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GNU GRUB manual * This is the documentation of GNU GRUB, the GRand Unified Bootloader, a flexible and powerful boot loader program for a wide range of architectures. This edition documents version 2.02~beta2. This manual is for GNU GRUB (version 2.02~beta2, 26 June 2015). 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:, 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:, Node: Overview, Next: History, Up: Introduction

1.1 Overview

Briefly, a «boot loader» is the first software program that runs when a computer starts. It is responsible for loading and transferring control to an operating system «kernel» software (such as Linux or GNU Mach). The kernel, in turn, initializes the rest of the operating system (e.g. a GNU system).

 GNU GRUB is a very powerful boot loader, which can load a wide

variety of free operating systems, as well as proprietary operating systems with chain-loading(1) (*note Overview-Footnote-1::). GRUB is designed to address the complexity of booting a personal computer; both the program and this manual are tightly bound to that computer platform, although porting to other platforms may be addressed in the future.

 One of the important features in GRUB is flexibility; GRUB

understands filesystems and kernel executable formats, so you can load an arbitrary operating system the way you like, without recording the physical position of your kernel on the disk. Thus you can load the kernel just by specifying its file name and the drive and partition where the kernel resides.

 When booting with GRUB, you can use either a command-line interface

(*note Command-line interface::), or a menu interface (*note Menu interface::). Using the command-line interface, you type the drive specification and file name of the kernel manually. In the menu interface, you just select an OS using the arrow keys. The menu is based on a configuration file which you prepare beforehand (*note Configuration::). While in the menu, you can switch to the command-line mode, and vice-versa. You can even edit menu entries before using them.

 In the following chapters, you will learn how to specify a drive, a

partition, and a file name (*note Naming convention::) to GRUB, how to install GRUB on your drive (*note Installation::), and how to boot your OSes (*note Booting::), step by step.

File:, Node: History, Next: 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:, 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

  • 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
  • Many more file systems are supported, including but not limited to

ext4, HFS+, and NTFS.

  • GRUB 2 can read files directly from LVM and RAID devices.
  • A graphical terminal and a graphical menu system are available.
  • GRUB 2's interface can be translated, including menu entry names.
  • The image files (*note Images::) that make up GRUB have been

reorganised; Stage 1, Stage 1.5, and Stage 2 are no more.

  • GRUB 2 puts many facilities in dynamically loaded modules, allowing

the core image to be smaller, and allowing the core image to be

   built in more flexible ways.

File:, Node: 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

Have a flexible command-line interface

   A fairly flexible command-line interface, accessible from the menu,
   is available to edit any preset commands, or write a new boot
   command set from scratch.  If no configuration file is present,
   GRUB drops to the command-line.
   The list of commands (*note Commands::) are a subset of those
   supported for configuration files.  Editing commands closely
   resembles the Bash command-line (*note Bash: (features)Command Line
   Editing.), with <TAB>-completion of commands, devices, partitions,
   and files in a directory depending on context.

Support multiple filesystem types

   Support multiple filesystem types transparently, plus a useful
   explicit blocklist notation.  The currently supported filesystem
   types are "Amiga Fast FileSystem (AFFS)", "AtheOS fs", "BeFS",
   "BtrFS" (including raid0, raid1, raid10, gzip and lzo), "cpio"
   (little- and big-endian bin, odc and newc variants), "Linux
   ext2/ext3/ext4", "DOS FAT12/FAT16/FAT32", "exFAT", "HFS", "HFS+",
   "ISO9660" (including Joliet, Rock-ridge and multi-chunk files),
   "JFS", "Minix fs" (versions 1, 2 and 3), "nilfs2", "NTFS"
   (including compression), "ReiserFS", "ROMFS", "Amiga Smart
   FileSystem (SFS)", "Squash4", "tar", "UDF", "BSD UFS/UFS2", "XFS",
   and "ZFS" (including lzjb, gzip, zle, mirror, stripe, raidz1/2/3
   and encryption in AES-CCM and AES-GCM). *Note Filesystem::, for
   more information.

Support automatic decompression

   Can decompress files which were compressed by 'gzip' or 'xz'(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

Be independent of drive geometry translations

   Unlike many other boot loaders, GRUB makes the particular drive
   translation irrelevant.  A drive installed and running with one
   translation may be converted to another translation without any
   adverse effects or changes in GRUB's configuration.

Detect all installed RAM

   GRUB can generally find all the installed RAM on a PC-compatible
   machine.  It uses an advanced BIOS query technique for finding all
   memory regions.  As described on the Multiboot Specification (*note
   Multiboot Specification: (multiboot)Top.), not all kernels make use
   of this information, but GRUB provides it for those who do.

Support Logical Block Address mode

   In traditional disk calls (called "CHS mode"), there is a geometry
   translation problem, that is, the BIOS cannot access over 1024
   cylinders, so the accessible space is limited to at least 508 MB
   and to at most 8GB. GRUB can't universally solve this problem, as
   there is no standard interface used in all machines.  However,
   several newer machines have the new interface, Logical Block
   Address ("LBA") mode.  GRUB automatically detects if LBA mode is
   available and uses it if available.  In LBA mode, GRUB can access
   the entire disk.

Support network booting

   GRUB is basically a disk-based boot loader but also has network
   support.  You can load OS images from a network by using the "TFTP"

Support remote terminals

   To support computers with no console, GRUB provides remote terminal
   support, so that you can control GRUB from a remote host.  Only
   serial terminal support is implemented at the moment.

File:, Node: 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:, 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:, 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:, 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:, 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.

 Note that 'grub-install' is actually just a shell script and the real

task is done by other tools such as 'grub-mkimage'. Therefore, you may run those commands directly to install GRUB, without using 'grub-install'. Don't do that, however, unless you are very familiar with the internals of GRUB. Installing a boot loader on a running OS may be extremely dangerous.

 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


   # 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:, 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:, 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 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:, 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 31 KiB), or the core image can be installed in a file system and a list of the blocks that make it up can be stored in the first sector of that partition.

 Each of these has different problems.  There is no way to reserve

space in the embedding area with complete safety, and some proprietary software is known to use it to make it difficult for users to work around licensing restrictions; and systems are sometimes partitioned without leaving enough space before the first partition. On the other hand, installing to a filesystem means that GRUB is vulnerable to its blocks being moved around by filesystem features such as tail packing, or even by aggressive fsck implementations, so this approach is quite fragile; and this approach can only be used if the '/boot' filesystem is on the same disk that the BIOS boots from, so that GRUB does not have to rely on guessing BIOS drive numbers.

 The GRUB development team generally recommends embedding GRUB before

the first partition, unless you have special requirements. You must ensure that the first partition starts at least 31 KiB (63 sectors) from the start of the disk; on modern disks, it is often a performance advantage to align partitions on larger boundaries anyway, so the first partition might start 1 MiB from the start of the disk.

GPT ===

Some newer systems use the GUID Partition Table (GPT) format. This was specified as part of the Extensible Firmware Interface (EFI), but it can also be used on BIOS platforms if system software supports it; for example, GRUB and GNU/Linux can be used in this configuration. With this format, it is possible to reserve a whole partition for GRUB, called the BIOS Boot Partition. GRUB can then be embedded into that partition without the risk of being overwritten by other software and without being contained in a filesystem which might move its blocks around.

 When creating a BIOS Boot Partition on a GPT system, you should make

sure that it is at least 31 KiB in size. (GPT-formatted disks are not usually particularly small, so we recommend that you make it larger than the bare minimum, such as 1 MiB, to allow plenty of room for growth.) You must also make sure that it has the proper partition type. Using GNU Parted, you can set this using a command such as the following:

   # parted /dev/DISK set PARTITION-NUMBER bios_grub on
 If you are using gdisk, set the partition type to '0xEF02'.  With

partitioning programs that require setting the GUID directly, it should be '21686148-6449-6e6f-744e656564454649'.

  • Caution:* Be very careful which partition you select! When GRUB

finds a BIOS Boot Partition during installation, it will automatically overwrite part of it. Make sure that the partition does not contain any other data.

File:, 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 * OS-specific notes:: Notes on some operating systems

File:, 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:, 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:, 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:, Node: Loopback booting, Next: OS-specific notes, 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:, Node: OS-specific notes, Prev: Loopback booting, Up: Booting

5.3 Some caveats on OS-specific issues

Here, we describe some caveats on several operating systems.

