end example
The default is to use the platform's native terminal output.
If this option is set, it overrides both @samp{GRUB_TERMINAL_INPUT} and
@samp{GRUB_TERMINAL_OUTPUT} to the same value.
A command to configure the serial port when using the serial console.
@xref{serial}. Defaults to @samp{serial}.
Command-line arguments to add to menu entries for the Linux kernel.
Unless @samp{GRUB_DISABLE_RECOVERY} is set to @samp{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
As @samp{GRUB_CMDLINE_LINUX}, but for GNU Mach.
The values of these options are passed to Xen hypervisor Xen menu entries,
for all respectively normal entries.
The values of these options replace the values of @samp{GRUB_CMDLINE_LINUX}
and @samp{GRUB_CMDLINE_LINUX_DEFAULT} for Linux and Xen menu entries.
Normally, @command{grub-mkconfig} will generate menu entries that use
universally-unique identifiers (UUIDs) to identify the root filesystem to
the Linux kernel, using a @samp{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 @samp{true}.
If this option is set to @samp{true}, disable the generation of recovery
mode menu entries.
If graphical video support is required, either because the @samp{gfxterm}
graphical terminal is in use or because @samp{GRUB_GFXPAYLOAD_LINUX} is set,
then @command{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 @command{grub-install} has been run, the available video drivers are
listed in @file{/boot/grub/video.lst}.
Set the resolution used on the @samp{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 @samp{auto}, which tries to select a preferred
resolution. @xref{gfxmode}.
Set a background image for use with the @samp{gfxterm} graphical terminal.
The value of this option must be a file readable by GRUB at boot time, and
it must end with @file{.png}, @file{.tga}, @file{.jpg}, or @file{.jpeg}.
The image will be scaled if necessary to fit the screen.
Set a theme for use with the @samp{gfxterm} graphical terminal.
Set to @samp{text} to force the Linux kernel to boot in normal text mode,
@samp{keep} to preserve the graphics mode set using @samp{GRUB_GFXMODE},
@samp{@var{width}x@var{height}}[@samp{x@var{depth}}] to set a particular
graphics mode, or a sequence of these separated by commas or semicolons to
try several modes in sequence. @xref{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 @samp{text} and
GRUB will tell Linux to boot in normal text mode.
Normally, @command{grub-mkconfig} will try to use the external
@command{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 @samp{true} to disable this.
List of space-separated FS UUIDs of filesystems to be ignored from os-prober
output. For efi chainloaders it's <UUID>@@<EFI FILE>
Normally, @command{grub-mkconfig} will generate top level menu entry for
the kernel with highest version number and put all other found kernels
or alternative menu entries for recovery mode in submenu. For entries returned
by @command{os-prober} first entry will be put on top level and all others
in submenu. If this option is set to @samp{y}, flat menu with all entries
on top level will be generated instead. Changing this option will require
changing existing values of @samp{GRUB_DEFAULT}, @samp{fallback} (@pxref{fallback})
and @samp{default} (@pxref{default}) environment variables as well as saved
default entry using @command{grub-set-default} and value used with
If set to @samp{y}, @command{grub-mkconfig} and @command{grub-install} will
check for encrypted disks and generate additional commands needed to access
them during boot. Note that in this case unattended boot is not possible
because GRUB will wait for passphrase to unlock encrypted container.
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 @ref{play}.
If this option is set, GRUB will issue a @ref{badram} command to filter
out specified regions of RAM.
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
@end table
The following options are still accepted for compatibility with existing
configurations, but have better replacements:
@table @samp
Wait this many seconds before displaying the menu. If @key{ESC} is pressed
during that time, display the menu and wait for input according to
@samp{GRUB_TIMEOUT}. If a hotkey associated with a menu entry is pressed,
boot the associated menu entry immediately. If the timeout expires before
either of these happens, display the menu for the number of seconds
specified in @samp{GRUB_TIMEOUT} before booting the default entry.
If you set @samp{GRUB_HIDDEN_TIMEOUT}, you should also set
@samp{GRUB_TIMEOUT=0} so that the menu is not displayed at all unless
@key{ESC} is pressed.
This option is unset by default, and is deprecated in favour of the less
confusing @samp{GRUB_TIMEOUT_STYLE=countdown} or
In conjunction with @samp{GRUB_HIDDEN_TIMEOUT}, set this to @samp{true} to
suppress the verbose countdown while waiting for a key to be pressed before
displaying the menu.
This option is unset by default, and is deprecated in favour of the less
confusing @samp{GRUB_TIMEOUT_STYLE=countdown}.
Variant of @samp{GRUB_HIDDEN_TIMEOUT}, used to support vendor-specific power
buttons. @xref{Vendor power-on keys}.
This option is unset by default, and is deprecated in favour of the less
confusing @samp{GRUB_TIMEOUT_STYLE=countdown} or
@end table
For more detailed customisation of @command{grub-mkconfig}'s output, you may
edit the scripts in @file{/etc/grub.d} directly.
@file{/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.
@node Shell-like scripting
@section Writing full configuration files directly
@c Some of this section is derived from the GNU Bash manual page, also
@c copyrighted by the FSF.
@file{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
@heading Words
A @dfn{word} is a sequence of characters considered as a single unit by
GRUB. Words are separated by @dfn{metacharacters}, which are the following
plus space, tab, and newline:
@{ @} | & $ ; < >
@end example
Quoting may be used to include metacharacters in words; see below.
@heading 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 @code{for} command:
! [[ ]] @{ @}
case do done elif else esac fi for function
if in menuentry select then time until while
@end example
Not all of these reserved words have a useful purpose yet; some are reserved
for future expansion.
@heading 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
There are three quoting mechanisms: the escape character, single quotes, and
double quotes.
A non-quoted backslash (\) is the @dfn{escape character}. It preserves the
literal value of the next character that follows, with the exception of
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 @samp{$} and @samp{\}.
The @samp{$} character retains its special meaning within double quotes.
The backslash retains its special meaning only when followed by one of the
following characters: @samp{$}, @samp{"}, @samp{\}, or newline. A
backslash-newline pair is treated as a line continuation (that is, it is
removed from the input stream and effectively ignored@footnote{Currently a
backslash-newline pair within a variable name is not handled properly, so
use this feature with some care.}). A double quote may be quoted within
double quotes by preceding it with a backslash.
@heading Variable expansion
The @samp{$} 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 (@pxref{Environment}).
Positional variable names consist of one or more digits. They represent
parameters passed to function calls, with @samp{$1} representing the first
parameter, and so on.
The special variable name @samp{?} expands to the exit status of the most
recently executed command. When positional variable names are active, other
special variable names @samp{@@}, @samp{*} and @samp{#} are defined and they
expand to all positional parameters with necessary quoting, positional
parameters without any quoting, and positional parameter count respectively.
@heading Comments
A word beginning with @samp{#} causes that word and all remaining characters
on that line to be ignored.
@heading Simple commands
A @dfn{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 @code{!} precedes the command, then the return value is instead the
logical negation of the command's exit status.
@heading Compound commands
A @dfn{compound command} is one of the following:
@table @asis
@item for @var{name} in @var{word} @dots{}; do @var{list}; done
The list of words following @code{in} is expanded, generating a list of
items. The variable @var{name} is set to each element of this list in turn,
and @var{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
@code{in} results in an empty list, no commands are executed, and the return
status is 0.
@item if @var{list}; then @var{list}; [elif @var{list}; then @var{list};] @dots{} [else @var{list};] fi
The @code{if} @var{list} is executed. If its exit status is zero, the
@code{then} @var{list} is executed. Otherwise, each @code{elif} @var{list}
is executed in turn, and if its exit status is zero, the corresponding
@code{then} @var{list} is executed and the command completes. Otherwise,
the @code{else} @var{list} is executed, if present. The exit status is the
exit status of the last command executed, or zero if no condition tested
@item while @var{cond}; do @var{list}; done
@itemx until @var{cond}; do @var{list}; done
The @code{while} command continuously executes the @code{do} @var{list} as
long as the last command in @var{cond} returns an exit status of zero. The
@code{until} command is identical to the @code{while} command, except that
the test is negated; the @code{do} @var{list} is executed as long as the
last command in @var{cond} returns a non-zero exit status. The exit status
of the @code{while} and @code{until} commands is the exit status of the last
@code{do} @var{list} command executed, or zero if none was executed.
@item function @var{name} @{ @var{command}; @dots{} @}
This defines a function named @var{name}. The @dfn{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
@var{name} is specified as the name of a simple command. Function
definitions do not affect the exit status in @code{$?}. When executed, the
exit status of a function is the exit status of the last command executed in
the body.
