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This is grub.info, produced by makeinfo version 6.3 from grub.texi.
This manual is for GNU GRUB (version 2.06, 10 May 2021).
Copyright (C)
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.
INFO-DIR-SECTION Kernel
START-INFO-DIR-ENTRY
* GRUB: (grub). The GRand Unified Bootloader
* grub-install: (grub)Invoking grub-install. Install GRUB on your drive
* grub-mkconfig: (grub)Invoking grub-mkconfig. Generate GRUB configuration
* grub-mkpasswd-pbkdf2: (grub)Invoking grub-mkpasswd-pbkdf2.
* grub-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-INFO-DIR-ENTRY

File: grub.info, Node: Top, Next: Introduction, Up: (dir)
GNU GRUB manual
***************
This is the documentation of GNU GRUB, the GRand Unified Bootloader, a
flexible and powerful boot loader program for a wide range of
architectures.
This edition documents version 2.06.
This manual is for GNU GRUB (version 2.06, 10 May 2021).
Copyright (C)
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.
* Menu:
* 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
tools
* 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::

File: grub.info, Node: Introduction, Next: Naming convention, Prev: Top, Up: Top
1 Introduction to GRUB
**********************
* Menu:
* Overview:: What exactly GRUB is and how to use it
* History:: From maggot to house fly
* Changes from GRUB Legacy:: Differences from previous versions
* Features:: GRUB features
* Role of a boot loader:: The role of a boot loader

File: grub.info, Node: Overview, Next: History, Up: Introduction
1.1 Overview
============
Briefly, a "boot loader" is the first software program that runs when a
computer starts. It is responsible for loading and transferring control
to an operating system "kernel" software (such as Linux or GNU Mach).
The kernel, in turn, initializes the rest of the operating system (e.g.
a GNU system).
GNU GRUB is a very powerful boot loader, which can load a wide
variety of free operating systems, as well as proprietary operating
systems with chain-loading(1) (*note Overview-Footnote-1::). GRUB is
designed to address the complexity of booting a personal computer; both
the program and this manual are tightly bound to that computer platform,
although porting to other platforms may be addressed in the future.
One of the important features in GRUB is flexibility; GRUB
understands filesystems and kernel executable formats, so you can load
an arbitrary operating system the way you like, without recording the
physical position of your kernel on the disk. Thus you can load the
kernel just by specifying its file name and the drive and partition
where the kernel resides.
When booting with GRUB, you can use either a command-line interface
(*note Command-line interface::), or a menu interface (*note Menu
interface::). Using the command-line interface, you type the drive
specification and file name of the kernel manually. In the menu
interface, you just select an OS using the arrow keys. The menu is
based on a configuration file which you prepare beforehand (*note
Configuration::). While in the menu, you can switch to the command-line
mode, and vice-versa. You can even edit menu entries before using them.
In the following chapters, you will learn how to specify a drive, a
partition, and a file name (*note Naming convention::) to GRUB, how to
install GRUB on your drive (*note Installation::), and how to boot your
OSes (*note Booting::), step by step.

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

File: grub.info, Node: History, Next: Changes from GRUB Legacy, Prev: Overview, Up: Introduction
1.2 History of GRUB
===================
GRUB originated in 1995 when Erich Boleyn was trying to boot the GNU
Hurd with the University of Utah's Mach 4 microkernel (now known as GNU
Mach). Erich and Brian Ford designed the Multiboot Specification (*note
Multiboot Specification: (multiboot)Top.), because they were determined
not to add to the large number of mutually-incompatible PC boot methods.
Erich then began modifying the FreeBSD boot loader so that it would
understand Multiboot. He soon realized that it would be a lot easier to
write his own boot loader from scratch than to keep working on the
FreeBSD boot loader, and so GRUB was born.
Erich added many features to GRUB, but other priorities prevented him
from keeping up with the demands of its quickly-expanding user base. In
1999, Gordon Matzigkeit and Yoshinori K. Okuji adopted GRUB as an
official GNU package, and opened its development by making the latest
sources available via anonymous CVS. *Note Obtaining and Building
GRUB::, for more information.
Over the next few years, GRUB was extended to meet many needs, but it
quickly became clear that its design was not keeping up with the
extensions being made to it, and we reached the point where it was very
difficult to make any further changes without breaking existing
features. Around 2002, Yoshinori K. Okuji started work on PUPA
(Preliminary Universal Programming Architecture for GNU GRUB), aiming to
rewrite the core of GRUB to make it cleaner, safer, more robust, and
more powerful. PUPA was eventually renamed to GRUB 2, and the original
version of GRUB was renamed to GRUB Legacy. Small amounts of
maintenance continued to be done on GRUB Legacy, but the last release
(0.97) was made in 2005 and at the time of writing it seems unlikely
that there will be another.
By around 2007, GNU/Linux distributions started to use GRUB 2 to
limited extents, and by the end of 2009 multiple major distributions
were installing it by default.

File: grub.info, Node: Changes from GRUB Legacy, Next: Features, Prev: History, Up: Introduction
1.3 Differences from previous versions
======================================
GRUB 2 is a rewrite of GRUB (*note History::), although it shares many
characteristics with the previous version, now known as GRUB Legacy.
Users of GRUB Legacy may need some guidance to find their way around
this new version.
* The configuration file has a new name ('grub.cfg' rather than
'menu.lst' or 'grub.conf'), new syntax (*note Configuration::) and
many new commands (*note Commands::). Configuration cannot be
copied over directly, although most GRUB Legacy users should not
find the syntax too surprising.
* 'grub.cfg' is typically automatically generated by 'grub-mkconfig'
(*note Simple configuration::). This makes it easier to handle
versioned kernel upgrades.
* Partition numbers in GRUB device names now start at 1, not 0 (*note
Naming convention::).
* The configuration file is now written in something closer to a full
scripting language: variables, conditionals, and loops are
available.
* A small amount of persistent storage is available across reboots,
using the 'save_env' and 'load_env' commands in GRUB and the
'grub-editenv' utility. This is not available in all
configurations (*note Environment block::).
* GRUB 2 has more reliable ways to find its own files and those of
target kernels on multiple-disk systems, and has commands (*note
search::) to find devices using file system labels or Universally
Unique Identifiers (UUIDs).
* GRUB 2 is available for several other types of system in addition
to the PC BIOS systems supported by GRUB Legacy: PC EFI, PC
coreboot, PowerPC, SPARC, and MIPS Lemote Yeeloong are all
supported.
* Many more file systems are supported, including but not limited to
ext4, HFS+, and NTFS.
* GRUB 2 can read files directly from LVM and RAID devices.
* A graphical terminal and a graphical menu system are available.
* GRUB 2's interface can be translated, including menu entry names.
* The image files (*note Images::) that make up GRUB have been
reorganised; Stage 1, Stage 1.5, and Stage 2 are no more.
* GRUB 2 puts many facilities in dynamically loaded modules, allowing
the core image to be smaller, and allowing the core image to be
built in more flexible ways.

File: grub.info, Node: Features, Next: Role of a boot loader, Prev: Changes from GRUB Legacy, Up: Introduction
1.4 GRUB features
=================
The primary requirement for GRUB is that it be compliant with the
"Multiboot Specification", which is described in *note Multiboot
Specification: (multiboot)Top.
The other goals, listed in approximate order of importance, are:
* Basic functions must be straightforward for end-users.
* Rich functionality to support kernel experts and designers.
* Backward compatibility for booting FreeBSD, NetBSD, OpenBSD, and
Linux. Proprietary kernels (such as DOS, Windows NT, and OS/2) are
supported via a chain-loading function.
Except for specific compatibility modes (chain-loading and the Linux
"piggyback" format), all kernels will be started in much the same state
as in the Multiboot Specification. Only kernels loaded at 1 megabyte or
above are presently supported. Any attempt to load below that boundary
will simply result in immediate failure and an error message reporting
the problem.
In addition to the requirements above, GRUB has the following
features (note that the Multiboot Specification doesn't require all the
features that GRUB supports):
Recognize multiple executable formats
Support many of the "a.out" variants plus "ELF". Symbol tables are
also loaded.
Support non-Multiboot kernels
Support many of the various free 32-bit kernels that lack Multiboot
compliance (primarily FreeBSD, NetBSD(1) (*note
Features-Footnote-1::), OpenBSD, and Linux). Chain-loading of
other boot loaders is also supported.
Load multiples modules
Fully support the Multiboot feature of loading multiple modules.
Load a configuration file
Support a human-readable text configuration file with preset boot
commands. You can also load another configuration file dynamically
and embed a preset configuration file in a GRUB image file. The
list of commands (*note Commands::) are a superset of those
supported on the command-line. An example configuration file is
provided in *note Configuration::.
Provide a menu interface
A menu interface listing preset boot commands, with a programmable
timeout, is available. There is no fixed limit on the number of
boot entries, and the current implementation has space for several
hundred.
Have a flexible command-line interface
A fairly flexible command-line interface, accessible from the menu,
is available to edit any preset commands, or write a new boot
command set from scratch. If no configuration file is present,
GRUB drops to the command-line.
The list of commands (*note Commands::) are a subset of those
supported for configuration files. Editing commands closely
resembles the Bash command-line (*note Bash: (features)Command Line
Editing.), with <TAB>-completion of commands, devices, partitions,
and files in a directory depending on context.
Support multiple filesystem types
Support multiple filesystem types transparently, plus a useful
explicit blocklist notation. The currently supported filesystem
types are "Amiga Fast FileSystem (AFFS)", "AtheOS fs", "BeFS",
"BtrFS" (including raid0, raid1, raid10, gzip and lzo), "cpio"
(little- and big-endian bin, odc and newc variants), "Linux
ext2/ext3/ext4", "DOS FAT12/FAT16/FAT32", "exFAT", "F2FS", "HFS",
"HFS+", "ISO9660" (including Joliet, Rock-ridge and multi-chunk
files), "JFS", "Minix fs" (versions 1, 2 and 3), "nilfs2", "NTFS"
(including compression), "ReiserFS", "ROMFS", "Amiga Smart
FileSystem (SFS)", "Squash4", "tar", "UDF", "BSD UFS/UFS2", "XFS",
and "ZFS" (including lzjb, gzip, zle, mirror, stripe, raidz1/2/3
and encryption in AES-CCM and AES-GCM). *Note Filesystem::, for
more information.
Support automatic decompression
Can decompress files which were compressed by 'gzip' or 'xz'(2)
(*note Features-Footnote-2::). 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.(3) (*note Features-Footnote-3::)
It is conceivable that some kernel modules should be loaded in a
compressed state, so a different module-loading command can be
specified to avoid uncompressing the modules.
Access data on any installed device
Support reading data from any or all floppies or hard disk(s)
recognized by the BIOS, independent of the setting of the root
device.
Be independent of drive geometry translations
Unlike many other boot loaders, GRUB makes the particular drive
translation irrelevant. A drive installed and running with one
translation may be converted to another translation without any
adverse effects or changes in GRUB's configuration.
Detect all installed RAM
GRUB can generally find all the installed RAM on a PC-compatible
machine. It uses an advanced BIOS query technique for finding all
memory regions. As described on the Multiboot Specification (*note
Multiboot Specification: (multiboot)Top.), not all kernels make use
of this information, but GRUB provides it for those who do.
Support Logical Block Address mode
In traditional disk calls (called "CHS mode"), there is a geometry
translation problem, that is, the BIOS cannot access over 1024
cylinders, so the accessible space is limited to at least 508 MB
and to at most 8GB. GRUB can't universally solve this problem, as
there is no standard interface used in all machines. However,
several newer machines have the new interface, Logical Block
Address ("LBA") mode. GRUB automatically detects if LBA mode is
available and uses it if available. In LBA mode, GRUB can access
the entire disk.
Support network booting
GRUB is basically a disk-based boot loader but also has network
support. You can load OS images from a network by using the "TFTP"
protocol.
Support remote terminals
To support computers with no console, GRUB provides remote terminal
support, so that you can control GRUB from a remote host. Only
serial terminal support is implemented at the moment.

File: grub.info, Node: Features-Footnotes, Up: Features
(1) The NetBSD/i386 kernel is Multiboot-compliant, but lacks support
for Multiboot modules.
(2) Only CRC32 data integrity check is supported (xz default is CRC64
so one should use -check=crc32 option). LZMA BCJ filters are supported.
(3) There are a few pathological cases where loading a very badly
organized ELF kernel might take longer, but in practice this never
happen.

File: grub.info, Node: Role of a boot loader, Prev: Features, Up: Introduction
1.5 The role of a boot loader
=============================
The following is a quotation from Gordon Matzigkeit, a GRUB fanatic:
Some people like to acknowledge both the operating system and
kernel when they talk about their computers, so they might say they
use "GNU/Linux" or "GNU/Hurd". Other people seem to think that the
kernel is the most important part of the system, so they like to
call their GNU operating systems "Linux systems."
I, personally, believe that this is a grave injustice, because the
_boot loader_ is the most important software of all. I used to
refer to the above systems as either "LILO"(1) (*note Role of a
boot loader-Footnote-1::) or "GRUB" systems.
Unfortunately, nobody ever understood what I was talking about; now
I just use the word "GNU" as a pseudonym for GRUB.
So, if you ever hear people talking about their alleged "GNU"
systems, remember that they are actually paying homage to the best
boot loader around... GRUB!
We, the GRUB maintainers, do not (usually) encourage Gordon's level
of fanaticism, but it helps to remember that boot loaders deserve
recognition. We hope that you enjoy using GNU GRUB as much as we did
writing it.

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

File: grub.info, Node: Naming convention, Next: OS-specific notes about grub tools, Prev: Introduction, Up: Top
2 Naming convention
*******************
The device syntax used in GRUB is a wee bit different from what you may
have seen before in your operating system(s), and you need to know it so
that you can specify a drive/partition.
Look at the following examples and explanations:
(fd0)
First of all, GRUB requires that the device name be enclosed with '('
and ')'. The 'fd' part means that it is a floppy disk. The number '0'
is the drive number, which is counted from _zero_. This expression
means that GRUB will use the whole floppy disk.
(hd0,msdos2)
Here, 'hd' means it is a hard disk drive. The first integer '0'
indicates the drive number, that is, the first hard disk, the string
'msdos' indicates the partition scheme, while the second integer, '2',
indicates the partition number (or the PC slice number in the BSD
terminology). The partition numbers are counted from _one_, not from
zero (as was the case in previous versions of GRUB). This expression
means the second partition of the first hard disk drive. In this case,
GRUB uses one partition of the disk, instead of the whole disk.
(hd0,msdos5)
This specifies the first "extended partition" of the first hard disk
drive. Note that the partition numbers for extended partitions are
counted from '5', regardless of the actual number of primary partitions
on your hard disk.
(hd1,msdos1,bsd1)
This means the BSD 'a' partition on first PC slice number of the
second hard disk.
Of course, to actually access the disks or partitions with GRUB, you
need to use the device specification in a command, like 'set root=(fd0)'
or 'parttool (hd0,msdos3) hidden-'. To help you find out which number
specifies a partition you want, the GRUB command-line (*note
Command-line interface::) options have argument completion. This means
that, for example, you only need to type
set root=(
followed by a <TAB>, and GRUB will display the list of drives,
partitions, or file names. So it should be quite easy to determine the
name of your target partition, even with minimal knowledge of the
syntax.
Note that GRUB does _not_ distinguish IDE from SCSI - it simply
counts the drive numbers from zero, regardless of their type. Normally,
any IDE drive number is less than any SCSI drive number, although that
is not true if you change the boot sequence by swapping IDE and SCSI
drives in your BIOS.
Now the question is, how to specify a file? Again, consider an
example:
(hd0,msdos1)/vmlinuz
This specifies the file named 'vmlinuz', found on the first partition
of the first hard disk drive. Note that the argument completion works
with file names, too.
That was easy, admit it. Now read the next chapter, to find out how
to actually install GRUB on your drive.

File: grub.info, Node: OS-specific notes about grub tools, Next: Installation, Prev: Naming convention, Up: Top
3 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:
# grub-install /dev/sda
On AROS we use another syntax. For volumes:
//:<volume name>
E.g.
//:DH0
For disks we use syntax:
//:<driver name>/unit/flags
E.g.
# grub-install //:ata.device/0/0
On Windows we use UNC path. For volumes it's typically
\\?\Volume{<GUID>}
\\?\<drive letter>:
E.g.
\\?\Volume{17f34d50-cf64-4b02-800e-51d79c3aa2ff}
\\?\C:
For disks it's
\\?\PhysicalDrive<number>
E.g.
# grub-install \\?\PhysicalDrive0
Beware that you may need to further escape the backslashes depending
on your shell.
When compiled with cygwin support then cygwin drive names are
automatically when needed. E.g.
# grub-install /dev/sda

File: grub.info, Node: Installation, Next: Booting, Prev: OS-specific notes about grub tools, Up: Top
4 Installation
**************
In order to install GRUB as your boot loader, you need to first install
the GRUB system and utilities under your UNIX-like operating system
(*note Obtaining and Building GRUB::). You can do this either from the
source tarball, or as a package for your OS.
After you have done that, you need to install the boot loader on a
drive (floppy or hard disk) by using the utility 'grub-install' (*note
Invoking grub-install::) on a UNIX-like OS.
GRUB comes with boot images, which are normally put in the directory
'/usr/lib/grub/<cpu>-<platform>' (for BIOS-based machines
'/usr/lib/grub/i386-pc'). Hereafter, the directory where GRUB images
are initially placed (normally '/usr/lib/grub/<cpu>-<platform>') will be
called the "image directory", and the directory where the boot loader
needs to find them (usually '/boot') will be called the "boot
directory".
* Menu:
* Installing GRUB using grub-install::
* Making a GRUB bootable CD-ROM::
* Device map::
* BIOS installation::

File: grub.info, Node: Installing GRUB using grub-install, Next: Making a GRUB bootable CD-ROM, Up: Installation
4.1 Installing GRUB using grub-install
======================================
For information on where GRUB should be installed on PC BIOS platforms,
*note BIOS installation::.
In order to install GRUB under a UNIX-like OS (such as GNU), invoke
the program 'grub-install' (*note Invoking grub-install::) as the
superuser ("root").
The usage is basically very simple. You only need to specify one
argument to the program, namely, where to install the boot loader. The
argument has to be either a device file (like '/dev/hda'). For example,
under Linux the following will install GRUB into the MBR of the first
IDE disk:
# grub-install /dev/sda
Likewise, under GNU/Hurd, this has the same effect:
# grub-install /dev/hd0
But all the above examples assume that GRUB should put images under
the '/boot' directory. If you want GRUB to put images under a directory
other than '/boot', you need to specify the option '--boot-directory'.
The typical usage is that you create a GRUB boot floppy with a
filesystem. Here is an example:
# mke2fs /dev/fd0
# mount -t ext2 /dev/fd0 /mnt
# mkdir /mnt/boot
# grub-install --boot-directory=/mnt/boot /dev/fd0
# umount /mnt
Some BIOSes have a bug of exposing the first partition of a USB drive
as a floppy instead of exposing the USB drive as a hard disk (they call
it "USB-FDD" boot). In such cases, you need to install like this:
# losetup /dev/loop0 /dev/sdb1
# mount /dev/loop0 /mnt/usb
# grub-install --boot-directory=/mnt/usb/bugbios --force --allow-floppy /dev/loop0
This install doesn't conflict with standard install as long as they
are in separate directories.
On EFI systems for fixed disk install you have to mount EFI System
Partition. If you mount it at '/boot/efi' then you don't need any
special arguments:
# grub-install
Otherwise you need to specify where your EFI System partition is
mounted:
# grub-install --efi-directory=/mnt/efi
For removable installs you have to use '--removable' and specify both
'--boot-directory' and '--efi-directory':
# grub-install --efi-directory=/mnt/usb --boot-directory=/mnt/usb/boot --removable

File: grub.info, Node: Making a GRUB bootable CD-ROM, Next: Device map, Prev: Installing GRUB using grub-install, Up: Installation
4.2 Making a GRUB bootable CD-ROM
=================================
GRUB supports the "no emulation mode" in the El Torito specification(1)
(*note Making a GRUB bootable CD-ROM-Footnote-1::). This means that you
can use the whole CD-ROM from GRUB and you don't have to make a floppy
or hard disk image file, which can cause compatibility problems.
For booting from a CD-ROM, GRUB uses a special image called
'cdboot.img', which is concatenated with 'core.img'. The 'core.img'
used for this should be built with at least the 'iso9660' and 'biosdisk'
modules. Your bootable CD-ROM will usually also need to include a
configuration file 'grub.cfg' and some other GRUB modules.
To make a simple generic GRUB rescue CD, you can use the
'grub-mkrescue' program (*note Invoking grub-mkrescue::):
$ grub-mkrescue -o grub.iso
You will often need to include other files in your image. To do
this, first make a top directory for the bootable image, say, 'iso':
$ mkdir iso
Make a directory for GRUB:
$ mkdir -p iso/boot/grub
If desired, make the config file 'grub.cfg' under 'iso/boot/grub'
(*note Configuration::), and copy any files and directories for the disc
to the directory 'iso/'.
Finally, make the image:
$ grub-mkrescue -o grub.iso iso
This produces a file named 'grub.iso', which then can be burned into
a CD (or a DVD), or written to a USB mass storage device.
The root device will be set up appropriately on entering your
'grub.cfg' configuration file, so you can refer to file names on the CD
without needing to use an explicit device name. This makes it easier to
produce rescue images that will work on both optical drives and USB mass
storage devices.

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

File: grub.info, Node: Device map, Next: BIOS installation, Prev: Making a GRUB bootable CD-ROM, Up: Installation
4.3 The map between BIOS drives and OS devices
==============================================
If the device map file exists, the GRUB utilities ('grub-probe', etc.)
read it to map BIOS drives to OS devices. This file consists of lines
like this:
(DEVICE) FILE
DEVICE is a drive specified in the GRUB syntax (*note Device
syntax::), and FILE is an OS file, which is normally a device file.
Historically, the device map file was used because GRUB device names
had to be used in the configuration file, and they were derived from
BIOS drive numbers. The map between BIOS drives and OS devices cannot
always be guessed correctly: for example, GRUB will get the order wrong
if you exchange the boot sequence between IDE and SCSI in your BIOS.
Unfortunately, even OS device names are not always stable. Modern
versions of the Linux kernel may probe drives in a different order from
boot to boot, and the prefix ('/dev/hd*' versus '/dev/sd*') may change
depending on the driver subsystem in use. As a result, the device map
file required frequent editing on some systems.
GRUB avoids this problem nowadays by using UUIDs or file system
labels when generating 'grub.cfg', and we advise that you do the same
for any custom menu entries you write. If the device map file does not
exist, then the GRUB utilities will assume a temporary device map on the
fly. This is often good enough, particularly in the common case of
single-disk systems.
However, the device map file is not entirely obsolete yet, and it is
used for overriding when current environment is different from the one
on boot. Most common case is if you use a partition or logical volume
as a disk for virtual machine. You can put any comments in the file if
needed, as the GRUB utilities assume that a line is just a comment if
the first character is '#'.

File: grub.info, Node: BIOS installation, Prev: Device map, Up: Installation
4.4 BIOS installation
=====================
MBR
===
The partition table format traditionally used on PC BIOS platforms is
called the Master Boot Record (MBR) format; this is the format that
allows up to four primary partitions and additional logical partitions.
With this partition table format, there are two ways to install GRUB: it
can be embedded in the area between the MBR and the first partition
(called by various names, such as the "boot track", "MBR gap", or
"embedding area", and which is usually at least 1000 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.
Modern tools usually leave MBR gap of at least 1023 KiB. This amount
is sufficient to cover most configurations. Hence this value is
recommended by the GRUB team.
Historically many tools left only 31 KiB of space. This is not
enough to parse reliably difficult structures like Btrfs, ZFS, RAID or
LVM, or to use difficult disk access methods like ahci. Hence GRUB will
warn if attempted to install into small MBR gap except in a small number
of configurations that were grandfathered. The grandfathered config
must:
* use biosdisk as disk access module for '/boot' * not use any
additional partition maps to access '/boot' * '/boot' must be on one of
following filesystems: * AFFS, AFS, BFS, cpio, newc, odc, ext2/3/4, FAT,
exFAT, F2FS, HFS, uncompressed HFS+, ISO9660, JFS, Minix, Minix2,
Minix3, NILFS2, NTFS, ReiserFS, ROMFS, SFS, tar, UDF, UFS1, UFS2, XFS
MBR gap has few technical 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. GRUB works it around by detecting
sectors by other software and avoiding them and protecting its own
sectors using Reed-Solomon encoding.
GRUB team recommends having MBR gap of at least 1000 KiB
Should it be not possible GRUB has support for a fallback solution
which is heavily recommended against. Installing to a filesystem means
that GRUB is vulnerable to its blocks being moved around by filesystem
features such as tail packing, or even by aggressive fsck
implementations, so this approach is quite fragile; and this approach
can only be used if the '/boot' filesystem is on the same disk that the
BIOS boots from, so that GRUB does not have to rely on guessing BIOS
drive numbers.
The GRUB development team generally recommends embedding GRUB before
the first partition, unless you have special requirements. You must
ensure that the first partition starts at least 1000 KiB (2000 sectors)
from the start of the disk; on modern disks, it is often a performance
advantage to align partitions on larger boundaries anyway, so the first
partition might start 1 MiB from the start of the disk.
GPT
===
Some newer systems use the GUID Partition Table (GPT) format. This was
specified as part of the Extensible Firmware Interface (EFI), but it can
also be used on BIOS platforms if system software supports it; for
example, GRUB and GNU/Linux can be used in this configuration. With
this format, it is possible to reserve a whole partition for GRUB,
called the BIOS Boot Partition. GRUB can then be embedded into that
partition without the risk of being overwritten by other software and
without being contained in a filesystem which might move its blocks
around.
When creating a BIOS Boot Partition on a GPT system, you should make
sure that it is at least 31 KiB in size. (GPT-formatted disks are not
usually particularly small, so we recommend that you make it larger than
the bare minimum, such as 1 MiB, to allow plenty of room for growth.)
You must also make sure that it has the proper partition type. Using
GNU Parted, you can set this using a command such as the following:
# parted /dev/DISK set PARTITION-NUMBER bios_grub on
If you are using gdisk, set the partition type to '0xEF02'. With
partitioning programs that require setting the GUID directly, it should
be '21686148-6449-6e6f-744e656564454649'.
*Caution:* Be very careful which partition you select! When GRUB
finds a BIOS Boot Partition during installation, it will automatically
overwrite part of it. Make sure that the partition does not contain any
other data.

