\input texinfo @c -*-texinfo-*- @c %**start of header @setfilename grub.info @include version.texi @settitle GNU GRUB Manual @value{VERSION} @c Unify all our little indices for now. @syncodeindex fn cp @syncodeindex vr cp @syncodeindex ky cp @syncodeindex pg cp @syncodeindex tp cp @c %**end of header @footnotestyle separate @paragraphindent 3 @finalout @copying This manual is for GNU GRUB (version @value{VERSION}, @value{UPDATED}). Copyright @copyright{} 1999,2000,2001,2002,2004,2006,2008,2009,2010 Free Software Foundation, Inc. @quotation Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections. @end quotation @end copying @dircategory Kernel @direntry * GRUB: (grub). The GRand Unified Bootloader * grub-install: (grub)Invoking grub-install. Install GRUB on your drive * grub-mkconfig: (grub)Invoking grub-mkconfig. Generate GRUB configuration * grub-mkpasswd-pbkdf2: (grub)Invoking grub-mkpasswd-pbkdf2. @end direntry @setchapternewpage odd @titlepage @sp 10 @title the GNU GRUB manual @subtitle The GRand Unified Bootloader, version @value{VERSION}, @value{UPDATED}. @author Gordon Matzigkeit @author Yoshinori K. Okuji @c The following two commands start the copyright page. @page @vskip 0pt plus 1filll @insertcopying @end titlepage @c Output the table of contents at the beginning. @contents @finalout @headings double @ifnottex @node Top @top GNU GRUB manual This is the documentation of GNU GRUB, the GRand Unified Bootloader, a flexible and powerful boot loader program for a wide range of architectures. This edition documents version @value{VERSION}. @insertcopying @end ifnottex @menu * Introduction:: Capturing the spirit of GRUB * Naming convention:: Names of your drives in GRUB * Installation:: Installing GRUB on your drive * Booting:: How to boot different operating systems * Configuration:: Writing your own configuration file * Network:: Downloading OS images from a network * Serial terminal:: Using GRUB via a serial line * Vendor power-on keys:: Changing GRUB behaviour on vendor power-on keys * Preset Menu:: Embedding a configuration file into GRUB * Images:: GRUB image files * Filesystem:: Filesystem syntax and semantics * Interface:: The menu and the command-line * Commands:: The list of available builtin commands * Security:: Authentication and authorisation * Troubleshooting:: Error messages produced by GRUB * Invoking grub-install:: How to use the GRUB installer * Invoking grub-mkconfig:: Generate a GRUB configuration file * Invoking grub-mkpasswd-pbkdf2:: Generate GRUB password hashes * Obtaining and Building GRUB:: How to obtain and build GRUB * Reporting bugs:: Where you should send a bug report * Future:: Some future plans on GRUB * Internals:: Hacking GRUB * Copying This Manual:: Copying This Manual * Index:: @end menu @node Introduction @chapter Introduction to GRUB @menu * Overview:: What exactly GRUB is and how to use it * History:: From maggot to house fly * Features:: GRUB features * Role of a boot loader:: The role of a boot loader @end menu @node Overview @section Overview Briefly, a @dfn{boot loader} is the first software program that runs when a computer starts. It is responsible for loading and transferring control to an operating system @dfn{kernel} software (such as Linux or GNU Mach). The kernel, in turn, initializes the rest of the operating system (e.g. a GNU system). GNU GRUB is a very powerful boot loader, which can load a wide variety of free operating systems, as well as proprietary operating systems with chain-loading@footnote{@dfn{chain-load} is the mechanism for loading unsupported operating systems by loading another boot loader. It is typically used for loading DOS or Windows.}. GRUB is designed to address the complexity of booting a personal computer; both the program and this manual are tightly bound to that computer platform, although porting to other platforms may be addressed in the future. One of the important features in GRUB is flexibility; GRUB understands filesystems and kernel executable formats, so you can load an arbitrary operating system the way you like, without recording the physical position of your kernel on the disk. Thus you can load the kernel just by specifying its file name and the drive and partition where the kernel resides. When booting with GRUB, you can use either a command-line interface (@pxref{Command-line interface}), or a menu interface (@pxref{Menu interface}). Using the command-line interface, you type the drive specification and file name of the kernel manually. In the menu interface, you just select an OS using the arrow keys. The menu is based on a configuration file which you prepare beforehand (@pxref{Configuration}). While in the menu, you can switch to the command-line mode, and vice-versa. You can even edit menu entries before using them. In the following chapters, you will learn how to specify a drive, a partition, and a file name (@pxref{Naming convention}) to GRUB, how to install GRUB on your drive (@pxref{Installation}), and how to boot your OSes (@pxref{Booting}), step by step. @node History @section History of GRUB GRUB originated in 1995 when Erich Boleyn was trying to boot the GNU Hurd with the University of Utah's Mach 4 microkernel (now known as GNU Mach). Erich and Brian Ford designed the Multiboot Specification (@pxref{Top, Multiboot Specification, Motivation, multiboot, The Multiboot Specification}), because they were determined not to add to the large number of mutually-incompatible PC boot methods. Erich then began modifying the FreeBSD boot loader so that it would understand Multiboot. He soon realized that it would be a lot easier to write his own boot loader from scratch than to keep working on the FreeBSD boot loader, and so GRUB was born. Erich added many features to GRUB, but other priorities prevented him from keeping up with the demands of its quickly-expanding user base. In 1999, Gordon Matzigkeit and Yoshinori K. Okuji adopted GRUB as an official GNU package, and opened its development by making the latest sources available via anonymous CVS. @xref{Obtaining and Building GRUB}, for more information. Over the next few years, GRUB was extended to meet many needs, but it quickly became clear that its design was not keeping up with the extensions being made to it, and we reached the point where it was very difficult to make any further changes without breaking existing features. Around 2002, Yoshinori K. Okuji started work on PUPA (Preliminary Universal Programming Architecture for GNU GRUB), aiming to rewrite the core of GRUB to make it cleaner, safer, more robust, and more powerful. PUPA was eventually renamed to GRUB 2, and the original version of GRUB was renamed to GRUB Legacy. Small amounts of maintenance continued to be done on GRUB Legacy, but the last release (0.97) was made in 2005 and at the time of writing it seems unlikely that there will be another. By around 2007, GNU/Linux distributions started to use GRUB 2 to limited extents, and by the end of 2009 multiple major distributions were installing it by default. @node Features @section GRUB features The primary requirement for GRUB is that it be compliant with the @dfn{Multiboot Specification}, which is described in @ref{Top, Multiboot Specification, Motivation, multiboot, The Multiboot Specification}. The other goals, listed in approximate order of importance, are: @itemize @bullet{} @item Basic functions must be straightforward for end-users. @item Rich functionality to support kernel experts and designers. @item Backward compatibility for booting FreeBSD, NetBSD, OpenBSD, and Linux. Proprietary kernels (such as DOS, Windows NT, and OS/2) are supported via a chain-loading function. @end itemize Except for