* Menu:

* GNU/Hurd:: * GNU/Linux:: * NetBSD:: * DOS/Windows::

File:, Node: GNU/Hurd, Next: GNU/Linux, Up: OS-specific notes

5.3.1 GNU/Hurd

Since GNU/Hurd is Multiboot-compliant, it is easy to boot it; there is nothing special about it. But do not forget that you have to specify a root partition to the kernel.

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

File:, Node: GNU/Linux, Next: NetBSD, Prev: GNU/Hurd, Up: OS-specific notes

5.3.2 GNU/Linux

It is relatively easy to boot GNU/Linux from GRUB, because it somewhat resembles to boot a Multiboot-compliant OS.

1. Set GRUB's root device to the same drive as GNU/Linux's.  The
   command 'search --set=root --file /vmlinuz' or similar may help you
   (*note search::).
2. Load the kernel using the command 'linux' (*note linux::):
        grub> linux /vmlinuz root=/dev/sda1
   If you need to specify some kernel parameters, just append them to
   the command.  For example, to set 'acpi' to 'off', do this:
        grub> linux /vmlinuz root=/dev/sda1 acpi=off
   See the documentation in the Linux source tree for complete
   information on the available options.
   With 'linux' GRUB uses 32-bit protocol.  Some BIOS services like
   APM or EDD aren't available with this protocol.  In this case you
   need to use 'linux16'
        grub> linux16 /vmlinuz root=/dev/sda1 acpi=off
3. If you use an initrd, execute the command 'initrd' (*note initrd::)
   after 'linux':
        grub> initrd /initrd
   If you used 'linux16' you need to use 'initrd16':
        grub> initrd16 /initrd
4. Finally, run the command 'boot' (*note boot::).
  • Caution:* If you use an initrd and specify the 'mem=' option to the

kernel to let it use less than actual memory size, you will also have to specify the same memory size to GRUB. To let GRUB know the size, run the command 'uppermem' _before_ loading the kernel. *Note uppermem::, for more information.

File:, Node: NetBSD, Next: DOS/Windows, Prev: GNU/Linux, Up: OS-specific notes

5.3.3 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
        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:, Node: DOS/Windows, Prev: NetBSD, Up: OS-specific notes

5.3.4 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


  • Caution:* This is effective only if DOS (or Windows) uses BIOS to

access the swapped disks. If that OS uses a special driver for the disks, this probably won't work.

 Another problem arises if you installed more than one set of

DOS/Windows onto one disk, because they could be confused if there are more than one primary partitions for DOS/Windows. Certainly you should avoid doing this, but there is a solution if you do want to do so. Use the partition hiding/unhiding technique.

 If GRUB "hides" a DOS (or Windows) partition (*note parttool::), DOS

(or Windows) will ignore the partition. If GRUB «unhides» a DOS (or Windows) partition, DOS (or Windows) will detect the partition. Thus, if you have installed DOS (or Windows) on the first and the second partition of the first hard disk, and you want to boot the copy on the first partition, do the following:

   parttool (hd0,1) hidden-
   parttool (hd0,2) hidden+
   set root=(hd0,1)
   chainloader +1
   parttool ${root} boot+

File:, Node: Configuration, Next: 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 * 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:, Node: Simple configuration, Next: Shell-like scripting, 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:


   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:
   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'.


   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::).


   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.


   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> is pressed during that time, it
   will display the menu and wait for input.  If a hotkey associated
   with a menu entry is pressed, it will boot the associated menu
   entry immediately.  If the timeout expires before either of these
   happens, it will boot the default entry.  In the 'countdown' case,
   it will show a one-line indication of the remaining time.


   Variants of the corresponding variables without the '_BUTTON'
   suffix, used to support vendor-specific power buttons.  *Note
   Vendor power-on keys::.


   Set by distributors of GRUB to their identifying name.  This is
   used to generate more informative menu entry titles.


   Select the terminal input device.  You may select multiple devices
   here, separated by spaces.
   Valid terminal input names depend on the platform, but may include
   'console' (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.


   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.


   If this option is set, it overrides both 'GRUB_TERMINAL_INPUT' and
   'GRUB_TERMINAL_OUTPUT' to the same value.


   A command to configure the serial port when using the serial
   console.  *Note serial::.  Defaults to 'serial'.


   Command-line arguments to add to menu entries for the Linux kernel.


   Unless 'GRUB_DISABLE_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




   As 'GRUB_CMDLINE_LINUX', but for GNU Mach.


   The values of these options are passed to Xen hypervisor Xen menu
   entries, for all respectively normal entries.


   The values of these options replace the values of
   Xen menu entries.


   Normally, 'grub-mkconfig' will generate menu entries that use
   universally-unique identifiers (UUIDs) to identify the root
   filesystem to the Linux kernel, using a 'root=UUID=...' kernel
   parameter.  This is usually more reliable, but in some cases it may
   not be appropriate.  To disable the use of UUIDs, set this option
   to 'true'.


   If this option is set to 'true', disable the generation of recovery
   mode menu entries.


   If graphical video support is required, either because the
   'gfxterm' graphical terminal is in use or because
   'GRUB_GFXPAYLOAD_LINUX' is set, then 'grub-mkconfig' will normally
   load all available GRUB video drivers and use the one most
   appropriate for your hardware.  If you need to override this for
   some reason, then you can set this option.
   After 'grub-install' has been run, the available video drivers are
   listed in '/boot/grub/video.lst'.


   Set the resolution used on the 'gfxterm' graphical terminal.  Note
   that you can only use modes which your graphics card supports via
   VESA BIOS Extensions (VBE), so for example native LCD panel
   resolutions may not be available.  The default is 'auto', which
   tries to select a preferred resolution.  *Note gfxmode::.


   Set a background image for use with the 'gfxterm' graphical
   terminal.  The value of this option must be a file readable by GRUB
   at boot time, and it must end with '.png', '.tga', '.jpg', or
   '.jpeg'.  The image will be scaled if necessary to fit the screen.


   Set a theme for use with the 'gfxterm' graphical terminal.


   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.


   Normally, 'grub-mkconfig' will try to use the external 'os-prober'
   program, if installed, to discover other operating systems
   installed on the same system and generate appropriate menu entries
   for them.  Set this option to 'true' to disable this.


   List of space-separated FS UUIDs of filesystems to be ignored from
   os-prober output.  For efi chainloaders it's <UUID>@<EFI FILE>


   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 'y',
   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'.


   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


   Play a tune on the speaker when GRUB starts.  This is particularly
   useful for users unable to see the screen.  The value of this
   option is passed directly to *note play::.


   If this option is set, GRUB will issue a *note badram:: command to
   filter out specified regions of RAM.


   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'.


   If this option is set, it overrides the default recordfail setting.
   A setting of -1 causes GRUB to wait for user input indefinitely.
   However, a false positive in the recordfail mechanism may occur if
   power is lost during boot before boot success is recorded in
   userspace.  The default setting is 30, which causes GRUB to wait
   for user input for thirty seconds before continuing.  This default
   allows interactive users the opportunity to switch to a different,
   working kernel, while avoiding a false positive causing the boot to
   block indefinitely on headless and appliance systems where access
   to a console is restricted or limited.
   This option is only effective when GRUB was configured with the
   '--enable-quick-boot' option.


   This option sets the English text of the string that will be
   displayed in parentheses to indicate that a boot option is provided
   to help users recover a broken system.  The default is "recovery
 The following options are still accepted for compatibility with

existing configurations, but have better replacements:


   Wait this many seconds before displaying the menu.  If <ESC> is
   pressed 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> is pressed.
   This option is unset by default, and is deprecated in favour of the
   less confusing 'GRUB_TIMEOUT_STYLE=countdown' or


   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'.


   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
 For more detailed customisation of 'grub-mkconfig''s output, you may

edit the scripts in '/etc/grub.d' directly. '/etc/grub.d/40_custom' is particularly useful for adding entire custom menu entries; simply type the menu entries you want to add at the end of that file, making sure to leave at least the first two lines intact.

File:, Node: Shell-like scripting, Next: Multi-boot manual config, Prev: Simple configuration, Up: Configuration

6.2 Writing full configuration files directly

'grub.cfg' is written in GRUB's built-in scripting language, which has a syntax quite similar to that of GNU Bash and other Bourne shell derivatives.


A «word» is a sequence of characters considered as a single unit by GRUB. Words are separated by «metacharacters», which are the following plus space, tab, and newline:

   { } | & $ ; < >
 Quoting may be used to include metacharacters in words; see below.