File: grub.info, Node: Booting, Next: Configuration, Prev: Installation, Up: Top
5 Booting
*********
GRUB can load Multiboot-compliant kernels in a consistent way, but for
some free operating systems you need to use some OS-specific magic.
* Menu:
* General boot methods:: How to boot OSes with GRUB generally
* Loopback booting:: Notes on booting from loopbacks
* LVM cache booting:: Notes on booting from LVM cache logical volume
* OS-specific notes:: Notes on some operating systems

File: grub.info, Node: General boot methods, Next: Loopback booting, Up: Booting
5.1 How to boot operating systems
=================================
GRUB has two distinct boot methods. One of the two is to load an
operating system directly, and the other is to chain-load another boot
loader which then will load an operating system actually. Generally
speaking, the former is more desirable, because you don't need to
install or maintain other boot loaders and GRUB is flexible enough to
load an operating system from an arbitrary disk/partition. However, the
latter is sometimes required, since GRUB doesn't support all the
existing operating systems natively.
* Menu:
* Loading an operating system directly::
* Chain-loading::

File: grub.info, Node: Loading an operating system directly, Next: Chain-loading, Up: General boot methods
5.1.1 How to boot an OS directly with GRUB
------------------------------------------
Multiboot (*note Multiboot Specification: (multiboot)Top.) is the native
format supported by GRUB. For the sake of convenience, there is also
support for Linux, FreeBSD, NetBSD and OpenBSD. If you want to boot
other operating systems, you will have to chain-load them (*note
Chain-loading::).
FIXME: this section is incomplete.
1. Run the command 'boot' (*note boot::).
However, DOS and Windows have some deficiencies, so you might have to
use more complicated instructions. *Note DOS/Windows::, for more
information.

File: grub.info, Node: Chain-loading, Prev: Loading an operating system directly, Up: General boot methods
5.1.2 Chain-loading an OS
-------------------------
Operating systems that do not support Multiboot and do not have specific
support in GRUB (specific support is available for Linux, FreeBSD,
NetBSD and OpenBSD) must be chain-loaded, which involves loading another
boot loader and jumping to it in real mode.
The 'chainloader' command (*note chainloader::) is used to set this
up. It is normally also necessary to load some GRUB modules and set the
appropriate root device. Putting this together, we get something like
this, for a Windows system on the first partition of the first hard
disk:
menuentry "Windows" {
insmod chain
insmod ntfs
set root=(hd0,1)
chainloader +1
}
On systems with multiple hard disks, an additional workaround may be
required. *Note DOS/Windows::.
Chain-loading is only supported on PC BIOS and EFI platforms.

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

File: grub.info, Node: LVM cache booting, Next: OS-specific notes, Prev: Loopback booting, Up: Booting
5.3 Booting from LVM cache logical volume
=========================================
The LVM cache logical volume is the logical volume consisting of the
original and the cache pool logical volume. The original is usually on
a larger and slower storage device while the cache pool is on a smaller
and faster one. The performance of the original volume can be improved
by storing the frequently used data on the cache pool to utilize the
greater performance of faster device.
GRUB boots from LVM cache logical volume merely by reading it's
original logical volume so that dirty data in cache pool volume is
disregarded. This is not a problem for "writethrough" cache mode as it
ensures that any data written will be stored both on the cache and the
origin LV. For the other cache mode "writeback", which delays writing
from the cache pool back to the origin LV to boost performance, GRUB may
fail to boot in the wake of accidental power outage due to it's
inability to assemble the cache device for reading the required dirty
data left behind. The situation will be improved after adding full
support to the LVM cache logical volume in the future.

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

File: grub.info, Node: GNU/Hurd, Next: GNU/Linux, Up: OS-specific notes
5.4.1 GNU/Hurd
--------------
Since GNU/Hurd is Multiboot-compliant, it is easy to boot it; there is
nothing special about it. But do not forget that you have to specify a
root partition to the kernel.
1. Set GRUB's root device to the same drive as GNU/Hurd's. The
command 'search --set=root --file /boot/gnumach.gz' or similar may
help you (*note search::).
2. Load the kernel and the modules, like this:
grub> multiboot /boot/gnumach.gz root=device:hd0s1
grub> module /hurd/ext2fs.static ext2fs --readonly \
--multiboot-command-line='${kernel-command-line}' \
--host-priv-port='${host-port}' \
--device-master-port='${device-port}' \
--exec-server-task='${exec-task}' -T typed '${root}' \
'$(task-create)' '$(task-resume)'
grub> module /lib/ld.so.1 exec /hurd/exec '$(exec-task=task-create)'
3. Finally, run the command 'boot' (*note boot::).

File: grub.info, Node: GNU/Linux, Next: NetBSD, Prev: GNU/Hurd, Up: OS-specific notes
5.4.2 GNU/Linux
---------------
It is relatively easy to boot GNU/Linux from GRUB, because it somewhat
resembles to boot a Multiboot-compliant OS.
1. Set GRUB's root device to the same drive as GNU/Linux's. The
command 'search --set=root --file /vmlinuz' or similar may help you
(*note search::).
2. Load the kernel using the command 'linux' (*note linux::):
grub> linux /vmlinuz root=/dev/sda1
If you need to specify some kernel parameters, just append them to
the command. For example, to set 'acpi' to 'off', do this:
grub> linux /vmlinuz root=/dev/sda1 acpi=off
See the documentation in the Linux source tree for complete
information on the available options.
With 'linux' GRUB uses 32-bit protocol. Some BIOS services like
APM or EDD aren't available with this protocol. In this case you
need to use 'linux16'
grub> linux16 /vmlinuz root=/dev/sda1 acpi=off
3. If you use an initrd, execute the command 'initrd' (*note initrd::)
after 'linux':
grub> initrd /initrd
If you used 'linux16' you need to use 'initrd16':
grub> initrd16 /initrd
4. Finally, run the command 'boot' (*note boot::).

File: grub.info, Node: NetBSD, Next: DOS/Windows, Prev: GNU/Linux, Up: OS-specific notes
5.4.3 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 'boot'.
1. 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> insmod part_bsd
grub> set root=(hd0,netbsd1)
For a disk with a GUID Partition Table (GPT), and assuming that the
NetBSD root partition is the third GPT partition, do this:
grub> insmod part_gpt
grub> set root=(hd0,gpt3)
2. Load the kernel using the command 'knetbsd':
grub> knetbsd /netbsd
Various options may be given to '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 this:
grub> knetbsd /netbsd -s -v
3. If needed, load kernel modules with the command
'knetbsd_module_elf'. A typical example is the module for the root
file system:
grub> knetbsd_module_elf /stand/amd64/6.0/modules/ffs/ffs.kmod
4. Finally, run the command 'boot' (*note boot::).

File: grub.info, Node: DOS/Windows, Prev: NetBSD, Up: OS-specific notes
5.4.4 DOS/Windows
-----------------
GRUB cannot boot DOS or Windows directly, so you must chain-load them
(*note Chain-loading::). However, their boot loaders have some critical
deficiencies, so it may not work to just chain-load them. To overcome
the problems, GRUB provides you with two helper functions.
If you have installed DOS (or Windows) on a non-first hard disk, you
have to use the disk swapping technique, because that OS cannot boot
from any disks but the first one. The workaround used in GRUB is the
command 'drivemap' (*note drivemap::), like this:
drivemap -s (hd0) (hd1)
This performs a "virtual" swap between your first and second hard
drive.
*Caution:* This is effective only if DOS (or Windows) uses BIOS to
access the swapped disks. If that OS uses a special driver for the
disks, this probably won't work.
Another problem arises if you installed more than one set of
DOS/Windows onto one disk, because they could be confused if there are
more than one primary partitions for DOS/Windows. Certainly you should
avoid doing this, but there is a solution if you do want to do so. Use
the partition hiding/unhiding technique.
If GRUB "hides" a DOS (or Windows) partition (*note parttool::), DOS
(or Windows) will ignore the partition. If GRUB "unhides" a DOS (or
Windows) partition, DOS (or Windows) will detect the partition. Thus,
if you have installed DOS (or Windows) on the first and the second
partition of the first hard disk, and you want to boot the copy on the
first partition, do the following:
parttool (hd0,1) hidden-
parttool (hd0,2) hidden+
set root=(hd0,1)
chainloader +1
parttool ${root} boot+
boot

File: grub.info, Node: Configuration, Next: Theme file format, Prev: Booting, Up: Top
6 Writing your own configuration file
*************************************
GRUB is configured using 'grub.cfg', usually located under '/boot/grub'.
This file is quite flexible, but most users will not need to write the
whole thing by hand.
* Menu:
* Simple configuration:: Recommended for most users
* Root Identifcation Heuristics:: Summary on how the root file system is identified.
* Shell-like scripting:: For power users and developers
* Multi-boot manual config:: For non-standard multi-OS scenarios
* Embedded configuration:: Embedding a configuration file into GRUB

File: grub.info, Node: Simple configuration, Next: Root Identifcation Heuristics, Up: Configuration
6.1 Simple configuration handling
=================================
The program 'grub-mkconfig' (*note Invoking grub-mkconfig::) generates
'grub.cfg' files suitable for most cases. It is suitable for use when
upgrading a distribution, and will discover available kernels and
attempt to generate menu entries for them.
'grub-mkconfig' does have some limitations. While adding extra
custom menu entries to the end of the list can be done by editing
'/etc/grub.d/40_custom' or creating '/boot/grub/custom.cfg', changing
the order of menu entries or changing their titles may require making
complex changes to shell scripts stored in '/etc/grub.d/'. This may be
improved in the future. In the meantime, those who feel that it would
be easier to write 'grub.cfg' directly are encouraged to do so (*note
Booting::, and *note Shell-like scripting::), and to disable any system
provided by their distribution to automatically run 'grub-mkconfig'.
The file '/etc/default/grub' controls the operation of
'grub-mkconfig'. It is sourced by a shell script, and so must be valid
POSIX shell input; normally, it will just be a sequence of 'KEY=value'
lines, but if the value contains spaces or other special characters then
it must be quoted. For example:
GRUB_TERMINAL_INPUT="console serial"
Valid keys in '/etc/default/grub' are as follows:
'GRUB_DEFAULT'
The default menu entry. This may be a number, in which case it
identifies the Nth entry in the generated menu counted from zero,
or the title of a menu entry, or the special string 'saved'. Using
the 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 {
...
}
then you can make this the default using:
GRUB_DEFAULT=example-gnu-linux
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 'saved', then the default menu entry will be
that saved by 'GRUB_SAVEDEFAULT' or 'grub-set-default'. This
relies on the environment block, which may not be available in all
situations (*note Environment block::).
The default is '0'.
'GRUB_SAVEDEFAULT'
If this option is set to 'true', then, when an entry is selected,
save it as a new default entry for use by future runs of GRUB. This
is only useful if 'GRUB_DEFAULT=saved'; it is a separate option
because 'GRUB_DEFAULT=saved' is useful without this option, in
conjunction with 'grub-set-default'. Unset by default. This
option relies on the environment block, which may not be available
in all situations (*note Environment block::).
'GRUB_TIMEOUT'
Boot the default entry this many seconds after the menu is
displayed, unless a key is pressed. The default is '5'. Set to
'0' to boot immediately without displaying the menu, or to '-1' to
wait indefinitely.
If 'GRUB_TIMEOUT_STYLE' is set to 'countdown' or 'hidden', the
timeout is instead counted before the menu is displayed.
'GRUB_TIMEOUT_STYLE'
If this option is unset or set to 'menu', then GRUB will display
the menu and then wait for the timeout set by 'GRUB_TIMEOUT' to
expire before booting the default entry. Pressing a key interrupts
the timeout.
If this option is set to 'countdown' or 'hidden', then, before
displaying the menu, GRUB will wait for the timeout set by
'GRUB_TIMEOUT' to expire. If <ESC> or <F4> are pressed, or <SHIFT>
is held down 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 'countdown' case, it will show a one-line indication
of the remaining time.
'GRUB_DEFAULT_BUTTON'
'GRUB_TIMEOUT_BUTTON'
'GRUB_TIMEOUT_STYLE_BUTTON'
'GRUB_BUTTON_CMOS_ADDRESS'
Variants of the corresponding variables without the '_BUTTON'
suffix, used to support vendor-specific power buttons. *Note
Vendor power-on keys::.
'GRUB_DISTRIBUTOR'
Set by distributors of GRUB to their identifying name. This is
used to generate more informative menu entry titles.
'GRUB_TERMINAL_INPUT'
Select the terminal input device. You may select multiple devices
here, separated by spaces.
Valid terminal input names depend on the platform, but may include
'console' (native platform console), 'serial' (serial terminal),
'serial_<port>' (serial terminal with explicit port selection),
'at_keyboard' (PC AT keyboard), or 'usb_keyboard' (USB keyboard
using the HID Boot Protocol, for cases where the firmware does not
handle this).
The default is to use the platform's native terminal input.
'GRUB_TERMINAL_OUTPUT'
Select the terminal output device. You may select multiple devices
here, separated by spaces.
Valid terminal output names depend on the platform, but may include
'console' (native platform console), 'serial' (serial terminal),
'serial_<port>' (serial terminal with explicit port selection),
'gfxterm' (graphics-mode output), 'vga_text' (VGA text output),
'mda_text' (MDA text output), 'morse' (Morse-coding using system
beeper) or 'spkmodem' (simple data protocol using system speaker).
'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 'spkmodem-recv' from 'util/spkmodem-recv.c' and run:
parecord --channels=1 --rate=48000 --format=s16le | ./spkmodem-recv
The default is to use the platform's native terminal output.
'GRUB_TERMINAL'
If this option is set, it overrides both 'GRUB_TERMINAL_INPUT' and
'GRUB_TERMINAL_OUTPUT' to the same value.
'GRUB_SERIAL_COMMAND'
A command to configure the serial port when using the serial
console. *Note serial::. Defaults to 'serial'.
'GRUB_CMDLINE_LINUX'
Command-line arguments to add to menu entries for the Linux kernel.
'GRUB_CMDLINE_LINUX_DEFAULT'
Unless 'GRUB_DISABLE_RECOVERY' is set to 'true', two menu entries
will be generated for each Linux kernel: one default entry and one
entry for recovery mode. This option lists command-line arguments
to add only to the default menu entry, after those listed in
'GRUB_CMDLINE_LINUX'.
'GRUB_CMDLINE_NETBSD'
'GRUB_CMDLINE_NETBSD_DEFAULT'
As 'GRUB_CMDLINE_LINUX' and 'GRUB_CMDLINE_LINUX_DEFAULT', but for
NetBSD.
'GRUB_CMDLINE_GNUMACH'
As 'GRUB_CMDLINE_LINUX', but for GNU Mach.
'GRUB_CMDLINE_XEN'
'GRUB_CMDLINE_XEN_DEFAULT'
The values of these options are passed to Xen hypervisor Xen menu
entries, for all respectively normal entries.
'GRUB_CMDLINE_LINUX_XEN_REPLACE'
'GRUB_CMDLINE_LINUX_XEN_REPLACE_DEFAULT'
The values of these options replace the values of
'GRUB_CMDLINE_LINUX' and 'GRUB_CMDLINE_LINUX_DEFAULT' for Linux and
Xen menu entries.
'GRUB_EARLY_INITRD_LINUX_CUSTOM'
'GRUB_EARLY_INITRD_LINUX_STOCK'
List of space-separated early initrd images to be loaded from
'/boot'. This is for loading things like CPU microcode, firmware,
ACPI tables, crypto keys, and so on. These early images will be
loaded in the order declared, and all will be loaded before the
actual functional initrd image.
'GRUB_EARLY_INITRD_LINUX_STOCK' is for your distribution to declare
images that are provided by the distribution. It should not be
modified without understanding the consequences. They will be
loaded first.
'GRUB_EARLY_INITRD_LINUX_CUSTOM' is for your custom created images.
The default stock images are as follows, though they may be
overridden by your distribution:
intel-uc.img intel-ucode.img amd-uc.img amd-ucode.img early_ucode.cpio microcode.cpio
'GRUB_DISABLE_LINUX_UUID'
Normally, 'grub-mkconfig' will generate menu entries that use
universally-unique identifiers (UUIDs) to identify the root
filesystem to the Linux kernel, using a 'root=UUID=...' kernel
parameter. This is usually more reliable, but in some cases it may
not be appropriate. To disable the use of UUIDs, set this option
to 'true'.
'GRUB_DISABLE_LINUX_PARTUUID'
If 'grub-mkconfig' cannot identify the root filesystem via its
universally-unique indentifier (UUID), 'grub-mkconfig' can use the
UUID of the partition containing the filesystem to identify the
root filesystem to the Linux kernel via a 'root=PARTUUID=...'
kernel parameter. This is not as reliable as using the filesystem
UUID, but is more reliable than using the Linux device names. When
'GRUB_DISABLE_LINUX_PARTUUID' is set to 'false', the Linux kernel
version must be 2.6.37 (3.10 for systems using the MSDOS partition
scheme) or newer. This option defaults to 'true'. To enable the
use of partition UUIDs, set this option to 'false'.
'GRUB_DISABLE_RECOVERY'
If this option is set to 'true', disable the generation of recovery
mode menu entries.
'GRUB_DISABLE_UUID'
Normally, 'grub-mkconfig' will generate menu entries that use
universally-unique identifiers (UUIDs) to identify various
filesystems to search for files. This is usually more reliable,
but in some cases it may not be appropriate. To disable this use
of UUIDs, set this option to 'true'. Setting this option to
'true', will also set the options 'GRUB_DISABLE_LINUX_UUID' and
'GRUB_DISABLE_LINUX_PARTUUID' to 'true', unless they have been
explicilty set to 'false'.
'GRUB_VIDEO_BACKEND'
If graphical video support is required, either because the
'gfxterm' graphical terminal is in use or because
'GRUB_GFXPAYLOAD_LINUX' is set, then 'grub-mkconfig' will normally
load all available GRUB video drivers and use the one most
appropriate for your hardware. If you need to override this for
some reason, then you can set this option.
After 'grub-install' has been run, the available video drivers are
listed in '/boot/grub/video.lst'.
'GRUB_GFXMODE'
Set the resolution used on the 'gfxterm' graphical terminal. Note
that you can only use modes which your graphics card supports via
VESA BIOS Extensions (VBE), so for example native LCD panel
resolutions may not be available. The default is 'auto', which
tries to select a preferred resolution. *Note gfxmode::.
'GRUB_BACKGROUND'
Set a background image for use with the 'gfxterm' graphical
terminal. The value of this option must be a file readable by GRUB
at boot time, and it must end with '.png', '.tga', '.jpg', or
'.jpeg'. The image will be scaled if necessary to fit the screen.
'GRUB_THEME'
Set a theme for use with the 'gfxterm' graphical terminal.
'GRUB_GFXPAYLOAD_LINUX'
Set to 'text' to force the Linux kernel to boot in normal text
mode, 'keep' to preserve the graphics mode set using
'GRUB_GFXMODE', 'WIDTHxHEIGHT'['xDEPTH'] to set a particular
graphics mode, or a sequence of these separated by commas or
semicolons to try several modes in sequence. *Note gfxpayload::.
Depending on your kernel, your distribution, your graphics card,
and the phase of the moon, note that using this option may cause
GNU/Linux to suffer from various display problems, particularly
during the early part of the boot sequence. If you have problems,
set this option to 'text' and GRUB will tell Linux to boot in
normal text mode.
'GRUB_DISABLE_OS_PROBER'
The 'grub-mkconfig' has a feature to use the external 'os-prober'
program to discover other operating systems installed on the same
machine and generate appropriate menu entries for them. It is
disabled by default since automatic and silent execution of
'os-prober', and creating boot entries based on that data, is a
potential attack vector. Set this option to 'false' to enable this
feature in the 'grub-mkconfig' command.
'GRUB_OS_PROBER_SKIP_LIST'
List of space-separated FS UUIDs of filesystems to be ignored from
os-prober output. For efi chainloaders it's <UUID>@<EFI FILE>
'GRUB_DISABLE_SUBMENU'
Normally, '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 'os-prober' first entry will be put on top
level and all others in submenu. If this option is set to 'true',
flat menu with all entries on top level will be generated instead.
Changing this option will require changing existing values of
'GRUB_DEFAULT', 'fallback' (*note fallback::) and 'default' (*note
default::) environment variables as well as saved default entry
using 'grub-set-default' and value used with 'grub-reboot'.
'GRUB_ENABLE_CRYPTODISK'
If set to 'y', 'grub-mkconfig' and '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.
'GRUB_INIT_TUNE'
Play a tune on the speaker when GRUB starts. This is particularly
useful for users unable to see the screen. The value of this
option is passed directly to *note play::.
'GRUB_BADRAM'
If this option is set, GRUB will issue a *note badram:: command to
filter out specified regions of RAM.
'GRUB_PRELOAD_MODULES'
This option may be set to a list of GRUB module names separated by
spaces. Each module will be loaded as early as possible, at the
start of 'grub.cfg'.
The following options are still accepted for compatibility with
existing configurations, but have better replacements:
'GRUB_HIDDEN_TIMEOUT'
Wait this many seconds before displaying the menu. If <ESC> or
<F4> are pressed, or <SHIFT> is held down during that time, display
the menu and wait for input according to '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 'GRUB_TIMEOUT' before booting the default entry.
If you set 'GRUB_HIDDEN_TIMEOUT', you should also set
'GRUB_TIMEOUT=0' so that the menu is not displayed at all unless
<ESC> or <F4> are pressed, or <SHIFT> is held down.
This option is unset by default, and is deprecated in favour of the
less confusing 'GRUB_TIMEOUT_STYLE=countdown' or
'GRUB_TIMEOUT_STYLE=hidden'.
'GRUB_HIDDEN_TIMEOUT_QUIET'
In conjunction with 'GRUB_HIDDEN_TIMEOUT', set this to 'true' to
suppress the verbose countdown while waiting for a key to be
pressed before displaying the menu.
This option is unset by default, and is deprecated in favour of the
less confusing 'GRUB_TIMEOUT_STYLE=countdown'.
'GRUB_HIDDEN_TIMEOUT_BUTTON'
Variant of 'GRUB_HIDDEN_TIMEOUT', used to support vendor-specific
power buttons. *Note Vendor power-on keys::.
This option is unset by default, and is deprecated in favour of the
less confusing 'GRUB_TIMEOUT_STYLE=countdown' or
'GRUB_TIMEOUT_STYLE=hidden'.
For more detailed customisation of 'grub-mkconfig''s output, you may
edit the scripts in '/etc/grub.d' directly. '/etc/grub.d/40_custom' is
particularly useful for adding entire custom menu entries; simply type
the menu entries you want to add at the end of that file, making sure to
leave at least the first two lines intact.