specific compatibility modes (chain-loading and the Linux @dfn{piggyback} format), all kernels will be started in much the same state as in the Multiboot Specification. Only kernels loaded at 1 megabyte or above are presently supported. Any attempt to load below that boundary will simply result in immediate failure and an error message reporting the problem. In addition to the requirements above, GRUB has the following features (note that the Multiboot Specification doesn't require all the features that GRUB supports): @table @asis @item Recognize multiple executable formats Support many of the @dfn{a.out} variants plus @dfn{ELF}. Symbol tables are also loaded. @item Support non-Multiboot kernels Support many of the various free 32-bit kernels that lack Multiboot compliance (primarily FreeBSD, NetBSD, OpenBSD, and Linux). Chain-loading of other boot loaders is also supported. @item Load multiples modules Fully support the Multiboot feature of loading multiple modules. @item Load a configuration file Support a human-readable text configuration file with preset boot commands. You can also load another configuration file dynamically and embed a preset configuration file in a GRUB image file. The list of commands (@pxref{Commands}) are a superset of those supported on the command-line. An example configuration file is provided in @ref{Configuration}. @item Provide a menu interface A menu interface listing preset boot commands, with a programmable timeout, is available. There is no fixed limit on the number of boot entries, and the current implementation has space for several hundred. @item Have a flexible command-line interface A fairly flexible command-line interface, accessible from the menu, is available to edit any preset commands, or write a new boot command set from scratch. If no configuration file is present, GRUB drops to the command-line. The list of commands (@pxref{Commands}) are a subset of those supported for configuration files. Editing commands closely resembles the Bash command-line (@pxref{Command Line Editing, Bash, Command Line Editing, features, Bash Features}), with @key{TAB}-completion of commands, devices, partitions, and files in a directory depending on context. @item Support multiple filesystem types Support multiple filesystem types transparently, plus a useful explicit blocklist notation. The currently supported filesystem types are @dfn{BSD FFS}, @dfn{DOS FAT16 and FAT32}, @dfn{Minix fs}, @dfn{Linux ext2fs}, @dfn{ReiserFS}, @dfn{JFS}, @dfn{XFS}, and @dfn{VSTa fs}. @xref{Filesystem}, for more information. @item Support automatic decompression Can decompress files which were compressed by @command{gzip}. This function is both automatic and transparent to the user (i.e. all functions operate upon the uncompressed contents of the specified files). This greatly reduces a file size and loading time, a particularly great benefit for floppies.@footnote{There are a few pathological cases where loading a very badly organized ELF kernel might take longer, but in practice this never happen.} It is conceivable that some kernel modules should be loaded in a compressed state, so a different module-loading command can be specified to avoid uncompressing the modules. @item Access data on any installed device Support reading data from any or all floppies or hard disk(s) recognized by the BIOS, independent of the setting of the root device. @item Be independent of drive geometry translations Unlike many other boot loaders, GRUB makes the particular drive translation irrelevant. A drive installed and running with one translation may be converted to another translation without any adverse effects or changes in GRUB's configuration. @item Detect all installed @sc{ram} GRUB can generally find all the installed @sc{ram} on a PC-compatible machine. It uses an advanced BIOS query technique for finding all memory regions. As described on the Multiboot Specification (@pxref{Top, Multiboot Specification, Motivation, multiboot, The Multiboot Specification}), not all kernels make use of this information, but GRUB provides it for those who do. @item Support Logical Block Address mode In traditional disk calls (called @dfn{CHS mode}), there is a geometry translation problem, that is, the BIOS cannot access over 1024 cylinders, so the accessible space is limited to at least 508 MB and to at most 8GB. GRUB can't universally solve this problem, as there is no standard interface used in all machines. However, several newer machines have the new interface, Logical Block Address (@dfn{LBA}) mode. GRUB automatically detects if LBA mode is available and uses it if available. In LBA mode, GRUB can access the entire disk. @item Support network booting GRUB is basically a disk-based boot loader but also has network support. You can load OS images from a network by using the @dfn{TFTP} protocol. @item Support remote terminals To support computers with no console, GRUB provides remote terminal support, so that you can control GRUB from a remote host. Only serial terminal support is implemented at the moment. @end table @node Role of a boot loader @section The role of a boot loader The following is a quotation from Gordon Matzigkeit, a GRUB fanatic: @quotation Some people like to acknowledge both the operating system and kernel when they talk about their computers, so they might say they use ``GNU/Linux'' or ``GNU/Hurd''. Other people seem to think that the kernel is the most important part of the system, so they like to call their GNU operating systems ``Linux systems.'' I, personally, believe that this is a grave injustice, because the @emph{boot loader} is the most important software of all. I used to refer to the above systems as either ``LILO''@footnote{The LInux LOader, a boot loader that everybody uses, but nobody likes.} or ``GRUB'' 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@dots{} GRUB! @end quotation We, the GRUB maintainers, do not (usually) encourage Gordon's level of fanaticism, but it helps to remember that boot loaders deserve recognition. We hope that you enjoy using GNU GRUB as much as we did writing it. @node Naming convention @chapter Naming convention The device syntax used in GRUB is a wee bit different from what you may have seen before in your operating system(s), and you need to know it so that you can specify a drive/partition. Look at the following examples and explanations: @example (fd0) @end example First of all, GRUB requires that the device name be enclosed with @samp{(} and @samp{)}. The @samp{fd} part means that it is a floppy disk. The number @samp{0} is the drive number, which is counted from @emph{zero}. This expression means that GRUB will use the whole floppy disk. @example (hd0,2) @end example Here, @samp{hd} means it is a hard disk drive. The first integer @samp{0} indicates the drive number, that is, the first hard disk, while the second integer, @samp{1}, indicates the partition number (or the @sc{pc} slice number in the BSD terminology). The partition numbers are counted from @emph{one}, not from zero (as was the case in previous versions of GRUB). This expression means the second partition of the first hard disk drive. In this case, GRUB uses one partition of the disk, instead of the whole disk. @example (hd0,5) @end example This specifies the first @dfn{extended partition} of the first hard disk drive. Note that the partition numbers for extended partitions are counted from @samp{5}, regardless of the actual number of primary partitions on your hard disk. @example (hd1,a) @end example This means the BSD @samp{a} partition of the second hard disk. If you need to specify which @sc{pc} slice number should be used, use something like this: @samp{(hd1,1,a)}. If the @sc{pc} slice number is omitted, GRUB searches for the first @sc{pc} slice which has a BSD @samp{a} partition. Of course, to actually access the disks or partitions with GRUB, you need to use the device specification in a command, like @samp{set root=(fd0)} or @samp{parttool (hd0,3) hidden-}. To help you find out which number specifies a partition you want, the GRUB command-line (@pxref{Command-line interface}) options have argument completion. This means that, for example, you only need to type @example set root=( @end example followed by a @key{TAB}, and GRUB will display the list of drives, partitions, or file names. So it should be quite easy to determine the name of your target partition, even with minimal knowledge of the syntax. Note that GRUB does @emph{not} distinguish IDE from SCSI - it simply counts the drive numbers from zero, regardless of their type. Normally, any IDE drive number is less than any SCSI drive number, although that is not true if you change the boot sequence by swapping IDE and SCSI drives in your BIOS. Now the question is, how to specify a file? Again, consider an example: @example (hd0,1)/vmlinuz @end example This specifies the file named @samp{vmlinuz}, found on the first partition of the first hard disk drive. Note that the argument completion works with file names, too. That was easy, admit it. Now read the next chapter, to find out how to actually install GRUB on your drive. @node Installation @chapter Installation In order to install GRUB as your boot loader, you need to first install the GRUB system and utilities under your UNIX-like operating system (@pxref{Obtaining and Building GRUB}). You can do this either from the source tarball, or as a package for your OS. After you have done that, you need to install the boot loader on a drive (floppy or hard disk). There are two ways of doing that - either using the utility @command{grub-install} (@pxref{Invoking grub-install}) on a UNIX-like OS, or by running GRUB itself from a floppy. These are quite similar, however the utility might probe a wrong BIOS drive, so you should be careful. Also, if you install GRUB on a UNIX-like OS, please make sure that you have an emergency boot disk ready, so that you can rescue your computer if, by any chance, your hard drive becomes unusable (unbootable). GRUB comes with boot images, which are normally put in the directory @file{/usr/lib/grub/i386-pc}. Hereafter, the directory where GRUB images are initially placed (normally @file{/usr/lib/grub/i386-pc}) will be called the @dfn{image directory}, and the directory where the boot loader needs to find them (usually @file{/boot/grub}) will be called the @dfn{boot directory}. @menu * Installing GRUB using grub-install:: * Making a GRUB bootable CD-ROM:: @end menu @node Installing GRUB using grub-install @section Installing GRUB using grub-install @strong{Caution:} This procedure is definitely less safe, because there are several ways in which your computer can become unbootable. For example, most operating systems don't tell GRUB how to map BIOS drives to OS devices correctly---GRUB merely @dfn{guesses} the mapping. This will succeed in most cases, but not always. Therefore, GRUB provides you with a map file called the @dfn{device map}, which you must fix if it is wrong. @xref{Device map}, for more details. If you still do want to install GRUB under a UNIX-like OS (such as @sc{gnu}), invoke the program @command{grub-install} (@pxref{Invoking grub-install}) as the superuser (@dfn{root}). The usage is basically very simple. You only need to specify one argument to the program, namely, where to install the boot loader. The argument can be either a device file (like @samp{/dev/hda}) or a partition specified in GRUB's notation. For example, under Linux the following will install GRUB into the MBR of the first IDE disk: @example # @kbd{grub-install /dev/hda} @end example Likewise, under GNU/Hurd, this has the same effect: @example # @kbd{grub-install /dev/hd0} @end example If it is the first BIOS drive, this is the same as well: @example # @kbd{grub-install '(hd0)'} @end example Or you can omit the parentheses: @example # @kbd{grub-install hd0} @end example But all the above examples assume that GRUB should use images under the root directory. If you want GRUB to use images under a directory other than the root directory, you need to specify the option @option{--root-directory}. The typical usage is that you create a GRUB boot floppy with a filesystem. Here is an example: @example @group # @kbd{mke2fs /dev/fd0} # @kbd{mount -t ext2 /dev/fd0 /mnt} # @kbd{grub-install --root-directory=/mnt fd0} # @kbd{umount /mnt} @end group @end example Another example is when you have a separate boot partition which is mounted at @file{/boot}. Since GRUB is a boot loader, it doesn't know anything about mountpoints at all. Thus, you need to run @command{grub-install} like this: @example # @kbd{grub-install --root-directory=/boot /dev/hda} @end example By the way, as noted above, it is quite difficult to guess BIOS drives correctly under a UNIX-like OS. Thus, @command{grub-install} will prompt you to check if it could really guess the correct mappings, after the installation. The format is defined in @ref{Device map}. Please be quite careful. If the output is wrong, it is unlikely that your computer will be able to boot with no problem. Note that @command{grub-install} is actually just a shell script and the real task is done by @command{grub-mkimage} and @command{grub-setup}. Therefore, you may run those commands directly to install GRUB, without using @command{grub-install}. Don't do that, however, unless you are very familiar with the internals of GRUB. Installing a boot loader on a running OS may be extremely dangerous. @node Making a GRUB bootable CD-ROM @section Making a GRUB bootable CD-ROM GRUB supports the @dfn{no emulation mode} in the El Torito specification@footnote{El Torito is a specification for bootable CD using BIOS functions.}. This means that you can use the whole CD-ROM from GRUB and you don't have to make a floppy or hard disk image file, which can cause compatibility problems. For booting from a CD-ROM, GRUB uses a special Stage 2 called @file{stage2_eltorito}. The only GRUB files you need to have in your bootable CD-ROM are this @file{stage2_eltorito} and optionally a config file @file{grub.cfg}. You don't need to use @file{stage1} or @file{stage2}, because El Torito is quite different from the standard boot process. Here is an example of procedures to make a bootable CD-ROM image. First, make a top directory for the bootable image, say, @samp{iso}: @example $ @kbd{mkdir iso} @end example Make a directory for GRUB: @example $ @kbd{mkdir -p iso/boot/grub} @end example Copy the file @file{stage2_eltorito}: @example $ @kbd{cp /usr/lib/grub/i386-pc/stage2_eltorito iso/boot/grub} @end example If desired, make the config file @file{grub.cfg} under @file{iso/boot/grub} (@pxref{Configuration}), and copy any files and directories for the disc to the directory @file{iso/}. Finally, make a ISO9660 image file like this: @example $ @kbd{mkisofs -R -b boot/grub/stage2_eltorito -no-emul-boot \ -boot-load-size 4 -boot-info-table -o grub.iso iso} @end example This produces a file named @file{grub.iso}, which then can be burned into a CD (or a DVD). @kbd{mkisofs} has already set up the disc to boot from the @kbd{boot/grub/stage2_eltorito} file, so there is no need to setup GRUB on the disc. (Note that the @kbd{-boot-load-size 4} bit is required for compatibility with the BIOS on many older machines.) You can use the device @samp{(cd)} to access a CD-ROM in your config file. This is not required; GRUB automatically