Reserved words

Reserved words have a special meaning to GRUB. The following words are recognised as reserved when unquoted and either the first word of a simple command or the third word of a 'for' command:

   ! [[ ]] { }
   case do done elif else esac fi for function
   if in menuentry select then time until while
 Not all of these reserved words have a useful purpose yet; some are

reserved for future expansion.


Quoting is used to remove the special meaning of certain characters or words. It can be used to treat metacharacters as part of a word, to prevent reserved words from being recognised as such, and to prevent variable expansion.

 There are three quoting mechanisms: the escape character, single

quotes, and double quotes.

 A non-quoted backslash (\) is the "escape character".  It preserves

the literal value of the next character that follows, with the exception of newline.

 Enclosing characters in single quotes preserves the literal value of

each character within the quotes. A single quote may not occur between single quotes, even when preceded by a backslash.

 Enclosing characters in double quotes preserves the literal value of

all characters within the quotes, with the exception of '$' and '\'. The '$' character retains its special meaning within double quotes. The backslash retains its special meaning only when followed by one of the following characters: '$', '«', '\', or newline. A backslash-newline pair is treated as a line continuation (that is, it is removed from the input stream and effectively ignored(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.


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

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:, Node: Multi-boot manual config, Next: Embedded configuration, Prev: Shell-like scripting, Up: Configuration

6.3 Multi-boot manual config

Currently autogenerating config files for multi-boot environments depends on os-prober and has several shortcomings. While fixing it is scheduled for the next release, meanwhile you can make use of the power of GRUB syntax and do it yourself. A possible configuration is detailed here, feel free to adjust to your needs.

 First create a separate GRUB partition, big enough to hold GRUB. Some

of the following entries show how to load OS installer images from this same partition, for that you obviously need to make the partition large enough to hold those images as well. Mount this partition on/mnt/boot and disable GRUB in all OSes and manually install self-compiled latest GRUB with:

 'grub-install --boot-directory=/mnt/boot /dev/sda'
 In all the OSes install GRUB tools but disable installing GRUB in

bootsector, so you'll have menu.lst and grub.cfg available for use. Also disable os-prober use by setting:

 in /etc/default/grub
 Then write a grub.cfg (/mnt/boot/grub/grub.cfg):
   menuentry "OS using grub2" {
      insmod xfs
      search --set=root --label OS1 --hint hd0,msdos8
      configfile /boot/grub/grub.cfg
   menuentry "OS using grub2-legacy" {
      insmod ext2
      search --set=root --label OS2 --hint hd0,msdos6
      legacy_configfile /boot/grub/menu.lst
   menuentry "Windows XP" {
      insmod ntfs
      search --set=root --label WINDOWS_XP --hint hd0,msdos1
      ntldr /ntldr
   menuentry "Windows 7" {
      insmod ntfs
      search --set=root --label WINDOWS_7 --hint hd0,msdos2
      ntldr /bootmgr
   menuentry "FreeBSD" {
             insmod zfs
             search --set=root --label freepool --hint hd0,msdos7
             kfreebsd /freebsd@/boot/kernel/kernel
             kfreebsd_module_elf /freebsd@/boot/kernel/opensolaris.ko
             kfreebsd_module_elf /freebsd@/boot/kernel/zfs.ko
             kfreebsd_module /freebsd@/boot/zfs/zpool.cache type=/boot/zfs/zpool.cache
             set kFreeBSD.vfs.root.mountfrom=zfs:freepool/freebsd
             set kFreeBSD.hw.psm.synaptics_support=1
   menuentry "experimental GRUB" {
             search --set=root --label GRUB --hint hd0,msdos5
             multiboot /experimental/grub/i386-pc/core.img
   menuentry "Fedora 16 installer" {
             search --set=root --label GRUB --hint hd0,msdos5
             linux /fedora/vmlinuz lang=en_US keymap=sg resolution=1280x800
             initrd /fedora/initrd.img
   menuentry "Fedora rawhide installer" {
             search --set=root --label GRUB --hint hd0,msdos5
             linux /fedora/vmlinuz repo= lang=en_US keymap=sg resolution=1280x800
             initrd /fedora/initrd.img
   menuentry "Debian sid installer" {
             search --set=root --label GRUB --hint hd0,msdos5
             linux /debian/dists/sid/main/installer-amd64/current/images/hd-media/vmlinuz
             initrd /debian/dists/sid/main/installer-amd64/current/images/hd-media/initrd.gz
 * 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:, Node: Embedded configuration, Prev: Multi-boot manual config, Up: Configuration

6.4 Embedding a configuration file into GRUB

GRUB supports embedding a configuration file directly into the core image, so that it is loaded before entering normal mode. This is useful, for example, when it is not straightforward to find the real configuration file, or when you need to debug problems with loading that file. 'grub-install' uses this feature when it is not using BIOS disk functions or when installing to a different disk from the one containing '/boot/grub', in which case it needs to use the 'search' command (*note search::) to find '/boot/grub'.

 To embed a configuration file, use the '-c' option to 'grub-mkimage'.

The file is copied into the core image, so it may reside anywhere on the file system, and may be removed after running 'grub-mkimage'.

 After the embedded configuration file (if any) is executed, GRUB will

load the 'normal' module (*note normal::), which will then read the real configuration file from '$prefix/grub.cfg'. By this point, the 'root' variable will also have been set to the root device name. For example, 'prefix' might be set to '(hd0,1)/boot/grub', and 'root' might be set to 'hd0,1'. Thus, in most cases, the embedded configuration file only needs to set the 'prefix' and 'root' variables, and then drop through to GRUB's normal processing. A typical example of this might look like this:

   search.fs_uuid 01234567-89ab-cdef-0123-456789abcdef root
   set prefix=($root)/boot/grub
 (The 'search_fs_uuid' module must be included in the core image for

this example to work.)

 In more complex cases, it may be useful to read other configuration

files directly from the embedded configuration file. This allows such things as reading files not called 'grub.cfg', or reading files from a directory other than that where GRUB's loadable modules are installed. To do this, include the 'configfile' and 'normal' modules in the core image, and embed a configuration file that uses the 'configfile' command to load another file. The following example of this also requires the 'echo', 'search_label', and 'test' modules to be included in the core image:

   search.fs_label grub root
   if [ -e /boot/grub/example/test1.cfg ]; then
       set prefix=($root)/boot/grub
       configfile /boot/grub/example/test1.cfg
       if [ -e /boot/grub/example/test2.cfg ]; then
           set prefix=($root)/boot/grub
           configfile /boot/grub/example/test2.cfg
           echo "Could not find an example configuration file!"
 The embedded configuration file may not contain menu entries

directly, but may only read them from elsewhere using 'configfile'.

File:, Node: 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 © 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:, 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.

 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):


   The network interface's IP address.  Read-only.


   The network interface's MAC address.  Read-only.


   The client host name provided by DHCP. Read-only.


   The client domain name provided by DHCP. Read-only.


   The path to the client's root disk provided by DHCP. Read-only.


   The path to additional DHCP vendor extensions provided by DHCP.


   The boot file name provided by DHCP. Read-only.


   The name of the DHCP server responsible for these boot parameters.


   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'


   The IP address of default interface.  Read-only.  This is alias for
   the 'net_${net_default_interface}_ip'.


   The default interface's MAC address.  Read-only.  This is alias for
   the 'net_${net_default_interface}_mac'.


   The default server used by network drives (*note Device syntax::).
   Read-write, although setting this is only useful before opening a
   network device.

File:, 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:, 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>


<Dell XPS M1530>


<Dell Latitude E4300>


<Asus EeePC 1005PE>

   84:1 (unconfirmed)
 To take full advantage of this function, install GRUB into the MBR

(*note Installing GRUB using grub-install::).

 If you have a laptop which has a similar feature and not in the above

list could you figure your address and contribute? To discover the address do the following:

  • boot normally
  • sudo modprobe nvram

sudo cat /dev/nvram | xxd > normal_button.txt

  • boot using vendor button
  • sudo modprobe nvram

sudo cat /dev/nvram | xxd > normal_vendor.txt

 Then compare these text files and find where a bit was toggled.  E.g.

in case of Dell XPS it was:

   byte 0x47: 20 --> 28
 It's a bit number 3 as seen from following table:

0 01 1 02 2 04 3 08 4 10 5 20 6 40 7 80

 0x47 is decimal 71.  Linux nvram implementation cuts first 14 bytes

of CMOS. So the real byte address in CMOS is 71+14=85 So complete address is 85:3

File:, 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:, 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:, 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:, Node: Device syntax, Next: File name syntax, Up: Filesystem

13.1 How to specify devices

The device syntax is like this:

 '[]' 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 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>.