File: grub.info, Node: Root Identifcation Heuristics, Next: Shell-like scripting, Prev: Simple configuration, Up: Configuration
6.2 Root Identifcation Heuristics
=================================
If the target operating system uses the Linux kernel, 'grub-mkconfig'
attempts to identify the root file system via a heuristic algoirthm.
This algorithm selects the identification method of the root file system
by considering three factors. The first is if an initrd for the target
operating system is also present. The second is
'GRUB_DISABLE_LINUX_UUID' and if set to 'true', prevents 'grub-mkconfig'
from identifying the root file system by its UUID. The third is
'GRUB_DISABLE_LINUX_PARTUUID' and if set to 'true', prevents
'grub-mkconfig' from identifying the root file system via the UUID of
its enclosing partition. If the variables are assigned any other value,
that value is considered equivalent to 'false'. The variables are also
considered to be set to 'false' if they are not set.
When booting, the Linux kernel will delegate the task of mounting the
root filesystem to the initrd. Most initrd images determine the root
file system by checking the Linux kernel's command-line for the 'root'
key and use its value as the identification method of the root file
system. To improve the reliability of booting, most initrd images also
allow the root file system to be identified by its UUID. Because of this
behavior, the 'grub-mkconfig' command will set 'root' to 'root=UUID=...'
to provide the initrd with the filesystem UUID of the root file system.
If no initrd is detected or 'GRUB_DISABLE_LINUX_UUID' is set to
'true' then 'grub-command' will identify the root filesystem by setting
the kernel command-line variable 'root' to 'root=PARTUUID=...' unless
'GRUB_DISABLE_LINUX_PARTUUID' is also set to 'true'. If
'GRUB_DISABLE_LINUX_PARTUUID' is also set to 'true', 'grub-command' will
identify by its Linux device name.
The following table summarizes the behavior of the 'grub-mkconfig'
command.
Initrd GRUB_DISABLE_LINUX_PARTUUID GRUB_DISABLE_LINUX_UUID Linux Root
detected Set To Set To ID Method
--------------------------------------------------------------------------------
false false false part UUID
false false true part UUID
false true false dev name
false true true dev name
true false false fs UUID
true false true part UUID
true true false fs UUID
true true true dev name
Remember, 'GRUB_DISABLE_LINUX_PARTUUID' and 'GRUB_DISABLE_LINUX_UUID'
are also considered to be set to 'false' when they are unset.

File: grub.info, Node: Shell-like scripting, Next: Multi-boot manual config, Prev: Root Identifcation Heuristics, Up: Configuration
6.3 Writing full configuration files directly
=============================================
'grub.cfg' is written in GRUB's built-in scripting language, which has a
syntax quite similar to that of GNU Bash and other Bourne shell
derivatives.
Words
=====
A "word" is a sequence of characters considered as a single unit by
GRUB. Words are separated by "metacharacters", which are the following
plus space, tab, and newline:
{ } | & $ ; < >
Quoting may be used to include metacharacters in words; see below.
Reserved words
==============
Reserved words have a special meaning to GRUB. The following words are
recognised as reserved when unquoted and either the first word of a
simple command or the third word of a 'for' command:
! [[ ]] { }
case do done elif else esac fi for function
if in menuentry select then time until while
Not all of these reserved words have a useful purpose yet; some are
reserved for future expansion.
Quoting
=======
Quoting is used to remove the special meaning of certain characters or
words. It can be used to treat metacharacters as part of a word, to
prevent reserved words from being recognised as such, and to prevent
variable expansion.
There are three quoting mechanisms: the escape character, single
quotes, and double quotes.
A non-quoted backslash (\) is the "escape character". It preserves
the literal value of the next character that follows, with the exception
of newline.
Enclosing characters in single quotes preserves the literal value of
each character within the quotes. A single quote may not occur between
single quotes, even when preceded by a backslash.
Enclosing characters in double quotes preserves the literal value of
all characters within the quotes, with the exception of '$' and '\'.
The '$' character retains its special meaning within double quotes. The
backslash retains its special meaning only when followed by one of the
following characters: '$', '"', '\', or newline. A backslash-newline
pair is treated as a line continuation (that is, it is removed from the
input stream and effectively ignored(1) (*note Shell-like
scripting-Footnote-1::)). A double quote may be quoted within double
quotes by preceding it with a backslash.
Variable expansion
==================
The '$' character introduces variable expansion. The variable name to
be expanded may be enclosed in braces, which are optional but serve to
protect the variable to be expanded from characters immediately
following it which could be interpreted as part of the name.
Normal variable names begin with an alphabetic character, followed by
zero or more alphanumeric characters. These names refer to entries in
the GRUB environment (*note Environment::).
Positional variable names consist of one or more digits. They
represent parameters passed to function calls, with '$1' representing
the first parameter, and so on.
The special variable name '?' expands to the exit status of the most
recently executed command. When positional variable names are active,
other special variable names '@', '*' and '#' are defined and they
expand to all positional parameters with necessary quoting, positional
parameters without any quoting, and positional parameter count
respectively.
Comments
========
A word beginning with '#' causes that word and all remaining characters
on that line to be ignored.
Simple commands
===============
A "simple command" is a sequence of words separated by spaces or tabs
and terminated by a semicolon or a newline. The first word specifies
the command to be executed. The remaining words are passed as arguments
to the invoked command.
The return value of a simple command is its exit status. If the
reserved word '!' precedes the command, then the return value is instead
the logical negation of the command's exit status.
Compound commands
=================
A "compound command" is one of the following:
for NAME in WORD ...; do LIST; done
The list of words following 'in' is expanded, generating a list of
items. The variable NAME is set to each element of this list in
turn, and LIST is executed each time. The return value is the exit
status of the last command that executes. If the expansion of the
items following 'in' results in an empty list, no commands are
executed, and the return status is 0.
if LIST; then LIST; [elif LIST; then LIST;] ... [else LIST;] fi
The 'if' LIST is executed. If its exit status is zero, the 'then'
LIST is executed. Otherwise, each 'elif' LIST is executed in turn,
and if its exit status is zero, the corresponding 'then' LIST is
executed and the command completes. Otherwise, the 'else' LIST is
executed, if present. The exit status is the exit status of the
last command executed, or zero if no condition tested true.
while COND; do LIST; done
until COND; do LIST; done
The 'while' command continuously executes the 'do' LIST as long as
the last command in COND returns an exit status of zero. The
'until' command is identical to the 'while' command, except that
the test is negated; the 'do' LIST is executed as long as the last
command in COND returns a non-zero exit status. The exit status of
the 'while' and 'until' commands is the exit status of the last
'do' LIST command executed, or zero if none was executed.
function NAME { COMMAND; ... }
This defines a function named NAME. The "body" of the function is
the list of commands within braces, each of which must be
terminated with a semicolon or a newline. This list of commands
will be executed whenever NAME is specified as the name of a simple
command. Function definitions do not affect the exit status in
'$?'. When executed, the exit status of a function is the exit
status of the last command executed in the body.
menuentry TITLE ['--class=class' ...] ['--users=users'] ['--unrestricted'] ['--hotkey=key'] ['--id=id'] { COMMAND; ... }
*Note menuentry::.
Built-in Commands
=================
Some built-in commands are also provided by GRUB script to help script
writers perform actions that are otherwise not possible. For example,
these include commands to jump out of a loop without fully completing
it, etc.
break ['n']
Exit from within a 'for', 'while', or 'until' loop. If 'n' is
specified, break 'n' levels. 'n' must be greater than or equal to
1. If 'n' is greater than the number of enclosing loops, all
enclosing loops are exited. The return value is 0 unless 'n' is
not greater than or equal to 1.
continue ['n']
Resume the next iteration of the enclosing 'for', 'while' or
'until' loop. If 'n' is specified, resume at the 'n'th enclosing
loop. 'n' must be greater than or equal to 1. If 'n' is greater
than the number of enclosing loops, the last enclosing loop (the
"top-level" loop) is resumed. The return value is 0 unless 'n' is
not greater than or equal to 1.
return ['n']
Causes a function to exit with the return value specified by 'n'.
If 'n' is omitted, the return status is that of the last command
executed in the function body. If used outside a function the
return status is false.
setparams ['arg'] ...
Replace positional parameters starting with '$1' with arguments to
'setparams'.
shift ['n']
The positional parameters from 'n'+1 ... are renamed to '$1'....
Parameters represented by the numbers '$#' down to '$#'-'n'+1 are
unset. 'n' must be a non-negative number less than or equal to
'$#'. If 'n' is 0, no parameters are changed. If 'n' is not
given, it is assumed to be 1. If 'n' is greater than '$#', the
positional parameters are not changed. The return status is
greater than zero if 'n' is greater than '$#' or less than zero;
otherwise 0.

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

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

File: grub.info, Node: Embedded configuration, Prev: Multi-boot manual config, Up: Configuration
6.5 Embedding a configuration file into GRUB
============================================
GRUB supports embedding a configuration file directly into the core
image, so that it is loaded before entering normal mode. This is
useful, for example, when it is not straightforward to find the real
configuration file, or when you need to debug problems with loading that
file. 'grub-install' uses this feature when it is not using BIOS disk
functions or when installing to a different disk from the one containing
'/boot/grub', in which case it needs to use the 'search' command (*note
search::) to find '/boot/grub'.
To embed a configuration file, use the '-c' option to 'grub-mkimage'.
The file is copied into the core image, so it may reside anywhere on the
file system, and may be removed after running 'grub-mkimage'.
After the embedded configuration file (if any) is executed, GRUB will
load the 'normal' module (*note normal::), which will then read the real
configuration file from '$prefix/grub.cfg'. By this point, the 'root'
variable will also have been set to the root device name. For example,
'prefix' might be set to '(hd0,1)/boot/grub', and 'root' might be set to
'hd0,1'. Thus, in most cases, the embedded configuration file only
needs to set the 'prefix' and 'root' variables, and then drop through to
GRUB's normal processing. A typical example of this might look like
this:
search.fs_uuid 01234567-89ab-cdef-0123-456789abcdef root
set prefix=($root)/boot/grub
(The 'search_fs_uuid' module must be included in the core image for
this example to work.)
In more complex cases, it may be useful to read other configuration
files directly from the embedded configuration file. This allows such
things as reading files not called 'grub.cfg', or reading files from a
directory other than that where GRUB's loadable modules are installed.
To do this, include the 'configfile' and 'normal' modules in the core
image, and embed a configuration file that uses the 'configfile' command
to load another file. The following example of this also requires the
'echo', 'search_label', and 'test' modules to be included in the core
image:
search.fs_label grub root
if [ -e /boot/grub/example/test1.cfg ]; then
set prefix=($root)/boot/grub
configfile /boot/grub/example/test1.cfg
else
if [ -e /boot/grub/example/test2.cfg ]; then
set prefix=($root)/boot/grub
configfile /boot/grub/example/test2.cfg
else
echo "Could not find an example configuration file!"
fi
fi
The embedded configuration file may not contain menu entries
directly, but may only read them from elsewhere using 'configfile'.

File: grub.info, Node: Theme file format, Next: Network, Prev: Configuration, Up: Top
7 Theme file format
*******************
7.1 Introduction
================
The GRUB graphical menu supports themes that can customize the layout
and appearance of the GRUB boot menu. The theme is configured through a
plain text file that specifies the layout of the various GUI components
(including the boot menu, timeout progress bar, and text messages) as
well as the appearance using colors, fonts, and images. Example is
available in docs/example_theme.txt
7.2 Theme Elements
==================
7.2.1 Colors
------------
Colors can be specified in several ways:
* HTML-style "#RRGGBB" or "#RGB" format, where *R*, *G*, and *B* are
hexadecimal digits (e.g., "#8899FF")
* as comma-separated decimal RGB values (e.g., "128, 128, 255")
* with "SVG 1.0 color names" (e.g., "cornflowerblue") which must be
specified in lowercase.
7.2.2 Fonts
-----------
The fonts GRUB uses "PFF2 font format" bitmap fonts. Fonts are
specified with full font names. Currently there is no provision for a
preference list of fonts, or deriving one font from another. Fonts are
loaded with the "loadfont" command in GRUB (*note loadfont::). To see
the list of loaded fonts, execute the "lsfonts" command (*note
lsfonts::). If there are too many fonts to fit on screen, do "set
pager=1" before executing "lsfonts".
7.2.3 Progress Bar
------------------
Figure 7.1
Figure 7.2
Progress bars are used to display the remaining time before GRUB boots
the default menu entry. To create a progress bar that will display the
remaining time before automatic boot, simply create a "progress_bar"
component with the id "__timeout__". This indicates to GRUB that the
progress bar should be updated as time passes, and it should be made
invisible if the countdown to automatic boot is interrupted by the user.
Progress bars may optionally have text displayed on them. This text
is controlled by variable "text" which contains a printf template with
the only argument %d is the number of seconds remaining. Additionally
special values "@TIMEOUT_NOTIFICATION_SHORT@",
"@TIMEOUT_NOTIFICATION_MIDDLE@", "@TIMEOUT_NOTIFICATION_LONG@" are
replaced with standard and translated templates.
7.2.4 Circular Progress Indicator
---------------------------------
The circular progress indicator functions similarly to the progress bar.
When given an id of "__timeout__", GRUB updates the circular progress
indicator's value to indicate the time remaining. For the circular
progress indicator, there are two images used to render it: the *center*
image, and the *tick* image. The center image is rendered in the center
of the component, while the tick image is used to render each mark along
the circumference of the indicator.
7.2.5 Labels
------------
Text labels can be placed on the boot screen. The font, color, and
horizontal alignment can be specified for labels. If a label is given
the id "__timeout__", then the "text" property for that label is also
updated with a message informing the user of the number of seconds
remaining until automatic boot. This is useful in case you want the
text displayed somewhere else instead of directly on the progress bar.
7.2.6 Boot Menu
---------------
The boot menu where GRUB displays the menu entries from the "grub.cfg"
file. It is a list of items, where each item has a title and an
optional icon. The icon is selected based on the *classes* specified
for the menu entry. If there is a PNG file named "myclass.png" in the
"grub/themes/icons" directory, it will be displayed for items which have
the class *myclass*. The boot menu can be customized in several ways,
such as the font and color used for the menu entry title, and by
specifying styled boxes for the menu itself and for the selected item
highlight.
7.2.7 Styled Boxes
------------------
One of the most important features for customizing the layout is the use
of *styled boxes*. A styled box is composed of 9 rectangular (and
potentially empty) regions, which are used to seamlessly draw the styled
box on screen:
Northwest (nw) North (n) Northeast (ne)
West (w) Center (c) East (e)
Southwest (sw) South (s) Southeast (se)
To support any size of box on screen, the center slice and the slices
for the top, bottom, and sides are all scaled to the correct size for
the component on screen, using the following rules:
1. The edge slices (north, south, east, and west) are scaled in the
direction of the edge they are adjacent to. For instance, the west
slice is scaled vertically.
2. The corner slices (northwest, northeast, southeast, and southwest)
are not scaled.
3. The center slice is scaled to fill the remaining space in the
middle.
As an example of how an image might be sliced up, consider the styled
box used for a terminal view.
Figure 7.3
7.2.8 Creating Styled Box Images
--------------------------------
The Inkscape_ scalable vector graphics editor is a very useful tool for
creating styled box images. One process that works well for slicing a
drawing into the necessary image slices is:
1. Create or open the drawing you'd like use.
2. Create a new layer on the top of the layer stack. Make it visible.
Select this layer as the current layer.
3. Draw 9 rectangles on your drawing where you'd like the slices to
be. Clear the fill option, and set the stroke to 1 pixel wide
solid stroke. The corners of the slices must meet precisely; if it
is off by a single pixel, it will probably be evident when the
styled box is rendered in the GRUB menu. You should probably go to
File | Document Properties | Grids and enable a grid or create a
guide (click on one of the rulers next to the drawing and drag over
the drawing; release the mouse button to place the guide) to help
place the rectangles precisely.
4. Right click on the center slice rectangle and choose Object
Properties. Change the "Id" to "slice_c" and click Set. Repeat
this for the remaining 8 rectangles, giving them Id values of
"slice_n", "slice_ne", "slice_e", and so on according to the
location.
5. Save the drawing.
6. Select all the slice rectangles. With the slice layer selected,
you can simply press Ctrl+A to select all rectangles. The status
bar should indicate that 9 rectangles are selected.
7. Click the layer hide icon for the slice layer in the layer palette.
The rectangles will remain selected, even though they are hidden.
8. Choose File | Export Bitmap and check the *Batch export 9 selected
objects* box. Make sure that *Hide all except selected* is
unchecked. click *Export*. This will create PNG files in the same
directory as the drawing, named after the slices. These can now be
used for a styled box in a GRUB theme.
7.3 Theme File Manual
=====================
The theme file is a plain text file. Lines that begin with "#" are
ignored and considered comments. (Note: This may not be the case if the
previous line ended where a value was expected.)
The theme file contains two types of statements:
1. Global properties.
2. Component construction.
7.3.1 Global Properties
-----------------------
7.3.2 Format
------------
Global properties are specified with the simple format:
* name1: value1
* name2: "value which may contain spaces"
* name3: #88F
In this example, name3 is assigned a color value.
7.3.3 Global Property List
--------------------------
title-text Specifies the text to display at the top
center of the screen as a title.
title-font Defines the font used for the title
message at the top of the screen.
title-color Defines the color of the title message.
message-font Currently unused. Left for backward
compatibility.
message-color Currently unused. Left for backward
compatibility.
message-bg-color Currently unused. Left for backward
compatibility.
desktop-image Specifies the image to use as the
background. It will be scaled to fit the
screen size or proportionally scaled
depending on the scale method.
desktop-image-scale-methodSpecifies 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".
desktop-image-h-align 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".
desktop-image-v-align 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".
desktop-color Specifies the color for the background if
*desktop-image* is not specified.
terminal-box Specifies the file name pattern for the
styled box slices used for the command
line terminal window. For example,
"terminal-box: terminal_*.png" will use
the images "terminal_c.png" as the center
area, "terminal_n.png" as the north (top)
edge, "terminal_nw.png" as the northwest
(upper left) corner, and so on. If the
image for any slice is not found, it will
simply be left empty.
terminal-border Specifies the border width of the
terminal window.
terminal-left Specifies the left coordinate of the
terminal window.
terminal-top Specifies the top coordinate of the
terminal window.
terminal-width Specifies the width of the terminal
window.
terminal-height Specifies the height of the terminal
window.
7.3.4 Component Construction
----------------------------
Greater customizability comes is provided by components. A tree of
components forms the user interface. *Containers* are components that
can contain other components, and there is always a single root
component which is an instance of a *canvas* container.
Components are created in the theme file by prefixing the type of
component with a '+' sign:
' + label { text="GRUB" font="aqui 11" color="#8FF" } '
properties of a component are specified as "name = value" (whitespace
surrounding tokens is optional and is ignored) where *value* may be:
* a single word (e.g., "align = center", "color = #FF8080"),
* a quoted string (e.g., "text = "Hello, World!""), or
* a tuple (e.g., "preferred_size = (120, 80)").
7.3.5 Component List
--------------------
The following is a list of the components and the properties they
support.
* label A label displays a line of text.
Properties:
id Set to "__timeout__" to display the time elapsed
to an automatical boot of the default entry.
text 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.
font The font to use for text display.
color The color of the text.
align The horizontal alignment of the text within the
component. Options are "left", "center" and
"right".
visible Set to "false" to hide the label.
* image A component that displays an image. The image is scaled to
fit the component.
Properties:
file The full path to the image file to load.
* progress_bar Displays a horizontally oriented progress bar. It can
be rendered using simple solid filled rectangles, or using a pair
of pixmap styled boxes.
Properties:
id Set to "__timeout__" to display the time elapsed
to an automatical boot of the default entry.
fg_color The foreground color for plain solid color
rendering.
bg_color The background color for plain solid color
rendering.
border_color The border color for plain solid color
rendering.
text_color The text color.
bar_style 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.
highlight_styleThe styled box specification for the highlighted
region of the progress bar. This box will be
used to paint just the highlighted region of the
bar, and will be increased in size as the bar
nears completion. Example: "progress_hl_*.png".
If the value is equal to "bar_style" then no
styled boxes will be shown.
highlight_overlayIf 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".
font The font to use for progress bar.
text 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
"@TIMEOUT_NOTIFICATION_SHORT@",
"@TIMEOUT_NOTIFICATION_MIDDLE@" or
"@TIMEOUT_NOTIFICATION_LONG@", then GRUB will
update this property with an informative message
as the timeout approaches.
* circular_progress Displays a circular progress indicator. The
appearance of this component is determined by two images: the
*center* image and the *tick* image. The center image is generally
larger and will be drawn in the center of the component. Around
the circumference of a circle within the component, the tick image
will be drawn a certain number of times, depending on the
properties of the component.
Properties:
id Set to "__timeout__" to display the time
elapsed to an automatical boot of the
default entry.
center_bitmap The file name of the image to draw in the
center of the component.
tick_bitmap The file name of the image to draw for
the tick marks.
num_ticks The number of ticks that make up a full
circle.
ticks_disappear Boolean value indicating whether tick
marks should progressively appear, or
progressively disappear as *value*
approaches *end*. Specify "true" or
"false". Default is "false".
start_angle 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.
* boot_menu Displays the GRUB boot menu. It allows selecting items
and executing them.
Properties:
item_font The font to use for the menu item
titles.
selected_item_font The font to use for the selected
menu item, or "inherit" (the
default) to use "item_font" for
the selected menu item as well.
item_color The color to use for the menu item
titles.
selected_item_color The color to use for the selected
menu item, or "inherit" (the
default) to use "item_color" for
the selected menu item as well.
icon_width The width of menu item icons.
Icons are scaled to the specified
size.
icon_height The height of menu item icons.
item_height The height of each menu item in
pixels.
item_padding The amount of space in pixels to
leave on each side of the menu
item contents.
item_icon_space The space between an item's icon
and the title text, in pixels.
item_spacing The amount of space to leave
between menu items, in pixels.
menu_pixmap_style The image file pattern for the
menu frame styled box. Example:
"menu_*.png" (this will use images
such as "menu_c.png",
"menu_w.png", 'menu_nw.png", etc.)
item_pixmap_style The image file pattern for the
item styled box.
selected_item_pixmap_style The image file pattern for the
selected item highlight styled
box.
scrollbar Boolean value indicating whether
the scroll bar should be drawn if
the frame and thumb styled boxes
are configured.
scrollbar_frame The image file pattern for the
entire scroll bar. Example:
"scrollbar_*.png"
scrollbar_thumb The image file pattern for the
scroll bar thumb (the part of the
scroll bar that moves as scrolling
occurs). Example:
"scrollbar_thumb_*.png"
scrollbar_thumb_overlay 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".
scrollbar_slice 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.
scrollbar_left_pad The left scrollbar padding in
pixels. Unused if
"scrollbar_slice" is "west".
scrollbar_right_pad The right scrollbar padding in
pixels. Unused if
"scrollbar_slice" is "east".
scrollbar_top_pad The top scrollbar padding in
pixels.
scrollbar_bottom_pad The bottom scrollbar padding in
pixels.
visible Set to "false" to hide the boot
menu.
* canvas Canvas is a container that allows manual placement of
components within it. It does not alter the positions of its child
components. It assigns all child components their preferred sizes.
* hbox The *hbox* container lays out its children from left to right,
giving each one its preferred width. The height of each child is
set to the maximum of the preferred heights of all children.
* vbox The *vbox* container lays out its children from top to bottom,
giving each one its preferred height. The width of each child is
set to the maximum of the preferred widths of all children.
7.3.6 Common properties
-----------------------
The following properties are supported by all components:
'left'
The distance from the left border of container to left border of
the object in either of three formats:
x Value in pixels
p% Percentage
p%+x mixture of both
'top'
The distance from the left border of container to left border of
the object in same format.
'width'
The width of object in same format.
'height'
The height of object in same format.
'id'
The identifier for the component. This can be any arbitrary
string. The ID can be used by scripts to refer to various
components in the GUI component tree. Currently, there is one
special ID value that GRUB recognizes:
"__timeout__" 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".

File: grub.info, Node: Network, Next: Serial terminal, Prev: Theme file format, Up: Top
8 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>
E.g. for i386-pc:
grub-mknetdir --net-directory=/srv/tftp --subdir=/boot/grub -d /usr/lib/grub/i386-pc
Then follow instructions printed out by grub-mknetdir on configuring
your DHCP server.
The grub.cfg file is placed in the same directory as the path output
by grub-mknetdir hereafter referred to as FWPATH. GRUB will search for
its configuration files in order using the following rules where the
appended value corresponds to a value on the client machine.
'(FWPATH)'/grub.cfg-'(UUID OF MACHINE)'
'(FWPATH)'/grub.cfg-'(MAC ADDRESS OF NIC)'
'(FWPATH)'/grub.cfg-'(IPv4 OR IPv6 ADDRESS)'
'(FWPATH)'/grub.cfg
The UUID is the Client Machine Identifier Option Definition as
specified in RFC 4578. The client will only attempt to loouk up a UUID
config file if it was provided by the DHCP server.
The client will only attempt to look up an IPv6 address config once,
however, it will try the IPv4 multiple times. The concrete example
below shows what would happen under the IPv4 case.
UUID: 7726a678-7fc0-4853-a4f6-c85ac36a120a
MAC: 52:54:00:ec:33:81
IPV4: 10.0.0.130 (0A000082)
'(FWPATH)'/grub.cfg-7726a678-7fc0-4853-a4f6-c85ac36a120a
'(FWPATH)'/grub.cfg-52-54-00-ec-33-81
'(FWPATH)'/grub.cfg-0A000082
'(FWPATH)'/grub.cfg-0A00008
'(FWPATH)'/grub.cfg-0A0000
'(FWPATH)'/grub.cfg-0A000
'(FWPATH)'/grub.cfg-0A00
'(FWPATH)'/grub.cfg-0A0
'(FWPATH)'/grub.cfg-0A
'(FWPATH)'/grub.cfg-0
'(FWPATH)'/grub.cfg
This feature is enabled by default but it can be disabled by setting
the 'feature_net_search_cfg' to 'n'. Since this happens before the
configuration file is read by GRUB, this option has to be disabled in an
embedded configuration file (*note Embedded configuration::).
After GRUB has started, files on the TFTP server will be accessible
via the '(tftp)' device.
The server IP address can be controlled by changing the '(tftp)'
device name to '(tftp,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 <INTERFACE> is placeholder for the name of network interface
(platform dependent):
'net_<INTERFACE>_ip'
The network interface's IP address. Read-only.
'net_<INTERFACE>_mac'
The network interface's MAC address. Read-only.
'net_<INTERFACE>_hostname'
The client host name provided by DHCP. Read-only.
'net_<INTERFACE>_domain'
The client domain name provided by DHCP. Read-only.
'net_<INTERFACE>_rootpath'
The path to the client's root disk provided by DHCP. Read-only.
'net_<INTERFACE>_extensionspath'
The path to additional DHCP vendor extensions provided by DHCP.
Read-only.
'net_<INTERFACE>_boot_file'
The boot file name provided by DHCP. Read-only.
'net_<INTERFACE>_dhcp_server_name'
The name of the DHCP server responsible for these boot parameters.
Read-only.
'net_<INTERFACE>_next_server'
The IP address of the next (usually, TFTP) server provided by DHCP.
Read-only.
'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 'net_default_ip' and 'net_default_mac'
'net_default_ip'
The IP address of default interface. Read-only. This is alias for
the 'net_${net_default_interface}_ip'.
'net_default_mac'
The default interface's MAC address. Read-only. This is alias for
the 'net_${net_default_interface}_mac'.
'net_default_server'
The default server used by network drives (*note Device syntax::).
Read-write, although setting this is only useful before opening a
network device.