@item menuentry @var{title} [@option{--class=class} @dots{}] [@option{--users=users}] [@option{--unrestricted}] [@option{--hotkey=key}] [@option{--id=id}] @{ @var{command}; @dots{} @}
@end table
@heading 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.
@table @asis
@item break [@code{n}]
Exit from within a @code{for}, @code{while}, or @code{until} loop. If
@code{n} is specified, break @code{n} levels. @code{n} must be greater than
or equal to 1. If @code{n} is greater than the number of enclosing loops,
all enclosing loops are exited. The return value is 0 unless @code{n} is
not greater than or equal to 1.
@item continue [@code{n}]
Resume the next iteration of the enclosing @code{for}, @code{while} or
@code{until} loop. If @code{n} is specified, resume at the @code{n}th
enclosing loop. @code{n} must be greater than or equal to 1. If @code{n}
is greater than the number of enclosing loops, the last enclosing loop (the
@dfn{top-level} loop) is resumed. The return value is 0 unless @code{n} is
not greater than or equal to 1.
@item return [@code{n}]
Causes a function to exit with the return value specified by @code{n}. If
@code{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
@item setparams [@code{arg}] @dots{}
Replace positional parameters starting with @code{$1} with arguments to
@item shift [@code{n}]
The positional parameters from @code{n}+1 @dots{} are renamed to
@code{$1}@dots{}. Parameters represented by the numbers @code{$#} down to
@code{$#}-@code{n}+1 are unset. @code{n} must be a non-negative number less
than or equal to @code{$#}. If @code{n} is 0, no parameters are changed.
If @code{n} is not given, it is assumed to be 1. If @code{n} is greater
than @code{$#}, the positional parameters are not changed. The return
status is greater than zero if @code{n} is greater than @code{$#} or less
than zero; otherwise 0.
@end table
@node Multi-boot manual config
@section 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
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:
@code{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:
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= 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
@end example
@item 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 @code{root=hd0,msdosX} but this is not recommended due to device name instability.
@end itemize
@node Embedded configuration
@section 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.
@command{grub-install} uses this feature when it is not using BIOS disk
functions or when installing to a different disk from the one containing
@file{/boot/grub}, in which case it needs to use the @command{search}
command (@pxref{search}) to find @file{/boot/grub}.
To embed a configuration file, use the @option{-c} option to
@command{grub-mkimage}. The file is copied into the core image, so it may
reside anywhere on the file system, and may be removed after running
After the embedded configuration file (if any) is executed, GRUB will load
the @samp{normal} module (@pxref{normal}), which will then read the real
configuration file from @file{$prefix/grub.cfg}. By this point, the
@code{root} variable will also have been set to the root device name. For
example, @code{prefix} might be set to @samp{(hd0,1)/boot/grub}, and
@code{root} might be set to @samp{hd0,1}. Thus, in most cases, the embedded
configuration file only needs to set the @code{prefix} and @code{root}
variables, and then drop through to GRUB's normal processing. A typical
example of this might look like this:
search.fs_uuid 01234567-89ab-cdef-0123-456789abcdef root
set prefix=($root)/boot/grub
@end group
@end example
(The @samp{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 @file{grub.cfg}, or reading files from a directory
other than that where GRUB's loadable modules are installed. To do this,
include the @samp{configfile} and @samp{normal} modules in the core image,
and embed a configuration file that uses the @command{configfile} command to
load another file. The following example of this also requires the
@command{echo}, @command{search_label}, and @command{test} modules to be
included in the core image:
search.fs_label grub root
if [ -e /boot/grub/example/test1.cfg ]; then
set prefix=($root)/boot/grub
configfile /boot/grub/example/test1.cfg
if [ -e /boot/grub/example/test2.cfg ]; then
set prefix=($root)/boot/grub
configfile /boot/grub/example/test2.cfg
echo "Could not find an example configuration file!"
@end group
@end example
The embedded configuration file may not contain menu entries directly, but
may only read them from elsewhere using @command{configfile}.
@node Theme file format
@chapter Theme file format
@section 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
@section Theme Elements
@subsection Colors
Colors can be specified in several ways:
@item HTML-style ``#RRGGBB'' or ``#RGB'' format, where *R*, *G*, and *B* are hexadecimal digits (e.g., ``#8899FF'')
@item as comma-separated decimal RGB values (e.g., ``128, 128, 255'')
@item with ``SVG 1.0 color names'' (e.g., ``cornflowerblue'') which must be specified in lowercase.
@end itemize
@subsection 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 (@ref{loadfont}). To see the list of
loaded fonts, execute the ``lsfonts'' command (@ref{lsfonts}). If there are too many fonts to
fit on screen, do ``set pager=1'' before executing ``lsfonts''.
@subsection Progress Bar
@float Figure, Pixmap-styled progress bar
@c @image{Theme_progress_bar,,,,png}
@end float
@float Figure, Plain progress bar, drawn with solid color.
@c @image{Theme_progress_bar_filled,,,,png}
@end float
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
``@@TIMEOUT_NOTIFICATION_LONG@@'' are replaced with standard and translated
@subsection Circular Progress Indicator
@c @image{Theme_circular_progress,,,,.png}
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
@subsection 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.
@subsection Boot Menu
@c @image{Theme_boot_menu,,,,.png}
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.
@subsection 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:
@multitable @columnfractions 0.3 0.3 0.3
@item Northwest (nw) @tab North (n) @tab Northeast (ne)
@item West (w) @tab Center (c) @tab East (e)
@item Southwest (sw) @tab South (s) @tab Southeast (se)
@end multitable
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:
@item 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.
@item The corner slices (northwest, northeast, southeast, and southwest) are not scaled.
@item The center slice is scaled to fill the remaining space in the middle.
@end enumerate
As an example of how an image might be sliced up, consider the styled box
used for a terminal view.
@float Figure, An example of the slices (in red) used for a terminal window. This drawing was created and sliced in Inkscape_, as the next section explains.
@c @image{Box_slice_example_terminal,,,,.png}
@end float
@subsection 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:
@item Create or open the drawing you'd like use.
@item Create a new layer on the top of the layer stack. Make it visible. Select this layer as the current layer.
@item 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.
@item 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.
@item Save the drawing.
@item 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.
@item Click the layer hide icon for the slice layer in the layer palette. The rectangles will remain selected, even though they are hidden.
@item 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.
@end enumerate
@section 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:
@item Global properties.
@item Component construction.
@end enumerate
@subsection Global Properties
@subsection Format
Global properties are specified with the simple format:
@item name1: value1
@item name2: "value which may contain spaces"
@item name3: #88F
@end itemize
In this example, name3 is assigned a color value.
@subsection Global Property List
@multitable @columnfractions 0.3 0.6
@item title-text
@tab Specifies the text to display at the top center of the screen as a title.
@item title-font
@tab Defines the font used for the title message at the top of the screen.
@item title-color
@tab Defines the color of the title message.
@item message-font
@tab Currently unused. Left for backward compatibility.
@item message-color
@tab Currently unused. Left for backward compatibility.
@item message-bg-color
@tab Currently unused. Left for backward compatibility.
@item desktop-image
@tab Specifies the image to use as the background. It will be scaled
to fit the screen size or proportionally scaled depending on the scale
@item desktop-image-scale-method
@tab Specifies the scaling method for the *desktop-image*. Options are
``stretch``, ``crop``, ``padding``, ``fitwidth``, ``fitheight``.
``stretch`` for fitting the screen size. Otherwise it is proportional
scaling of a part of *desktop-image* to the part of the screen.
``crop`` part of the *desktop-image* will be proportionally scaled to
fit the screen sizes. ``padding`` the entire *desktop-image* will be
contained on the screen. ``fitwidth`` for fitting the *desktop-image*'s
width with screen width. ``fitheight`` for fitting the *desktop-image*'s
height with the screen height. Default is ``stretch``.
@item desktop-image-h-align
@tab Specifies the horizontal alignment of the *desktop-image* if
*desktop-image-scale-method* isn't equeal to ``stretch``. Options are
``left``, ``center``, ``right``. Default is ``center``.
@item desktop-image-v-align
@tab Specifies the vertical alignment of the *desktop-image* if
*desktop-image-scale-method* isn't equeal to ``stretch``. Options are
``top``, ``center``, ``bottom``. Default is ``center``.
@item desktop-color
@tab Specifies the color for the background if *desktop-image* is not
@item terminal-box
@tab 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.
@item terminal-border
@tab Specifies the border width of the terminal window.
@item terminal-left
@tab Specifies the left coordinate of the terminal window.