sets the root device to @samp{(cd)} when booted from a CD-ROM. It is only necessary to refer to @samp{(cd)} if you want to access other drives as well. @node Booting @chapter Booting GRUB can load Multiboot-compliant kernels in a consistent way, but for some free operating systems you need to use some OS-specific magic. @menu * General boot methods:: How to boot OSes with GRUB generally * OS-specific notes:: Notes on some operating systems @end menu @node General boot methods @section How to boot operating systems GRUB has two distinct boot methods. One of the two is to load an operating system directly, and the other is to chain-load another boot loader which then will load an operating system actually. Generally speaking, the former is more desirable, because you don't need to install or maintain other boot loaders and GRUB is flexible enough to load an operating system from an arbitrary disk/partition. However, the latter is sometimes required, since GRUB doesn't support all the existing operating systems natively. @menu * Loading an operating system directly:: * Chain-loading:: @end menu @node Loading an operating system directly @subsection How to boot an OS directly with GRUB Multiboot (@pxref{Top, Multiboot Specification, Motivation, multiboot, The Multiboot Specification}) is the native format supported by GRUB. For the sake of convenience, there is also support for Linux, FreeBSD, NetBSD and OpenBSD. If you want to boot other operating systems, you will have to chain-load them (@pxref{Chain-loading}). FIXME: this section is incomplete. @enumerate @item Run the command @command{boot} (@pxref{boot}). @end enumerate However, DOS and Windows have some deficiencies, so you might have to use more complicated instructions. @xref{DOS/Windows}, for more information. @node Chain-loading @subsection Chain-loading an OS Operating systems that do not support Multiboot and do not have specific support in GRUB (specific support is available for Linux, FreeBSD, NetBSD and OpenBSD) must be chain-loaded, which involves loading another boot loader and jumping to it in real mode. The @command{chainloader} command (@pxref{chainloader}) is used to set this up. It is normally also necessary to load some GRUB modules and set the appropriate root device. Putting this together, we get something like this, for a Windows system on the first partition of the first hard disk: @verbatim menuentry "Windows" { insmod chain insmod ntfs set root=(hd0,1) chainloader +1 } @end verbatim @c FIXME: document UUIDs. On systems with multiple hard disks, an additional workaround may be required. @xref{DOS/Windows}. Chain-loading is only supported on PC BIOS and EFI platforms. @node OS-specific notes @section Some caveats on OS-specific issues Here, we describe some caveats on several operating systems. @menu * GNU/Hurd:: * GNU/Linux:: * DOS/Windows:: @end menu @node GNU/Hurd @subsection GNU/Hurd Since GNU/Hurd is Multiboot-compliant, it is easy to boot it; there is nothing special about it. But do not forget that you have to specify a root partition to the kernel. FIXME: this section is incomplete. @enumerate @item Run the command @command{boot} (@pxref{boot}). @end enumerate @node GNU/Linux @subsection GNU/Linux It is relatively easy to boot GNU/Linux from GRUB, because it somewhat resembles to boot a Multiboot-compliant OS. FIXME: this section is incomplete. @enumerate @item Set GRUB's root device to the same drive as GNU/Linux's. @item Finally, run the command @command{boot} (@pxref{boot}). @end enumerate @strong{Caution:} If you use an initrd and specify the @samp{mem=} option to the kernel to let it use less than actual memory size, you will also have to specify the same memory size to GRUB. To let GRUB know the size, run the command @command{uppermem} @emph{before} loading the kernel. @xref{uppermem}, for more information. @node DOS/Windows @subsection DOS/Windows GRUB cannot boot DOS or Windows directly, so you must chain-load them (@pxref{Chain-loading}). However, their boot loaders have some critical deficiencies, so it may not work to just chain-load them. To overcome the problems, GRUB provides you with two helper functions. If you have installed DOS (or Windows) on a non-first hard disk, you have to use the disk swapping technique, because that OS cannot boot from any disks but the first one. The workaround used in GRUB is the command @command{drivemap} (@pxref{drivemap}), like this: @example drivemap -s (hd0) (hd1) @end example This performs a @dfn{virtual} swap between your first and second hard drive. @strong{Caution:} This is effective only if DOS (or Windows) uses BIOS to access the swapped disks. If that OS uses a special driver for the disks, this probably won't work. Another problem arises if you installed more than one set of DOS/Windows onto one disk, because they could be confused if there are more than one primary partitions for DOS/Windows. Certainly you should avoid doing this, but there is a solution if you do want to do so. Use the partition hiding/unhiding technique. If GRUB @dfn{hides} a DOS (or Windows) partition (@pxref{parttool}), DOS (or Windows) will ignore the partition. If GRUB @dfn{unhides} a DOS (or Windows) partition, DOS (or Windows) will detect the partition. Thus, if you have installed DOS (or Windows) on the first and the second partition of the first hard disk, and you want to boot the copy on the first partition, do the following: @example @group parttool (hd0,1) hidden- parttool (hd0,2) hidden+ set root=(hd0,1) chainloader +1 parttool @verb{'${root}'} boot+ boot @end group @end example @node Configuration @chapter Writing your own configuration file GRUB is configured using @file{grub.cfg}, usually located under @file{/boot/grub}. This file is quite flexible, but most users will not need to write the whole thing by hand. @menu * Simple configuration:: Recommended for most users * Shell-like scripting:: For power users and developers @end menu @node Simple configuration @section Simple configuration handling The program @command{grub-mkconfig} (@pxref{Invoking grub-mkconfig}) generates @file{grub.cfg} files suitable for most cases. It is suitable for use when upgrading a distribution, and will discover available kernels and attempt to generate menu entries for them. The file @file{/etc/default/grub} controls the operation of @command{grub-mkconfig}. It is sourced by a shell script, and so must be valid POSIX shell input; normally, it will just be a sequence of @samp{KEY=value} lines, but if the value contains spaces or other special characters then it must be quoted. For example: @example GRUB_TERMINAL_INPUT="console serial" @end example Valid keys in @file{/etc/default/grub} are as follows: @table @samp @item GRUB_DEFAULT The default menu entry. This may be a number, in which case it identifies the Nth entry in the generated menu counted from zero, or the full name of a menu entry, or the special string @samp{saved}. Using the full name may be useful if you want to set a menu entry as the default even though there may be a variable number of entries before it. If you set this to @samp{saved}, then the default menu entry will be that saved by @samp{GRUB_SAVEDEFAULT}, @command{grub-set-default}, or @command{grub-reboot}. The default is @samp{0}. @item GRUB_SAVEDEFAULT If this option is set to @samp{true}, then, when an entry is selected, save it as a new default entry for use by future runs of GRUB. This is only useful if @samp{GRUB_DEFAULT=saved}; it is a separate option because @samp{GRUB_DEFAULT=saved} is useful without this option, in conjunction with @command{grub-set-default} or @command{grub-reboot}. Unset by default. @item GRUB_TIMEOUT Boot the default