File: grub.info, Node: Serial terminal, Next: Vendor power-on keys, Prev: Network, Up: Top
9 Using GRUB via a serial line
******************************
This chapter describes how to use the serial terminal support in GRUB.
If you have many computers or computers with no display/keyboard, it
could be very useful to control the computers through serial
communications. To connect one computer with another via a serial line,
you need to prepare a null-modem (cross) serial cable, and you may need
to have multiport serial boards, if your computer doesn't have extra
serial ports. In addition, a terminal emulator is also required, such
as minicom. Refer to a manual of your operating system, for more
information.
As for GRUB, the instruction to set up a serial terminal is quite
simple. Here is an example:
grub> serial --unit=0 --speed=9600
grub> terminal_input serial; terminal_output serial
The command 'serial' initializes the serial unit 0 with the speed
9600bps. The serial unit 0 is usually called 'COM1', so, if you want to
use COM2, you must specify '--unit=1' instead. This command accepts
many other options, so please refer to *note serial::, for more details.
The commands 'terminal_input' (*note terminal_input::) and
'terminal_output' (*note terminal_output::) choose which type of
terminal you want to use. In the case above, the terminal will be a
serial terminal, but you can also pass 'console' to the command, as
'terminal_input serial console'. In this case, a terminal in which you
press any key will be selected as a GRUB terminal. In the example
above, note that you need to put both commands on the same command line,
as you will lose the ability to type commands on the console after the
first command.
However, note that GRUB assumes that your terminal emulator is
compatible with VT100 by default. This is true for most terminal
emulators nowadays, but you should pass the option '--dumb' to the
command if your terminal emulator is not VT100-compatible or implements
few VT100 escape sequences. If you specify this option then GRUB
provides you with an alternative menu interface, because the normal menu
requires several fancy features of your terminal.

File: grub.info, Node: Vendor power-on keys, Next: Images, Prev: Serial terminal, Up: Top
10 Using GRUB with vendor power-on keys
***************************************
Some laptop vendors provide an additional power-on button which boots
another OS. GRUB supports such buttons with the 'GRUB_TIMEOUT_BUTTON',
'GRUB_TIMEOUT_STYLE_BUTTON', 'GRUB_DEFAULT_BUTTON', and
'GRUB_BUTTON_CMOS_ADDRESS' variables in default/grub (*note Simple
configuration::). 'GRUB_TIMEOUT_BUTTON', 'GRUB_TIMEOUT_STYLE_BUTTON',
and 'GRUB_DEFAULT_BUTTON' are used instead of the corresponding
variables without the '_BUTTON' suffix when powered on using the special
button. 'GRUB_BUTTON_CMOS_ADDRESS' is vendor-specific and partially
model-specific. Values known to the GRUB team are:
<Dell XPS M1330M>
121:3
<Dell XPS M1530>
85:3
<Dell Latitude E4300>
85:3
<Asus EeePC 1005PE>
84:1 (unconfirmed)
<LENOVO ThinkPad T410s (2912W1C)>
101:3
To take full advantage of this function, install GRUB into the MBR
(*note Installing GRUB using grub-install::).
If you have a laptop which has a similar feature and not in the above
list could you figure your address and contribute? To discover the
address do the following:
* boot normally
* sudo modprobe nvram
sudo cat /dev/nvram | xxd > normal_button.txt
* boot using vendor button
* sudo modprobe nvram
sudo cat /dev/nvram | xxd > normal_vendor.txt
Then compare these text files and find where a bit was toggled. E.g.
in case of Dell XPS it was:
byte 0x47: 20 --> 28
It's a bit number 3 as seen from following table:
0 01
1 02
2 04
3 08
4 10
5 20
6 40
7 80
0x47 is decimal 71. Linux nvram implementation cuts first 14 bytes
of CMOS. So the real byte address in CMOS is 71+14=85 So complete
address is 85:3

File: grub.info, Node: Images, Next: Core image size limitation, Prev: Vendor power-on keys, Up: Top
11 GRUB image files
*******************
GRUB consists of several images: a variety of bootstrap images for
starting GRUB in various ways, a kernel image, and a set of modules
which are combined with the kernel image to form a core image. Here is
a short overview of them.
'boot.img'
On PC BIOS systems, this image is the first part of GRUB to start.
It is written to a master boot record (MBR) or to the boot sector
of a partition. Because a PC boot sector is 512 bytes, the size of
this image is exactly 512 bytes.
The sole function of 'boot.img' is to read the first sector of the
core image from a local disk and jump to it. Because of the size
restriction, 'boot.img' cannot understand any file system
structure, so 'grub-install' hardcodes the location of the first
sector of the core image into 'boot.img' when installing GRUB.
'diskboot.img'
This image is used as the first sector of the core image when
booting from a hard disk. It reads the rest of the core image into
memory and starts the kernel. Since file system handling is not
yet available, it encodes the location of the core image using a
block list format.
'cdboot.img'
This image is used as the first sector of the core image when
booting from a CD-ROM drive. It performs a similar function to
'diskboot.img'.
'pxeboot.img'
This image is used as the start of the core image when booting from
the network using PXE. *Note Network::.
'lnxboot.img'
This image may be placed at the start of the core image in order to
make GRUB look enough like a Linux kernel that it can be booted by
LILO using an 'image=' section.
'kernel.img'
This image contains GRUB's basic run-time facilities: frameworks
for device and file handling, environment variables, the rescue
mode command-line parser, and so on. It is rarely used directly,
but is built into all core images.
'core.img'
This is the core image of GRUB. It is built dynamically from the
kernel image and an arbitrary list of modules by the 'grub-mkimage'
program. Usually, it contains enough modules to access
'/boot/grub', and loads everything else (including menu handling,
the ability to load target operating systems, and so on) from the
file system at run-time. The modular design allows the core image
to be kept small, since the areas of disk where it must be
installed are often as small as 32KB.
*Note BIOS installation::, for details on where the core image can
be installed on PC systems.
'*.mod'
Everything else in GRUB resides in dynamically loadable modules.
These are often loaded automatically, or built into the core image
if they are essential, but may also be loaded manually using the
'insmod' command (*note insmod::).
For GRUB Legacy users
=====================
GRUB 2 has a different design from GRUB Legacy, and so correspondences
with the images it used cannot be exact. Nevertheless, GRUB Legacy
users often ask questions in the terms they are familiar with, and so
here is a brief guide to how GRUB 2's images relate to that.
'stage1'
Stage 1 from GRUB Legacy was very similar to 'boot.img' in GRUB 2,
and they serve the same function.
'*_stage1_5'
In GRUB Legacy, Stage 1.5's function was to include enough
filesystem code to allow the much larger Stage 2 to be read from an
ordinary filesystem. In this respect, its function was similar to
'core.img' in GRUB 2. However, 'core.img' is much more capable
than Stage 1.5 was; since it offers a rescue shell, it is sometimes
possible to recover manually in the event that it is unable to load
any other modules, for example if partition numbers have changed.
'core.img' is built in a more flexible way, allowing GRUB 2 to
support reading modules from advanced disk types such as LVM and
RAID.
GRUB Legacy could run with only Stage 1 and Stage 2 in some limited
configurations, while GRUB 2 requires 'core.img' and cannot work
without it.
'stage2'
GRUB 2 has no single Stage 2 image. Instead, it loads modules from
'/boot/grub' at run-time.
'stage2_eltorito'
In GRUB 2, images for booting from CD-ROM drives are now
constructed using 'cdboot.img' and 'core.img', making sure that the
core image contains the 'iso9660' module. It is usually best to
use the 'grub-mkrescue' program for this.
'nbgrub'
There is as yet no equivalent for 'nbgrub' in GRUB 2; it was used
by Etherboot and some other network boot loaders.
'pxegrub'
In GRUB 2, images for PXE network booting are now constructed using
'pxeboot.img' and 'core.img', making sure that the core image
contains the 'pxe' and 'pxecmd' modules. *Note Network::.

File: grub.info, Node: Core image size limitation, Next: Filesystem, Prev: Images, Up: Top
12 Core image size limitation
*****************************
Heavily limited platforms:
* 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.
* 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.
* i386-ieee1275: kernel.img (.text + .data + .bss) + modules is
limited by memory available at 0x10000, at most 596K
Lightly limited platforms:
* *-xen: limited only by adress space and RAM size.
* 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
* All EFI platforms: limited by contiguous RAM size and possibly
firmware bugs
* 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.
* 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
* 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)
* 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
* powerpc-ieee1275: kernel.img (.text + .data + .bss) + modules is
limited by space available at 0x200000

File: grub.info, Node: Filesystem, Next: Interface, Prev: Core image size limitation, Up: Top
13 Filesystem syntax and semantics
**********************************
GRUB uses a special syntax for specifying disk drives which can be
accessed by BIOS. Because of BIOS limitations, GRUB cannot distinguish
between IDE, ESDI, SCSI, or others. You must know yourself which BIOS
device is equivalent to which OS device. Normally, that will be clear
if you see the files in a device or use the command 'search' (*note
search::).
* Menu:
* Device syntax:: How to specify devices
* File name syntax:: How to specify files
* Block list syntax:: How to specify block lists

File: grub.info, Node: Device syntax, Next: File name syntax, Up: Filesystem
13.1 How to specify devices
===========================
The device syntax is like this:
(DEVICE[,PARTMAP-NAME1PART-NUM1[,PARTMAP-NAME2PART-NUM2[,...]]])
'[]' means the parameter is optional. DEVICE depends on the disk
driver in use. BIOS and EFI disks use either 'fd' or 'hd' followed by a
digit, like 'fd0', or 'cd'. AHCI, PATA (ata), crypto, USB use the name
of driver followed by a number. Memdisk and host are limited to one
disk and so it's refered just by driver name. RAID (md), ofdisk
(ieee1275 and nand), LVM (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 'loopback' command. Hostdisk uses names
specified in device.map as long as it's of the form [fhc]d[0-9]* or
hostdisk/<OS DEVICE>. For crypto and RAID (md) additionally you can use
the syntax <driver name>uuid/<uuid>. For LVM additionally you can use
the syntax lvmid/<volume-group-uuid>/<volume-uuid>.
(fd0)
(hd0)
(cd)
(ahci0)
(ata0)
(crypto0)
(usb0)
(cryptouuid/123456789abcdef0123456789abcdef0)
(mduuid/123456789abcdef0123456789abcdef0)
(lvm/system-root)
(lvmid/F1ikgD-2RES-306G-il9M-7iwa-4NKW-EbV1NV/eLGuCQ-L4Ka-XUgR-sjtJ-ffch-bajr-fCNfz5)
(md/myraid)
(md/0)
(ieee1275/disk2)
(ieee1275//pci@1f\,0/ide@d/disk@2)
(nand)
(memdisk)
(host)
(myloop)
(hostdisk//dev/sda)
PART-NUM represents the partition number of DEVICE, starting from
one. PARTNAME is optional but is recommended since disk may have
several top-level partmaps. Specifying third and later component you
can access to subpartitions.
The syntax '(hd0)' represents using the entire disk (or the MBR when
installing GRUB), while the syntax '(hd0,1)' represents using the first
partition of the disk (or the boot sector of the partition when
installing GRUB).
(hd0,msdos1)
(hd0,msdos1,msdos5)
(hd0,msdos1,bsd3)
(hd0,netbsd1)
(hd0,gpt1)
(hd0,1,3)
If you enabled the network support, the special drives
'(PROTOCOL[,SERVER])' are also available. Supported protocols are
'http' and 'tftp'. If SERVER is omitted, value of environment variable
'net_default_server' is used. Before using the network drive, you must
initialize the network. *Note Network::, for more information.
If you boot GRUB from a CD-ROM, '(cd)' is available. *Note Making a
GRUB bootable CD-ROM::, for details.

File: grub.info, Node: File name syntax, Next: Block list syntax, Prev: Device syntax, Up: Filesystem
13.2 How to specify files
=========================
There are two ways to specify files, by "absolute file name" and by
"block list".
An absolute file name resembles a Unix absolute file name, using '/'
for the directory separator (not '\' as in DOS). One example is
'(hd0,1)/boot/grub/grub.cfg'. This means the file '/boot/grub/grub.cfg'
in the first partition of the first hard disk. If you omit the device
name in an absolute file name, GRUB uses GRUB's "root device"
implicitly. So if you set the root device to, say, '(hd1,1)' by the
command 'set root=(hd1,1)' (*note set::), then '/boot/kernel' is the
same as '(hd1,1)/boot/kernel'.
On ZFS filesystem the first path component must be
VOLUME'@'[SNAPSHOT]. So '/rootvol@snap-129/boot/grub/grub.cfg' refers
to file '/boot/grub/grub.cfg' in snapshot of volume 'rootvol' with name
'snap-129'. Trailing '@' after volume name is mandatory even if
snapshot name is omitted.

File: grub.info, Node: Block list syntax, Prev: File name syntax, Up: Filesystem
13.3 How to specify block lists
===============================
A block list is used for specifying a file that doesn't appear in the
filesystem, like a chainloader. The syntax is
'[OFFSET]+LENGTH[,[OFFSET]+LENGTH]...'. Here is an example:
0+100,200+1,300+300
This represents that GRUB should read blocks 0 through 99, block 200,
and blocks 300 through 599. If you omit an offset, then GRUB assumes
the offset is zero.
Like the file name syntax (*note File name syntax::), if a blocklist
does not contain a device name, then GRUB uses GRUB's "root device". So
'(hd0,2)+1' is the same as '+1' when the root device is '(hd0,2)'.

File: grub.info, Node: Interface, Next: Environment, Prev: Filesystem, Up: Top
14 GRUB's user interface
************************
GRUB has both a simple menu interface for choosing preset entries from a
configuration file, and a highly flexible command-line for performing
any desired combination of boot commands.
GRUB looks for its configuration file as soon as it is loaded. If
one is found, then the full menu interface is activated using whatever
entries were found in the file. If you choose the "command-line" menu
option, or if the configuration file was not found, then GRUB drops to
the command-line interface.
* Menu:
* Command-line interface:: The flexible command-line interface
* Menu interface:: The simple menu interface
* Menu entry editor:: Editing a menu entry

File: grub.info, Node: Command-line interface, Next: Menu interface, Up: Interface
14.1 The flexible command-line interface
========================================
The command-line interface provides a prompt and after it an editable
text area much like a command-line in Unix or DOS. Each command is
immediately executed after it is entered(1) (*note Command-line
interface-Footnote-1::). The commands (*note Command-line and menu
entry commands::) are a subset of those available in the configuration
file, used with exactly the same syntax.
Cursor movement and editing of the text on the line can be done via a
subset of the functions available in the Bash shell:
<C-f>
<PC right key>
Move forward one character.
<C-b>
<PC left key>
Move back one character.
<C-a>
<HOME>
Move to the start of the line.
<C-e>
<END>
Move the the end of the line.
<C-d>
<DEL>
Delete the character underneath the cursor.
<C-h>
<BS>
Delete the character to the left of the cursor.
<C-k>
Kill the text from the current cursor position to the end of the
line.
<C-u>
Kill backward from the cursor to the beginning of the line.
<C-y>
Yank the killed text back into the buffer at the cursor.
<C-p>
<PC up key>
Move up through the history list.
<C-n>
<PC down key>
Move down through the history list.
When typing commands interactively, if the cursor is within or before
the first word in the command-line, pressing the <TAB> key (or <C-i>)
will display a listing of the available commands, and if the cursor is
after the first word, the '<TAB>' will provide a completion listing of
disks, partitions, and file names depending on the context. Note that
to obtain a list of drives, one must open a parenthesis, as 'root ('.
Note that you cannot use the completion functionality in the TFTP
filesystem. This is because TFTP doesn't support file name listing for
the security.

File: grub.info, Node: Command-line interface-Footnotes, Up: Command-line interface
(1) However, this behavior will be changed in the future version, in
a user-invisible way.

File: grub.info, Node: Menu interface, Next: Menu entry editor, Prev: Command-line interface, Up: Interface
14.2 The simple menu interface
==============================
The menu interface is quite easy to use. Its commands are both
reasonably intuitive and described on screen.
Basically, the menu interface provides a list of "boot entries" to
the user to choose from. Use the arrow keys to select the entry of
choice, then press <RET> to run it. An optional timeout is available to
boot the default entry (the first one if not set), which is aborted by
pressing any key.
Commands are available to enter a bare command-line by pressing <c>
(which operates exactly like the non-config-file version of GRUB, but
allows one to return to the menu if desired by pressing <ESC>) or to
edit any of the "boot entries" by pressing <e>.
If you protect the menu interface with a password (*note Security::),
all you can do is choose an entry by pressing <RET>, or press <p> to
enter the password.

File: grub.info, Node: Menu entry editor, Prev: Menu interface, Up: Interface
14.3 Editing a menu entry
=========================
The menu entry editor looks much like the main menu interface, but the
lines in the menu are individual commands in the selected entry instead
of entry names.
If an <ESC> is pressed in the editor, it aborts all the changes made
to the configuration entry and returns to the main menu interface.
Each line in the menu entry can be edited freely, and you can add new
lines by pressing <RET> at the end of a line. To boot the edited entry,
press <Ctrl-x>.
Although GRUB unfortunately does not support "undo", you can do
almost the same thing by just returning to the main menu using <ESC>.

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

File: grub.info, Node: Special environment variables, Next: Environment block, Up: Environment
15.1 Special environment variables
==================================
These variables have special meaning to GRUB.
* Menu:
* 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_<INTERFACE>_boot_file::
* net_<INTERFACE>_dhcp_server_name::
* net_<INTERFACE>_domain::
* net_<INTERFACE>_extensionspath::
* net_<INTERFACE>_hostname::
* net_<INTERFACE>_ip::
* net_<INTERFACE>_mac::
* net_<INTERFACE>_next_server::
* net_<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::

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

File: grub.info, Node: check_signatures, Next: chosen, Prev: biosnum, Up: Special environment variables
15.1.2 check_signatures
-----------------------
This variable controls whether GRUB enforces digital signature
validation on loaded files. *Note Using digital signatures::.

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

File: grub.info, Node: cmdpath, Next: color_highlight, Prev: chosen, Up: Special environment variables
15.1.4 cmdpath
--------------
The location from which 'core.img' was loaded as an absolute directory
name (*note 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.

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

File: grub.info, Node: color_normal, Next: config_directory, Prev: color_highlight, Up: Special environment variables
15.1.6 color_normal
-------------------
This variable contains the "normal" foreground and background terminal
colors, separated by a slash ('/'). Setting this variable changes those
colors. Each color must be a name from the following list:
* black
* blue
* green
* cyan
* red
* magenta
* brown
* light-gray
* dark-gray
* light-blue
* light-green
* light-cyan
* light-red
* light-magenta
* yellow
* white
The default is 'light-gray/black'.
The color support support varies from terminal to terminal.
'morse' has no color support at all.
'mda_text' color support is limited to highlighting by black/white
reversal.
'console' on ARC, EMU and IEEE1275, 'serial_*' and 'spkmodem' are
governed by terminfo and support only 8 colors if in modes 'vt100-color'
(default for console on emu), 'arc' (default for console on ARC),
'ieee1275' (default for console on IEEE1275). When in mode 'vt100' then
the color support is limited to highlighting by black/white reversal.
When in mode '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.
'console' on EFI and BIOS and 'vga_text' support all 16 colors.
'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.

File: grub.info, Node: config_directory, Next: config_file, Prev: color_normal, Up: Special environment variables
15.1.7 config_directory
-----------------------
This variable is automatically set by GRUB to the directory part of
current configuration file name (*note config_file::).

File: grub.info, Node: config_file, Next: debug, Prev: config_directory, Up: Special environment variables
15.1.8 config_file
------------------
This variable is automatically set by GRUB to the name of configuration
file that is being processed by commands 'configfile' (*note
configfile::) or 'normal' (*note normal::). It is restored to the
previous value when command completes.

File: grub.info, Node: debug, Next: default, Prev: config_file, Up: Special environment variables
15.1.9 debug
------------
This variable may be set to enable debugging output from various
components of GRUB. The value is a list of debug facility names
separated by whitespace or ',', or 'all' to enable all available
debugging output. The facility names are the first argument to
grub_dprintf. Consult source for more details.

File: grub.info, Node: default, Next: fallback, Prev: debug, Up: Special environment variables
15.1.10 default
---------------
If this variable is set, it identifies a menu entry that should be
selected by default, possibly after a timeout (*note timeout::). The
entry may be identified by number (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 {
...
}
then you can make this the default using:
default=example-gnu-linux
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 '>'. 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
The more recent release of Minix would then be identified as 'Other
platforms>Minix>Version 3.4.0', or as '1>0>0', or as
'other>minix>minix-3.4.0'.
This variable is often set by 'GRUB_DEFAULT' (*note Simple
configuration::), 'grub-set-default', or 'grub-reboot'.

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

File: grub.info, Node: gfxmode, Next: gfxpayload, Prev: fallback, Up: Special environment variables
15.1.12 gfxmode
---------------
If this variable is set, it sets the resolution used on the 'gfxterm'
graphical terminal. Note that you can only use modes which your
graphics card supports via VESA BIOS Extensions (VBE), so for example
native LCD panel resolutions may not be available. The default is
'auto', which selects a platform-specific default that should look
reasonable. Supported modes can be listed by 'videoinfo' command in
GRUB.
The resolution may be specified as a sequence of one or more modes,
separated by commas (',') or semicolons (';'); each will be tried in
turn until one is found. Each mode should be either 'auto',
'WIDTHxHEIGHT', or 'WIDTHxHEIGHTxDEPTH'.

File: grub.info, Node: gfxpayload, Next: gfxterm_font, Prev: gfxmode, Up: Special environment variables
15.1.13 gfxpayload
------------------
If this variable is set, it controls the video mode in which the Linux
kernel starts up, replacing the 'vga=' boot option (*note linux::). It
may be set to 'text' to force the Linux kernel to boot in normal text
mode, 'keep' to preserve the graphics mode set using 'gfxmode', or any
of the permitted values for 'gfxmode' to set a particular graphics mode
(*note gfxmode::).
Depending on your kernel, your distribution, your graphics card, and
the phase of the moon, note that using this option may cause GNU/Linux
to suffer from various display problems, particularly during the early
part of the boot sequence. If you have problems, set this variable to
'text' and GRUB will tell Linux to boot in normal text mode.
The default is platform-specific. On platforms with a native text
mode (such as PC BIOS platforms), the default is 'text'. Otherwise the
default may be 'auto' or a specific video mode.
This variable is often set by 'GRUB_GFXPAYLOAD_LINUX' (*note Simple
configuration::).

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

File: grub.info, Node: grub_cpu, Next: grub_platform, Prev: gfxterm_font, Up: Special environment variables
15.1.15 grub_cpu
----------------
In normal mode (*note normal::), GRUB sets the 'grub_cpu' variable to
the CPU type for which GRUB was built (e.g. 'i386' or 'powerpc').

File: grub.info, Node: grub_platform, Next: icondir, Prev: grub_cpu, Up: Special environment variables
15.1.16 grub_platform
---------------------
In normal mode (*note normal::), GRUB sets the 'grub_platform' variable
to the platform for which GRUB was built (e.g. 'pc' or 'efi').

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

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

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

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

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

File: grub.info, Node: net_<INTERFACE>_boot_file, Next: net_<INTERFACE>_dhcp_server_name, Prev: menu_color_normal, Up: Special environment variables
15.1.22 net_<INTERFACE>_boot_file
---------------------------------
*Note Network::.