@item terminal-top
@tab Specifies the top coordinate of the terminal window.
@item terminal-width
@tab Specifies the width of the terminal window.
@item terminal-height
@tab Specifies the height of the terminal window.
@end multitable
@subsection 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:
@code{ + 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:
@item a single word (e.g., ``align = center``, ``color = #FF8080``),
@item a quoted string (e.g., ``text = "Hello, World!"``), or
@item a tuple (e.g., ``preferred_size = (120, 80)``).
@end itemize
@subsection Component List
The following is a list of the components and the properties they support.
@item label
A label displays a line of text.
@multitable @columnfractions 0.2 0.7
@item id
@tab Set to ``__timeout__`` to display the time elapsed to an automatical
boot of the default entry.
@item text
@tab The text to display. If ``id`` is set to ``__timeout__`` and no
``text`` property is set then the amount of seconds will be shown.
If set to ``@@KEYMAP_SHORT@@``, ``@@KEYMAP_MIDDLE@@`` or
``@@KEYMAP_LONG@@`` then predefined hotkey information will be shown.
@item font
@tab The font to use for text display.
@item color
@tab The color of the text.
@item align
@tab The horizontal alignment of the text within the component.
Options are ``left``, ``center`` and ``right``.
@item visible
@tab Set to ``false`` to hide the label.
@end multitable
@item image
A component that displays an image. The image is scaled to fit
the component.
@multitable @columnfractions 0.2 0.7
@item file
@tab The full path to the image file to load.
@end multitable
@item 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.
@multitable @columnfractions 0.2 0.7
@item id
@tab Set to ``__timeout__`` to display the time elapsed to an automatical
boot of the default entry.
@item fg_color
@tab The foreground color for plain solid color rendering.
@item bg_color
@tab The background color for plain solid color rendering.
@item border_color
@tab The border color for plain solid color rendering.
@item text_color
@tab The text color.
@item bar_style
@tab The styled box specification for the frame of the progress bar.
Example: ``progress_frame_*.png``
If the value is equal to ``highlight_style`` then no styled boxes
will be shown.
@item highlight_style
@tab The 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``.
If the value is equal to ``bar_style`` then no styled boxes
will be shown.
@item highlight_overlay
@tab If this option is set to ``true`` then the highlight box
side slices (every slice except the center slice) will overlay the
frame box side slices. And the center slice of the highlight box
can move all the way (from top to bottom), being drawn on the center
slice of the frame box. That way we can make a progress bar with
round-shaped edges so there won't be a free space from the highlight to
the frame in top and bottom scrollbar positions. Default is ``false``.
@item font
@tab The font to use for progress bar.
@item text
@tab The text to display on the progress bar. If the progress bar's ID
is set to ``__timeout__`` and the value of this property is set to
or ``@@TIMEOUT_NOTIFICATION_LONG@@``, then GRUB will update this
property with an informative message as the timeout approaches.
@end multitable
@item 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.
@multitable @columnfractions 0.3 0.6
@item id
@tab Set to ``__timeout__`` to display the time elapsed to an automatical
boot of the default entry.
@item center_bitmap
@tab The file name of the image to draw in the center of the component.
@item tick_bitmap
@tab The file name of the image to draw for the tick marks.
@item num_ticks
@tab The number of ticks that make up a full circle.
@item ticks_disappear
@tab Boolean value indicating whether tick marks should progressively appear,
or progressively disappear as *value* approaches *end*. Specify
``true`` or ``false``. Default is ``false``.
@item start_angle
@tab The position of the first tick mark to appear or disappear.
Measured in "parrots", 1 "parrot" = 1 / 256 of the full circle.
Use values ``xxx deg`` or ``xxx \xc2\xb0`` to set the angle in degrees.
@end multitable
@item boot_menu
Displays the GRUB boot menu. It allows selecting items and executing them.
@multitable @columnfractions 0.4 0.5
@item item_font
@tab The font to use for the menu item titles.
@item selected_item_font
@tab 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 item_color
@tab The color to use for the menu item titles.
@item selected_item_color
@tab The color to use for the selected menu item, or ``inherit`` (the default)
to use ``item_color`` for the selected menu item as well.
@item icon_width
@tab The width of menu item icons. Icons are scaled to the specified size.
@item icon_height
@tab The height of menu item icons.
@item item_height
@tab The height of each menu item in pixels.
@item item_padding
@tab The amount of space in pixels to leave on each side of the menu item
@item item_icon_space
@tab The space between an item's icon and the title text, in pixels.
@item item_spacing
@tab The amount of space to leave between menu items, in pixels.
@item menu_pixmap_style
@tab 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.)
@item item_pixmap_style
@tab The image file pattern for the item styled box.
@item selected_item_pixmap_style
@tab The image file pattern for the selected item highlight styled box.
@item scrollbar
@tab Boolean value indicating whether the scroll bar should be drawn if the
frame and thumb styled boxes are configured.
@item scrollbar_frame
@tab The image file pattern for the entire scroll bar.
Example: ``scrollbar_*.png``
@item scrollbar_thumb
@tab The image file pattern for the scroll bar thumb (the part of the scroll
bar that moves as scrolling occurs).
Example: ``scrollbar_thumb_*.png``
@item scrollbar_thumb_overlay
@tab If this option is set to ``true`` then the scrollbar thumb
side slices (every slice except the center slice) will overlay the
scrollbar frame side slices. And the center slice of the scrollbar_thumb
can move all the way (from top to bottom), being drawn on the center
slice of the scrollbar frame. That way we can make a scrollbar with
round-shaped edges so there won't be a free space from the thumb to
the frame in top and bottom scrollbar positions. Default is ``false``.
@item scrollbar_slice
@tab The menu frame styled box's slice in which the scrollbar will be
drawn. Possible values are ``west``, ``center``, ``east`` (default).
``west`` - the scrollbar will be drawn in the west slice (right-aligned).
``east`` - the scrollbar will be drawn in the east slice (left-aligned).
``center`` - the scrollbar will be drawn in the center slice.
Note: in case of ``center`` slice:
a) If the scrollbar should be drawn then boot menu entry's width is
decreased by the scrollbar's width and the scrollbar is drawn at the
right side of the center slice.
b) If the scrollbar won't be drawn then the boot menu entry's width
is the width of the center slice.
c) We don't necessary need the menu pixmap box to display the scrollbar.
@item scrollbar_left_pad
@tab The left scrollbar padding in pixels.
Unused if ``scrollbar_slice`` is ``west``.
@item scrollbar_right_pad
@tab The right scrollbar padding in pixels.
Unused if ``scrollbar_slice`` is ``east``.
@item scrollbar_top_pad
@tab The top scrollbar padding in pixels.
@item scrollbar_bottom_pad
@tab The bottom scrollbar padding in pixels.
@item visible
@tab Set to ``false`` to hide the boot menu.
@end multitable
@item 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.
@item 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.
@item 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.
@end itemize
@subsection Common properties
The following properties are supported by all components:
@table @samp
@item left
The distance from the left border of container to left border of the object in either of three formats:
@multitable @columnfractions 0.2 0.7
@item x @tab Value in pixels
@item p% @tab Percentage
@item p%+x @tab mixture of both
@end multitable
@item top
The distance from the left border of container to left border of the object in same format.
@item width
The width of object in same format.
@item height
The height of object in same format.
@item 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
@multitable @columnfractions 0.2 0.7
@item ``__timeout__``
@tab Component with this ID will be updated by GRUB and will indicate
time elapsed to an automatical boot of the default entry.
Affected components: ``label``, ``circular_progress``, ``progress_bar``.
@end multitable
@end table
@node Network
@chapter Booting GRUB from the network
The following instructions don't work for *-emu, i386-qemu, i386-coreboot,
i386-multiboot, mips_loongson, mips-arc and mips_qemu_mips
To generate a netbootable directory, run:
grub-mknetdir --net-directory=/srv/tftp --subdir=/boot/grub -d /usr/lib/grub/<platform>
@end group
@end example
E.g. for i386-pc:
grub-mknetdir --net-directory=/srv/tftp --subdir=/boot/grub -d /usr/lib/grub/i386-pc
@end group
@end example
Then follow instructions printed out by grub-mknetdir on configuring your DHCP
After GRUB has started, files on the TFTP server will be accessible via the
@samp{(tftp)} device.
The server IP address can be controlled by changing the
@samp{(tftp)} device name to @samp{(tftp,@var{server-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. In the following description
@var{<interface>} is placeholder for the name of network interface (platform
@table @samp
@item net_@var{<interface>}_ip
The network interface's IP address. Read-only.