 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).

 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:, 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:, 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:

 This represents that GRUB should read blocks 0 through 99, block 200,

and blocks 300 through 599. If you omit an offset, then GRUB assumes the offset is zero.

 Like the file name syntax (*note File name syntax::), if a blocklist

does not contain a device name, then GRUB uses GRUB's «root device». So '(hd0,2)+1' is the same as '+1' when the root device is '(hd0,2)'.

File:, Node: Interface, Next: 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:, 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.


   Kill the text from the current cursor position to the end of the


   Kill backward from the cursor to the beginning of the line.


   Yank the killed text back into the buffer at the cursor.

<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:, 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:, 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:, 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:, 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:: * 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>_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:, 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:, 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:, 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:, 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:, 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:, Node: color_normal, Next: debug, 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


 '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:, Node: debug, Next: default, Prev: color_normal, Up: Special environment variables

15.1.7 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:, Node: default, Next: fallback, Prev: debug, Up: Special environment variables

15.1.8 default

If this variable is set, it identifies a menu entry that should be selected by default, possibly after a timeout (*note timeout::). The entry may be identified by number or by 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:
 If the entry is in a submenu, then it must be identified using the

titles of each of the submenus starting from the top level followed by the number or title of the menu entry itself, separated by '>'. For example, take the following menu structure:

   Submenu 1
     Menu Entry 1
     Menu Entry 2
   Submenu 2
     Submenu 3
       Menu Entry 3
       Menu Entry 4
     Menu Entry 5
 "Menu Entry 3" would then be identified as 'Submenu 2>Submenu 3>Menu

Entry 3'.

 This variable is often set by 'GRUB_DEFAULT' (*note Simple

configuration::), 'grub-set-default', or 'grub-reboot'.

File:, Node: fallback, Next: gfxmode, Prev: default, Up: Special environment variables

15.1.9 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:, Node: gfxmode, Next: gfxpayload, Prev: fallback, Up: Special environment variables

15.1.10 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:, Node: gfxpayload, Next: gfxterm_font, Prev: gfxmode, Up: Special environment variables

15.1.11 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


File:, Node: gfxterm_font, Next: grub_cpu, Prev: gfxpayload, Up: Special environment variables

15.1.12 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:, Node: grub_cpu, Next: grub_platform, Prev: gfxterm_font, Up: Special environment variables

15.1.13 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:, Node: grub_platform, Next: icondir, Prev: grub_cpu, Up: Special environment variables

15.1.14 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:, Node: icondir, Next: lang, Prev: grub_platform, Up: Special environment variables

15.1.15 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:, Node: lang, Next: locale_dir, Prev: icondir, Up: Special environment variables

15.1.16 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:, Node: locale_dir, Next: menu_color_highlight, Prev: lang, Up: Special environment variables

15.1.17 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:, Node: menu_color_highlight, Next: menu_color_normal, Prev: locale_dir, Up: Special environment variables

15.1.18 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


File:, Node: menu_color_normal, Next: net_<INTERFACE>_boot_file, Prev: menu_color_highlight, Up: Special environment variables

15.1.19 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:, Node: net_<INTERFACE>_boot_file, Next: net_<INTERFACE>_dhcp_server_name, Prev: menu_color_normal, Up: Special environment variables

15.1.20 net_<INTERFACE>_boot_file

*Note Network::.

File:, Node: net_<INTERFACE>_dhcp_server_name, Next: net_<INTERFACE>_domain, Prev: net_<INTERFACE>_boot_file, Up: Special environment variables

15.1.21 net_<INTERFACE>_dhcp_server_name

*Note Network::.

File:, Node: net_<INTERFACE>_domain, Next: net_<INTERFACE>_extensionspath, Prev: net_<INTERFACE>_dhcp_server_name, Up: Special environment variables

15.1.22 net_<INTERFACE>_domain

*Note Network::.

File:, Node: net_<INTERFACE>_extensionspath, Next: net_<INTERFACE>_hostname, Prev: net_<INTERFACE>_domain, Up: Special environment variables

15.1.23 net_<INTERFACE>_extensionspath

*Note Network::.

File:, Node: net_<INTERFACE>_hostname, Next: net_<INTERFACE>_ip, Prev: net_<INTERFACE>_extensionspath, Up: Special environment variables

15.1.24 net_<INTERFACE>_hostname

*Note Network::.

File:, Node: net_<INTERFACE>_ip, Next: net_<INTERFACE>_mac, Prev: net_<INTERFACE>_hostname, Up: Special environment variables

15.1.25 net_<INTERFACE>_ip

*Note Network::.

File:, Node: net_<INTERFACE>_mac, Next: net_<INTERFACE>_rootpath, Prev: net_<INTERFACE>_ip, Up: Special environment variables

15.1.26 net_<INTERFACE>_mac

*Note Network::.

File:, Node: net_<INTERFACE>_rootpath, Next: net_default_interface, Prev: net_<INTERFACE>_mac, Up: Special environment variables

15.1.27 net_<INTERFACE>_rootpath

*Note Network::.

File:, Node: net_default_interface, Next: net_default_ip, Prev: net_<INTERFACE>_rootpath, Up: Special environment variables

15.1.28 net_default_interface

*Note Network::.

File:, Node: net_default_ip, Next: net_default_mac, Prev: net_default_interface, Up: Special environment variables

15.1.29 net_default_ip

*Note Network::.

File:, Node: net_default_mac, Next: net_default_server, Prev: net_default_ip, Up: Special environment variables

15.1.30 net_default_mac

*Note Network::.

File:, Node: net_default_server, Next: pager, Prev: net_default_mac, Up: Special environment variables

15.1.31 net_default_server

*Note Network::.

File:, Node: pager, Next: prefix, Prev: net_default_server, Up: Special environment variables

15.1.32 pager

If set to '1', pause output after each screenful and wait for keyboard input. The default is not to pause output.

File:, Node: prefix, Next: pxe_blksize, Prev: pager, Up: Special environment variables

15.1.33 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:, Node: pxe_blksize, Next: pxe_default_gateway, Prev: prefix, Up: Special environment variables

15.1.34 pxe_blksize

*Note Network::.

File:, Node: pxe_default_gateway, Next: pxe_default_server, Prev: pxe_blksize, Up: Special environment variables

15.1.35 pxe_default_gateway

*Note Network::.

File:, Node: pxe_default_server, Next: root, Prev: pxe_default_gateway, Up: Special environment variables

15.1.36 pxe_default_server

*Note Network::.

File:, Node: root, Next: superusers, Prev: pxe_default_server, Up: Special environment variables

15.1.37 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:, Node: superusers, Next: theme, Prev: root, Up: Special environment variables

15.1.38 superusers

This variable may be set to a list of superuser names to enable authentication support. *Note Security::.

File:, Node: theme, Next: timeout, Prev: superusers, Up: Special environment variables

15.1.39 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


File:, Node: timeout, Next: timeout_style, Prev: theme, Up: Special environment variables

15.1.40 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


File:, Node: timeout_style, Prev: timeout, Up: Special environment variables

15.1.41 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:, 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:, 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:, 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:, 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:, 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

File:, 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:, 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:, 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:, 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:, Node: terminfo, Prev: terminal_output, Up: General commands

16.2.4 terminfo

– Command: terminfo [-a|-u|-v] [term]