File: grub.info, Node: net_<INTERFACE>_dhcp_server_name, Next: net_<INTERFACE>_domain, Prev: net_<INTERFACE>_boot_file, Up: Special environment variables
15.1.23 net_<INTERFACE>_dhcp_server_name
----------------------------------------
*Note Network::.

File: grub.info, Node: net_<INTERFACE>_domain, Next: net_<INTERFACE>_extensionspath, Prev: net_<INTERFACE>_dhcp_server_name, Up: Special environment variables
15.1.24 net_<INTERFACE>_domain
------------------------------
*Note Network::.

File: grub.info, Node: net_<INTERFACE>_extensionspath, Next: net_<INTERFACE>_hostname, Prev: net_<INTERFACE>_domain, Up: Special environment variables
15.1.25 net_<INTERFACE>_extensionspath
--------------------------------------
*Note Network::.

File: grub.info, Node: net_<INTERFACE>_hostname, Next: net_<INTERFACE>_ip, Prev: net_<INTERFACE>_extensionspath, Up: Special environment variables
15.1.26 net_<INTERFACE>_hostname
--------------------------------
*Note Network::.

File: grub.info, Node: net_<INTERFACE>_ip, Next: net_<INTERFACE>_mac, Prev: net_<INTERFACE>_hostname, Up: Special environment variables
15.1.27 net_<INTERFACE>_ip
--------------------------
*Note Network::.

File: grub.info, Node: net_<INTERFACE>_mac, Next: net_<INTERFACE>_next_server, Prev: net_<INTERFACE>_ip, Up: Special environment variables
15.1.28 net_<INTERFACE>_mac
---------------------------
*Note Network::.

File: grub.info, Node: net_<INTERFACE>_next_server, Next: net_<INTERFACE>_rootpath, Prev: net_<INTERFACE>_mac, Up: Special environment variables
15.1.29 net_<INTERFACE>_next_server
-----------------------------------
*Note Network::.

File: grub.info, Node: net_<INTERFACE>_rootpath, Next: net_default_interface, Prev: net_<INTERFACE>_next_server, Up: Special environment variables
15.1.30 net_<INTERFACE>_rootpath
--------------------------------
*Note Network::.

File: grub.info, Node: net_default_interface, Next: net_default_ip, Prev: net_<INTERFACE>_rootpath, Up: Special environment variables
15.1.31 net_default_interface
-----------------------------
*Note Network::.

File: grub.info, Node: net_default_ip, Next: net_default_mac, Prev: net_default_interface, Up: Special environment variables
15.1.32 net_default_ip
----------------------
*Note Network::.

File: grub.info, Node: net_default_mac, Next: net_default_server, Prev: net_default_ip, Up: Special environment variables
15.1.33 net_default_mac
-----------------------
*Note Network::.

File: grub.info, Node: net_default_server, Next: pager, Prev: net_default_mac, Up: Special environment variables
15.1.34 net_default_server
--------------------------
*Note Network::.

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

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

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

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

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

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

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

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

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

File: grub.info, Node: timeout_style, Prev: timeout, Up: Special environment variables
15.1.44 timeout_style
---------------------
This variable may be set to 'menu', 'countdown', or 'hidden' to control
the way in which the timeout (*note timeout::) interacts with displaying
the menu. See the documentation of 'GRUB_TIMEOUT_STYLE' (*note Simple
configuration::) for details.

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

File: grub.info, Node: Commands, Next: Internationalisation, Prev: Environment, Up: Top
16 The list of available commands
*********************************
In this chapter, we list all commands that are available in GRUB.
Commands belong to different groups. A few can only be used in the
global section of the configuration file (or "menu"); most of them can
be entered on the command-line and can be used either anywhere in the
menu or specifically in the menu entries.
In rescue mode, only the 'insmod' (*note insmod::), 'ls' (*note
ls::), 'set' (*note set::), and 'unset' (*note unset::) commands are
normally available. If you end up in rescue mode and do not know what
to do, then *note GRUB only offers a rescue shell::.
* Menu:
* Menu-specific commands::
* General commands::
* Command-line and menu entry commands::
* Networking commands::

File: grub.info, Node: Menu-specific commands, Next: General commands, Up: Commands
16.1 The list of commands for the menu only
===========================================
The semantics used in parsing the configuration file are the following:
* The files _must_ be in plain-text format.
* '#' at the beginning of a line in a configuration file means it is
only a comment.
* Options are separated by spaces.
* All numbers can be either decimal or hexadecimal. A hexadecimal
number must be preceded by '0x', and is case-insensitive.
These commands can only be used in the menu:
* Menu:
* menuentry:: Start a menu entry
* submenu:: Group menu entries

File: grub.info, Node: menuentry, Next: submenu, Up: Menu-specific commands
16.1.1 menuentry
----------------
-- Command: menuentry TITLE ['--class=class' ...] ['--users=users']
['--unrestricted'] ['--hotkey=key'] ['--id=id'] [ARG ...] {
COMMAND; ... }
This defines a GRUB menu entry named TITLE. When this entry is
selected from the menu, GRUB will set the CHOSEN environment
variable to value of '--id' if '--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
'boot' command.
The '--class' option may be used any number of times to group menu
entries into classes. Menu themes may display different classes
using different styles.
The '--users' option grants specific users access to specific menu
entries. *Note Security::.
The '--unrestricted' option grants all users access to specific
menu entries. *Note Security::.
The '--hotkey' option associates a hotkey with a menu entry. KEY
may be a single letter, or one of the aliases 'backspace', 'tab',
or 'delete'.
The '--id' may be used to associate unique identifier with a menu
entry. ID is string of ASCII aphanumeric characters, underscore
and hyphen and should not start with a digit.
All other arguments including TITLE are passed as positional
parameters when list of commands is executed with TITLE always
assigned to '$1'.

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

File: grub.info, Node: General commands, Next: Command-line and menu entry commands, Prev: Menu-specific commands, Up: Commands
16.2 The list of general commands
=================================
Commands usable anywhere in the menu and in the command-line.
* Menu:
* serial:: Set up a serial device
* terminal_input:: Manage input terminals
* terminal_output:: Manage output terminals
* terminfo:: Define terminal type

File: grub.info, Node: serial, Next: terminal_input, Up: General commands
16.2.1 serial
-------------
-- Command: serial ['--unit=unit'] ['--port=port'] ['--speed=speed']
['--word=word'] ['--parity=parity'] ['--stop=stop']
Initialize a serial device. UNIT is a number in the range 0-3
specifying which serial port to use; default is 0, which
corresponds to the port often called COM1. PORT is the I/O port
where the UART is to be found; if specified it takes precedence
over UNIT. SPEED is the transmission speed; default is 9600. WORD
and STOP are the number of data bits and stop bits. Data bits must
be in the range 5-8 and stop bits must be 1 or 2. Default is 8
data bits and one stop bit. PARITY is one of 'no', 'odd', 'even'
and defaults to 'no'.
The serial port is not used as a communication channel unless the
'terminal_input' or 'terminal_output' command is used (*note
terminal_input::, *note terminal_output::).
See also *note Serial terminal::.

File: grub.info, Node: terminal_input, Next: terminal_output, Prev: serial, Up: General commands
16.2.2 terminal_input
---------------------
-- Command: terminal_input ['--append'|'--remove'] [terminal1]
[terminal2] ...
List or select an input terminal.
With no arguments, list the active and available input terminals.
With '--append', add the named terminals to the list of active
input terminals; any of these may be used to provide input to GRUB.
With '--remove', remove the named terminals from the active list.
With no options but a list of terminal names, make only the listed
terminal names active.

File: grub.info, Node: terminal_output, Next: terminfo, Prev: terminal_input, Up: General commands
16.2.3 terminal_output
----------------------
-- Command: terminal_output ['--append'|'--remove'] [terminal1]
[terminal2] ...
List or select an output terminal.
With no arguments, list the active and available output terminals.
With '--append', add the named terminals to the list of active
output terminals; all of these will receive output from GRUB.
With '--remove', remove the named terminals from the active list.
With no options but a list of terminal names, make only the listed
terminal names active.

File: grub.info, Node: terminfo, Prev: terminal_output, Up: General commands
16.2.4 terminfo
---------------
-- Command: terminfo ['-a'|'-u'|'-v'] ['-g WxH'] [term] [type]
Define the capabilities of your terminal by giving the name of an
entry in the terminfo database, which should correspond roughly to
a 'TERM' environment variable in Unix.
The currently available terminal types are 'vt100', 'vt100-color',
'ieee1275', and 'dumb'. If you need other terminal types, please
contact us to discuss the best way to include support for these in
GRUB.
The '-a' ('--ascii'), '-u' ('--utf8'), and '-v' ('--visual-utf8')
options control how non-ASCII text is displayed. '-a' specifies an
ASCII-only terminal; '-u' specifies logically-ordered UTF-8; and
'-v' specifies "visually-ordered UTF-8" (in other words, arranged
such that a terminal emulator without bidirectional text support
will display right-to-left text in the proper order; this is not
really proper UTF-8, but a workaround).
The '-g' ('--geometry') can be used to specify terminal geometry.
If no option or terminal type is specified, the current terminal
type is printed.

File: grub.info, Node: Command-line and menu entry commands, Next: Networking commands, Prev: General commands, Up: Commands
16.3 The list of command-line and menu entry commands
=====================================================
These commands are usable in the command-line and in menu entries. If
you forget a command, you can run the command 'help' (*note help::).
* Menu:
* [:: 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
* cutmem:: Remove memory regions
* 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
* rdmsr:: Read values from model-specific registers
* 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
* smbios:: Retrieve SMBIOS information
* 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
* verify_detached:: Verify detached digital signature
* videoinfo:: List available video modes
* wrmsr:: Write values to model-specific registers
* xen_hypervisor:: Load xen hypervisor binary (only on AArch64)
* xen_module:: Load xen modules for xen hypervisor (only on AArch64)

File: grub.info, Node: [, Next: acpi, Up: Command-line and menu entry commands
16.3.1 [
--------
-- Command: '[' expression ']'
Alias for 'test EXPRESSION' (*note test::).

File: grub.info, Node: acpi, Next: authenticate, Prev: [, Up: Command-line and menu entry commands
16.3.2 acpi
-----------
-- Command: acpi ['-1'|'-2']
['--exclude=table1,...'|'--load-only=table1,...']
['--oemid=id'] ['--oemtable=table'] ['--oemtablerev=rev']
['--oemtablecreator=creator'] ['--oemtablecreatorrev=rev']
['--no-ebda'] filename ...
Modern BIOS systems normally implement the Advanced Configuration
and Power Interface (ACPI), and define various tables that describe
the interface between an ACPI-compliant operating system and the
firmware. In some cases, the tables provided by default only work
well with certain operating systems, and it may be necessary to
replace some of them.
Normally, this command will replace the Root System Description
Pointer (RSDP) in the Extended BIOS Data Area to point to the new
tables. If the '--no-ebda' option is used, the new tables will be
known only to GRUB, but may be used by GRUB's EFI emulation.
Note: The command is not allowed when lockdown is enforced (*note
Lockdown::). Otherwise an attacker can instruct the GRUB to load
an SSDT table to overwrite the kernel lockdown configuration and
later load and execute unsigned code.

File: grub.info, Node: authenticate, Next: background_color, Prev: acpi, Up: Command-line and menu entry commands
16.3.3 authenticate
-------------------
-- Command: authenticate [userlist]
Check whether user is in USERLIST or listed in the value of
variable 'superusers'. See *note superusers:: for valid user list
format. If 'superusers' is empty, this command returns true.
*Note Security::.

File: grub.info, Node: background_color, Next: background_image, Prev: authenticate, Up: Command-line and menu entry commands
16.3.4 background_color
-----------------------
-- Command: background_color color
Set background color for active terminal. For valid color
specifications see *note Colors: Theme file format. Background
color can be changed only when using 'gfxterm' for terminal output.
This command sets color of empty areas without text. Text
background color is controlled by environment variables
COLOR_NORMAL, COLOR_HIGHLIGHT, MENU_COLOR_NORMAL,
MENU_COLOR_HIGHLIGHT. *Note Special environment variables::.

File: grub.info, Node: background_image, Next: badram, Prev: background_color, Up: Command-line and menu entry commands
16.3.5 background_image
-----------------------
-- Command: background_image [['--mode' 'stretch'|'normal'] file]
Load background image for active terminal from FILE. Image is
stretched to fill up entire screen unless option '--mode' 'normal'
is given. Without arguments remove currently loaded background
image. Background image can be changed only when using 'gfxterm'
for terminal output.

File: grub.info, Node: badram, Next: blocklist, Prev: background_image, Up: Command-line and menu entry commands
16.3.6 badram
-------------
-- Command: badram addr,mask[,addr,mask...]
Filter out bad RAM.
This command notifies the memory manager that specified regions of
RAM ought to be filtered out (usually, because they're damaged).
This remains in effect after a payload kernel has been loaded by
GRUB, as long as the loaded kernel obtains its memory map from
GRUB. Kernels that support this include Linux, GNU Mach, the kernel
of FreeBSD and Multiboot kernels in general.
Syntax is the same as provided by the Memtest86+ utility
(http://www.memtest.org/): a list of address/mask pairs. Given a
page-aligned address and a base address / mask pair, if all the
bits of the page-aligned address that are enabled by the mask match
with the base address, it means this page is to be filtered. This
syntax makes it easy to represent patterns that are often result of
memory damage, due to physical distribution of memory cells.
The command is similar to 'cutmem' command.
Note: The command is not allowed when lockdown is enforced (*note
Lockdown::). This prevents removing EFI memory regions to
potentially subvert the security mechanisms provided by the UEFI
secure boot.

File: grub.info, Node: blocklist, Next: boot, Prev: badram, Up: Command-line and menu entry commands
16.3.7 blocklist
----------------
-- Command: blocklist file
Print a block list (*note Block list syntax::) for FILE.

File: grub.info, Node: boot, Next: cat, Prev: blocklist, Up: Command-line and menu entry commands
16.3.8 boot
-----------
-- Command: boot
Boot the OS or chain-loader which has been loaded. Only necessary
if running the fully interactive command-line (it is implicit at
the end of a menu entry).

File: grub.info, Node: cat, Next: chainloader, Prev: boot, Up: Command-line and menu entry commands
16.3.9 cat
----------
-- Command: cat ['--dos'] file
Display the contents of the file FILE. This command may be useful
to remind you of your OS's root partition:
grub> cat /etc/fstab
If the '--dos' option is used, then carriage return / new line
pairs will be displayed as a simple new line. Otherwise, the
carriage return will be displayed as a control character ('<d>') to
make it easier to see when boot problems are caused by a file
formatted using DOS-style line endings.

File: grub.info, Node: chainloader, Next: clear, Prev: cat, Up: Command-line and menu entry commands
16.3.10 chainloader
-------------------
-- Command: chainloader ['--force'] file
Load FILE as a chain-loader. Like any other file loaded by the
filesystem code, it can use the blocklist notation (*note Block
list syntax::) to grab the first sector of the current partition
with '+1'. If you specify the option '--force', then load FILE
forcibly, whether it has a correct signature or not. This is
required when you want to load a defective boot loader, such as SCO
UnixWare 7.1.

File: grub.info, Node: clear, Next: cmosclean, Prev: chainloader, Up: Command-line and menu entry commands
16.3.11 clear
-------------
-- Command: clear
Clear the screen.

File: grub.info, Node: cmosclean, Next: cmosdump, Prev: clear, Up: Command-line and menu entry commands
16.3.12 cmosclean
-----------------
-- Command: cmosclean byte:bit
Clear value of bit in CMOS at location BYTE:BIT. This command is
available only on platforms that support CMOS.

File: grub.info, Node: cmosdump, Next: cmostest, Prev: cmosclean, Up: Command-line and menu entry commands
16.3.13 cmosdump
----------------
-- Dump: CMOS contents
Dump full CMOS contents as hexadecimal values. This command is
available only on platforms that support CMOS.

File: grub.info, Node: cmostest, Next: cmp, Prev: cmosdump, Up: Command-line and menu entry commands
16.3.14 cmostest
----------------
-- Command: cmostest byte:bit
Test value of bit in CMOS at location BYTE:BIT. Exit status is
zero if bit is set, non zero otherwise. This command is available
only on platforms that support CMOS.

File: grub.info, Node: cmp, Next: configfile, Prev: cmostest, Up: Command-line and menu entry commands
16.3.15 cmp
-----------
-- Command: cmp file1 file2
Compare the file FILE1 with the file FILE2. If they differ in
size, print the sizes like this:
Differ in size: 0x1234 [foo], 0x4321 [bar]
If the sizes are equal but the bytes at an offset differ, then
print the bytes like this:
Differ at the offset 777: 0xbe [foo], 0xef [bar]
If they are completely identical, nothing will be printed.

File: grub.info, Node: configfile, Next: cpuid, Prev: cmp, Up: Command-line and menu entry commands
16.3.16 configfile
------------------
-- Command: configfile file
Load FILE as a configuration file. If FILE defines any menu
entries, then show a menu containing them immediately. Any
environment variable changes made by the commands in FILE will not
be preserved after 'configfile' returns.

File: grub.info, Node: cpuid, Next: crc, Prev: configfile, Up: Command-line and menu entry commands
16.3.17 cpuid
-------------
-- Command: cpuid [-l] [-p]
Check for CPU features. This command is only available on x86
systems.
With the '-l' option, return true if the CPU supports long mode
(64-bit).
With the '-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 '-l'. This may change in the future.

File: grub.info, Node: crc, Next: cryptomount, Prev: cpuid, Up: Command-line and menu entry commands
16.3.18 crc
-----------
-- Command: crc arg ...
Alias for 'hashsum --hash crc32 arg ...'. See command 'hashsum'
(*note hashsum::) for full description.

File: grub.info, Node: cryptomount, Next: cutmem, Prev: crc, Up: Command-line and menu entry commands
16.3.19 cryptomount
-------------------
-- Command: cryptomount device|'-u' uuid|'-a'|'-b'
Setup access to encrypted device. If necessary, passphrase is
requested interactively. Option DEVICE configures specific grub
device (*note Naming convention::); option '-u' UUID configures
device with specified UUID; option '-a' configures all detected
encrypted devices; option '-b' configures all geli containers that
have boot flag set.
GRUB suports devices encrypted using LUKS, LUKS2 and geli. Note
that necessary modules (LUKS, LUKS2 and GELI) have to be loaded
manually before this command can be used. For LUKS2 only the
PBKDF2 key derivation function is supported, as Argon2 is not yet
supported.
Also, note that, unlike filesystem UUIDs, UUIDs for encrypted
devices must be specified without dash separators.

File: grub.info, Node: cutmem, Next: date, Prev: cryptomount, Up: Command-line and menu entry commands
16.3.20 cutmem
--------------
-- Command: cutmem from[K|M|G] to[K|M|G]
Remove any memory regions in specified range.
This command notifies the memory manager that specified regions of
RAM ought to be filtered out. 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.
The command is similar to 'badram' command.
Note: The command is not allowed when lockdown is enforced (*note
Lockdown::). This prevents removing EFI memory regions to
potentially subvert the security mechanisms provided by the UEFI
secure boot.

File: grub.info, Node: date, Next: devicetree, Prev: cutmem, Up: Command-line and menu entry commands
16.3.21 date
------------
-- Command: date [[year-]month-day] [hour:minute[:second]]
With no arguments, print the current date and time.
Otherwise, take the current date and time, change any elements
specified as arguments, and set the result as the new date and
time. For example, 'date 01-01' will set the current month and day
to January 1, but leave the year, hour, minute, and second
unchanged.

File: grub.info, Node: devicetree, Next: distrust, Prev: date, Up: Command-line and menu entry commands
16.3.22 devicetree
------------------
-- 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.
Note: The command is not allowed when lockdown is enforced (*note
Lockdown::). This is done to prevent subverting various security
mechanisms.

File: grub.info, Node: distrust, Next: drivemap, Prev: devicetree, Up: Command-line and menu entry commands
16.3.23 distrust
----------------
-- Command: distrust pubkey_id
Remove public key PUBKEY_ID from GRUB's keyring of trusted keys.
PUBKEY_ID is the last four bytes (eight hexadecimal digits) of the
GPG v4 key id, which is also the output of 'list_trusted' (*note
list_trusted::). Outside of GRUB, the key id can be obtained using
'gpg --fingerprint'). These keys are used to validate signatures
when environment variable 'check_signatures' is set to 'enforce'
(*note check_signatures::), and by some invocations of
'verify_detached' (*note verify_detached::). *Note Using digital
signatures::, for more information.

File: grub.info, Node: drivemap, Next: echo, Prev: distrust, Up: Command-line and menu entry commands
16.3.24 drivemap
----------------
-- Command: drivemap '-l'|'-r'|['-s'] from_drive to_drive
Without options, map the drive FROM_DRIVE to the drive TO_DRIVE.
This is necessary when you chain-load some operating systems, such
as DOS, if such an OS resides at a non-first drive. For
convenience, any partition suffix on the drive is ignored, so you
can safely use ${root} as a drive specification.
With the '-s' option, perform the reverse mapping as well, swapping
the two drives.
With the '-l' option, list the current mappings.
With the '-r' option, reset all mappings to the default values.
For example:
drivemap -s (hd0) (hd1)

File: grub.info, Node: echo, Next: eval, Prev: drivemap, Up: Command-line and menu entry commands
16.3.25 echo
------------
-- Command: echo ['-n'] ['-e'] string ...
Display the requested text and, unless the '-n' option is used, a
trailing new line. If there is more than one string, they are
separated by spaces in the output. As usual in GRUB commands,
variables may be substituted using '${var}'.
The '-e' option enables interpretation of backslash escapes. The
following sequences are recognised:
'\\'
backslash
'\a'
alert (BEL)
'\c'
suppress trailing new line
'\f'
form feed
'\n'
new line
'\r'
carriage return
'\t'
horizontal tab
'\v'
vertical tab
When interpreting backslash escapes, backslash followed by any
other character will print that character.

File: grub.info, Node: eval, Next: export, Prev: echo, Up: Command-line and menu entry commands
16.3.26 eval
------------
-- Command: eval string ...
Concatenate arguments together using single space as separator and
evaluate result as sequence of GRUB commands.

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

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

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

File: grub.info, Node: gptsync, Next: halt, Prev: gettext, Up: Command-line and menu entry commands
16.3.30 gptsync
---------------
-- Command: gptsync device [partition[+/-[type]]] ...
Disks using the GUID Partition Table (GPT) also have a legacy
Master Boot Record (MBR) partition table for compatibility with the
BIOS and with older operating systems. The legacy MBR can only
represent a limited subset of GPT partition entries.
This command populates the legacy MBR with the specified PARTITION
entries on DEVICE. Up to three partitions may be used.
TYPE is an MBR partition type code; prefix with '0x' if you want to
enter this in hexadecimal. The separator between PARTITION and
TYPE may be '+' to make the partition active, or '-' to make it
inactive; only one partition may be active. If both the separator
and type are omitted, then the partition will be inactive.

File: grub.info, Node: halt, Next: hashsum, Prev: gptsync, Up: Command-line and menu entry commands
16.3.31 halt
------------
-- Command: halt '--no-apm'
The command halts the computer. If the '--no-apm' option is
specified, no APM BIOS call is performed. Otherwise, the computer
is shut down using APM.

File: grub.info, Node: hashsum, Next: help, Prev: halt, Up: Command-line and menu entry commands
16.3.32 hashsum
---------------
-- Command: hashsum '--hash' hash '--keep-going' '--uncompress'
'--check' file ['--prefix' dir]|file ...
Compute or verify file hashes. Hash type is selected with option
'--hash'. Supported hashes are: 'adler32', 'crc64', 'crc32',
'crc32rfc1510', 'crc24rfc2440', 'md4', 'md5', 'ripemd160', 'sha1',
'sha224', 'sha256', 'sha512', 'sha384', 'tiger192', 'tiger',
'tiger2', 'whirlpool'. Option '--uncompress' uncompresses files
before computing hash.
When list of files is given, hash of each file is computed and
printed, followed by file name, each file on a new line.
When option '--check' is given, it points to a file that contains
list of HASH NAME pairs in the same format as used by UNIX 'md5sum'
command. Option '--prefix' may be used to give directory where
files are located. Hash verification stops after the first
mismatch was found unless option '--keep-going' was given. The
exit code '$?' is set to 0 if hash verification is successful. If
it fails, '$?' is set to a nonzero value.

File: grub.info, Node: help, Next: initrd, Prev: hashsum, Up: Command-line and menu entry commands
16.3.33 help
------------
-- Command: help [pattern ...]
Display helpful information about builtin commands. If you do not
specify PATTERN, this command shows short descriptions of all
available commands.
If you specify any PATTERNS, it displays longer information about
each of the commands whose names begin with those PATTERNS.