entry this many seconds after the menu is displayed, unless a key is pressed. The default is @samp{5}. Set to @samp{0} to boot immediately without displaying the menu, or to @samp{-1} to wait indefinitely. @item GRUB_HIDDEN_TIMEOUT Wait this many seconds for a key to be pressed before displaying the menu. If no key is pressed during that time, boot immediately. Unset by default. @item GRUB_HIDDEN_TIMEOUT_QUIET In conjunction with @samp{GRUB_HIDDEN_TIMEOUT}, set this to @samp{true} to suppress the verbose countdown while waiting for a key to be pressed before displaying the menu. Unset by default. @item GRUB_DEFAULT_BUTTON @itemx GRUB_TIMEOUT_BUTTON @itemx GRUB_HIDDEN_TIMEOUT_BUTTON @itemx GRUB_BUTTON_CMOS_ADDRESS Variants of the corresponding variables without the @samp{_BUTTON} suffix, used to support vendor-specific power buttons. @xref{Vendor power-on keys}. @item GRUB_DISTRIBUTOR Set by distributors of GRUB to their identifying name. This is used to generate more informative menu entry titles. @item GRUB_TERMINAL_INPUT Select the terminal input device. You may select multiple devices here, separated by spaces. Valid terminal input names depend on the platform, but may include @samp{console} (PC BIOS and EFI consoles), @samp{serial} (serial terminal), @samp{ofconsole} (Open Firmware console), @samp{at_keyboard} (PC AT keyboard, mainly useful with Coreboot), or @samp{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. @item GRUB_TERMINAL_OUTPUT Select the terminal output device. You may select multiple devices here, separated by spaces. Valid terminal output names depend on the platform, but may include @samp{console} (PC BIOS and EFI consoles), @samp{serial} (serial terminal), @samp{gfxterm} (graphics-mode output), @samp{ofconsole} (Open Firmware console), or @samp{vga_text} (VGA text output, mainly useful with Coreboot). The default is to use the platform's native terminal output. @item GRUB_TERMINAL If this option is set, it overrides both @samp{GRUB_TERMINAL_INPUT} and @samp{GRUB_TERMINAL_OUTPUT} to the same value. @item GRUB_SERIAL_COMMAND A command to configure the serial port when using the serial console. @xref{serial}. Defaults to @samp{serial}. @item GRUB_CMDLINE_LINUX Command-line arguments to add to menu entries for the Linux kernel. @item GRUB_CMDLINE_LINUX_DEFAULT Unless @samp{GRUB_DISABLE_LINUX_RECOVERY} is set, 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 @samp{GRUB_CMDLINE_LINUX}. @item GRUB_CMDLINE_NETBSD @itemx GRUB_CMDLINE_NETBSD_DEFAULT As @samp{GRUB_CMDLINE_LINUX} and @samp{GRUB_CMDLINE_LINUX_DEFAULT}, but for NetBSD. @item GRUB_DISABLE_LINUX_UUID Normally, @command{grub-mkconfig} will generate menu entries that use universally-unique identifiers (UUIDs) to identify the root filesystem to the Linux kernel, using a @samp{root=UUID=...} kernel parameter. This is usually more reliable, but in some cases it may not be appropriate. To disable the use of UUIDs, set this option to @samp{true}. @item GRUB_DISABLE_LINUX_RECOVERY Disable the generation of recovery mode menu entries for Linux. @item GRUB_DISABLE_NETBSD_RECOVERY Disable the generation of recovery mode menu entries for NetBSD. @item GRUB_GFXMODE Set the resolution used on the @samp{gfxterm} graphical terminal. Note that you can only use modes which your graphics card supports via VESA BIOS Extensions (VBE), so for example native LCD panel resolutions may not be available. The default is @samp{640x480}. @item GRUB_BACKGROUND Set a background image for use with the @samp{gfxterm} graphical terminal. The value of this option must be a file readable by GRUB at boot time, and it must end with @file{.png}, @file{.tga}, @file{.jpg}, or @file{.jpeg}. The image will be scaled if necessary to fit the screen. @item GRUB_THEME Set a theme for use with the @samp{gfxterm} graphical terminal. @xref{Themes}. @item GRUB_GFXPAYLOAD_LINUX Set to @samp{text} to force the Linux kernel to boot in normal text mode, @samp{keep} to preserve the graphics mode set using @samp{GRUB_GFXMODE}, @samp{@var{width}x@var{height}}[@samp{x@var{depth}}] to set a particular graphics mode, or a sequence of these separated by commas or semicolons to try several modes in sequence. 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, simply unset this option and GRUB will tell Linux to boot in normal text mode. @item GRUB_DISABLE_OS_PROBER Normally, @command{grub-mkconfig} will try to use the external @command{os-prober} program, if installed, to discover other operating systems installed on the same system and generate appropriate menu entries for them. Set this option to @samp{true} to disable this. @item GRUB_INIT_TUNE Play a tune on the speaker when GRUB starts. This is particularly useful for users unable to see the screen. The value of this option is passed directly to @ref{play}. @end table For more detailed customisation of @command{grub-mkconfig}'s output, you may edit the scripts in @file{/etc/grub.d} directly. @file{/etc/grub.d/40_custom} is particularly useful for adding entire custom menu entries; simply type the menu entries you want to add at the end of that file, making sure to leave at least the first two lines intact. @node Shell-like scripting @section Writing full configuration files directly @node Network @chapter Booting GRUB from the network The following instructions only work on PC BIOS systems where the Preboot eXecution Environment (PXE) is available. To generate a PXE boot image, run: @example @group grub-mkimage --format=i386-pc --output=core.img --prefix='(pxe)/boot/grub' pxe pxecmd cat /boot/grub/pxeboot.img core.img >grub.pxe @end group @end example Copy @file{grub.pxe}, @file{/boot/grub/*.mod}, and @file{/boot/grub/*.lst} to the PXE (TFTP) server, ensuring that @file{*.mod} and @file{*.lst} are accessible via the @file{/boot/grub/} path from the TFTP server root. Set the DHCP server configuration to offer @file{grub.pxe} as the boot file (the @samp{filename} option in ISC dhcpd). After GRUB has started, files on the TFTP server will be accessible via the @samp{(pxe)} device. The server and gateway IP address can be controlled by changing the @samp{(pxe)} device name to @samp{(pxe:@var{server-ip})} or @samp{(pxe:@var{server-ip}:@var{gateway-ip})}. Note that this should be changed both in the prefix and in any references to the device name in the configuration file. GRUB provides several environment variables which may be used to inspect or change the behaviour of the PXE device: @table @samp @item net_pxe_ip The IP address of this machine. Read-only. @item net_pxe_mac The network interface's MAC address. Read-only. @item net_pxe_hostname The client host name provided by DHCP. Read-only. @item net_pxe_domain The client domain name provided by DHCP. Read-only. @item net_pxe_rootpath The path to the client's root disk provided by DHCP. Read-only. @item net_pxe_extensionspath The path to additional DHCP vendor extensions provided by DHCP. Read-only. @item net_pxe_boot_file The boot file name provided by DHCP. Read-only. @item net_pxe_dhcp_server_name The name of the DHCP server responsible for these boot parameters. Read-only. @item net_pxe_blksize The PXE transfer block size. Read-write, defaults to 512. @item pxe_default_server The default PXE server. Read-write, although setting this is only useful before opening a PXE device. @item pxe_default_gateway The default gateway to use when contacting the PXE server. Read-write, although setting this is only useful before opening a PXE device. @end table @node Serial terminal @chapter Using GRUB via a serial line This chapter describes how to use the serial terminal support in GRUB. If you have many computers or computers with no display/keyboard, it