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

File:, Node: Command-line and menu entry commands, 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 * date:: Display or set current date and time * devicetree:: Load a device tree blob * distrust:: Remove a pubkey from trusted keys * drivemap:: Map a drive to another * echo:: Display a line of text * eval:: Evaluate agruments as GRUB commands * export:: Export an environment variable * false:: Do nothing, unsuccessfully * gettext:: Translate a string * gptsync:: Fill an MBR based on GPT entries * halt:: Shut down your computer * hashsum:: Compute or check hash checksum * help:: Show help messages * initrd:: Load a Linux initrd * initrd16:: Load a Linux initrd (16-bit mode) * insmod:: Insert a module * keystatus:: Check key modifier status * linux:: Load a Linux kernel * linux16:: Load a Linux kernel (16-bit mode) * list_env:: List variables in environment block * list_trusted:: List trusted public keys * load_env:: Load variables from environment block * loadfont:: Load font files * loopback:: Make a device from a filesystem image * ls:: List devices or files * lsfonts:: List loaded fonts * lsmod:: Show loaded modules * md5sum:: Compute or check MD5 hash * module:: Load module for multiboot kernel * multiboot:: Load multiboot compliant kernel * nativedisk:: Switch to native disk drivers * normal:: Enter normal mode * normal_exit:: Exit from normal mode * parttool:: Modify partition table entries * password:: Set a clear-text password * password_pbkdf2:: Set a hashed password * play:: Play a tune * probe:: Retrieve device info * pxe_unload:: Unload the PXE environment * read:: Read user input * reboot:: Reboot your computer * regexp:: Test if regular expression matches string * rmmod:: Remove a module * save_env:: Save variables to environment block * search:: Search devices by file, label, or UUID * sendkey:: Emulate keystrokes * set:: Set an environment variable * sha1sum:: Compute or check SHA1 hash * sha256sum:: Compute or check SHA256 hash * sha512sum:: Compute or check SHA512 hash * sleep:: Wait for a specified number of seconds * source:: Read a configuration file in same context * test:: Check file types and compare values * true:: Do nothing, successfully * trust:: Add public key to list of trusted keys * unset:: Unset an environment variable * uppermem:: Set the upper memory size * verify_detached:: Verify detached digital signature * videoinfo:: List available video modes

File:, Node: [, Next: acpi, Up: Command-line and menu entry commands

16.3.1 [

– Command: '[' expression ']'

   Alias for 'test EXPRESSION' (*note test::).

File:, Node: acpi, Next: authenticate, Prev: [, Up: Command-line and menu entry commands

16.3.2 acpi

– Command: acpi ['-1'|'-2']

        ['--oemid=id'] ['--oemtable=table'] ['--oemtablerev=rev']
        ['--oemtablecreator=creator'] ['--oemtablecreatorrev=rev']
        ['--no-ebda'] filename ...
   Modern BIOS systems normally implement the Advanced Configuration
   and Power Interface (ACPI), and define various tables that describe
   the interface between an ACPI-compliant operating system and the
   firmware.  In some cases, the tables provided by default only work
   well with certain operating systems, and it may be necessary to
   replace some of them.
   Normally, this command will replace the Root System Description
   Pointer (RSDP) in the Extended BIOS Data Area to point to the new
   tables.  If the '--no-ebda' option is used, the new tables will be
   known only to GRUB, but may be used by GRUB's EFI emulation.

File:, Node: 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:, 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
   MENU_COLOR_HIGHLIGHT.  *Note Special environment variables::.

File:, Node: background_image, Next: badram, Prev: background_color, Up: Command-line and menu entry commands

16.3.5 background_image

– Command: background_image '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:, 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 ( a list of address/mask pairs. Given a page-aligned address and a base address / mask pair, if all the bits of the page-aligned address that are enabled by the mask match with the base address, it means this page is to be filtered. This syntax makes it easy to represent patterns that are often result of memory damage, due to physical distribution of memory cells. File:, Node: blocklist, Next: boot, Prev: badram, Up: Command-line and menu entry commands 16.3.7 blocklist ---------------- -- Command: blocklist file Print a block list (*note Block list syntax::) for FILE. File:, Node: boot, Next: cat, Prev: blocklist, Up: Command-line and menu entry commands 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:, 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:, 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:, Node: clear, Next: cmosclean, Prev: chainloader, Up: Command-line and menu entry commands 16.3.11 clear ------------- -- Command: clear Clear the screen. File:, 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:, 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:, 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:, 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:, 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:, Node: cpuid, Next: crc, Prev: configfile, Up: Command-line and menu entry commands 16.3.17 cpuid ------------- -- Command: cpuid [-l] Check for CPU features. This command is only available on x86 systems. With the '-l' option, return true if the CPU supports long mode (64-bit). If invoked without options, this command currently behaves as if it had been invoked with '-l'. This may change in the future. File:, 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:, Node: cryptomount, Next: date, 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 and geli. Note that necessary modules (LUKS and GELI) have to be loaded manually before this command can be used. File:, Node: date, Next: devicetree, Prev: cryptomount, Up: Command-line and menu entry commands 16.3.20 date ------------ -- Command: date [[year-]month-day] [hour:minute[:second

   With no arguments, print the current date and time.
   Otherwise, take the current date and time, change any elements
   specified as arguments, and set the result as the new date and
   time.  For example, 'date 01-01' will set the current month and day
   to January 1, but leave the year, hour, minute, and second

File:, Node: devicetree, Next: distrust, Prev: date, Up: Command-line and menu entry commands

16.3.21 linux

– 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

File:, Node: distrust, Next: drivemap, Prev: devicetree, Up: Command-line and menu entry commands

16.3.22 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:, Node: drivemap, Next: echo, Prev: distrust, Up: Command-line and menu entry commands

16.3.23 drivemap

– Command: drivemap '-l'|'-r'|['-s'] from_drive to_drive

   Without options, map the drive FROM_DRIVE to the drive TO_DRIVE.
   This is necessary when you chain-load some operating systems, such
   as DOS, if such an OS resides at a non-first drive.  For
   convenience, any partition suffix on the drive is ignored, so you
   can safely use ${root} as a drive specification.
   With the '-s' option, perform the reverse mapping as well, swapping
   the two drives.
   With the '-l' option, list the current mappings.
   With the '-r' option, reset all mappings to the default values.
   For example:
        drivemap -s (hd0) (hd1)

File:, Node: echo, Next: eval, Prev: drivemap, Up: Command-line and menu entry commands

16.3.24 echo

– Command: echo ['-n'] ['-e'] string …

   Display the requested text and, unless the '-n' option is used, a
   trailing new line.  If there is more than one string, they are
   separated by spaces in the output.  As usual in GRUB commands,
   variables may be substituted using '${var}'.
   The '-e' option enables interpretation of backslash escapes.  The
   following sequences are recognised:
        alert (BEL)
        suppress trailing new line
        form feed
        new line
        carriage return
        horizontal tab
        vertical tab
   When interpreting backslash escapes, backslash followed by any
   other character will print that character.

File:, Node: eval, Next: export, Prev: echo, Up: Command-line and menu entry commands

16.3.25 eval

– Command: eval string …

   Concatenate arguments together using single space as separator and
   evaluate result as sequence of GRUB commands.

File:, Node: export, Next: false, Prev: eval, Up: Command-line and menu entry commands

16.3.26 export

– Command: export envvar

   Export the environment variable ENVVAR.  Exported variables are
   visible to subsidiary configuration files loaded using

File:, Node: false, Next: gettext, Prev: export, Up: Command-line and menu entry commands

16.3.27 false

– Command: false

   Do nothing, unsuccessfully.  This is mainly useful in control
   constructs such as 'if' and 'while' (*note Shell-like scripting::).

File:, Node: gettext, Next: gptsync, Prev: false, Up: Command-line and menu entry commands

16.3.28 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

File:, Node: gptsync, Next: halt, Prev: gettext, Up: Command-line and menu entry commands

16.3.29 gptsync

– Command: gptsync device [partition[+/-[type]]] …

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

File:, Node: halt, Next: hashsum, Prev: gptsync, Up: Command-line and menu entry commands

16.3.30 halt

– Command: halt '–no-apm'

   The command halts the computer.  If the '--no-apm' option is
   specified, no APM BIOS call is performed.  Otherwise, the computer
   is shut down using APM.

File:, Node: hashsum, Next: help, Prev: halt, Up: Command-line and menu entry commands

16.3.31 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:, Node: help, Next: initrd, Prev: hashsum, Up: Command-line and menu entry commands

16.3.32 help

– Command: help [pattern …]

   Display helpful information about builtin commands.  If you do not
   specify PATTERN, this command shows short descriptions of all
   available commands.
   If you specify any PATTERNS, it displays longer information about
   each of the commands whose names begin with those PATTERNS.

File:, Node: initrd, Next: initrd16, Prev: help, Up: Command-line and menu entry commands

16.3.33 initrd

– Command: initrd file

   Load an initial ramdisk for a Linux kernel image, and set the
   appropriate parameters in the Linux setup area in memory.  This may
   only be used after the 'linux' command (*note linux::) has been
   run.  See also *note GNU/Linux::.