File: grub.info, Node: initrd, Next: initrd16, Prev: help, Up: Command-line and menu entry commands
16.3.34 initrd
--------------
-- Command: initrd file [file ...]
Load, in order, all initial ramdisks for a Linux kernel image, and
set the appropriate parameters in the Linux setup area in memory.
This may only be used after the 'linux' command (*note linux::) has
been run. See also *note GNU/Linux::.

File: grub.info, Node: initrd16, Next: insmod, Prev: initrd, Up: Command-line and menu entry commands
16.3.35 initrd16
----------------
-- Command: initrd16 file [file ...]
Load, in order, all initial ramdisks for a Linux kernel image to be
booted in 16-bit mode, and set the appropriate parameters in the
Linux setup area in memory. This may only be used after the
'linux16' command (*note linux16::) has been run. See also *note
GNU/Linux::.
This command is only available on x86 systems.

File: grub.info, Node: insmod, Next: keystatus, Prev: initrd16, Up: Command-line and menu entry commands
16.3.36 insmod
--------------
-- Command: insmod module
Insert the dynamic GRUB module called MODULE.

File: grub.info, Node: keystatus, Next: linux, Prev: insmod, Up: Command-line and menu entry commands
16.3.37 keystatus
-----------------
-- Command: keystatus ['--shift'] ['--ctrl'] ['--alt']
Return true if the Shift, Control, or Alt modifier keys are held
down, as requested by options. This is useful in scripting, to
allow some user control over behaviour without having to wait for a
keypress.
Checking key modifier status is only supported on some platforms.
If invoked without any options, the 'keystatus' command returns
true if and only if checking key modifier status is supported.

File: grub.info, Node: linux, Next: linux16, Prev: keystatus, Up: Command-line and menu entry commands
16.3.38 linux
-------------
-- Command: linux file ...
Load a Linux kernel image from FILE. The rest of the line is
passed verbatim as the "kernel command-line". Any initrd must be
reloaded after using this command (*note initrd::).
On x86 systems, the kernel will be booted using the 32-bit boot
protocol. Note that this means that the 'vga=' boot option will
not work; if you want to set a special video mode, you will need to
use GRUB commands such as 'set gfxpayload=1024x768' or 'set
gfxpayload=keep' (to keep the same mode as used in GRUB) instead.
GRUB can automatically detect some uses of 'vga=' and translate
them to appropriate settings of 'gfxpayload'. The 'linux16'
command (*note linux16::) avoids this restriction.

File: grub.info, Node: linux16, Next: list_env, Prev: linux, Up: Command-line and menu entry commands
16.3.39 linux16
---------------
-- Command: linux16 file ...
Load a Linux kernel image from FILE in 16-bit mode. The rest of
the line is passed verbatim as the "kernel command-line". Any
initrd must be reloaded after using this command (*note
initrd16::).
The kernel will be booted using the traditional 16-bit boot
protocol. As well as bypassing problems with 'vga=' described in
*note linux::, this permits booting some other programs that
implement the Linux boot protocol for the sake of convenience.
This command is only available on x86 systems.

File: grub.info, Node: list_env, Next: list_trusted, Prev: linux16, Up: Command-line and menu entry commands
16.3.40 list_env
----------------
-- Command: list_env ['--file' file]
List all variables in the environment block file. *Note
Environment block::.
The '--file' option overrides the default location of the
environment block.

File: grub.info, Node: list_trusted, Next: load_env, Prev: list_env, Up: Command-line and menu entry commands
16.3.41 list_trusted
--------------------
-- Command: list_trusted
List all public keys trusted by GRUB for validating signatures.
The output is in GPG's v4 key fingerprint format (i.e., the output
of 'gpg --fingerprint'). The least significant four bytes (last
eight hexadecimal digits) can be used as an argument to 'distrust'
(*note distrust::). *Note Using digital signatures::, for more
information about uses for these keys.

File: grub.info, Node: load_env, Next: loadfont, Prev: list_trusted, Up: Command-line and menu entry commands
16.3.42 load_env
----------------
-- Command: load_env ['--file' file] ['--skip-sig']
[whitelisted_variable_name] ...
Load all variables from the environment block file into the
environment. *Note Environment block::.
The '--file' option overrides the default location of the
environment block.
The '--skip-sig' option skips signature checking even when the
value of environment variable 'check_signatures' is set to
'enforce' (*note check_signatures::).
If one or more variable names are provided as arguments, they are
interpreted as a whitelist of variables to load from the
environment block file. Variables set in the file but not present
in the whitelist are ignored.
The '--skip-sig' option should be used with care, and should always
be used in concert with a whitelist of acceptable variables whose
values should be set. Failure to employ a carefully constructed
whitelist could result in reading a malicious value into critical
environment variables from the file, such as setting
'check_signatures=no', modifying 'prefix' to boot from an
unexpected location or not at all, etc.
When used with care, '--skip-sig' and the whitelist enable an
administrator to configure a system to boot only signed
configurations, but to allow the user to select from among multiple
configurations, and to enable "one-shot" boot attempts and
"savedefault" behavior. *Note Using digital signatures::, for more
information.

File: grub.info, Node: loadfont, Next: loopback, Prev: load_env, Up: Command-line and menu entry commands
16.3.43 loadfont
----------------
-- Command: loadfont file ...
Load specified font files. Unless absolute pathname is given, FILE
is assumed to be in directory '$prefix/fonts' with suffix '.pf2'
appended. *Note Fonts: Theme file format.

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

File: grub.info, Node: ls, Next: lsfonts, Prev: loopback, Up: Command-line and menu entry commands
16.3.45 ls
----------
-- Command: ls [arg ...]
List devices or files.
With no arguments, print all devices known to GRUB.
If the argument is a device name enclosed in parentheses (*note
Device syntax::), then print the name of the filesystem of that
device.
If the argument is a directory given as an absolute file name
(*note File name syntax::), then list the contents of that
directory.

File: grub.info, Node: lsfonts, Next: lsmod, Prev: ls, Up: Command-line and menu entry commands
16.3.46 lsfonts
---------------
-- Command: lsfonts
List loaded fonts.

File: grub.info, Node: lsmod, Next: md5sum, Prev: lsfonts, Up: Command-line and menu entry commands
16.3.47 lsmod
-------------
-- Command: lsmod
Show list of loaded modules.

File: grub.info, Node: md5sum, Next: module, Prev: lsmod, Up: Command-line and menu entry commands
16.3.48 md5sum
--------------
-- Command: md5sum arg ...
Alias for 'hashsum --hash md5 arg ...'. See command 'hashsum'
(*note hashsum::) for full description.

File: grub.info, Node: module, Next: multiboot, Prev: md5sum, Up: Command-line and menu entry commands
16.3.49 module
--------------
-- Command: module [--nounzip] file [arguments]
Load a module for multiboot kernel image. The rest of the line is
passed verbatim as the module command line.

File: grub.info, Node: multiboot, Next: nativedisk, Prev: module, Up: Command-line and menu entry commands
16.3.50 multiboot
-----------------
-- Command: multiboot [--quirk-bad-kludge]
[--quirk-modules-after-kernel] file ...
Load a multiboot kernel image from FILE. The rest of the line is
passed verbatim as the "kernel command-line". Any module must be
reloaded after using this command (*note module::).
Some kernels have known problems. You need to specify -quirk-* for
those. -quirk-bad-kludge is a problem seen in several products
that they include loading kludge information with invalid data in
ELF file. GRUB prior to 0.97 and some custom builds preferred ELF
information while 0.97 and GRUB 2 use kludge. Use this option to
ignore kludge. Known affected systems: old Solaris, SkyOS.
-quirk-modules-after-kernel is needed for kernels which load at
relatively high address e.g. 16MiB mark and can't cope with
modules stuffed between 1MiB mark and beginning of the kernel.
Known afftected systems: VMWare.

File: grub.info, Node: nativedisk, Next: normal, Prev: multiboot, Up: Command-line and menu entry commands
16.3.51 nativedisk
------------------
-- Command: nativedisk
Switch from firmware disk drivers to native ones. Really useful
only on platforms where both firmware and native disk drives are
available. Currently i386-pc, i386-efi, i386-ieee1275 and
x86_64-efi.

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

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

File: grub.info, Node: parttool, Next: password, Prev: normal_exit, Up: Command-line and menu entry commands
16.3.54 parttool
----------------
-- Command: parttool partition commands
Make various modifications to partition table entries.
Each COMMAND is either a boolean option, in which case it must be
followed with '+' or '-' (with no intervening space) to enable or
disable that option, or else it takes a value in the form
'COMMAND=VALUE'.
Currently, 'parttool' is only useful on DOS partition tables (also
known as Master Boot Record, or MBR). On these partition tables,
the following commands are available:
'boot' (boolean)
When enabled, this makes the selected partition be the active
(bootable) partition on its disk, clearing the active flag on
all other partitions. This command is limited to _primary_
partitions.
'type' (value)
Change the type of an existing partition. The value must be a
number in the range 0-0xFF (prefix with '0x' to enter it in
hexadecimal).
'hidden' (boolean)
When enabled, this hides the selected partition by setting the
"hidden" bit in its partition type code; when disabled,
unhides the selected partition by clearing this bit. This is
useful only when booting DOS or Windows and multiple primary
FAT partitions exist in one disk. See also *note
DOS/Windows::.

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

File: grub.info, Node: password_pbkdf2, Next: play, Prev: password, Up: Command-line and menu entry commands
16.3.56 password_pbkdf2
-----------------------
-- Command: password_pbkdf2 user hashed-password
Define a user named USER with password hash HASHED-PASSWORD. Use
'grub-mkpasswd-pbkdf2' (*note Invoking grub-mkpasswd-pbkdf2::) to
generate password hashes. *Note Security::.

File: grub.info, Node: play, Next: probe, Prev: password_pbkdf2, Up: Command-line and menu entry commands
16.3.57 play
------------
-- Command: play file | tempo [pitch1 duration1] [pitch2 duration2] ...
Plays a tune
If the argument is a file name (*note File name syntax::), play the
tune recorded in it. The file format is first the tempo as an
unsigned 32bit little-endian number, then pairs of unsigned 16bit
little-endian numbers for pitch and duration pairs.
If the arguments are a series of numbers, play the inline tune.
The tempo is the base for all note durations. 60 gives a 1-second
base, 120 gives a half-second base, etc. Pitches are Hz. Set
pitch to 0 to produce a rest.

File: grub.info, Node: probe, Next: rdmsr, Prev: play, Up: Command-line and menu entry commands
16.3.58 probe
-------------
-- Command: probe ['--set' var]
'--driver'|'--partmap'|'--fs'|'--fs-uuid'|'--label'|'--part-uuid'
device
Retrieve device information. If option '--set' is given, assign
result to variable VAR, otherwise print information on the screen.
The option '--part-uuid' is currently only implemented for MSDOS
and GPT formatted disks.

File: grub.info, Node: rdmsr, Next: read, Prev: probe, Up: Command-line and menu entry commands
16.3.59 rdmsr
-------------
-- Command:: rdmsr 0xADDR [-v VARNAME]
Read a model-specific register at address 0xADDR. If the parameter
'-v' is used and an environment variable VARNAME is given, set that
environment variable to the value that was read.
Please note that on SMP systems, reading from a MSR that has a
scope per hardware thread, implies that the value that is returned
only applies to the particular cpu/core/thread that runs the
command.
Also, if you specify a reserved or unimplemented MSR address, it
will cause a general protection exception (which is not currently
being handled) and the system will reboot.

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

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

File: grub.info, Node: regexp, Next: rmmod, Prev: reboot, Up: Command-line and menu entry commands
16.3.62 regexp
--------------
-- Command: regexp ['--set' [number:]var] regexp string
Test if regular expression REGEXP matches STRING. Supported
regular expressions are POSIX.2 Extended Regular Expressions. If
option '--set' is given, store NUMBERth matched subexpression in
variable VAR. Subexpressions are numbered in order of their
opening parentheses starting from '1'. NUMBER defaults to '1'.

File: grub.info, Node: rmmod, Next: save_env, Prev: regexp, Up: Command-line and menu entry commands
16.3.63 rmmod
-------------
-- Command: rmmod module
Remove a loaded MODULE.

File: grub.info, Node: save_env, Next: search, Prev: rmmod, Up: Command-line and menu entry commands
16.3.64 save_env
----------------
-- Command: save_env ['--file' file] var ...
Save the named variables from the environment to the environment
block file. *Note Environment block::.
The '--file' option overrides the default location of the
environment block.
This command will operate successfully even when environment
variable 'check_signatures' is set to 'enforce' (*note
check_signatures::), since it writes to disk and does not alter the
behavior of GRUB based on any contents of disk that have been read.
It is possible to modify a digitally signed environment block file
from within GRUB using this command, such that its signature will
no longer be valid on subsequent boots. Care should be taken in
such advanced configurations to avoid rendering the system
unbootable. *Note Using digital signatures::, for more
information.

File: grub.info, Node: search, Next: sendkey, Prev: save_env, Up: Command-line and menu entry commands
16.3.65 search
--------------
-- Command: search ['--file'|'--label'|'--fs-uuid'] ['--set' [var]]
['--no-floppy'] name
Search devices by file ('-f', '--file'), filesystem label ('-l',
'--label'), or filesystem UUID ('-u', '--fs-uuid').
If the '--set' option is used, the first device found is set as the
value of environment variable VAR. The default variable is 'root'.
The '--no-floppy' option prevents searching floppy devices, which
can be slow.
The 'search.file', 'search.fs_label', and 'search.fs_uuid' commands
are aliases for 'search --file', 'search --label', and 'search
--fs-uuid' respectively.

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

File: grub.info, Node: set, Next: sha1sum, Prev: sendkey, Up: Command-line and menu entry commands
16.3.67 set
-----------
-- Command: set [envvar=value]
Set the environment variable ENVVAR to VALUE. If invoked with no
arguments, print all environment variables with their values.

File: grub.info, Node: sha1sum, Next: sha256sum, Prev: set, Up: Command-line and menu entry commands
16.3.68 sha1sum
---------------
-- Command: sha1sum arg ...
Alias for 'hashsum --hash sha1 arg ...'. See command 'hashsum'
(*note hashsum::) for full description.

File: grub.info, Node: sha256sum, Next: sha512sum, Prev: sha1sum, Up: Command-line and menu entry commands
16.3.69 sha256sum
-----------------
-- Command: sha256sum arg ...
Alias for 'hashsum --hash sha256 arg ...'. See command 'hashsum'
(*note hashsum::) for full description.

File: grub.info, Node: sha512sum, Next: sleep, Prev: sha256sum, Up: Command-line and menu entry commands
16.3.70 sha512sum
-----------------
-- Command: sha512sum arg ...
Alias for 'hashsum --hash sha512 arg ...'. See command 'hashsum'
(*note hashsum::) for full description.

File: grub.info, Node: sleep, Next: smbios, Prev: sha512sum, Up: Command-line and menu entry commands
16.3.71 sleep
-------------
-- Command: sleep ['--verbose'] ['--interruptible'] count
Sleep for COUNT seconds. If option '--interruptible' is given,
allow pressing <ESC>, <F4> or holding down <SHIFT> to interrupt
sleep. With '--verbose' show countdown of remaining seconds. Exit
code is set to 0 if timeout expired and to 1 if timeout was
interrupted using any of the mentioned keys.

File: grub.info, Node: smbios, Next: source, Prev: sleep, Up: Command-line and menu entry commands
16.3.72 smbios
--------------
-- Command: smbios ['--type' TYPE] ['--handle' HANDLE] ['--match'
MATCH] ('--get-byte' | '--get-word' | '--get-dword' |
'--get-qword' | '--get-string' | '--get-uuid') OFFSET ['--set'
VARIABLE]
Retrieve SMBIOS information.
The 'smbios' command returns the value of a field in an SMBIOS
structure. The following options determine which structure to
select.
* Specifying '--type' will select structures with a matching
TYPE. The type can be any integer from 0 to 255.
* Specifying '--handle' will select structures with a matching
HANDLE. The handle can be any integer from 0 to 65535.
* Specifying '--match' will select structure number MATCH in the
filtered list of structures; e.g. 'smbios --type 4 --match 2'
will select the second Process Information (Type 4) structure.
The list is always ordered the same as the hardware's SMBIOS
table. The match number must be a positive integer. If
unspecified, the first matching structure will be selected.
The remaining options determine which field in the selected SMBIOS
structure to return. Only one of these options may be specified at
a time.
* When given '--get-byte', return the value of the byte at
OFFSET bytes into the selected SMBIOS structure. It will be
formatted as an unsigned decimal integer.
* When given '--get-word', return the value of the word (two
bytes) at OFFSET bytes into the selected SMBIOS structure. It
will be formatted as an unsigned decimal integer.
* When given '--get-dword', return the value of the dword (four
bytes) at OFFSET bytes into the selected SMBIOS structure. It
will be formatted as an unsigned decimal integer.
* When given '--get-qword', return the value of the qword (eight
bytes) at OFFSET bytes into the selected SMBIOS structure. It
will be formatted as an unsigned decimal integer.
* When given '--get-string', return the string with its index
found at OFFSET bytes into the selected SMBIOS structure.
* When given '--get-uuid', return the value of the UUID (sixteen
bytes) at OFFSET bytes into the selected SMBIOS structure. It
will be formatted as lower-case hyphenated hexadecimal digits,
with the first three fields as little-endian, and the rest
printed byte-by-byte.
The default action is to print the value of the requested field to
the console, but a variable name can be specified with '--set' to
store the value instead of printing it.
For example, this will store and then display the system
manufacturer's name.
smbios --type 1 --get-string 4 --set system_manufacturer
echo $system_manufacturer

File: grub.info, Node: source, Next: test, Prev: smbios, Up: Command-line and menu entry commands
16.3.73 source
--------------
-- Command: source file
Read FILE as a configuration file, as if its contents had been
incorporated directly into the sourcing file. Unlike 'configfile'
(*note configfile::), this executes the contents of FILE without
changing context: any environment variable changes made by the
commands in FILE will be preserved after 'source' returns, and the
menu will not be shown immediately.

File: grub.info, Node: test, Next: true, Prev: source, Up: Command-line and menu entry commands
16.3.74 test
------------
-- Command: test expression
Evaluate EXPRESSION and return zero exit status if result is true,
non zero status otherwise.
EXPRESSION is one of:
STRING1 '==' STRING2
the strings are equal
STRING1 '!=' STRING2
the strings are not equal
STRING1 '<' STRING2
STRING1 is lexicographically less than STRING2
STRING1 '<=' STRING2
STRING1 is lexicographically less or equal than STRING2
STRING1 '>' STRING2
STRING1 is lexicographically greater than STRING2
STRING1 '>=' STRING2
STRING1 is lexicographically greater or equal than STRING2
INTEGER1 '-eq' INTEGER2
INTEGER1 is equal to INTEGER2
INTEGER1 '-ge' INTEGER2
INTEGER1 is greater than or equal to INTEGER2
INTEGER1 '-gt' INTEGER2
INTEGER1 is greater than INTEGER2
INTEGER1 '-le' INTEGER2
INTEGER1 is less than or equal to INTEGER2
INTEGER1 '-lt' INTEGER2
INTEGER1 is less than INTEGER2
INTEGER1 '-ne' INTEGER2
INTEGER1 is not equal to INTEGER2
PREFIXINTEGER1 '-pgt' PREFIXINTEGER2
INTEGER1 is greater than INTEGER2 after stripping off common
non-numeric PREFIX.
PREFIXINTEGER1 '-plt' PREFIXINTEGER2
INTEGER1 is less than INTEGER2 after stripping off common
non-numeric PREFIX.
FILE1 '-nt' FILE2
FILE1 is newer than FILE2 (modification time). Optionally
numeric BIAS may be directly appended to '-nt' in which case
it is added to the first file modification time.
FILE1 '-ot' FILE2
FILE1 is older than FILE2 (modification time). Optionally
numeric BIAS may be directly appended to '-ot' in which case
it is added to the first file modification time.
'-d' FILE
FILE exists and is a directory
'-e' FILE
FILE exists
'-f' FILE
FILE exists and is not a directory
'-s' FILE
FILE exists and has a size greater than zero
'-n' STRING
the length of STRING is nonzero
STRING
STRING is equivalent to '-n STRING'
'-z' STRING
the length of STRING is zero
'(' EXPRESSION ')'
EXPRESSION is true
'!' EXPRESSION
EXPRESSION is false
EXPRESSION1 '-a' EXPRESSION2
both EXPRESSION1 and EXPRESSION2 are true
EXPRESSION1 EXPRESSION2
both EXPRESSION1 and EXPRESSION2 are true. This syntax is not
POSIX-compliant and is not recommended.
EXPRESSION1 '-o' EXPRESSION2
either EXPRESSION1 or EXPRESSION2 is true

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

File: grub.info, Node: trust, Next: unset, Prev: true, Up: Command-line and menu entry commands
16.3.76 trust
-------------
-- Command: trust ['--skip-sig'] pubkey_file
Read public key from PUBKEY_FILE and add it to GRUB's internal list
of trusted public keys. These keys are used to validate digital
signatures when environment variable 'check_signatures' is set to
'enforce'. Note that if 'check_signatures' is set to 'enforce'
when 'trust' executes, then PUBKEY_FILE must itself be properly
signed. The '--skip-sig' option can be used to disable
signature-checking when reading PUBKEY_FILE itself. It is expected
that '--skip-sig' is useful for testing and manual booting. *Note
Using digital signatures::, for more information.

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

File: grub.info, Node: verify_detached, Next: videoinfo, Prev: unset, Up: Command-line and menu entry commands
16.3.78 verify_detached
-----------------------
-- Command: verify_detached ['--skip-sig'] file signature_file
[pubkey_file]
Verifies a GPG-style detached signature, where the signed file is
FILE, and the signature itself is in file SIGNATURE_FILE.
Optionally, a specific public key to use can be specified using
PUBKEY_FILE. When environment variable 'check_signatures' is set
to 'enforce', then PUBKEY_FILE must itself be properly signed by an
already-trusted key. An unsigned PUBKEY_FILE can be loaded by
specifying '--skip-sig'. If PUBKEY_FILE is omitted, then public
keys from GRUB's trusted keys (*note list_trusted::, *note trust::,
and *note distrust::) are tried.
Exit code '$?' is set to 0 if the signature validates successfully.
If validation fails, it is set to a non-zero value. *Note Using
digital signatures::, for more information.

File: grub.info, Node: videoinfo, Next: wrmsr, Prev: verify_detached, Up: Command-line and menu entry commands
16.3.79 videoinfo
-----------------
-- Command: videoinfo [[WxH]xD]
List available video modes. If resolution is given, show only
matching modes.

File: grub.info, Node: wrmsr, Next: xen_hypervisor, Prev: videoinfo, Up: Command-line and menu entry commands
16.3.80 wrmsr
-------------
-- Command:: wrmsr 0xADDR 0xVALUE
Write a 0xVALUE to a model-specific register at address 0xADDR.
Please note that on SMP systems, writing to a MSR that has a scope
per hardware thread, implies that the value that is written only
applies to the particular cpu/core/thread that runs the command.
Also, if you specify a reserved or unimplemented MSR address, it
will cause a general protection exception (which is not currently
being handled) and the system will reboot.
Note: The command is not allowed when lockdown is enforced (*note
Lockdown::). This is done to prevent subverting various security
mechanisms.

File: grub.info, Node: xen_hypervisor, Next: xen_module, Prev: wrmsr, Up: Command-line and menu entry commands
16.3.81 xen_hypervisor
----------------------
-- Command: xen_hypervisor file [arguments] ...
Load a Xen hypervisor binary from FILE. The rest of the line is
passed verbatim as the "kernel command-line". Any other binaries
must be reloaded after using this command. This command is only
available on AArch64 systems.

File: grub.info, Node: xen_module, Prev: xen_hypervisor, Up: Command-line and menu entry commands
16.3.82 xen_module
------------------
-- Command: xen_module [--nounzip] file [arguments]
Load a module for xen hypervisor at the booting process of xen.
The rest of the line is passed verbatim as the module command line.
Modules should be loaded in the following order: - dom0 kernel
image - dom0 ramdisk if present - XSM policy if present This
command is only available on AArch64 systems.

File: grub.info, Node: Networking commands, Prev: Command-line and menu entry commands, Up: Commands
16.4 The list of networking commands
====================================
* Menu:
* net_add_addr:: Add a network address
* net_add_dns:: Add a DNS server
* net_add_route:: Add routing entry
* net_bootp:: Perform a bootp/DHCP autoconfiguration
* net_del_addr:: Remove IP address from interface
* net_del_dns:: Remove a DNS server
* net_del_route:: Remove a route entry
* net_dhcp:: Perform a DHCP autoconfiguration
* net_get_dhcp_option:: Retrieve DHCP options
* net_ipv6_autoconf:: Perform IPv6 autoconfiguration
* net_ls_addr:: List interfaces
* net_ls_cards:: List network cards
* net_ls_dns:: List DNS servers
* net_ls_routes:: List routing entries
* net_nslookup:: Perform a DNS lookup

File: grub.info, Node: net_add_addr, Next: net_add_dns, Up: Networking commands
16.4.1 net_add_addr
-------------------
-- Command: net_add_addr INTERFACE CARD ADDRESS
Configure additional network INTERFACE with ADDRESS on a network
CARD. ADDRESS can be either IP in dotted decimal notation, or
symbolic name which is resolved using DNS lookup. If successful,
this command also adds local link routing entry to the default
subnet of ADDRESS with name INTERFACE':local' via INTERFACE.