could be very useful to control the computers through serial communications. To connect one computer with another via a serial line, you need to prepare a null-modem (cross) serial cable, and you may need to have multiport serial boards, if your computer doesn't have extra serial ports. In addition, a terminal emulator is also required, such as minicom. Refer to a manual of your operating system, for more information. As for GRUB, the instruction to set up a serial terminal is quite simple. First of all, make sure that you haven't specified the option @option{--disable-serial} to the configure script when you built your GRUB images. If you get them in binary form, probably they have serial terminal support already. Then, initialize your serial terminal after GRUB starts up. Here is an example: @example @group grub> @kbd{serial --unit=0 --speed=9600} grub> @kbd{terminal serial} @end group @end example The command @command{serial} initializes the serial unit 0 with the speed 9600bps. The serial unit 0 is usually called @samp{COM1}, so, if you want to use COM2, you must specify @samp{--unit=1} instead. This command accepts many other options, so please refer to @ref{serial}, for more details. The commands @command{terminal_input} (@pxref{terminal_input}) and @command{terminal_output} (@pxref{terminal_output} choose which type of terminal you want to use. In the case above, the terminal will be a serial terminal, but you can also pass @code{console} to the command, as @samp{terminal serial console}. In this case, a terminal in which you press any key will be selected as a GRUB terminal. However, note that GRUB assumes that your terminal emulator is compatible with VT100 by default. This is true for most terminal emulators nowadays, but you should pass the option @option{--dumb} to the command if your terminal emulator is not VT100-compatible or implements few VT100 escape sequences. If you specify this option then GRUB provides you with an alternative menu interface, because the normal menu requires several fancy features of your terminal. @node Vendor power-on keys @chapter Using GRUB with vendor power-on keys Some laptop vendor provide an additional power-on button which boots another OS. GRUB supports such buttons with GRUB_TIMEOUT_BUTTON, GRUB_DEFAULT_BUTTON, GRUB_HIDDEN_TIMEOUT_BUTTON and GRUB_BUTTON_CMOS_ADDRESS variables in default/grub. GRUB_TIMEOUT_BUTTON, GRUB_DEFAULT_BUTTON and GRUB_HIDDEN_TIMEOUT_BUTTON are used instead of corresponding variables without _BUTTON suffix when powered using special button. GRUB_BUTTON_CMOS_ADDRESS is vendor specific and partially model-specific. Values known to GRUB team are: @table @key @item Dell XPS M1530 85:3 @item Asus EeePC 1005PE 84:1 (unconfirmed) @end table To take full advantage of this function install GRUB into MBR. @node Filesystem @chapter Filesystem syntax and semantics GRUB uses a special syntax for specifying disk drives which can be accessed by BIOS. Because of BIOS limitations, GRUB cannot distinguish between IDE, ESDI, SCSI, or others. You must know yourself which BIOS device is equivalent to which OS device. Normally, that will be clear if you see the files in a device or use the command @command{search} (@pxref{search}). @menu * Device syntax:: How to specify devices * File name syntax:: How to specify files * Block list syntax:: How to specify block lists @end menu @node Device syntax @section How to specify devices The device syntax is like this: @example @code{(@var{device}[,@var{part-num}][,@var{bsd-subpart-letter}])} @end example @samp{[]} means the parameter is optional. @var{device} should be either @samp{fd} or @samp{hd} followed by a digit, like @samp{fd0}. But you can also set @var{device} to a hexadecimal or a decimal number which is a BIOS drive number, so the following are equivalent: @example (hd0) (0x80) (128) @end example @var{part-num} represents the partition number of @var{device}, starting from one for primary partitions and from five for extended partitions, and @var{bsd-subpart-letter} represents the BSD disklabel subpartition, such as @samp{a} or @samp{e}. A shortcut for specifying BSD subpartitions is @code{(@var{device},@var{bsd-subpart-letter})}, in this case, GRUB searches for the first PC partition containing a BSD disklabel, then finds the subpartition @var{bsd-subpart-letter}. Here is an example: @example (hd0,a) @end example The syntax @samp{(hd0)} represents using the entire disk (or the MBR when installing GRUB), while the syntax @samp{(hd0,1)} represents using the first partition of the disk (or the boot sector of the partition when installing GRUB). If you enabled the network support, the special drive @samp{(pxe)} is also available. Before using the network drive, you must initialize the network. @xref{Network}, for more information. If you boot GRUB from a CD-ROM, @samp{(cd)} is available. @xref{Making a GRUB bootable CD-ROM}, for details. @node File name syntax @section How to specify files There are two ways to specify files, by @dfn{absolute file name} and by @dfn{block list}. An absolute file name resembles a Unix absolute file name, using @samp{/} for the directory separator (not @samp{\} as in DOS). One example is @samp{(hd0,1)/boot/grub/grub.cfg}. This means the file @file{/boot/grub/grub.cfg} in the first partition of the first hard disk. If you omit the device name in an absolute file name, GRUB uses GRUB's @dfn{root device} implicitly. So if you set the root device to, say, @samp{(hd1,1)} by the command @samp{set root=(hd1,1)} (@pxref{set}), then @code{/boot/kernel} is the same as @code{(hd1,1)/boot/kernel}. @node Block list syntax @section How to specify block lists A block list is used for specifying a file that doesn't appear in the filesystem, like a chainloader. The syntax is @code{[@var{offset}]+@var{length}[,[@var{offset}]+@var{length}]@dots{}}. Here is an example: @example @code{0+100,200+1,300+300} @end example This represents that GRUB should read blocks 0 through 99, block 200, and blocks 300 through 599. If you omit an offset, then GRUB assumes the offset is zero. Like the file name syntax (@pxref{File name syntax}), if a blocklist does not contain a device name, then GRUB uses GRUB's @dfn{root device}. So @code{(hd0,2)+1} is the same as @code{+1} when the root device is @samp{(hd0,2)}. @node Interface @chapter GRUB's user interface GRUB has both a simple menu interface for choosing preset entries from a configuration file, and a highly flexible command-line for performing any desired combination of boot commands. GRUB looks for its configuration file as soon as it is loaded. If one is found, then the full menu interface is activated using whatever entries were found in the file. If you choose the @dfn{command-line} menu option, or if the configuration file was not found, then GRUB drops to the command-line interface. @menu * Command-line interface:: The flexible command-line interface * Menu interface:: The simple menu interface * Menu entry editor:: Editing a menu entry @end menu @node Command-line interface @section The flexible command-line interface The command-line interface provides a prompt and after it an editable text area much like a command-line in Unix or DOS. Each command is immediately executed after it is entered@footnote{However, this behavior will be changed in the future version, in a user-invisible way.