File:, Node: initrd16, Next: insmod, Prev: initrd, Up: Command-line and menu entry commands

16.3.34 initrd16

– Command: initrd16 file

   Load an initial ramdisk for a Linux kernel image to be booted in
   16-bit mode, and set the appropriate parameters in the Linux setup
   area in memory.  This may only be used after the 'linux16' command
   (*note linux16::) has been run.  See also *note GNU/Linux::.
   This command is only available on x86 systems.

File:, Node: insmod, Next: keystatus, Prev: initrd16, Up: Command-line and menu entry commands

16.3.35 insmod

– Command: insmod module

   Insert the dynamic GRUB module called MODULE.

File:, Node: keystatus, Next: linux, Prev: insmod, Up: Command-line and menu entry commands

16.3.36 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
   Checking key modifier status is only supported on some platforms.
   If invoked without any options, the 'keystatus' command returns
   true if and only if checking key modifier status is supported.

File:, Node: linux, Next: linux16, Prev: keystatus, Up: Command-line and menu entry commands

16.3.37 linux

– Command: linux file …

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

File:, Node: linux16, Next: list_env, Prev: linux, Up: Command-line and menu entry commands

16.3.38 linux16

– Command: linux16 file …

   Load a Linux kernel image from FILE in 16-bit mode.  The rest of
   the line is passed verbatim as the "kernel command-line".  Any
   initrd must be reloaded after using this command (*note
   The kernel will be booted using the traditional 16-bit boot
   protocol.  As well as bypassing problems with 'vga=' described in
   *note linux::, this permits booting some other programs that
   implement the Linux boot protocol for the sake of convenience.
   This command is only available on x86 systems.

File:, Node: list_env, Next: list_trusted, Prev: linux16, Up: Command-line and menu entry commands

16.3.39 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:, Node: list_trusted, Next: load_env, Prev: list_env, Up: Command-line and menu entry commands

16.3.40 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:, Node: load_env, Next: loadfont, Prev: list_trusted, Up: Command-line and menu entry commands

16.3.41 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

File:, Node: loadfont, Next: loopback, Prev: load_env, Up: Command-line and menu entry commands

16.3.42 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:, Node: loopback, Next: ls, Prev: loadfont, Up: Command-line and menu entry commands

16.3.43 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

File:, Node: ls, Next: lsfonts, Prev: loopback, Up: Command-line and menu entry commands

16.3.44 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
   If the argument is a directory given as an absolute file name
   (*note File name syntax::), then list the contents of that

File:, Node: lsfonts, Next: lsmod, Prev: ls, Up: Command-line and menu entry commands

16.3.45 lsfonts

– Command: lsfonts

   List loaded fonts.

File:, Node: lsmod, Next: md5sum, Prev: lsfonts, Up: Command-line and menu entry commands

16.3.46 lsmod

– Command: lsmod

   Show list of loaded modules.

File:, Node: md5sum, Next: module, Prev: lsmod, Up: Command-line and menu entry commands

16.3.47 md5sum

– Command: md5sum arg …

   Alias for 'hashsum --hash md5 arg ...'.  See command 'hashsum'
   (*note hashsum::) for full description.

File:, Node: module, Next: multiboot, Prev: md5sum, Up: Command-line and menu entry commands

16.3.48 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:, Node: multiboot, Next: nativedisk, Prev: module, Up: Command-line and menu entry commands

16.3.49 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 prefered ELF
   information while 0.97 and GRUB 2 use kludge.  Use this option to
   ignore kludge.  Known affected systems: old Solaris, SkyOS.
  1. 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:, Node: nativedisk, Next: normal, Prev: multiboot, Up: Command-line and menu entry commands

16.3.50 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

File:, Node: normal, Next: normal_exit, Prev: nativedisk, Up: Command-line and menu entry commands

16.3.51 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:, Node: normal_exit, Next: parttool, Prev: normal, Up: Command-line and menu entry commands

16.3.52 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:, Node: parttool, Next: password, Prev: normal_exit, Up: Command-line and menu entry commands

16.3.53 parttool

– Command: parttool partition commands

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

File:, Node: password, Next: password_pbkdf2, Prev: parttool, Up: Command-line and menu entry commands

16.3.54 password

– Command: password user clear-password

   Define a user named USER with password CLEAR-PASSWORD.  *Note

File:, Node: password_pbkdf2, Next: play, Prev: password, Up: Command-line and menu entry commands

16.3.55 password_pbkdf2

– Command: password_pbkdf2 user hashed-password

   Define a user named USER with password hash HASHED-PASSWORD.  Use
   'grub-mkpasswd-pbkdf2' (*note Invoking grub-mkpasswd-pbkdf2::) to
   generate password hashes.  *Note Security::.

File:, Node: play, Next: probe, Prev: password_pbkdf2, Up: Command-line and menu entry commands

16.3.56 play

– Command: play file | tempo [pitch1 duration1] [pitch2 duration2] …

   Plays a tune
   If the argument is a file name (*note File name syntax::), play the
   tune recorded in it.  The file format is first the tempo as an
   unsigned 32bit little-endian number, then pairs of unsigned 16bit
   little-endian numbers for pitch and duration pairs.
   If the arguments are a series of numbers, play the inline tune.
   The tempo is the base for all note durations.  60 gives a 1-second
   base, 120 gives a half-second base, etc.  Pitches are Hz.  Set
   pitch to 0 to produce a rest.

File:, Node: probe, Next: pxe_unload, Prev: play, Up: Command-line and menu entry commands

16.3.57 probe

– Command: probe ['–set' var]

        '--driver'|'--partmap'|'--fs'|'--fs-uuid'|'--label' device
   Retrieve device information.  If option '--set' is given, assign
   result to variable VAR, otherwise print information on the screen.

File:, Node: pxe_unload, Next: read, Prev: probe, Up: Command-line and menu entry commands

16.3.58 pxe_unload

– Command: pxe_unload

   Unload the PXE environment (*note Network::).
   This command is only available on PC BIOS systems.

File:, Node: read, Next: reboot, Prev: pxe_unload, Up: Command-line and menu entry commands

16.3.59 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:, Node: reboot, Next: regexp, Prev: read, Up: Command-line and menu entry commands

16.3.60 reboot

– Command: reboot

   Reboot the computer.

File:, Node: regexp, Next: rmmod, Prev: reboot, Up: Command-line and menu entry commands

16.3.61 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:, Node: rmmod, Next: save_env, Prev: regexp, Up: Command-line and menu entry commands

16.3.62 rmmod

– Command: rmmod module

   Remove a loaded MODULE.

File:, Node: save_env, Next: search, Prev: rmmod, Up: Command-line and menu entry commands

16.3.63 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

File:, Node: search, Next: sendkey, Prev: save_env, Up: Command-line and menu entry commands

16.3.64 search

– Command: search ['–file'|'–label'|'–fs-uuid'] ['–set' [var]]

        ['--no-floppy'] name
   Search devices by file ('-f', '--file'), filesystem label ('-l',
   '--label'), or filesystem UUID ('-u', '--fs-uuid').
   If the '--set' option is used, the first device found is set as the
   value of environment variable VAR.  The default variable is 'root'.
   The '--no-floppy' option prevents searching floppy devices, which
   can be slow.
   The 'search.file', 'search.fs_label', and 'search.fs_uuid' commands
   are aliases for 'search --file', 'search --label', and 'search
   --fs-uuid' respectively.

File:, Node: sendkey, Next: set, Prev: search, Up: Command-line and menu entry commands

16.3.65 sendkey

– Command: sendkey

        '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
   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
   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:, Node: set, Next: sha1sum, Prev: sendkey, Up: Command-line and menu entry commands

16.3.66 set

– Command: set [envvar=value]

   Set the environment variable ENVVAR to VALUE.  If invoked with no
   arguments, print all environment variables with their values.

File:, Node: sha1sum, Next: sha256sum, Prev: set, Up: Command-line and menu entry commands

16.3.67 sha1sum

– Command: sha1sum arg …

   Alias for 'hashsum --hash sha1 arg ...'.  See command 'hashsum'
   (*note hashsum::) for full description.

File:, Node: sha256sum, Next: sha512sum, Prev: sha1sum, Up: Command-line and menu entry commands

16.3.68 sha256sum

– Command: sha256sum arg …

   Alias for 'hashsum --hash sha256 arg ...'.  See command 'hashsum'
   (*note hashsum::) for full description.