@item net_@var{<interface>}_mac
The network interface's MAC address. Read-only.
@item net_@var{<interface>}_hostname
The client host name provided by DHCP. Read-only.
@item net_@var{<interface>}_domain
The client domain name provided by DHCP. Read-only.
@item net_@var{<interface>}_rootpath
The path to the client's root disk provided by DHCP. Read-only.
@item net_@var{<interface>}_extensionspath
The path to additional DHCP vendor extensions provided by DHCP. Read-only.
@item net_@var{<interface>}_boot_file
The boot file name provided by DHCP. Read-only.
@item net_@var{<interface>}_dhcp_server_name
The name of the DHCP server responsible for these boot parameters.
@item net_@var{<interface>}_next_server
The IP address of the next (usually, TFTP) server provided by DHCP.
@item net_default_interface
Initially set to name of network interface that was used to load grub.
Read-write, although setting it affects only interpretation of
@samp{net_default_ip} and @samp{net_default_mac}
@item net_default_ip
The IP address of default interface. Read-only. This is alias for the
@item net_default_mac
The default interface's MAC address. Read-only. This is alias for the
@item net_default_server
The default server used by network drives (@pxref{Device syntax}). Read-write,
although setting this is only useful before opening a network device.
@end table
@node Serial terminal
@chapter Using GRUB via a serial line
This chapter describes how to use the serial terminal support in GRUB.
If you have many computers or computers with no display/keyboard, it
could be very useful to control the computers through serial
communications. To connect one computer with another via a serial line,
you need to prepare a null-modem (cross) serial cable, and you may need
to have multiport serial boards, if your computer doesn't have extra
serial ports. In addition, a terminal emulator is also required, such as
minicom. Refer to a manual of your operating system, for more
As for GRUB, the instruction to set up a serial terminal is quite
simple. Here is an example:
grub> @kbd{serial --unit=0 --speed=9600}
grub> @kbd{terminal_input serial; terminal_output serial}
@end group
@end example
The command @command{serial} initializes the serial unit 0 with the
speed 9600bps. The serial unit 0 is usually called @samp{COM1}, so, if
you want to use COM2, you must specify @samp{--unit=1} instead. This
command accepts many other options, so please refer to @ref{serial},
for more details.
The commands @command{terminal_input} (@pxref{terminal_input}) and
@command{terminal_output} (@pxref{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 @code{console} to the command,
as @samp{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
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 @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.
@node Vendor power-on keys
@chapter 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 @samp{GRUB_TIMEOUT_BUTTON},
@samp{GRUB_BUTTON_CMOS_ADDRESS} variables in default/grub (@pxref{Simple
configuration}). @samp{GRUB_TIMEOUT_BUTTON},
instead of the corresponding variables without the @samp{_BUTTON} suffix
when powered on using the special button. @samp{GRUB_BUTTON_CMOS_ADDRESS}
is vendor-specific and partially model-specific. Values known to the GRUB
team are:
@table @key
@item Dell XPS M1330M
@item Dell XPS M1530
@item Dell Latitude E4300
@item Asus EeePC 1005PE
84:1 (unconfirmed)
@item LENOVO ThinkPad T410s (2912W1C)
@end table
To take full advantage of this function, install GRUB into the MBR
(@pxref{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:
@item boot normally
sudo modprobe nvram
sudo cat /dev/nvram | xxd > normal_button.txt
@end example
@item boot using vendor button
sudo modprobe nvram
sudo cat /dev/nvram | xxd > normal_vendor.txt
@end example
@end itemize
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
@end example
It's a bit number 3 as seen from following table:
@multitable @columnfractions .2 .2
@item 0 @tab 01
@item 1 @tab 02
@item 2 @tab 04
@item 3 @tab 08
@item 4 @tab 10
@item 5 @tab 20
@item 6 @tab 40
@item 7 @tab 80
@end multitable
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
@node Images
@chapter GRUB image files
@c FIXME: parts of this section are specific to PC BIOS right now.
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.
@table @file
@item 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
The sole function of @file{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,
@file{boot.img} cannot understand any file system structure, so
@command{grub-install} hardcodes the location of the first sector of the
core image into @file{boot.img} when installing GRUB.
@item 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.
@item 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 @file{diskboot.img}.
@item pxeboot.img
This image is used as the start of the core image when booting from the
network using PXE. @xref{Network}.
@item 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
@samp{image=} section.
@item 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
@item 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 @command{grub-mkimage}
program. Usually, it contains enough modules to access @file{/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.
@xref{BIOS installation}, for details on where the core image can be
installed on PC systems.
@item *.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 @command{insmod}
command (@pxref{insmod}).
@end table
@heading 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.
@table @file
@item stage1
Stage 1 from GRUB Legacy was very similar to @file{boot.img} in GRUB 2, and
they serve the same function.
@item *_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 @file{core.img} in GRUB 2.
However, @file{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. @file{core.img} is built in a more flexible way,
allowing GRUB 2 to support reading modules from advanced disk types such as
GRUB Legacy could run with only Stage 1 and Stage 2 in some limited
configurations, while GRUB 2 requires @file{core.img} and cannot work
without it.
@item stage2
GRUB 2 has no single Stage 2 image. Instead, it loads modules from
@file{/boot/grub} at run-time.
@item stage2_eltorito
In GRUB 2, images for booting from CD-ROM drives are now constructed using
@file{cdboot.img} and @file{core.img}, making sure that the core image
contains the @samp{iso9660} module. It is usually best to use the
@command{grub-mkrescue} program for this.
@item nbgrub
There is as yet no equivalent for @file{nbgrub} in GRUB 2; it was used by
Etherboot and some other network boot loaders.
@item pxegrub
In GRUB 2, images for PXE network booting are now constructed using
@file{pxeboot.img} and @file{core.img}, making sure that the core image
contains the @samp{pxe} and @samp{pxecmd} modules. @xref{Network}.
@end table
@node Core image size limitation
@chapter Core image size limitation
Heavily limited platforms:
@item i386-pc (normal and PXE): the core image size (compressed) is limited by 458240 bytes.
kernel.img (.text + .data + .bss, uncompressed) is limited by 392704 bytes.
module size (uncompressed) + kernel.img (.text + .data, uncompressed) is limited by the size of contiguous chunk at 1M address.
@item sparc64-ieee1275: kernel.img (.text + .data + .bss) + modules + 256K (stack) + 2M (heap) is limited by space available at 0x4400. On most platforms it's just 3 or 4M since ieee1275 maps only so much.
@item i386-ieee1275: kernel.img (.text + .data + .bss) + modules is limited by memory available at 0x10000, at most 596K
@end itemize
Lightly limited platforms:
@item *-xen: limited only by adress space and RAM size.
@item i386-qemu: kernel.img (.text + .data + .bss) is limited by 392704 bytes.
(core.img would be limited by ROM size but it's unlimited on qemu
@item All EFI platforms: limited by contiguous RAM size and possibly firmware bugs
@item Coreboot and multiboot. kernel.img (.text + .data + .bss) is limited by 392704 bytes.
module size is limited by the size of contiguous chunk at 1M address.
@item mipsel-loongson (ELF), mips(el)-qemu_mips (ELF): if uncompressed:
kernel.img (.text + .data) + modules is limited by the space from 80200000 forward
if compressed:
kernel.img (.text + .data, uncompressed) + modules (uncompressed)
+ (modules + kernel.img (.text + .data)) (compressed)
+ decompressor is limited by the space from 80200000 forward
@item mipsel-loongson (Flash), mips(el)-qemu_mips (Flash): kernel.img (.text + .data) + modules is limited by the space from 80200000 forward
core.img (final) is limited by flash size (512K on yeeloong and fulooong)
@item mips-arc: if uncompressed:
kernel.img (.text + .data) is limited by the space from 8bd00000 forward
modules + dummy decompressor is limited by the space from 8bd00000 backward
if compressed:
kernel.img (.text + .data, uncompressed) is limited by the space from 8bd00000 forward
modules (uncompressed) + (modules + kernel.img (.text + .data)) (compressed, aligned to 1M)
+ 1M (decompressor + scratch space) is limited by the space from 8bd00000 backward
@item powerpc-ieee1275: kernel.img (.text + .data + .bss) + modules is limited by space available at 0x200000
@end itemize
@node Filesystem
@chapter Filesystem syntax and semantics
GRUB uses a special syntax for specifying disk drives which can be
accessed by BIOS. Because of BIOS limitations, GRUB cannot distinguish
between IDE, ESDI, SCSI, or others. You must know yourself which BIOS
device is equivalent to which OS device. Normally, that will be clear if
you see the files in a device or use the command @command{search}
* Device syntax:: How to specify devices
* File name syntax:: How to specify files
* Block list syntax:: How to specify block lists
@end menu
@node Device syntax
@section How to specify devices
The device syntax is like this:
@end example
@samp{[]} means the parameter is optional. @var{device} depends on the disk
driver in use. BIOS and EFI disks use either @samp{fd} or @samp{hd} followed
by a digit, like @samp{fd0}, or @samp{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
RAID (md), ofdisk (ieee1275 and nand), LVM (lvm), LDM, virtio (vdsk)
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 @command{loopback} command.