File: grub.info, Node: net_add_dns, Next: net_add_route, Prev: net_add_addr, Up: Networking commands
16.4.2 net_add_dns
------------------
-- Command: net_add_dns SERVER
Resolve SERVER IP address and add to the list of DNS servers used
during name lookup.

File: grub.info, Node: net_add_route, Next: net_bootp, Prev: net_add_dns, Up: Networking commands
16.4.3 net_add_route
--------------------
-- Command: net_add_route SHORTNAME IP[/PREFIX] [INTERFACE | 'gw'
GATEWAY]
Add route to network with address IP as modified by PREFIX via
either local INTERFACE or GATEWAY. PREFIX is optional and defaults
to 32 for IPv4 address and 128 for IPv6 address. Route is
identified by SHORTNAME which can be used to remove it (*note
net_del_route::).

File: grub.info, Node: net_bootp, Next: net_del_addr, Prev: net_add_route, Up: Networking commands
16.4.4 net_bootp
----------------
-- Command: net_bootp [CARD]
Alias for net_dhcp, for compatibility with older Grub versions.
Will perform the same DHCP handshake with potential fallback to
BOOTP as the net_dhcp command (*note net_dhcp::).

File: grub.info, Node: net_del_addr, Next: net_del_dns, Prev: net_bootp, Up: Networking commands
16.4.5 net_del_addr
-------------------
-- Command: net_del_addr INTERFACE
Remove configured INTERFACE with associated address.

File: grub.info, Node: net_del_dns, Next: net_del_route, Prev: net_del_addr, Up: Networking commands
16.4.6 net_del_dns
------------------
-- Command: net_del_dns ADDRESS
Remove ADDRESS from list of servers used during name lookup.

File: grub.info, Node: net_del_route, Next: net_dhcp, Prev: net_del_dns, Up: Networking commands
16.4.7 net_del_route
--------------------
-- Command: net_del_route SHORTNAME
Remove route entry identified by SHORTNAME.

File: grub.info, Node: net_dhcp, Next: net_get_dhcp_option, Prev: net_del_route, Up: Networking commands
16.4.8 net_dhcp
---------------
-- Command: net_dhcp [CARD]
Perform configuration of CARD using DHCP protocol. If no card name
is specified, try to configure all existing cards. Falls back to
the BOOTP protocol, if needed. If configuration was successful,
interface with name CARD':dhcp' and configured address is added to
CARD. Additionally the following DHCP options are recognized and
processed:
'1 (Subnet Mask)'
Used to calculate network local routing entry for interface
CARD':dhcp'.
'3 (Router)'
Adds default route entry with the name CARD':dhcp:default' via
gateway from DHCP option. Note that only option with single
route is accepted.
'6 (Domain Name Server)'
Adds all servers from option value to the list of servers used
during name resolution.
'12 (Host Name)'
Sets environment variable 'net_'<CARD>'_dhcp_hostname' (*note
net_<INTERFACE>_hostname::) to the value of option.
'15 (Domain Name)'
Sets environment variable 'net_'<CARD>'_dhcp_domain' (*note
net_<INTERFACE>_domain::) to the value of option.
'17 (Root Path)'
Sets environment variable 'net_'<CARD>'_dhcp_rootpath' (*note
net_<INTERFACE>_rootpath::) to the value of option.
'18 (Extensions Path)'
Sets environment variable 'net_'<CARD>'_dhcp_extensionspath'
(*note net_<INTERFACE>_extensionspath::) to the value of
option.
'66 (TFTP Server Name)'
Sets environment variable 'net_'<CARD>'_dhcp_server_name'
(*note net_<INTERFACE>_dhcp_server_name::) to the value of
option.
'67 (Filename)'
Sets environment variable 'net_'<CARD>'_boot_file' (*note
net_<INTERFACE>_boot_file::) to the value of option.

File: grub.info, Node: net_get_dhcp_option, Next: net_ipv6_autoconf, Prev: net_dhcp, Up: Networking commands
16.4.9 net_get_dhcp_option
--------------------------
-- Command: net_get_dhcp_option VAR INTERFACE NUMBER TYPE
Request DHCP option NUMBER of TYPE via INTERFACE. TYPE can be one
of 'string', 'number' or 'hex'. If option is found, assign its
value to variable VAR. Values of types 'number' and 'hex' are
converted to string representation.

File: grub.info, Node: net_ipv6_autoconf, Next: net_ls_addr, Prev: net_get_dhcp_option, Up: Networking commands
16.4.10 net_ipv6_autoconf
-------------------------
-- Command: net_ipv6_autoconf [CARD]
Perform IPv6 autoconfiguration by adding to the CARD interface with
name CARD':link' and link local MAC-based address. If no card is
specified, perform autoconfiguration for all existing cards.

File: grub.info, Node: net_ls_addr, Next: net_ls_cards, Prev: net_ipv6_autoconf, Up: Networking commands
16.4.11 net_ls_addr
-------------------
-- Command: net_ls_addr
List all configured interfaces with their MAC and IP addresses.

File: grub.info, Node: net_ls_cards, Next: net_ls_dns, Prev: net_ls_addr, Up: Networking commands
16.4.12 net_ls_cards
--------------------
-- Command: net_ls_cards
List all detected network cards with their MAC address.

File: grub.info, Node: net_ls_dns, Next: net_ls_routes, Prev: net_ls_cards, Up: Networking commands
16.4.13 net_ls_dns
------------------
-- Command: net_ls_dns
List addresses of DNS servers used during name lookup.

File: grub.info, Node: net_ls_routes, Next: net_nslookup, Prev: net_ls_dns, Up: Networking commands
16.4.14 net_ls_routes
---------------------
-- Command: net_ls_routes
List routing entries.

File: grub.info, Node: net_nslookup, Prev: net_ls_routes, Up: Networking commands
16.4.15 net_nslookup
--------------------
-- Command: net_nslookup NAME [SERVER]
Resolve address of NAME using DNS server SERVER. If no server is
given, use default list of servers.

File: grub.info, Node: Internationalisation, Next: Security, Prev: Commands, Up: Top
17 Internationalisation
***********************
17.1 Charset
============
GRUB uses UTF-8 internally other than in rendering where some
GRUB-specific appropriate representation is used. All text files
(including config) are assumed to be encoded in UTF-8.
17.2 Filesystems
================
NTFS, JFS, UDF, HFS+, exFAT, long filenames in FAT, Joliet part of
ISO9660 are treated as UTF-16 as per specification. AFS and BFS are
read as UTF-8, again according to specification. BtrFS, cpio, tar,
squash4, minix, minix2, minix3, ROMFS, ReiserFS, XFS, ext2, ext3, ext4,
FAT (short names), F2FS, RockRidge part of ISO9660, nilfs2, UFS1, UFS2
and ZFS are assumed to be UTF-8. This might be false on systems
configured with legacy charset but as long as the charset used is
superset of ASCII you should be able to access ASCII-named files. And
it's recommended to configure your system to use UTF-8 to access the
filesystem, convmv may help with migration. ISO9660 (plain) filenames
are specified as being ASCII or being described with unspecified escape
sequences. GRUB assumes that the ISO9660 names are UTF-8 (since any
ASCII is valid UTF-8). There are some old CD-ROMs which use CP437 in
non-compliant way. You're still able to access files with names
containing only ASCII characters on such filesystems though. You're
also able to access any file if the filesystem contains valid Joliet
(UTF-16) or RockRidge (UTF-8). AFFS, SFS and HFS never use unicode and
GRUB assumes them to be in Latin1, Latin1 and MacRoman respectively.
GRUB handles filesystem case-insensitivity however no attempt is
performed at case conversion of international characters so e.g. a file
named lowercase greek alpha is treated as different from the one named
as uppercase alpha. The filesystems in questions are NTFS (except POSIX
namespace), HFS+ (configurable at mkfs time, default insensitive), SFS
(configurable at mkfs time, default insensitive), JFS (configurable at
mkfs time, default sensitive), HFS, AFFS, FAT, exFAT and ZFS
(configurable on per-subvolume basis by property "casesensitivity",
default sensitive). On ZFS subvolumes marked as case insensitive files
containing lowercase international characters are inaccessible. Also
like all supported filesystems except HFS+ and ZFS (configurable on
per-subvolume basis by property "normalization", default none) GRUB
makes no attempt at check of canonical equivalence so a file name
u-diaresis is treated as distinct from u+combining diaresis. This
however means that in order to access file on HFS+ its name must be
specified in normalisation form D. On normalized ZFS subvolumes
filenames out of normalisation are inaccessible.
17.3 Output terminal
====================
Firmware output console "console" on ARC and IEEE1275 are limited to
ASCII.
BIOS firmware console and VGA text are limited to ASCII and some
pseudographics.
None of above mentioned is appropriate for displaying international
and any unsupported character is replaced with question mark except
pseudographics which we attempt to approximate with ASCII.
EFI console on the other hand nominally supports UTF-16 but actual
language coverage depends on firmware and may be very limited.
The encoding used on serial can be chosen with 'terminfo' as either
ASCII, UTF-8 or "visual UTF-8". Last one is against the specification
but results in correct rendering of right-to-left on some readers which
don't have own bidi implementation.
On emu GRUB checks if charset is UTF-8 and uses it if so and uses
ASCII otherwise.
When using gfxterm or gfxmenu GRUB itself is responsible for
rendering the text. In this case GRUB is limited by loaded fonts. If
fonts contain all required characters then bidirectional text, cursive
variants and combining marks other than enclosing, half (e.g. left half
tilde or combining overline) and double ones. Ligatures aren't
supported though. This should cover European, Middle Eastern (if you
don't mind lack of lam-alif ligature in Arabic) and East Asian scripts.
Notable unsupported scripts are Brahmic family and derived as well as
Mongolian, Tifinagh, Korean Jamo (precomposed characters have no
problem) and tonal writing (2e5-2e9). GRUB also ignores deprecated (as
specified in Unicode) characters (e.g. tags). GRUB also doesn't handle
so called "annotation characters" If you can complete either of two
lists or, better, propose a patch to improve rendering, please contact
developer team.
17.4 Input terminal
===================
Firmware console on BIOS, IEEE1275 and ARC doesn't allow you to enter
non-ASCII characters. EFI specification allows for such but author is
unaware of any actual implementations. Serial input is currently
limited for latin1 (unlikely to change). Own keyboard implementations
(at_keyboard and usb_keyboard) supports any key but work on
one-char-per-keystroke. So no dead keys or advanced input method. Also
there is no keymap change hotkey. In practice it makes difficult to
enter any text using non-Latin alphabet. Moreover all current input
consumers are limited to ASCII.
17.5 Gettext
============
GRUB supports being translated. For this you need to have language *.mo
files in $prefix/locale, load gettext module and set "lang" variable.
17.6 Regexp
===========
Regexps work on unicode characters, however no attempt at checking
cannonical equivalence has been made. Moreover the classes like
[:alpha:] match only ASCII subset.
17.7 Other
==========
Currently GRUB always uses YEAR-MONTH-DAY HOUR:MINUTE:SECOND [WEEKDAY]
24-hour datetime format but weekdays are translated. GRUB always uses
the decimal number format with [0-9] as digits and . as descimal
separator and no group separator. IEEE1275 aliases are matched
case-insensitively except non-ASCII which is matched as binary. Similar
behaviour is for matching OSBundleRequired. Since IEEE1275 aliases and
OSBundleRequired don't contain any non-ASCII it should never be a
problem in practice. Case-sensitive identifiers are matched as raw
strings, no canonical equivalence check is performed. Case-insenstive
identifiers are matched as RAW but additionally [a-z] is equivalent to
[A-Z]. GRUB-defined identifiers use only ASCII and so should
user-defined ones. Identifiers containing non-ASCII may work but aren't
supported. Only the ASCII space characters (space U+0020, tab U+000b,
CR U+000d and LF U+000a) are recognised. Other unicode space characters
aren't a valid field separator. 'test' (*note test::) tests <, >, <=,
>=, -pgt and -plt compare the strings in the lexicographical order of
unicode codepoints, replicating the behaviour of test from coreutils.
environment variables and commands are listed in the same order.

File: grub.info, Node: Security, Next: Platform limitations, Prev: Internationalisation, Up: Top
18 Security
***********
* Menu:
* Authentication and authorisation:: Users and access control
* Using digital signatures:: Booting digitally signed code
* UEFI secure boot and shim:: Booting digitally signed PE files
* Secure Boot Advanced Targeting:: Embedded information for generation number based revocation
* Measured Boot:: Measuring boot components
* Lockdown:: Lockdown when booting on a secure setup

File: grub.info, Node: Authentication and authorisation, Next: Using digital signatures, Up: Security
18.1 Authentication and authorisation in GRUB
=============================================
By default, the boot loader interface is accessible to anyone with
physical access to the console: anyone can select and edit any menu
entry, and anyone can get direct access to a GRUB shell prompt. For
most systems, this is reasonable since anyone with direct physical
access has a variety of other ways to gain full access, and requiring
authentication at the boot loader level would only serve to make it
difficult to recover broken systems.
However, in some environments, such as kiosks, it may be appropriate
to lock down the boot loader to require authentication before performing
certain operations.
The 'password' (*note password::) and 'password_pbkdf2' (*note
password_pbkdf2::) commands can be used to define users, each of which
has an associated password. 'password' sets the password in plain text,
requiring 'grub.cfg' to be secure; 'password_pbkdf2' sets the password
hashed using the Password-Based Key Derivation Function (RFC 2898),
requiring the use of 'grub-mkpasswd-pbkdf2' (*note Invoking
grub-mkpasswd-pbkdf2::) to generate password hashes.
In order to enable authentication support, the 'superusers'
environment variable must be set to a list of usernames, separated by
any of spaces, commas, semicolons, pipes, or ampersands. Superusers are
permitted to use the GRUB command line, edit menu entries, and execute
any menu entry. If 'superusers' is set, then use of the command line
and editing of menu entries are automatically restricted to superusers.
Setting 'superusers' to empty string effectively disables both access to
CLI and editing of menu entries. Note: The environment variable needs
to be exported to also affect the section defined by the 'submenu'
command (*note submenu::).
Other users may be allowed to execute specific menu entries by giving
a list of usernames (as above) using the '--users' option to the
'menuentry' command (*note menuentry::). If the '--unrestricted' option
is used for a menu entry, then that entry is unrestricted. If the
'--users' option is not used for a menu entry, then that only superusers
are able to use it.
Putting this together, a typical 'grub.cfg' fragment might look like
this:
set superusers="root"
password_pbkdf2 root grub.pbkdf2.sha512.10000.biglongstring
password user1 insecure
menuentry "May be run by any user" --unrestricted {
set root=(hd0,1)
linux /vmlinuz
}
menuentry "Superusers only" --users "" {
set root=(hd0,1)
linux /vmlinuz single
}
menuentry "May be run by user1 or a superuser" --users user1 {
set root=(hd0,2)
chainloader +1
}
The 'grub-mkconfig' program does not yet have built-in support for
generating configuration files with authentication. You can use
'/etc/grub.d/40_custom' to add simple superuser authentication, by
adding 'set superusers=' and 'password' or 'password_pbkdf2' commands.

File: grub.info, Node: Using digital signatures, Next: UEFI secure boot and shim, Prev: Authentication and authorisation, Up: Security
18.2 Using digital signatures in GRUB
=====================================
GRUB's 'core.img' can optionally provide enforcement that all files
subsequently read from disk are covered by a valid digital signature.
This document does *not* cover how to ensure that your platform's
firmware (e.g., Coreboot) validates 'core.img'.
If environment variable 'check_signatures' (*note check_signatures::)
is set to 'enforce', then every attempt by the GRUB 'core.img' to load
another file 'foo' implicitly invokes 'verify_detached foo foo.sig'
(*note verify_detached::). 'foo.sig' must contain a valid digital
signature over the contents of 'foo', which can be verified with a
public key currently trusted by GRUB (*note list_trusted::, *note
trust::, and *note distrust::). If validation fails, then file 'foo'
cannot be opened. This failure may halt or otherwise impact the boot
process.
An initial trusted public key can be embedded within the GRUB
'core.img' using the '--pubkey' option to 'grub-install' (*note Invoking
grub-install::).
GRUB uses GPG-style detached signatures (meaning that a file
'foo.sig' will be produced when file 'foo' is signed), and currently
supports the DSA and RSA signing algorithms. A signing key can be
generated as follows:
gpg --gen-key
An individual file can be signed as follows:
gpg --detach-sign /path/to/file
For successful validation of all of GRUB's subcomponents and the
loaded OS kernel, they must all be signed. One way to accomplish this
is the following (after having already produced the desired 'grub.cfg'
file, e.g., by running 'grub-mkconfig' (*note Invoking grub-mkconfig::):
# Edit /dev/shm/passphrase.txt to contain your signing key's passphrase
for i in `find /boot -name "*.cfg" -or -name "*.lst" -or \
-name "*.mod" -or -name "vmlinuz*" -or -name "initrd*" -or \
-name "grubenv"`;
do
gpg --batch --detach-sign --passphrase-fd 0 $i < \
/dev/shm/passphrase.txt
done
shred /dev/shm/passphrase.txt
See also: *note check_signatures::, *note verify_detached::, *note
trust::, *note list_trusted::, *note distrust::, *note load_env::, *note
save_env::.
Note that internally signature enforcement is controlled by setting
the environment variable 'check_signatures' equal to 'enforce'. Passing
one or more '--pubkey' options to 'grub-mkimage' implicitly defines
'check_signatures' equal to 'enforce' in 'core.img' prior to processing
any configuration files.
Note that signature checking does *not* prevent an attacker with
(serial, physical, ...) console access from dropping manually to the
GRUB console and executing:
set check_signatures=no
To prevent this, password-protection (*note Authentication and
authorisation::) is essential. Note that even with GRUB password
protection, GRUB itself cannot prevent someone with physical access to
the machine from altering that machine's firmware (e.g., Coreboot or
BIOS) configuration to cause the machine to boot from a different
(attacker-controlled) device. GRUB is at best only one link in a secure
boot chain.

File: grub.info, Node: UEFI secure boot and shim, Next: Secure Boot Advanced Targeting, Prev: Using digital signatures, Up: Security
18.3 UEFI secure boot and shim support
======================================
The GRUB, except the 'chainloader' command, works with the UEFI secure
boot and the shim. This functionality is provided by the shim_lock
verifier. It is built into the 'core.img' and is registered if the UEFI
secure boot is enabled. The 'shim_lock' variable is set to 'y' when
shim_lock verifier is registered. If it is desired to use UEFI secure
boot without shim, one can disable shim_lock by disabling shim
verification with MokSbState UEFI variable or by building grub image
with '--disable-shim-lock' option.
All GRUB modules not stored in the 'core.img', OS kernels, ACPI
tables, Device Trees, etc. have to be signed, e.g, using PGP.
Additionally, the commands that can be used to subvert the UEFI secure
boot mechanism, such as 'iorw' and 'memrw' will not be available when
the UEFI secure boot is enabled. This is done for security reasons and
are enforced by the GRUB Lockdown mechanism (*note Lockdown::).

File: grub.info, Node: Secure Boot Advanced Targeting, Next: Measured Boot, Prev: UEFI secure boot and shim, Up: Security
18.4 Embedded information for generation number based revocation
================================================================
The Secure Boot Advanced Targeting (SBAT) is a mechanism to allow the
revocation of components in the boot path by using generation numbers
embedded into the EFI binaries. The SBAT metadata is located in an
.sbat data section that has set of UTF-8 strings as comma-separated
values (CSV). See <https://github.com/rhboot/shim/blob/main/SBAT.md> for
more details.
To add a data section containing the SBAT information into the
binary, the '--sbat' option of 'grub-mkimage' command should be used.
The content of a CSV file, encoded with UTF-8, is copied as is to the
.sbat data section into the generated EFI binary. The CSV file can be
stored anywhere on the file system.
grub-mkimage -O x86_64-efi -o grubx64.efi -p '(tftp)/grub' --sbat sbat.csv efinet tftp

File: grub.info, Node: Measured Boot, Next: Lockdown, Prev: Secure Boot Advanced Targeting, Up: Security
18.5 Measuring boot components
==============================
If the tpm module is loaded and the platform has a Trusted Platform
Module installed, GRUB will log each command executed and each file
loaded into the TPM event log and extend the PCR values in the TPM
correspondingly. All events will be logged into the PCR described below
with a type of EV_IPL and an event description as described below.
Event type PCR Description
---------------------------------------------------------------------------
Command 8 All executed commands (including those
from configuration files) will be logged
and measured as entered with a prefix of
"grub_cmd: "
Kernel command line 8 Any command line passed to a kernel will
be logged and measured as entered with a
prefix of "kernel_cmdline: "
Module command line 8 Any command line passed to a kernel
module will be logged and measured as
entered with a prefix of "module_cmdline:
"
Files 9 Any file read by GRUB will be logged and
measured with a descriptive text
corresponding to the filename.
GRUB will not measure its own 'core.img' - it is expected that
firmware will carry this out. GRUB will also not perform any
measurements until the tpm module is loaded. As such it is recommended
that the tpm module be built into 'core.img' in order to avoid a
potential gap in measurement between 'core.img' being loaded and the tpm
module being loaded.
Measured boot is currently only supported on EFI platforms.

File: grub.info, Node: Lockdown, Prev: Measured Boot, Up: Security
18.6 Lockdown when booting on a secure setup
============================================
The GRUB can be locked down when booted on a secure boot environment,
for example if the UEFI secure boot is enabled. On a locked down
configuration, the GRUB will be restricted and some operations/commands
cannot be executed.
The 'lockdown' variable is set to 'y' when the GRUB is locked down.
Otherwise it does not exit.