File:, Node: sha512sum, Next: sleep, Prev: sha256sum, Up: Command-line and menu entry commands

16.3.69 sha512sum

– Command: sha512sum arg …

   Alias for 'hashsum --hash sha512 arg ...'.  See command 'hashsum'
   (*note hashsum::) for full description.

File:, Node: sleep, Next: source, Prev: sha512sum, Up: Command-line and menu entry commands

16.3.70 sleep

– Command: sleep ['–verbose'] ['–interruptible'] count

   Sleep for COUNT seconds.  If option '--interruptible' is given,
   allow <ESC> 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 by <ESC>.

File:, Node: source, Next: test, Prev: sleep, Up: Command-line and menu entry commands

16.3.71 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:, Node: test, Next: true, Prev: source, Up: Command-line and menu entry commands

16.3.72 test

– Command: test expression

   Evaluate EXPRESSION and return zero exit status if result is true,
   non zero status otherwise.
   EXPRESSION is one of:
        the strings are equal
        the strings are not equal
        STRING1 is lexicographically less than STRING2
        STRING1 is lexicographically less or equal than STRING2
        STRING1 is lexicographically greater than STRING2
        STRING1 is lexicographically greater or equal than STRING2
        INTEGER1 is equal to INTEGER2
        INTEGER1 is greater than or equal to INTEGER2
        INTEGER1 is greater than INTEGER2
        INTEGER1 is less than or equal to INTEGER2
        INTEGER1 is less than INTEGER2
        INTEGER1 is not equal to INTEGER2
        INTEGER1 is greater than INTEGER2 after stripping off common
        non-numeric PREFIX.
        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 is equivalent to '-n STRING'
   '-z' STRING
        the length of STRING is zero
   '(' EXPRESSION ')'
        EXPRESSION is true
        EXPRESSION is false
        both EXPRESSION1 and EXPRESSION2 are true
        either EXPRESSION1 or EXPRESSION2 is true

File:, Node: true, Next: trust, Prev: test, Up: Command-line and menu entry commands

16.3.73 true

– Command: true

   Do nothing, successfully.  This is mainly useful in control
   constructs such as 'if' and 'while' (*note Shell-like scripting::).

File:, Node: trust, Next: unset, Prev: true, Up: Command-line and menu entry commands

16.3.74 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:, Node: unset, Next: uppermem, Prev: trust, Up: Command-line and menu entry commands

16.3.75 unset

– Command: unset envvar

   Unset the environment variable ENVVAR.

File:, Node: uppermem, Next: verify_detached, Prev: unset, Up: Command-line and menu entry commands

16.3.76 uppermem

This command is not yet implemented for GRUB 2, although it is planned.

File:, Node: verify_detached, Next: videoinfo, Prev: uppermem, Up: Command-line and menu entry commands

16.3.77 verify_detached

– Command: verify_detached ['–skip-sig'] file signature_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:, Node: videoinfo, Prev: verify_detached, Up: Command-line and menu entry commands

16.3.78 videoinfo

– Command: videoinfo [[WxH]xD]

   List available video modes.  If resolution is given, show only
   matching modes.

File:, 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 autoconfiguration * net_del_addr:: Remove IP address from interface * net_del_dns:: Remove a DNS server * net_del_route:: Remove a route entry * 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:, 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:, 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:, 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'

   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

File:, Node: net_bootp, Next: net_del_addr, Prev: net_add_route, Up: Networking commands

16.4.4 net_bootp

– Command: net_bootp [CARD]

   Perform configuration of CARD using DHCP protocol.  If no card name
   is specified, try to configure all existing cards.  If
   configuration was successful, interface with name CARD':dhcp' and
   configured address is added to CARD.  If server provided gateway
   information in DHCP ACK packet, it is added as route entry with the
   name CARD':dhcp:gw'.  Additionally the following DHCP options are
   recognized and processed:
   '1 (Subnet Mask)'
        Used to calculate network local routing entry for interface
   '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

File:, 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:, 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:, Node: net_del_route, Next: net_get_dhcp_option, 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:, Node: net_get_dhcp_option, Next: net_ipv6_autoconf, Prev: net_del_route, Up: Networking commands

16.4.8 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:, Node: net_ipv6_autoconf, Next: net_ls_addr, Prev: net_get_dhcp_option, Up: Networking commands

16.4.9 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:, Node: net_ls_addr, Next: net_ls_cards, Prev: net_ipv6_autoconf, Up: Networking commands

16.4.10 net_ls_addr

– Command: net_ls_addr

   List all configured interfaces with their MAC and IP addresses.

File:, Node: net_ls_cards, Next: net_ls_dns, Prev: net_ls_addr, Up: Networking commands

16.4.11 net_ls_cards

– Command: net_ls_cards

   List all detected network cards with their MAC address.

File:, Node: net_ls_dns, Next: net_ls_routes, Prev: net_ls_cards, Up: Networking commands

16.4.12 net_ls_dns

– Command: net_ls_dns

   List addresses of DNS servers used during name lookup.

File:, Node: net_ls_routes, Next: net_nslookup, Prev: net_ls_dns, Up: Networking commands

16.4.13 net_ls_routes

– Command: net_ls_routes

   List routing entries.

File:, Node: net_nslookup, Prev: net_ls_routes, Up: Networking commands

16.4.14 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:, 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), 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:, 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

File:, 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 is automatically restricted to superusers.

 Other users may be given access to specific menu entries by giving a

list of usernames (as above) using the '–users' option to the 'menuentry' command (*note menuentry::). If the '–unrestricted' option is used for a menu entry, then that entry is unrestricted. If the '–users' option is not used for a menu entry, then that only superusers are able to use it.

 Putting this together, a typical 'grub.cfg' fragment might look like


   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:, Node: Using digital signatures, 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.

 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"`;
     gpg --batch --detach-sign --passphrase-fd 0 $i < \
   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:, 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. 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. 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 hints guess guess guess guess PCI yes yes yes yes badram yes yes yes yes compression always pointless no no exit yes no no no ia32 EFI amd64 EFI ia32 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 hints guess guess good guess PCI yes yes yes no badram yes yes no yes compression no no no no exit yes yes yes yes Loongson sparc64 Powerpc ARC video yes no yes no console N/A ASCII ASCII ASCII charset network no yes (*) yes no ATA/AHCI yes no no no AT keyboard yes no no no Speaker no no no no USB yes no no no chainloader yes no no no cpuid no no no no hints good good good no PCI yes no no no badram yes (*) no no no compression configurable no no configurable exit no yes yes yes MIPS qemu emu video no yes console CP437 Unicode (*) charset network no yes ATA/AHCI yes no AT keyboard yes no Speaker no no USB N/A yes chainloader yes no cpuid no no hints guess no PCI no no badram yes (*) no compression configurable no exit no yes File:, 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):


 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)
 * 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:, 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 cbfstoll from Coreboot package (for coreboot

                     platform only)

GRUB_COREBOOT_ROM empty Coreboot ROM GRUB_QEMU_OPTS additional options to be supplied to QEMU

 Required files are:

kfreebsd_env.i386 32-bit kFreeBSD device hints kfreebsd.i386 32-bit FreeBSD kernel image kfreebsd.x86_64, same from 64-bit kFreeBSD kfreebsd_env.x86_64 knetbsd.i386 32-bit NetBSD kernel image knetbsd.miniroot.i386 32-bit kNetBSD miniroot.kmod. knetbsd.x86_64, same from 64-bit kNetBSD knetbsd.miniroot.x86_64 kopenbsd.i386 32-bit OpenBSD kernel bsd.rd image kopenbsd.x86_64 same from 64-bit kOpenBSD linux.i386 32-bit Linux linux.x86_64 64-bit Linux

File:, Node: Troubleshooting, Next: Invoking grub-install, Prev: Supported kernels, Up: Top

22 Error messages produced by GRUB * Menu: * GRUB only offers a rescue shell:: File:, Node: GRUB only offers a rescue shell, 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. '' (*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:, 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/' 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:, 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:, 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:, 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
 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:


   Print a summary of the command-line options and exit.


   Print the version number of GRUB and exit.

File:, 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:


   Print a summary of the command-line options and exit.


   Print the version number of GRUB and exit.

'-o FILE' '–output=FILE'

   Save output in FILE.  This "option" is required.


   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).


   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.


   Use FILE as the 'xorriso' program, rather than the built-in


   Use FILE as the 'grub-mkimage' program, rather than the built-in

File:, 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:, 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:


   Print a summary of the command-line options and exit.