Hostdisk uses names specified in 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>. For LVM additionally you can use the syntax
@end example
@var{part-num} represents the partition number of @var{device}, starting
from one. @var{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 @samp{(hd0)} represents using the entire disk (or the
MBR when installing GRUB), while the syntax @samp{(hd0,1)}
represents using the first partition of the disk (or the boot sector
of the partition when installing GRUB).
@end example
If you enabled the network support, the special drives
@code{(@var{protocol}[,@var{server}])} are also available. Supported protocols
are @samp{http} and @samp{tftp}. If @var{server} is omitted, value of
environment variable @samp{net_default_server} is used.
Before using the network drive, you must initialize the network.
@xref{Network}, for more information.
If you boot GRUB from a CD-ROM, @samp{(cd)} is available. @xref{Making
a GRUB bootable CD-ROM}, for details.
@node File name syntax
@section How to specify files
There are two ways to specify files, by @dfn{absolute file name} and by
@dfn{block list}.
An absolute file name resembles a Unix absolute file name, using
@samp{/} for the directory separator (not @samp{\} as in DOS). One
example is @samp{(hd0,1)/boot/grub/grub.cfg}. This means the file
@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 @dfn{root device} implicitly. So if you set the root device to,
say, @samp{(hd1,1)} by the command @samp{set root=(hd1,1)} (@pxref{set}),
then @code{/boot/kernel} is the same as @code{(hd1,1)/boot/kernel}.
On ZFS filesystem the first path component must be
So @samp{/rootvol@@snap-129/boot/grub/grub.cfg} refers to file
@samp{/boot/grub/grub.cfg} in snapshot of volume @samp{rootvol} with name
@samp{snap-129}. Trailing @samp{@@} after volume name is mandatory even if
snapshot name is omitted.
@node Block list syntax
@section 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
Here is an example:
@end example
This represents that GRUB should read blocks 0 through 99, block 200,
and blocks 300 through 599. If you omit an offset, then GRUB assumes
the offset is zero.
Like the file name syntax (@pxref{File name syntax}), if a blocklist
does not contain a device name, then GRUB uses GRUB's @dfn{root
device}. So @code{(hd0,2)+1} is the same as @code{+1} when the root
device is @samp{(hd0,2)}.
@node Interface
@chapter GRUB's user interface
GRUB has both a simple menu interface for choosing preset entries from a
configuration file, and a highly flexible command-line for performing
any desired combination of boot commands.
GRUB looks for its configuration file as soon as it is loaded. If one
is found, then the full menu interface is activated using whatever
entries were found in the file. If you choose the @dfn{command-line} menu
option, or if the configuration file was not found, then GRUB drops to
the command-line interface.
* Command-line interface:: The flexible command-line interface
* Menu interface:: The simple menu interface
* Menu entry editor:: Editing a menu entry
@end menu
@node Command-line interface
@section The flexible command-line interface
The command-line interface provides a prompt and after it an editable
text area much like a command-line in Unix or DOS. Each command is
immediately executed after it is entered@footnote{However, this
behavior will be changed in the future version, in a user-invisible
way.}. The commands (@pxref{Command-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:
@table @key
@item C-f
@itemx PC right key
Move forward one character.
@item C-b
@itemx PC left key
Move back one character.
@item C-a
@itemx HOME
Move to the start of the line.
@item C-e
@itemx END
Move the the end of the line.
@item C-d
@itemx DEL
Delete the character underneath the cursor.
@item C-h
@itemx BS
Delete the character to the left of the cursor.
@item C-k
Kill the text from the current cursor position to the end of the line.
@item C-u
Kill backward from the cursor to the beginning of the line.
@item C-y
Yank the killed text back into the buffer at the cursor.
@item C-p
@itemx PC up key
Move up through the history list.
@item C-n
@itemx PC down key
Move down through the history list.
@end table
When typing commands interactively, if the cursor is within or before
the first word in the command-line, pressing the @key{TAB} key (or
@key{C-i}) will display a listing of the available commands, and if the
cursor is after the first word, the @kbd{@key{TAB}} will provide a
completion listing of disks, partitions, and file names depending on the
context. Note that to obtain a list of drives, one must open a
parenthesis, as @command{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.
@node Menu interface
@section The simple menu interface
The menu interface is quite easy to use. Its commands are both
reasonably intuitive and described on screen.
Basically, the menu interface provides a list of @dfn{boot entries} to
the user to choose from. Use the arrow keys to select the entry of
choice, then press @key{RET} to run it. An optional timeout is
available to boot the default entry (the first one if not set), which is
aborted by pressing any key.
Commands are available to enter a bare command-line by pressing @key{c}
(which operates exactly like the non-config-file version of GRUB, but
allows one to return to the menu if desired by pressing @key{ESC}) or to
edit any of the @dfn{boot entries} by pressing @key{e}.
If you protect the menu interface with a password (@pxref{Security}),
all you can do is choose an entry by pressing @key{RET}, or press
@key{p} to enter the password.
@node Menu entry editor
@section Editing a menu entry
The menu entry editor looks much like the main menu interface, but the
lines in the menu are individual commands in the selected entry instead
of entry names.
If an @key{ESC} is pressed in the editor, it aborts all the changes made
to the configuration entry and returns to the main menu interface.
Each line in the menu entry can be edited freely, and you can add new lines
by pressing @key{RET} at the end of a line. To boot the edited entry, press
Although GRUB unfortunately does not support @dfn{undo}, you can do almost
the same thing by just returning to the main menu using @key{ESC}.
@node Environment
@chapter 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 (@pxref{set}), unset (@pxref{unset}), or
looked up (@pxref{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.
* Special environment variables::
* Environment block::
@end menu
@node Special environment variables
@section Special environment variables
These variables have special meaning to GRUB.
* biosnum::
* check_signatures::
* chosen::
* cmdpath::
* color_highlight::
* color_normal::
* config_directory::
* config_file::
* debug::
* default::
* fallback::
* gfxmode::
* gfxpayload::
* gfxterm_font::
* grub_cpu::
* grub_platform::
* icondir::
* lang::
* locale_dir::
* menu_color_highlight::
* menu_color_normal::
* net_@var{<interface>}_boot_file::
* net_@var{<interface>}_dhcp_server_name::
* net_@var{<interface>}_domain::
* net_@var{<interface>}_extensionspath::
* net_@var{<interface>}_hostname::
* net_@var{<interface>}_ip::
* net_@var{<interface>}_mac::
* net_@var{<interface>}_next_server::
* net_@var{<interface>}_rootpath::
* net_default_interface::
* net_default_ip::
* net_default_mac::
* net_default_server::
* pager::
* prefix::
* pxe_blksize::
* pxe_default_gateway::
* pxe_default_server::
* root::
* superusers::
* theme::
* timeout::
* timeout_style::
@end menu
@node biosnum
@subsection biosnum
When chain-loading another boot loader (@pxref{Chain-loading}), GRUB may
need to know what BIOS drive number corresponds to the root device
(@pxref{root}) so that it can set up registers properly. If the
@var{biosnum} variable is set, it overrides GRUB's own means of guessing
For an alternative approach which also changes BIOS drive mappings for the
chain-loaded system, @pxref{drivemap}.
@node check_signatures
@subsection check_signatures
This variable controls whether GRUB enforces digital signature
validation on loaded files. @xref{Using digital signatures}.
@node chosen
@subsection chosen
When executing a menu entry, GRUB sets the @var{chosen} variable to the
title of the entry being executed.
If the menu entry is in one or more submenus, then @var{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 @samp{>}.
@node cmdpath
@subsection cmdpath
The location from which @file{core.img} was loaded as an absolute
directory name (@pxref{File name syntax}). This is set by GRUB at
startup based on information returned by platform firmware. Not every
platform provides this information and some may return only device
without path name.
@node color_highlight
@subsection color_highlight
This variable contains the ``highlight'' foreground and background terminal
colors, separated by a slash (@samp{/}). Setting this variable changes
those colors. For the available color names, @pxref{color_normal}.
The default is @samp{black/light-gray}.