File: grub.info, Node: Platform limitations, Next: Platform-specific operations, Prev: Security, Up: Top
19 Platform limitations
***********************
GRUB2 is designed to be portable and is actually ported across
platforms. We try to keep all platforms at the level. Unfortunately
some platforms are better supported than others. This is detailed in
current and 2 following sections.
All platforms have an artificially GRUB imposed disk size restriction
of 1 EiB. In some cases, larger disk sizes can be used, but access will
not be allowed beyond 1 EiB.
LUKS2 devices with size larger than 16 EiB are currently not
supported. They can not be created as crypto devices by cryptomount, so
can not even be partially read from. LUKS have no limitations other
than those imposed by the format.
ARC platform is unable to change datetime (firmware doesn't seem to
provide a function for it). EMU has similar limitation.
On EMU platform no serial port is available.
Console charset refers only to firmware-assisted console. gfxterm is
always Unicode (see Internationalisation section for its limitations).
Serial is configurable to UTF-8 or ASCII (see Internationalisation). In
case of qemu and coreboot ports the refered console is vga_text.
Loongson always uses gfxterm.
Most limited one is ASCII. CP437 provides additionally
pseudographics. GRUB2 doesn't use any language characters from CP437 as
often CP437 is replaced by national encoding compatible only in
pseudographics. Unicode is the most versatile charset which supports
many languages. However the actual console may be much more limited
depending on firmware
On BIOS, network is supported only if the image is loaded through
network. On sparc64, GRUB is unable to determine which server it was
booted from.
Direct ATA/AHCI support allows to circumvent various firmware
limitations but isn't needed for normal operation except on baremetal
ports.
AT keyboard support allows keyboard layout remapping and support for
keys not available through firmware. It isn't needed for normal
operation except baremetal ports.
Speaker allows morse and spkmodem communication.
USB support provides benefits similar to ATA (for USB disks) or AT
(for USB keyboards). In addition it allows USBserial.
Chainloading refers to the ability to load another bootloader through
the same protocol
Hints allow faster disk discovery by already knowing in advance which
is the disk in question. On some platforms hints are correct unless you
move the disk between boots. On other platforms it's just an educated
guess. Note that hint failure results in just reduced performance, not
a failure
BadRAM is the ability to mark some of the RAM as "bad". Note: due to
protocol limitations mips-loongson (with Linux protocol) and
mips-qemu_mips can use only memory up to first hole.
Bootlocation is ability of GRUB to automatically detect where it
boots from. "disk" means the detection is limited to detecting the disk
with partition being discovered on install time. "partition" means that
disk and partiton can be automatically discovered. "file" means that
boot image file name as well as disk and partition can be discovered.
For consistency, default install ignores partition and relies solely on
disk detection. If no bootlocation discovery is available or boot and
grub-root disks are different, UUID is used instead. On ARC if no
device to install to is specified, UUID is used instead as well.
BIOS Coreboot Multiboot Qemu
video yes yes yes yes
console CP437 CP437 CP437 CP437
charset
network yes (*) no no no
ATA/AHCI yes yes yes yes
AT keyboard yes yes yes yes
Speaker yes yes yes yes
USB yes yes yes yes
chainloader local yes yes no
cpuid partial partial partial partial
rdmsr partial partial partial partial
wrmsr partial partial partial partial
hints guess guess guess guess
PCI yes yes yes yes
badram yes yes yes yes
compression always pointless no no
exit yes no no no
bootlocation disk no no no
ia32 EFI amd64 EFI ia32 Itanium
IEEE1275
video yes yes no no
console Unicode Unicode ASCII Unicode
charset
network yes yes yes yes
ATA/AHCI yes yes yes no
AT keyboard yes yes yes no
Speaker yes yes yes no
USB yes yes yes no
chainloader local local no local
cpuid partial partial partial no
rdmsr partial partial partial no
wrmsr partial partial partial no
hints guess guess good guess
PCI yes yes yes no
badram yes yes no yes
compression no no no no
exit yes yes yes yes
bootlocation file file file, file
ignored
Loongson sparc64 Powerpc ARC
video yes no yes no
console N/A ASCII ASCII ASCII
charset
network no yes (*) yes no
ATA/AHCI yes no no no
AT keyboard yes no no no
Speaker no no no no
USB yes no no no
chainloader yes no no no
cpuid no no no no
rdmsr no no no no
wrmsr no no no no
hints good good good no
PCI yes no no no
badram yes (*) no no no
compression configurable no no configurable
exit no yes yes yes
bootlocation no partition file file (*)
MIPS qemu emu xen
video no yes no
console CP437 Unicode (*) ASCII
charset
network no yes no
ATA/AHCI yes no no
AT keyboard yes no no
Speaker no no no
USB N/A yes no
chainloader yes no yes
cpuid no no yes
rdmsr no no yes
wrmsr no no yes
hints guess no no
PCI no no no
badram yes (*) no no
compression configurable no no
exit no yes no
bootlocation no file no

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

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

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

File: grub.info, Node: GRUB only offers a rescue shell, Next: Firmware stalls instead of booting GRUB, Up: Troubleshooting
22.1 GRUB only offers a rescue shell
====================================
GRUB's normal start-up procedure involves setting the 'prefix'
environment variable to a value set in the core image by 'grub-install',
setting the 'root' variable to match, loading the 'normal' module from
the prefix, and running the 'normal' command (*note normal::). This
command is responsible for reading '/boot/grub/grub.cfg', running the
menu, and doing all the useful things GRUB is supposed to do.
If, instead, you only get a rescue shell, this usually means that
GRUB failed to load the 'normal' module for some reason. It may be
possible to work around this temporarily: for instance, if the reason
for the failure is that 'prefix' is wrong (perhaps it refers to the
wrong device, or perhaps the path to '/boot/grub' was not correctly made
relative to the device), then you can correct this and enter normal mode
manually:
# Inspect the current prefix (and other preset variables):
set
# Find out which devices are available:
ls
# Set to the correct value, which might be something like this:
set prefix=(hd0,1)/grub
set root=(hd0,1)
insmod normal
normal
However, any problem that leaves you in the rescue shell probably
means that GRUB was not correctly installed. It may be more useful to
try to reinstall it properly using 'grub-install DEVICE' (*note Invoking
grub-install::). When doing this, there are a few things to remember:
* Drive ordering in your operating system may not be the same as the
boot drive ordering used by your firmware. Do not assume that your
first hard drive (e.g. '/dev/sda') is the one that your firmware
will boot from. 'device.map' (*note Device map::) can be used to
override this, but it is usually better to use UUIDs or file system
labels and avoid depending on drive ordering entirely.
* At least on BIOS systems, if you tell 'grub-install' to install
GRUB to a partition but GRUB has already been installed in the
master boot record, then the GRUB installation in the partition
will be ignored.
* If possible, it is generally best to avoid installing GRUB to a
partition (unless it is a special partition for the use of GRUB
alone, such as the BIOS Boot Partition used on GPT). Doing this
means that GRUB may stop being able to read its core image due to a
file system moving blocks around, such as while defragmenting,
running checks, or even during normal operation. Installing to the
whole disk device is normally more robust.
* Check that GRUB actually knows how to read from the device and file
system containing '/boot/grub'. It will not be able to read from
encrypted devices with unsupported encryption scheme, nor from file
systems for which support has not yet been added to GRUB.

File: grub.info, Node: Firmware stalls instead of booting GRUB, Prev: GRUB only offers a rescue shell, Up: Troubleshooting
22.2 Firmware stalls instead of booting GRUB
============================================
The EFI implementation of some older MacBook laptops stalls when it gets
presented a grub-mkrescue ISO image for x86_64-efi target on an USB
stick. Affected are models of year 2010 or earlier. Workaround is to
zeroize the bytes 446 to 461 of the EFI partition, where mformat has put
a partition table entry which claims partition start at block 0. This
change will not hamper bootability on other machines.

File: grub.info, Node: Invoking grub-install, Next: Invoking grub-mkconfig, Prev: Troubleshooting, Up: Top
23 Invoking grub-install
************************
The program 'grub-install' generates a GRUB core image using
'grub-mkimage' and installs it on your system. You must specify the
device name on which you want to install GRUB, like this:
grub-install INSTALL_DEVICE
The device name INSTALL_DEVICE is an OS device name or a GRUB device
name.
'grub-install' accepts the following options:
'--help'
Print a summary of the command-line options and exit.
'--version'
Print the version number of GRUB and exit.
'--boot-directory=DIR'
Install GRUB images under the directory 'DIR/grub/' This option is
useful when you want to install GRUB into a separate partition or a
removable disk. If this option is not specified then it defaults
to '/boot', so
grub-install /dev/sda
is equivalent to
grub-install --boot-directory=/boot/ /dev/sda
Here is an example in which you have a separate "boot" partition
which is mounted on '/mnt/boot':
grub-install --boot-directory=/mnt/boot /dev/sdb
'--recheck'
Recheck the device map, even if '/boot/grub/device.map' already
exists. You should use this option whenever you add/remove a disk
into/from your computer.
'--no-rs-codes'
By default on x86 BIOS systems, 'grub-install' will use some extra
space in the bootloader embedding area for Reed-Solomon
error-correcting codes. This enables GRUB to still boot
successfully if some blocks are corrupted. The exact amount of
protection offered is dependent on available space in the embedding
area. R sectors of redundancy can tolerate up to R/2 corrupted
sectors. This redundancy may be cumbersome if attempting to
cryptographically validate the contents of the bootloader embedding
area, or in more modern systems with GPT-style partition tables
(*note BIOS installation::) where GRUB does not reside in any
unpartitioned space outside of the MBR. Disable the Reed-Solomon
codes with this option.

File: grub.info, Node: Invoking grub-mkconfig, Next: Invoking grub-mkpasswd-pbkdf2, Prev: Invoking grub-install, Up: Top
24 Invoking grub-mkconfig
*************************
The program 'grub-mkconfig' generates a configuration file for GRUB
(*note Simple configuration::).
grub-mkconfig -o /boot/grub/grub.cfg
'grub-mkconfig' accepts the following options:
'--help'
Print a summary of the command-line options and exit.
'--version'
Print the version number of GRUB and exit.
'-o FILE'
'--output=FILE'
Send the generated configuration file to FILE. The default is to
send it to standard output.

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

File: grub.info, Node: Invoking grub-mkrelpath, Next: Invoking grub-mkrescue, Prev: Invoking grub-mkpasswd-pbkdf2, Up: Top
26 Invoking grub-mkrelpath
**************************
The program 'grub-mkrelpath' makes a file system path relative to the
root of its containing file system. For instance, if '/usr' is a mount
point, then:
$ grub-mkrelpath /usr/share/grub/unicode.pf2
'/share/grub/unicode.pf2'
This is mainly used internally by other GRUB utilities such as
'grub-mkconfig' (*note Invoking grub-mkconfig::), but may occasionally
also be useful for debugging.
'grub-mkrelpath' accepts the following options:
'--help'
Print a summary of the command-line options and exit.
'--version'
Print the version number of GRUB and exit.

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

File: grub.info, Node: Invoking grub-mount, Next: Invoking grub-probe, Prev: Invoking grub-mkrescue, Up: Top
28 Invoking grub-mount
**********************
The program 'grub-mount' performs a read-only mount of any file system
or file system image that GRUB understands, using GRUB's file system
drivers via FUSE. (It is only available if FUSE development files were
present when GRUB was built.) This has a number of uses:
* It provides a convenient way to check how GRUB will view a file
system at boot time. You can use normal command-line tools to
compare that view with that of your operating system, making it
easy to find bugs.
* It offers true read-only mounts. Linux does not have these for
journalling file systems, because it will always attempt to replay
the journal at mount time; while you can temporarily mark the block
device read-only to avoid this, that causes the mount to fail.
Since GRUB intentionally contains no code for writing to file
systems, it can easily provide a guaranteed read-only mount
mechanism.
* It allows you to examine any file system that GRUB understands
without needing to load additional modules into your running
kernel, which may be useful in constrained environments such as
installers.
* Since it can examine file system images (contained in regular
files) just as easily as file systems on block devices, you can use
it to inspect any file system image that GRUB understands with only
enough privileges to use FUSE, even if nobody has yet written a
FUSE module specifically for that file system type.
Using 'grub-mount' is normally as simple as:
grub-mount /dev/sda1 /mnt
'grub-mount' must be given one or more images and a mount point as
non-option arguments (if it is given more than one image, it will treat
them as a RAID set), and also accepts the following options:
'--help'
Print a summary of the command-line options and exit.
'--version'
Print the version number of GRUB and exit.
'-C'
'--crypto'
Mount encrypted devices, prompting for a passphrase if necessary.
'-d STRING'
'--debug=STRING'
Show debugging output for conditions matching STRING.
'-K prompt|FILE'
'--zfs-key=prompt|FILE'
Load a ZFS encryption key. If you use 'prompt' as the argument,
'grub-mount' will read a passphrase from the terminal; otherwise,
it will read key material from the specified file.
'-r DEVICE'
'--root=DEVICE'
Set the GRUB root device to DEVICE. You do not normally need to
set this; 'grub-mount' will automatically set the root device to
the root of the supplied file system.
If DEVICE is just a number, then it will be treated as a partition
number within the supplied image. This means that, if you have an
image of an entire disk in 'disk.img', then you can use this
command to mount its second partition:
grub-mount -r 2 disk.img mount-point
'-v'
'--verbose'
Print verbose messages.

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

File: grub.info, Node: Invoking grub-script-check, Next: Obtaining and Building GRUB, Prev: Invoking grub-probe, Up: Top
30 Invoking grub-script-check
*****************************
The program 'grub-script-check' takes a GRUB script file (*note
Shell-like scripting::) and checks it for syntax errors, similar to
commands such as 'sh -n'. It may take a PATH as a non-option argument;
if none is supplied, it will read from standard input.
grub-script-check /boot/grub/grub.cfg
'grub-script-check' accepts the following options:
'--help'
Print a summary of the command-line options and exit.
'--version'
Print the version number of GRUB and exit.
'-v'
'--verbose'
Print each line of input after reading it.

File: grub.info, Node: Obtaining and Building GRUB, Next: Reporting bugs, Prev: Invoking grub-script-check, Up: Top
Appendix A How to obtain and build GRUB
***************************************
*Caution:* GRUB requires binutils-2.9.1.0.23 or later because the
GNU assembler has been changed so that it can produce real 16bits
machine code between 2.9.1 and 2.9.1.0.x. See
<http://sources.redhat.com/binutils/>, to obtain information on how
to get the latest version.
GRUB is available from the GNU alpha archive site
<ftp://ftp.gnu.org/gnu/grub> or any of its mirrors. The file will be
named grub-version.tar.gz. The current version is 2.06, so the file you
should grab is:
<ftp://ftp.gnu.org/gnu/grub/grub-2.06.tar.gz>
To unbundle GRUB use the instruction:
zcat grub-2.06.tar.gz | tar xvf -
which will create a directory called 'grub-2.06' with all the
sources. You can look at the file 'INSTALL' for detailed instructions
on how to build and install GRUB, but you should be able to just do:
cd grub-2.06
./configure
make install
Also, the latest version is available using Git. See
<http://www.gnu.org/software/grub/grub-download.html> for more
information.

File: grub.info, Node: Reporting bugs, Next: Future, Prev: Obtaining and Building GRUB, Up: Top
Appendix B Reporting bugs
*************************
These are the guideline for how to report bugs. Take a look at this
list below before you submit bugs:
1. Before getting unsettled, read this manual through and through.
Also, see the GNU GRUB FAQ
(http://www.gnu.org/software/grub/grub-faq.html).
2. Always mention the information on your GRUB. The version number and
the configuration are quite important. If you build it yourself,
write the options specified to the configure script and your
operating system, including the versions of gcc and binutils.
3. If you have trouble with the installation, inform us of how you
installed GRUB. Don't omit error messages, if any. Just 'GRUB
hangs up when it boots' is not enough.
The information on your hardware is also essential. These are
especially important: the geometries and the partition tables of
your hard disk drives and your BIOS.
4. If GRUB cannot boot your operating system, write down _everything_
you see on the screen. Don't paraphrase them, like 'The foo OS
crashes with GRUB, even though it can boot with the bar boot loader
just fine'. Mention the commands you executed, the messages
printed by them, and information on your operating system including
the version number.
5. Explain what you wanted to do. It is very useful to know your
purpose and your wish, and how GRUB didn't satisfy you.
6. If you can investigate the problem yourself, please do. That will
give you and us much more information on the problem. Attaching a
patch is even better.
When you attach a patch, make the patch in unified diff format, and
write ChangeLog entries. But, even when you make a patch, don't
forget to explain the problem, so that we can understand what your
patch is for.
7. Write down anything that you think might be related. Please
understand that we often need to reproduce the same problem you
encountered in our environment. So your information should be
sufficient for us to do the same thing--Don't forget that we cannot
see your computer directly. If you are not sure whether to state a
fact or leave it out, state it! Reporting too many things is much
better than omitting something important.
If you follow the guideline above, submit a report to the Bug
Tracking System (http://savannah.gnu.org/bugs/?group=grub).
Alternatively, you can submit a report via electronic mail to
<bug-grub@gnu.org>, but we strongly recommend that you use the Bug
Tracking System, because e-mail can be passed over easily.
Once we get your report, we will try to fix the bugs.

File: grub.info, Node: Future, Next: Copying This Manual, Prev: Reporting bugs, Up: Top
Appendix C Where GRUB will go
*****************************
GRUB 2 is now quite stable and used in many production systems. We are
currently working towards a 2.0 release.
If you are interested in the development of GRUB 2, take a look at
the homepage (http://www.gnu.org/software/grub/grub.html).

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

File: grub.info, Node: GNU Free Documentation License, Up: Copying This Manual
D.1 GNU Free Documentation License
==================================
Version 1.2, November 2002
Copyright (C) 2000,2001,2002 Free Software Foundation, Inc.
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
0. PREAMBLE
The purpose of this License is to make a manual, textbook, or other
functional and useful document "free" in the sense of freedom: to
assure everyone the effective freedom to copy and redistribute it,
with or without modifying it, either commercially or
noncommercially. Secondarily, this License preserves for the
author and publisher a way to get credit for their work, while not
being considered responsible for modifications made by others.
This License is a kind of "copyleft", which means that derivative
works of the document must themselves be free in the same sense.
It complements the GNU General Public License, which is a copyleft
license designed for free software.
We have designed this License in order to use it for manuals for
free software, because free software needs free documentation: a
free program should come with manuals providing the same freedoms
that the software does. But this License is not limited to
software manuals; it can be used for any textual work, regardless
of subject matter or whether it is published as a printed book. We
recommend this License principally for works whose purpose is
instruction or reference.
1. APPLICABILITY AND DEFINITIONS
This License applies to any manual or other work, in any medium,
that contains a notice placed by the copyright holder saying it can
be distributed under the terms of this License. Such a notice
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to use that work under the conditions stated herein. The
"Document", below, refers to any such manual or work. Any member
of the public is a licensee, and is addressed as "you". You accept
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A "Modified Version" of the Document means any work containing the
Document or a portion of it, either copied verbatim, or with
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A "Secondary Section" is a named appendix or a front-matter section
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The "Invariant Sections" are certain Secondary Sections whose
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The "Cover Texts" are certain short passages of text that are
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that says that the Document is released under this License. A
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A "Transparent" copy of the Document means a machine-readable copy,
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plus such following pages as are needed to hold, legibly, the
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Page" means the text near the most prominent appearance of the
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A section "Entitled XYZ" means a named subunit of the Document
whose title either is precisely XYZ or contains XYZ in parentheses
following text that translates XYZ in another language. (Here XYZ
stands for a specific section name mentioned below, such as
"Acknowledgements", "Dedications", "Endorsements", or "History".)
To "Preserve the Title" of such a section when you modify the
Document means that it remains a section "Entitled XYZ" according
to this definition.
The Document may include Warranty Disclaimers next to the notice
which states that this License applies to the Document. These
Warranty Disclaimers are considered to be included by reference in
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implication that these Warranty Disclaimers may have is void and
has no effect on the meaning of this License.
2. VERBATIM COPYING
You may copy and distribute the Document in any medium, either
commercially or noncommercially, provided that this License, the
copyright notices, and the license notice saying this License
applies to the Document are reproduced in all copies, and that you
add no other conditions whatsoever to those of this License. You
may not use technical measures to obstruct or control the reading
or further copying of the copies you make or distribute. However,
you may accept compensation in exchange for copies. If you
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conditions in section 3.
You may also lend copies, under the same conditions stated above,
and you may publicly display copies.
3. COPYING IN QUANTITY
If you publish printed copies (or copies in media that commonly
have printed covers) of the Document, numbering more than 100, and
the Document's license notice requires Cover Texts, you must
enclose the copies in covers that carry, clearly and legibly, all
these Cover Texts: Front-Cover Texts on the front cover, and
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and legibly identify you as the publisher of these copies. The
front cover must present the full title with all words of the title
equally prominent and visible. You may add other material on the
covers in addition. Copying with changes limited to the covers, as
long as they preserve the title of the Document and satisfy these
conditions, can be treated as verbatim copying in other respects.
If the required texts for either cover are too voluminous to fit
legibly, you should put the first ones listed (as many as fit
reasonably) on the actual cover, and continue the rest onto
adjacent pages.
If you publish or distribute Opaque copies of the Document
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Transparent copy along with each Opaque copy, or state in or with
each Opaque copy a computer-network location from which the general
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copies in quantity, to ensure that this Transparent copy will
remain thus accessible at the stated location until at least one
year after the last time you distribute an Opaque copy (directly or
through your agents or retailers) of that edition to the public.
It is requested, but not required, that you contact the authors of
the Document well before redistributing any large number of copies,
to give them a chance to provide you with an updated version of the
Document.
4. MODIFICATIONS
You may copy and distribute a Modified Version of the Document
under the conditions of sections 2 and 3 above, provided that you
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Modified Version filling the role of the Document, thus licensing
distribution and modification of the Modified Version to whoever
possesses a copy of it. In addition, you must do these things in
the Modified Version:
A. Use in the Title Page (and on the covers, if any) a title
distinct from that of the Document, and from those of previous
versions (which should, if there were any, be listed in the
History section of the Document). You may use the same title
as a previous version if the original publisher of that
version gives permission.
B. List on the Title Page, as authors, one or more persons or
entities responsible for authorship of the modifications in
the Modified Version, together with at least five of the
principal authors of the Document (all of its principal
authors, if it has fewer than five), unless they release you
from this requirement.
C. State on the Title page the name of the publisher of the
Modified Version, as the publisher.
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E. Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.
F. Include, immediately after the copyright notices, a license
notice giving the public permission to use the Modified
Version under the terms of this License, in the form shown in
the Addendum below.
G. Preserve in that license notice the full lists of Invariant
Sections and required Cover Texts given in the Document's
license notice.
H. Include an unaltered copy of this License.
I. Preserve the section Entitled "History", Preserve its Title,
and add to it an item stating at least the title, year, new
authors, and publisher of the Modified Version as given on the
Title Page. If there is no section Entitled "History" in the
Document, create one stating the title, year, authors, and
publisher of the Document as given on its Title Page, then add
an item describing the Modified Version as stated in the
previous sentence.
J. Preserve the network location, if any, given in the Document
for public access to a Transparent copy of the Document, and
likewise the network locations given in the Document for
previous versions it was based on. These may be placed in the
"History" section. You may omit a network location for a work
that was published at least four years before the Document
itself, or if the original publisher of the version it refers
to gives permission.
K. For any section Entitled "Acknowledgements" or "Dedications",
Preserve the Title of the section, and preserve in the section
all the substance and tone of each of the contributor
acknowledgements and/or dedications given therein.
L. Preserve all the Invariant Sections of the Document, unaltered
in their text and in their titles. Section numbers or the
equivalent are not considered part of the section titles.
M. Delete any section Entitled "Endorsements". Such a section
may not be included in the Modified Version.
N. Do not retitle any existing section to be Entitled
"Endorsements" or to conflict in title with any Invariant
Section.
O. Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or
appendices that qualify as Secondary Sections and contain no
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some or all of these sections as invariant. To do this, add their
titles to the list of Invariant Sections in the Modified Version's
license notice. These titles must be distinct from any other
section titles.
You may add a section Entitled "Endorsements", provided it contains
nothing but endorsements of your Modified Version by various
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has been approved by an organization as the authoritative
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You may add a passage of up to five words as a Front-Cover Text,
and a passage of up to 25 words as a Back-Cover Text, to the end of
the list of Cover Texts in the Modified Version. Only one passage
of Front-Cover Text and one of Back-Cover Text may be added by (or
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The author(s) and publisher(s) of the Document do not by this
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5. COMBINING DOCUMENTS
You may combine the Document with other documents released under
this License, under the terms defined in section 4 above for
modified versions, provided that you include in the combination all
of the Invariant Sections of all of the original documents,
unmodified, and list them all as Invariant Sections of your
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their Warranty Disclaimers.
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multiple identical Invariant Sections may be replaced with a single
copy. If there are multiple Invariant Sections with the same name
but different contents, make the title of each such section unique
by adding at the end of it, in parentheses, the name of the
original author or publisher of that section if known, or else a
unique number. Make the same adjustment to the section titles in
the list of Invariant Sections in the license notice of the
combined work.
In the combination, you must combine any sections Entitled
"History" in the various original documents, forming one section
Entitled "History"; likewise combine any sections Entitled
"Acknowledgements", and any sections Entitled "Dedications". You
must delete all sections Entitled "Endorsements."
6. COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other
documents released under this License, and replace the individual
copies of this License in the various documents with a single copy
that is included in the collection, provided that you follow the
rules of this License for verbatim copying of each of the documents
in all other respects.
You may extract a single document from such a collection, and
distribute it individually under this License, provided you insert
a copy of this License into the extracted document, and follow this
License in all other respects regarding verbatim copying of that
document.
7. AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other
separate and independent documents or works, in or on a volume of a
storage or distribution medium, is called an "aggregate" if the
copyright resulting from the compilation is not used to limit the
legal rights of the compilation's users beyond what the individual
works permit. When the Document is included in an aggregate, this
License does not apply to the other works in the aggregate which
are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these
copies of the Document, then if the Document is less than one half
of the entire aggregate, the Document's Cover Texts may be placed
on covers that bracket the Document within the aggregate, or the
electronic equivalent of covers if the Document is in electronic
form. Otherwise they must appear on printed covers that bracket
the whole aggregate.
8. TRANSLATION
Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section
4. Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections. You may include a
translation of this License, and all the license notices in the
Document, and any Warranty Disclaimers, provided that you also
include the original English version of this License and the
original versions of those notices and disclaimers. In case of a
disagreement between the translation and the original version of
this License or a notice or disclaimer, the original version will
prevail.
If a section in the Document is Entitled "Acknowledgements",
"Dedications", or "History", the requirement (section 4) to
Preserve its Title (section 1) will typically require changing the
actual title.
9. TERMINATION
You may not copy, modify, sublicense, or distribute the Document
except as expressly provided for under this License. Any other
attempt to copy, modify, sublicense or distribute the Document is
void, and will automatically terminate your rights under this
License. However, parties who have received copies, or rights,
from you under this License will not have their licenses terminated
so long as such parties remain in full compliance.
10. FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of
the GNU Free Documentation License from time to time. Such new
versions will be similar in spirit to the present version, but may
differ in detail to address new problems or concerns. See
<http://www.gnu.org/copyleft/>.
Each version of the License is given a distinguishing version
number. If the Document specifies that a particular numbered
version of this License "or any later version" applies to it, you
have the option of following the terms and conditions either of
that specified version or of any later version that has been
published (not as a draft) by the Free Software Foundation. If the
Document does not specify a version number of this License, you may
choose any version ever published (not as a draft) by the Free
Software Foundation.
D.1.1 ADDENDUM: How to use this License for your documents
----------------------------------------------------------
To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:
Copyright (C) YEAR YOUR NAME.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2
or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
Texts. A copy of the license is included in the section entitled ``GNU
Free Documentation License''.
If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the "with...Texts." line with this:
with the Invariant Sections being LIST THEIR TITLES, with
the Front-Cover Texts being LIST, and with the Back-Cover Texts
being LIST.
If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.
If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of free
software license, such as the GNU General Public License, to permit
their use in free software.
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