   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/'.

'-t TARGET' '–target=TARGET'

   Print information about the given path or device as defined by
   TARGET.  The available targets and their meanings are:
        GRUB filesystem module.
        Filesystem Universally Unique Identifier (UUID).
        Filesystem label.
        GRUB device name.
        System device name.
        GRUB partition map module.
        GRUB abstraction module (e.g.  'lvm').
        Crypto device UUID.
        MBR partition type code (two hexadecimal digits).
        A string of platform search hints suitable for passing to the
        'search' command (*note search::).
        Search hints for the PC BIOS platform.
        Search hints for the IEEE1275 platform.
        Search hints for platforms where disks are addressed directly
        rather than via firmware.
        Search hints for the EFI platform.
        Search hints for the ARC platform.
        A guess at a reasonable GRUB drive name for this device, which
        may be used as a fallback if the 'search' command fails.
        System device name for the whole disk.

'-v' '–verbose'

   Print verbose messages.

File:, 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:


   Print a summary of the command-line options and exit.


   Print the version number of GRUB and exit.

'-v' '–verbose'

   Print each line of input after reading it.

File:, 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- or later because the GNU assembler has been changed so that it can produce real 16bits machine code between 2.9.1 and See <>, to obtain information on how to get the latest version. GRUB is available from the GNU alpha archive site <> or any of its mirrors. The file will be named grub-version.tar.gz. The current version is 2.02~beta2, so the file you should grab is: <> To unbundle GRUB use the instruction: zcat grub-2.02~beta2.tar.gz | tar xvf - which will create a directory called 'grub-2.02~beta2' 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-2.02~beta2 ./configure make install Also, the latest version is available using Git. See <> for more information. File:, Node: Reporting bugs, Next: Future, Prev: Obtaining and Building GRUB, Up: Top Appendix B Reporting bugs * These are the guideline for how to report bugs. Take a look at this list below before you submit bugs: 1. Before getting unsettled, read this manual through and through. Also, see the GNU GRUB FAQ ( 2. Always mention the information on your GRUB. The version number and the configuration are quite important. If you build it yourself, write the options specified to the configure script and your operating system, including the versions of gcc and binutils. 3. If you have trouble with the installation, inform us of how you installed GRUB. Don't omit error messages, if any. Just 'GRUB hangs up when it boots' is not enough. The information on your hardware is also essential. These are especially important: the geometries and the partition tables of your hard disk drives and your BIOS. 4. If GRUB cannot boot your operating system, write down _everything_ you see on the screen. Don't paraphrase them, like 'The foo OS crashes with GRUB, even though it can boot with the bar boot loader just fine'. Mention the commands you executed, the messages printed by them, and information on your operating system including the version number. 5. Explain what you wanted to do. It is very useful to know your purpose and your wish, and how GRUB didn't satisfy you. 6. If you can investigate the problem yourself, please do. That will give you and us much more information on the problem. Attaching a patch is even better. When you attach a patch, make the patch in unified diff format, and write ChangeLog entries. But, even when you make a patch, don't forget to explain the problem, so that we can understand what your patch is for. 7. Write down anything that you think might be related. Please understand that we often need to reproduce the same problem you 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 ( Alternatively, you can submit a report via electronic mail to, but we strongly recommend that you use the Bug Tracking System, because e-mail can be passed over easily. Once we get your report, we will try to fix the bugs. File:, Node: Future, Next: 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 ( File:, 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:, Node: GNU Free Documentation License, Up: Copying This Manual

D.1 GNU Free Documentation License

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   combined work in its license notice, and that you preserve all
   their Warranty Disclaimers.
   The combined work need only contain one copy of this License, and
   multiple identical Invariant Sections may be replaced with a single
   copy.  If there are multiple Invariant Sections with the same name
   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."
   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
   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.
   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
   If a section in the Document is Entitled "Acknowledgements",
   "Dedications", or "History", the requirement (section 4) to
   Preserve its Title (section 1) will typically require changing the
   actual title.
   You may not copy, modify, sublicense, or distribute the Document
   except as expressly provided for under this License.  Any other
   attempt to copy, modify, sublicense or distribute the Document is
   void, and will automatically terminate your rights under this
   License.  However, parties who have received copies, or rights,
   from you under this License will not have their licenses terminated
   so long as such parties remain in full compliance.
   The Free Software Foundation may publish new, revised versions of
   the GNU Free Documentation License from time to time.  Such new
   versions will be similar in spirit to the present version, but may
   differ in detail to address new problems or concerns.  See
   Each version of the License is given a distinguishing version
   number.  If the Document specifies that a particular numbered
   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.

File:, Node: Index, Prev: Copying This Manual, Up: Top

Index *

* Menu:

* '[': [. (line 6) * acpi: acpi. (line 6) * authenticate: authenticate. (line 6) * background_color: background_color. (line 6) * background_image: background_image. (line 6) * badram: badram. (line 6) * blocklist: blocklist. (line 6) * boot: boot. (line 6) * cat: cat. (line 6) * chainloader: chainloader. (line 6) * clear: clear. (line 6) * CMOS: cmosdump. (line 6) * cmosclean: cmosclean. (line 6) * cmostest: cmostest. (line 6) * cmp: cmp. (line 6) * configfile: configfile. (line 6) * cpuid: cpuid. (line 6) * crc: crc. (line 6) * cryptomount: cryptomount. (line 6) * date: date. (line 6) * devicetree: devicetree. (line 6) * distrust: distrust. (line 6) * drivemap: drivemap. (line 6) * echo: echo. (line 6) * eval: eval. (line 6) * export: export. (line 6) * false: false. (line 6) * FDL, GNU Free Documentation License: GNU Free Documentation License.

                                                              (line 6)

* gettext: gettext. (line 6) * gptsync: gptsync. (line 6) * halt: halt. (line 6) * hashsum: hashsum. (line 6) * help: help. (line 6) * initrd: initrd. (line 6) * initrd16: initrd16. (line 6) * insmod: insmod. (line 6) * keystatus: keystatus. (line 6) * linux: linux. (line 6) * linux16: linux16. (line 6) * list_env: list_env. (line 6) * list_trusted: list_trusted. (line 6) * loadfont: loadfont. (line 6) * load_env: load_env. (line 6) * loopback: loopback. (line 6) * ls: ls. (line 6) * lsfonts: lsfonts. (line 6) * lsmod: lsmod. (line 6) * md5sum: md5sum. (line 6) * menuentry: menuentry. (line 6) * module: module. (line 6) * multiboot: multiboot. (line 6) * nativedisk: nativedisk. (line 6) * net_add_addr: net_add_addr. (line 6) * net_add_dns: net_add_dns. (line 6) * net_add_route: net_add_route. (line 6) * net_bootp: net_bootp. (line 6) * net_del_addr: net_del_addr. (line 6) * net_del_dns: net_del_dns. (line 6) * net_del_route: net_del_route. (line 6) * net_get_dhcp_option: net_get_dhcp_option. (line 6) * net_ipv6_autoconf: net_ipv6_autoconf. (line 6) * net_ls_addr: net_ls_addr. (line 6) * net_ls_cards: net_ls_cards. (line 6) * net_ls_dns: net_ls_dns. (line 6) * net_ls_routes: net_ls_routes. (line 6) * net_nslookup: net_nslookup. (line 6) * normal: normal. (line 6) * normal_exit: normal_exit. (line 6) * parttool: parttool. (line 6) * password: password. (line 6) * password_pbkdf2: password_pbkdf2. (line 6) * play: play. (line 6) * probe: probe. (line 6) * pxe_unload: pxe_unload. (line 6) * read: read. (line 6) * reboot: reboot. (line 6) * regexp: regexp. (line 6) * rmmod: rmmod. (line 6) * save_env: save_env. (line 6) * search: search. (line 6) * sendkey: sendkey. (line 6) * serial: serial. (line 6) * set: set. (line 6) * sha1sum: sha1sum. (line 6) * sha256sum: sha256sum. (line 6) * sha512sum: sha512sum. (line 6) * sleep: sleep. (line 6) * source: source. (line 6) * submenu: submenu. (line 6) * terminal_input: terminal_input. (line 6) * terminal_output: terminal_output. (line 6) * terminfo: terminfo. (line 6) * test: test. (line 6) * true: true. (line 6) * trust: trust. (line 6) * unset: unset. (line 6) * verify_detached: verify_detached. (line 6) * videoinfo: videoinfo. (line 6)