@node color_normal
@subsection color_normal
This variable contains the ``normal'' foreground and background terminal
colors, separated by a slash (@samp{/}). Setting this variable changes
those colors. Each color must be a name from the following list:
@itemize @bullet
@item black
@item blue
@item green
@item cyan
@item red
@item magenta
@item brown
@item light-gray
@item dark-gray
@item light-blue
@item light-green
@item light-cyan
@item light-red
@item light-magenta
@item yellow
@item white
@end itemize
The default is @samp{light-gray/black}.
The color support support varies from terminal to terminal.
@samp{morse} has no color support at all.
@samp{mda_text} color support is limited to highlighting by
black/white reversal.
@samp{console} on ARC, EMU and IEEE1275, @samp{serial_*} and
@samp{spkmodem} are governed by terminfo and support
only 8 colors if in modes @samp{vt100-color} (default for console on emu),
@samp{arc} (default for console on ARC), @samp{ieee1275} (default
for console on IEEE1275). When in mode @samp{vt100}
then the color support is limited to highlighting by black/white
reversal. When in mode @samp{dumb} there is no color support.
When console supports no colors this setting is ignored.
When console supports 8 colors, then the colors from the
second half of the previous list are mapped to the
matching colors of first half.
@samp{console} on EFI and BIOS and @samp{vga_text} support all 16 colors.
@samp{gfxterm} supports all 16 colors and would be theoretically extendable
to support whole rgb24 palette but currently there is no compelling reason
to go beyond the current 16 colors.
@node config_directory
@subsection config_directory
This variable is automatically set by GRUB to the directory part of
current configuration file name (@pxref{config_file}).
@node config_file
@subsection config_file
This variable is automatically set by GRUB to the name of configuration file that is being
processed by commands @command{configfile} (@pxref{configfile}) or @command{normal}
(@pxref{normal}). It is restored to the previous value when command completes.
@node debug
@subsection 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 @samp{,}, or @samp{all} to enable all available debugging
output. The facility names are the first argument to grub_dprintf. Consult
source for more details.
@node default
@subsection default
If this variable is set, it identifies a menu entry that should be
selected by default, possibly after a timeout (@pxref{timeout}). The
entry may be identified by number (starting from 0 at each level of
the hierarchy), by title, or by id.
For example, if you have:
menuentry 'Example GNU/Linux distribution' --class gnu-linux --id example-gnu-linux {
@end verbatim
then you can make this the default using:
@end example
If the entry is in a submenu, then it must be identified using the
number, title, or id of each of the submenus starting from the top
level, followed by the number, title, or id of the menu entry itself,
with each element separated by @samp{>}. For example, take the
following menu structure:
GNU/Hurd --id gnu-hurd
Standard Boot --id=gnu-hurd-std
Rescue shell --id=gnu-hurd-rescue
Other platforms --id=other
Minix --id=minix
Version 3.4.0 --id=minix-3.4.0
Version 3.3.0 --id=minix-3.3.0
GRUB Invaders --id=grub-invaders
@end example
The more recent release of Minix would then be identified as
@samp{Other platforms>Minix>Version 3.4.0}, or as @samp{1>0>0}, or as
This variable is often set by @samp{GRUB_DEFAULT} (@pxref{Simple
configuration}), @command{grub-set-default}, or @command{grub-reboot}.
@node fallback
@subsection 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 @samp{default} (@pxref{default}).
@node gfxmode
@subsection gfxmode
If this variable is set, it sets the resolution used on the @samp{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 @samp{auto}, which
selects a platform-specific default that should look reasonable. Supported
modes can be listed by @samp{videoinfo} command in GRUB.
The resolution may be specified as a sequence of one or more modes,
separated by commas (@samp{,}) or semicolons (@samp{;}); each will be tried
in turn until one is found. Each mode should be either @samp{auto},
@samp{@var{width}x@var{height}}, or
@node gfxpayload
@subsection gfxpayload
If this variable is set, it controls the video mode in which the Linux
kernel starts up, replacing the @samp{vga=} boot option (@pxref{linux}). It
may be set to @samp{text} to force the Linux kernel to boot in normal text
mode, @samp{keep} to preserve the graphics mode set using @samp{gfxmode}, or
any of the permitted values for @samp{gfxmode} to set a particular graphics
mode (@pxref{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 @samp{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 @samp{text}. Otherwise the
default may be @samp{auto} or a specific video mode.
This variable is often set by @samp{GRUB_GFXPAYLOAD_LINUX} (@pxref{Simple
@node gfxterm_font
@subsection gfxterm_font
If this variable is set, it names a font to use for text on the
@samp{gfxterm} graphical terminal. Otherwise, @samp{gfxterm} may use any
available font.
@node grub_cpu
@subsection grub_cpu
In normal mode (@pxref{normal}), GRUB sets the @samp{grub_cpu} variable to
the CPU type for which GRUB was built (e.g. @samp{i386} or @samp{powerpc}).
@node grub_platform
@subsection grub_platform
In normal mode (@pxref{normal}), GRUB sets the @samp{grub_platform} variable
to the platform for which GRUB was built (e.g. @samp{pc} or @samp{efi}).
@node icondir
@subsection 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 @samp{icons}
directory. @xref{Theme file format}.
@node lang
@subsection lang
If this variable is set, it names the language code that the
@command{gettext} command (@pxref{gettext}) uses to translate strings. For
example, French would be named as @samp{fr}, and Simplified Chinese as
@command{grub-mkconfig} (@pxref{Simple configuration}) will try to set a
reasonable default for this variable based on the system locale.
@node locale_dir
@subsection locale_dir
If this variable is set, it names the directory where translation files may
be found (@pxref{gettext}), usually @file{/boot/grub/locale}. Otherwise,
internationalization is disabled.
@command{grub-mkconfig} (@pxref{Simple configuration}) will set a reasonable
default for this variable if internationalization is needed and any
translation files are available.
@node menu_color_highlight
@subsection menu_color_highlight
This variable contains the foreground and background colors to be used for
the highlighted menu entry, separated by a slash (@samp{/}). Setting this
variable changes those colors. For the available color names,
The default is the value of @samp{color_highlight}
@node menu_color_normal
@subsection menu_color_normal
This variable contains the foreground and background colors to be used for
non-highlighted menu entries, separated by a slash (@samp{/}). Setting this
variable changes those colors. For the available color names,
The default is the value of @samp{color_normal} (@pxref{color_normal}).
@node net_@var{<interface>}_boot_file
@subsection net_@var{<interface>}_boot_file
@node net_@var{<interface>}_dhcp_server_name
@subsection net_@var{<interface>}_dhcp_server_name
@node net_@var{<interface>}_domain
@subsection net_@var{<interface>}_domain
@node net_@var{<interface>}_extensionspath
@subsection net_@var{<interface>}_extensionspath
@node net_@var{<interface>}_hostname
@subsection net_@var{<interface>}_hostname
@node net_@var{<interface>}_ip
@subsection net_@var{<interface>}_ip
@node net_@var{<interface>}_mac
@subsection net_@var{<interface>}_mac
@node net_@var{<interface>}_next_server
@subsection net_@var{<interface>}_next_server
@node net_@var{<interface>}_rootpath
@subsection net_@var{<interface>}_rootpath
@node net_default_interface
@subsection net_default_interface
@node net_default_ip
@subsection net_default_ip
@node net_default_mac
@subsection net_default_mac
@node net_default_server
@subsection net_default_server
@node pager
@subsection pager
If set to @samp{1}, pause output after each screenful and wait for keyboard
input. The default is not to pause output.
@node prefix
@subsection prefix
The location of the @samp{/boot/grub} directory as an absolute file name
(@pxref{File name syntax}). This is normally set by GRUB at startup based
on information provided by @command{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.
@node pxe_blksize
@subsection pxe_blksize
@node pxe_default_gateway
@subsection pxe_default_gateway
@node pxe_default_server
@subsection pxe_default_server
@node root
@subsection root
The root device name (@pxref{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 @samp{prefix}
For example, if GRUB was installed to the first partition of the first hard
disk, then @samp{prefix} might be set to @samp{(hd0,msdos1)/boot/grub} and
@samp{root} to @samp{hd0,msdos1}.
@node superusers
@subsection superusers
This variable may be set to a list of superuser names to enable
authentication support. @xref{Security}.
@node theme
@subsection theme
This variable may be set to a directory containing a GRUB graphical menu
theme. @xref{Theme file format}.
This variable is often set by @samp{GRUB_THEME} (@pxref{Simple
@node timeout
@subsection 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 @samp{0}
means to boot the default entry immediately without displaying the menu; a
timeout of @samp{-1} (or unset) means to wait indefinitely.
If @samp{timeout_style} (@pxref{timeout_style}) is set to @samp{countdown}
or @samp{hidden}, the timeout is instead counted before the menu is
This variable is often set by @samp{GRUB_TIMEOUT} (@pxref{Simple
@node timeout_style
@subsection timeout_style
This variable may be set to @samp{menu}, @samp{countdown}, or @samp{hidden}
to control the way in which the timeout (@pxref{timeout}) interacts with
displaying the menu. See the documentation of @samp{GRUB_TIMEOUT_STYLE}
(@pxref{Simple configuration}) for details.
@node Environment block
@section 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 @file{/boot/grub/grubenv} (although you should not assume this). At boot
time, the @command{load_env} command (@pxref{load_env}) loads environment
variables from it, and the @command{save_env} (@pxref{save_env}) command
saves environment variables to it. From a running system, the
@command{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).
@command{grub-mkconfig} uses this facility to implement
@samp{GRUB_SAVEDEFAULT} (@pxref{Simple configuration}).
@node Commands
@chapter 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 @command{insmod} (@pxref{insmod}), @command{ls}
(@pxref{ls}), @command{set} (@pxref{set}), and @command{unset}
(@pxref{unset}) commands are normally available. If you end up in rescue
mode and do not know what to do, then @pxref{GRUB only offers a rescue
* Menu-specific commands::
* General commands::
* Command-line and menu entry commands::
* Networking commands::
@end menu
@node Menu-specific commands
@section The list of commands for the menu only
The semantics used in parsing the configuration file are the following:
@itemize @bullet
The files @emph{must} be in plain-text format.
@samp{#} 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 @samp{0x}, and is case-insensitive.
@end itemize
These commands can only be used in the menu:
* menuentry:: Start a menu entry
* submenu:: Group menu entries
@end menu
@node menuentry
@subsection menuentry
@deffn Command menuentry @var{title} @
[@option{--class=class} @dots{}] [@option{--users=users}] @
[@option{--unrestricted}] [@option{--hotkey=key}] [@option{--id=id}] @
[@var{arg} @dots{}] @{ @var{command}; @dots{} @}
This defines a GRUB menu entry named @var{title}. When this entry is
selected from the menu, GRUB will set the @var{chosen} environment variable
to value of @option{--id} if @option{--id} is given, 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 @command{boot} command.
The @option{--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 @option{--users} option grants specific users access to specific menu
entries. @xref{Security}.
The @option{--unrestricted} option grants all users access to specific menu
entries. @xref{Security}.
The @option{--hotkey} option associates a hotkey with a menu entry.
@var{key} may be a single letter, or one of the aliases @samp{backspace},
@samp{tab}, or @samp{delete}.
The @option{--id} may be used to associate unique identifier with a menu entry.
@var{id} is string of ASCII aphanumeric characters, underscore and hyphen
and should not start with a digit.
All other arguments including @var{title} are passed as positional parameters
when list of commands is executed with @var{title} always assigned to @code{$1}.
@end deffn
@node submenu
@subsection submenu
@deffn Command submenu @var{title} @
[@option{--class=class} @dots{}] [@option{--users=users}] @
[@option{--unrestricted}] [@option{--hotkey=key}] [@option{--id=id}] @
@{ @var{menu entries} @dots{} @}
This defines a submenu. An entry called @var{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 @command{menuentry} command
@end deffn
@node General commands
@section The list of general commands
Commands usable anywhere in the menu and in the command-line.
* serial:: Set up a serial device
* terminal_input:: Manage input terminals
* terminal_output:: Manage output terminals
* terminfo:: Define terminal type
@end menu
@node serial
@subsection serial
@deffn Command serial [@option{--unit=unit}] [@option{--port=port}] [@option{--speed=speed}] [@option{--word=word}] [@option{--parity=parity}] [@option{--stop=stop}]
Initialize a serial device. @var{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. @var{port} is the I/O port where the UART
is to be found; if specified it takes precedence over @var{unit}.
@var{speed} is the transmission speed; default is 9600. @var{word} and
@var{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. @var{parity} is one of @samp{no}, @samp{odd},
@samp{even} and defaults to @samp{no}.
The serial port is not used as a communication channel unless the
@command{terminal_input} or @command{terminal_output} command is used
(@pxref{terminal_input}, @pxref{terminal_output}).
See also @ref{Serial terminal}.
@end deffn
@node terminal_input
@subsection terminal_input
@deffn Command terminal_input [@option{--append}|@option{--remove}] @
[terminal1] [terminal2] @dots{}
List or select an input terminal.
With no arguments, list the active and available input terminals.
With @option{--append}, add the named terminals to the list of active input
terminals; any of these may be used to provide input to GRUB.
With @option{--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.
@end deffn
@node terminal_output
@subsection terminal_output
@deffn Command terminal_output [@option{--append}|@option{--remove}] @
[terminal1] [terminal2] @dots{}
List or select an output terminal.
With no arguments, list the active and available output terminals.
With @option{--append}, add the named terminals to the list of active output
terminals; all of these will receive output from GRUB.
With @option{--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.
@end deffn
@node terminfo
@subsection terminfo
@deffn 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 @samp{TERM}
environment variable in Unix.
The currently available terminal types are @samp{vt100}, @samp{vt100-color},
@samp{ieee1275}, and @samp{dumb}. If you need other terminal types, please
contact us to discuss the best way to include support for these in GRUB.
The @option{-a} (@option{--ascii}), @option{-u} (@option{--utf8}), and
@option{-v} (@option{--visual-utf8}) options control how non-ASCII text is
displayed. @option{-a} specifies an ASCII-only terminal; @option{-u}
specifies logically-ordered UTF-8; and @option{-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
@end deffn
@node Command-line and menu entry commands
@section 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 @command{help}
* [:: Check file types and compare values
* acpi:: Load ACPI tables
* authenticate:: Check whether user is in user list
* background_color:: Set background color for active terminal
* background_image:: Load background image for active terminal
* 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
* clear:: Clear the screen
* cmosclean:: Clear bit in CMOS
* cmosdump:: Dump CMOS contents
* cmostest:: Test bit in CMOS
* cmp:: Compare two files
* configfile:: Load a configuration file
* cpuid:: Check for CPU features
* crc:: Compute or check CRC32 checksums
* cryptomount:: Mount a crypto device
* date:: Display or set current date and time
* devicetree:: Load a device tree blob
* distrust:: Remove a pubkey from trusted keys
* drivemap:: Map a drive to another
* echo:: Display a line of text
* eval:: Evaluate agruments as GRUB commands
* 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
* hashsum:: Compute or check hash checksum
* 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
* list_trusted:: List trusted public keys
* load_env:: Load variables from environment block
* loadfont:: Load font files
* loopback:: Make a device from a filesystem image
* ls:: List devices or files
* lsfonts:: List loaded fonts
* lsmod:: Show loaded modules
* md5sum:: Compute or check MD5 hash
* module:: Load module for multiboot kernel
* multiboot:: Load multiboot compliant kernel
* nativedisk:: Switch to native disk drivers
* 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
* probe:: Retrieve device info
* pxe_unload:: Unload the PXE environment
* read:: Read user input
* reboot:: Reboot your computer
* regexp:: Test if regular expression matches string
* rmmod:: Remove a module
* save_env:: Save variables to environment block
* search:: Search devices by file, label, or UUID
* sendkey:: Emulate keystrokes
* set:: Set an environment variable
* sha1sum:: Compute or check SHA1 hash
* sha256sum:: Compute or check SHA256 hash
* sha512sum:: Compute or check SHA512 hash
* sleep:: Wait for a specified number of seconds
* source:: Read a configuration file in same context
* test:: Check file types and compare values
* true:: Do nothing, successfully
* trust:: Add public key to list of trusted keys
* unset:: Unset an environment variable
* uppermem:: Set the upper memory size
@comment * vbeinfo:: List available video modes
* verify_detached:: Verify detached digital signature
* videoinfo:: List available video modes
@comment * xen_*:: Xen boot commands for AArch64
* xen_hypervisor:: Load xen hypervisor binary (only on AArch64)
* xen_module:: Load xen modules for xen hypervisor (only on AArch64)
@end menu
@node [
@subsection [
@deffn Command @code{[} expression @code{]}
Alias for @code{test @var{expression}} (@pxref{test}).
@end deffn
@node acpi
@subsection acpi
@deffn Command acpi [@option{-1}|@option{-2}] @
[@option{--exclude=table1,@dots{}}|@option{--load-only=table1,@dots{}}] @
[@option{--oemid=id}] [@option{--oemtable=table}] @
[@option{--oemtablerev=rev}] [@option{--oemtablecreator=creator}] @
[@option{--oemtablecreatorrev=rev}] [@option{--no-ebda}] @
filename @dots{}
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
@option{--no-ebda} option is used, the new tables will be known only to
GRUB, but may be used by GRUB's EFI emulation.
@end deffn
@node authenticate
@subsection authenticate
@deffn Command authenticate [userlist]
Check whether user is in @var{userlist} or listed in the value of variable
@samp{superusers}. See @pxref{superusers} for valid user list format.
If @samp{superusers} is empty, this command returns true. @xref{Security}.
@end deffn
@node background_color
@subsection background_color
@deffn Command background_color color
Set background color for active terminal. For valid color specifications see
@pxref{Theme file format, ,Colors}. Background color can be changed only when
using @samp{gfxterm} for terminal output.
This command sets color of empty areas without text. Text background color
is controlled by environment variables @var{color_normal}, @var{color_highlight},
@var{menu_color_normal}, @var{menu_color_highlight}. @xref{Special environment variables}.
@end deffn
@node background_image
@subsection background_image
@deffn Command background_image [[@option{--mode} @samp{stretch}|@samp{normal}] file]
Load background image for active terminal from @var{file}. Image is stretched
to fill up entire screen unless option @option{--mode} @samp{normal} is given.
Without arguments remove currently loaded background image. Background image
can be changed only when using @samp{gfxterm} for terminal output.
@end deffn
@node badram
@subsection badram
@deffn Command badram addr,mask[,addr,mask...]
Filter out bad RAM.
@end deffn
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 @uref{,
Memtest86+ utility}: a list of address/mask pairs. Given a page-aligned
address and a base address / mask pair, if all the bits of the page-aligned
address that are enabled by the mask match with the base address, it means
this page is to be filtered. This syntax makes it easy to represent patterns
that are often result of memory damage, due to physical distribution of memory
@node blocklist
@subsection blocklist
@deffn Command blocklist file
Print a block list (@pxref{Block list syntax}) for @var{file}.
@end deffn
@node boot
@subsection boot
@deffn 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).
@end deffn
@node cat
@subsection cat
@deffn Command cat [@option{--dos}] file
Display the contents of the file @var{file}. This command may be useful
to remind you of your OS's root partition:
grub> @kbd{cat /etc/fstab}
@end example
If the @option{--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 (@samp{<d>}) to make it easier to see
when boot problems are caused by a file formatted using DOS-style line
@end deffn
@node chainloader
@subsection chainloader
@deffn Command chainloader [@option{--force}] file
Load @var{file} as a chain-loader. Like any other file loaded by the
filesystem code, it can use the blocklist notation (@pxref{Block list
syntax}) to grab the first sector of the current partition with @samp{+1}.
If you specify the option @option{--force}, then load @var{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.
@end deffn
@node clear
@subsection clear
@deffn Command clear
Clear the screen.
@end deffn
@node cmosclean
@subsection cmosclean
@deffn Command cmosclean byte:bit
Clear value of bit in CMOS at location @var{byte}:@var{bit}. This command
is available only on platforms that support CMOS.
@end deffn
@node cmosdump
@subsection cmosdump
@deffn Dump CMOS contents
Dump full CMOS contents as hexadecimal values. This command is available only
on platforms that support CMOS.
@end deffn
@node cmostest
@subsection cmostest
@deffn Command cmostest byte:bit
Test value of bit in CMOS at location @var{byte}:@var{bit}. Exit status
is zero if bit is set, non zero otherwise. This command is available only
on platforms that support CMOS.
@end deffn
@node cmp
@subsection cmp
@deffn Command cmp file1 file2
Compare the file @var{file1} with the file @var{file2}. If they differ
in size, print the sizes like this:
Differ in size: 0x1234 [foo], 0x4321 [bar]
@end example
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]
@end example
If they are completely identical, nothing will be printed.
@end deffn
@node configfile
@subsection configfile
@deffn Command configfile file
Load @var{file} as a configuration file. If @var{file} defines any menu
entries, then show a menu containing them immediately. Any environment
variable changes made by the commands in @var{file} will not be preserved
after @command{configfile} returns.
@end deffn
@node cpuid
@subsection cpuid
@deffn Command cpuid [-l] [-p]
Check for CPU features. This command is only available on x86 systems.
With the @option{-l} option, return true if the CPU supports long mode
With the @option{-p} option, return true if the CPU supports Physical
Address Extension (PAE).
If invoked without options, this command currently behaves as if it had been
invoked with @option{-l}. This may change in the future.
@end deffn
@node crc
@subsection crc
@deffn Command crc arg @dots{}
Alias for @code{hashsum --hash crc32 arg @dots{}}. See command @command{hashsum}
(@pxref{hashsum}) for full description.
@end deffn
@node cryptomount
@subsection cryptomount
@deffn Command cryptomount device|@option{-u} uuid|@option{-a}|@option{-b}
Setup access to encrypted device. If necessary, passphrase
is requested interactively. Option @var{device} configures specific grub device
(@pxref{Naming convention}); option @option{-u} @var{uuid} configures device
with specified @var{uuid}; option @option{-a} configures all detected encrypted
devices; option @option{-b} configures all geli containers that have boot flag set.
GRUB suports devices encrypted using LUKS and geli. Note that necessary modules (@var{luks} and @var{geli}) have to be loaded manually before this command can
be used.
@end deffn
@node date
@subsection date
@deffn 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.
@end deffn
@node devicetree
@subsection linux
@deffn Command devicetree file
Load a device tree blob (.dtb) from a filesystem, for later use by a Linux
kernel. Does not perform merging with any device tree supplied by firmware,
but rather replaces it completely.
@end deffn
@node distrust
@subsection distrust
@deffn Command distrust pubkey_id
Remove public key @var{pubkey_id} from GRUB's keyring of trusted keys.
@var{pubkey_id} is the last four bytes (eight hexadecimal digits) of
the GPG v4 key id, which is also the output of @command{list_trusted}
(@pxref{list_trusted}). Outside of GRUB, the key id can be obtained
using @code{gpg --fingerprint}).
These keys are used to validate signatures when environment variable
@code{check_signatures} is set to @code{enforce}
(@pxref{check_signatures}), and by some invocations of
@command{verify_detached} (@pxref{verify_detached}). @xref{Using
digital signatures}, for more information.
@end deffn
@node drivemap
@subsection drivemap
@deffn Command drivemap @option{-l}|@option{-r}|[@option{-s}] @
from_drive to_drive
Without options, map the drive @var{from_drive} to the drive @var{to_drive}.
This is necessary when you chain-load some operating systems, such as DOS,
if such an OS resides at a non-first drive. For convenience, any partition
suffix on the drive is ignored, so you can safely use @verb{'${root}'} as a
drive specification.
With the @option{-s} option, perform the reverse mapping as well, swapping
the two drives.
With the @option{-l} option, list the current mappings.
With the @option{-r} option, reset all mappings to the default values.
For example:
drivemap -s (hd0) (hd1)
@end example
@end deffn
@node echo
@subsection echo
@deffn Command echo [@option{-n}] [@option{-e}] string @dots{}
Display the requested text and, unless the @option{-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 @samp{$@{var@}}.
The @option{-e} option enables interpretation of backslash escapes. The
following sequences are recognised:
@table @code
@item \\
@item \a
alert (BEL)
@item \c
suppress trailing new line
@item \f
form feed
@item \n
new line
@item \r
carriage return
@item \t
horizontal tab
@item \v
vertical tab
@end table
When interpreting backslash escapes, backslash followed by any other
character will print that character.
@end deffn
@node eval
@subsection eval
@deffn Command eval string ...
Concatenate arguments together using single space as separator and evaluate
result as sequence of GRUB commands.
@end deffn
@node export
@subsection export
@deffn Command export envvar
Export the environment variable @var{envvar}. Exported variables are visible
to subsidiary configuration files loaded using @command{configfile}.
@end deffn
@node false
@subsection false
@deffn Command false
Do nothing, unsuccessfully. This is mainly useful in control constructs
such as @code{if} and @code{while} (@pxref{Shell-like scripting}).
@end deffn
@node gettext
@subsection gettext
@deffn Command gettext string
Translate @var{string} into the current language.
The current language code is stored in the @samp{lang} variable in GRUB's
environment (@pxref{lang}). Translation files in MO format are read from
@samp{locale_dir} (@pxref{locale_dir}), usually @file{/boot/grub/locale}.
@end deffn
@node gptsync
@subsection gptsync