}. The commands (@pxref{Command-line and menu entry commands}) are a subset of those available in the configuration file, used with exactly the same syntax. Cursor movement and editing of the text on the line can be done via a subset of the functions available in the Bash shell: @table @key @item C-f @itemx PC right key Move forward one character. @item C-b @itemx PC left key Move back one character. @item C-a @itemx HOME Move to the start of the line. @item C-e @itemx END Move the the end of the line. @item C-d @itemx DEL Delete the character underneath the cursor. @item C-h @itemx BS Delete the character to the left of the cursor. @item C-k Kill the text from the current cursor position to the end of the line. @item C-u Kill backward from the cursor to the beginning of the line. @item C-y Yank the killed text back into the buffer at the cursor. @item C-p @itemx PC up key Move up through the history list. @item C-n @itemx PC down key Move down through the history list. @end table When typing commands interactively, if the cursor is within or before the first word in the command-line, pressing the @key{TAB} key (or @key{C-i}) will display a listing of the available commands, and if the cursor is after the first word, the @kbd{@key{TAB}} will provide a completion listing of disks, partitions, and file names depending on the context. Note that to obtain a list of drives, one must open a parenthesis, as @command{root (}. Note that you cannot use the completion functionality in the TFTP filesystem. This is because TFTP doesn't support file name listing for the security. @node Menu interface @section The simple menu interface The menu interface is quite easy to use. Its commands are both reasonably intuitive and described on screen. Basically, the menu interface provides a list of @dfn{boot entries} to the user to choose from. Use the arrow keys to select the entry of choice, then press @key{RET} to run it. An optional timeout is available to boot the default entry (the first one if not set), which is aborted by pressing any key. Commands are available to enter a bare command-line by pressing @key{c} (which operates exactly like the non-config-file version of GRUB, but allows one to return to the menu if desired by pressing @key{ESC}) or to edit any of the @dfn{boot entries} by pressing @key{e}. If you protect the menu interface with a password (@pxref{Security}), all you can do is choose an entry by pressing @key{RET}, or press @key{p} to enter the password. @node Menu entry editor @section Editing a menu entry The menu entry editor looks much like the main menu interface, but the lines in the menu are individual commands in the selected entry instead of entry names. If an @key{ESC} is pressed in the editor, it aborts all the changes made to the configuration entry and returns to the main menu interface. When a particular line is selected, the editor places the user in a special version of the GRUB command-line to edit that line. When the user hits @key{RET}, GRUB replaces the line in question in the boot entry with the changes (unless it was aborted via @key{ESC}, in which case the changes are thrown away). If you want to add a new line to the menu entry, press @key{o} if adding a line after the current line or press @key{O} if before the current line. To delete a line, hit the key @key{d}. Although GRUB unfortunately does not support @dfn{undo}, you can do almost the same thing by just returning to the main menu. @node Commands @chapter The list of available commands In this chapter, we list all commands that are available in GRUB. Commands belong to different groups. A few can only be used in the global section of the configuration file (or ``menu''); most of them can be entered on the command-line and can be used either anywhere in the menu or specifically in the menu entries. @menu * Menu-specific commands:: * General commands:: * Command-line and menu entry commands:: @end menu @node Menu-specific commands @section The list of commands for the menu only The semantics used in parsing the configuration file are the following: @itemize @bullet @item The menu-specific commands have to be used before any others. @item The files @emph{must} be in plain-text format. @item @samp{#} at the beginning of a line in a configuration file means it is only a comment. @item Options are separated by spaces. @item All numbers can be either decimal or hexadecimal. A hexadecimal number must be preceded by @samp{0x}, and is case-insensitive. @item Extra options or text at the end of the line are ignored unless otherwise specified. @item Unrecognized commands are added to the current entry, except before entries start, where they are ignored. @end itemize These commands can only be used in the menu: @menu * menuentry:: Start a menu entry @end menu @node menuentry @subsection menuentry @deffn Command title name @dots{} Start a new boot entry, and set its name to the contents of the rest of the line, starting with the first non-space character. @end deffn @node General commands @section 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 @end menu @node serial @subsection serial @deffn Command serial [@option{--unit=unit}] [@option{--port=port}] [@option{--speed=speed}] [@option{--word=word}] [@option{--parity=parity}] [@option{--stop=stop}] Initialize a serial device. @var{unit} is a number in the range 0-3 specifying which serial port to use; default is 0, which corresponds to the port often called COM1. @var{port} is the I/O port where the UART is to be found; if specified it takes precedence over @var{unit}. @var{speed} is the transmission speed; default is 9600. @var{word} and @var{stop} are the number of data bits and stop bits. Data bits must be in the range 5-8 and stop bits must be 1 or 2. Default is 8 data bits and one stop bit. @var{parity} is one of @samp{no}, @samp{odd}, @samp{even} and defaults to @samp{no}. The serial port is not used as a communication channel unless the @command{terminal_input} or @command{terminal_output} command is used (@pxref{terminal_input}, @pxref{terminal_output}). This command is only available if GRUB is compiled with serial support. See also @ref{Serial terminal}. @end deffn @node terminal_input @subsection terminal_input @deffn Command terminal_input [@option{--append}|@option{--remove}] @ [terminal1] [terminal2] @dots{} List or select an input terminal. With no arguments, list the active and available input terminals. With @option{--append}, add the named terminals to the list of active input terminals; any of these may be used to provide input to GRUB. With @option{--remove}, remove the named terminals from the active list. With no options but a list of terminal names, make only the listed terminal names active. @end deffn @node terminal_output @subsection terminal_output @deffn Command terminal_output [@option{--append}|@option{--remove}] @ [terminal1] [terminal2] @dots{} List or select an output terminal. With no arguments, list the active and available output terminals. With @option{--append}, add the named terminals to the list of active output terminals; all of these will receive output from GRUB. With @option{--remove}, remove the named terminals from the active list. With no options but a list of terminal names, make only the listed terminal names active. @end deffn @node terminfo @subsection terminfo @deffn Command terminfo [term] Define the capabilities of your terminal by giving the name of an entry in the terminfo database, which should correspond roughly to a @samp{TERM} environment variable in Unix. At the moment, only @samp{vt100} is supported in GRUB 2. If you need other terminal types, please contact us to discuss the best way to include support for these in GRUB. If no option is specified, the current terminal type is printed. @end deffn @node Command-line and menu entry commands @section The list of command-line and menu entry commands These commands are usable in the command-line and in menu entries. If you forget a command, you can run the command @command{help} (@pxref{help}). @menu * acpi:: Load ACPI tables * blocklist:: Print a block list * boot:: Start up your operating system * cat:: Show the contents of a file * chainloader:: Chain-load another boot loader * cmp:: Compare two files * configfile:: Load a configuration file * crc:: Calculate CRC32 checksums * date:: Display or set current date and time * drivemap:: Map a drive to another * echo:: Display a line of text * export:: Export an environment variable * gettext:: Translate a string * gptsync:: Fill an MBR based on GPT entries * halt:: Shut down your computer * help:: Show help messages * insmod:: Insert a module * keystatus:: Check key modifier status * ls:: List devices or files * parttool:: Modify partition table entries * password:: Set a clear-text password * password_pbkdf2:: Set a hashed password * play:: Play a tune * pxe_unload:: Unload the PXE environment * reboot:: Reboot your computer * search:: Search devices by file, label, or UUID * set:: Set an environment variable * unset:: Unset an environment variable * uppermem:: Set the upper memory size @end menu @node acpi @subsection acpi @deffn Command acpi [@option{-1}|@option{-2}] @ [@option{--exclude=table1,@dots{}}|@option{--load-only=table1,@dots{}}] @ [@option{--oemid=id}] [@option{--oemtable=table}] @ [@option{--oemtablerev=rev}] [@option{--oemtablecreator=creator}] @ [@option{--oemtablecreatorrev=rev}] [@option{--no-ebda}] @ filename @dots{} Modern BIOS systems normally implement the Advanced Configuration and Power Interface (ACPI), and define various tables that describe the interface between an ACPI-compliant operating system and the firmware. In some cases, the tables provided by default only work well with certain operating systems, and it may be necessary to replace some of them. Normally, this command will replace the Root System Description Pointer (RSDP) in the Extended BIOS Data Area to point to the new tables. If the @option{--no-ebda} option is used, the new tables will be known only to GRUB, but may be used by GRUB's EFI emulation. @end deffn @node blocklist @subsection blocklist @deffn Command blocklist file Print a block list (@pxref{Block list syntax}) for @var{file}. @end deffn @node boot @subsection boot @deffn Command boot Boot the OS or chain-loader which has been loaded. Only necessary if running the fully interactive command-line (it is implicit at the end of a menu entry). @end deffn @node cat @subsection cat @deffn Command cat file Display the contents of the file @var{file}. This command may be useful to remind you of your OS's root partition: @example grub> @kbd{cat /etc/fstab} @end example @end deffn @node chainloader @subsection chainloader @deffn Command chainloader [@option{--force}] file Load @var{file} as a chain-loader. Like any other file loaded by the filesystem code, it can use the blocklist notation (@pxref{Block list syntax}) to grab the first sector of the current partition with @samp{+1}. If you specify the option @option{--force}, then load @var{file} forcibly, whether it has a correct signature or not. This is required when you want to load a defective boot loader, such as SCO UnixWare 7.1. @end deffn @node cmp @subsection cmp @deffn Command cmp file1 file2 Compare the file @var{file1} with the file @var{file2}. If they differ in size, print the sizes like this: @example Differ in size: 0x1234 [foo], 0x4321 [bar] @end example If the sizes are equal but the bytes at an offset differ, then print the bytes like this: @example Differ at the offset 777: 0xbe [foo], 0xef [bar] @end example If they are completely identical, nothing will be printed. @end deffn @node configfile @subsection configfile @deffn Command configfile file Load @var{file} as a configuration file. @end deffn @node crc @subsection crc @deffn Command crc file Display the CRC32 checksum of @var{file}. @end deffn @node date @subsection date @deffn Command date [[year-]month-day] [hour:minute[:second]] With no arguments, print the current date and time. Otherwise, take the current date and time, change any elements specified as arguments, and set the result as the new date and time. For example, `date 01-01' will set the current month and day to January 1, but leave the year, hour, minute, and second unchanged. @end deffn @node drivemap @subsection drivemap @deffn Command drivemap @option{-l}|@option{-r}|[@option{-s}] @ from_drive to_drive Without options, map the drive @var{from_drive} to the drive @var{to_drive}. This is necessary when you chain-load some operating systems, such as DOS, if such an OS resides at a non-first drive. For convenience, any partition suffix on the drive is ignored, so you can safely use @verb{'${root}'} as a drive specification. With the @option{-s} option, perform the reverse mapping as well, swapping the two drives. With the @option{-l} option, list the current mappings. With the @option{-r} option, reset all mappings to the default values. For example: @example drivemap -s (hd0) (hd1) @end example @end deffn @node echo @subsection echo @deffn Command echo [@option{-n}] [@option{-e}] string @dots{} Display the requested text and, unless the @option{-n} option is used, a trailing new line. If there is more than one string, they are separated by spaces in the output. As usual in GRUB commands, variables may be substituted using @samp{$@{var@}}. The @option{-e} option enables interpretation of backslash escapes. The following sequences are recognised: @table @code @item \\ backslash @item \a alert (BEL) @item \c suppress trailing new line @item \f form feed @item \n new line @item \r carriage return @item \t horizontal tab @item \v vertical tab @end table When interpreting backslash escapes, backslash followed by any other character will print that character. @end deffn @node export @subsection export @deffn Command export envvar Export the environment variable @var{envvar}. Exported variables are visible to subsidiary configuration files loaded using @command{configfile}. @end deffn @node gettext @subsection gettext @deffn Command gettext string Translate @var{string} into the current language. The current language code is stored in the @samp{lang} variable in GRUB's environment. Translation files in MO format are read from @samp{locale_dir}, usually @file{/boot/grub/locale}. @end deffn @node gptsync @subsection gptsync @deffn Command gptsync device [partition[+/-[type]]] @dots{} 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 @var{partition} entries on @var{device}. Up to three partitions may be used. @var{type} is an MBR partition type code; prefix with @samp{0x} if you want to enter this in hexadecimal. The separator between @var{partition} and @var{type} may be @samp{+} to make the partition active, or @samp{-} to make it inactive; only one partition may be active. If both the separator and type are omitted, then the partition will be inactive. @end deffn @node halt @subsection halt @deffn Command halt @option{--no-apm} The command halts the computer. If the @option{--no-apm} option is specified, no APM BIOS call is performed. Otherwise, the computer is shut down using APM. @end deffn @node help @subsection help @deffn Command help [pattern @dots{}] Display helpful information about builtin commands. If you do not specify @var{pattern}, this command shows short descriptions of all available commands. If you specify any @var{patterns}, it displays longer information about each of the commands whose names begin with those @var{patterns}. @end deffn @node insmod @subsection insmod @deffn Command insmod module Insert the dynamic GRUB module called @var{module}. @end deffn @node keystatus @subsection keystatus @deffn Command keystatus [@option{--shift}] [@option{--ctrl}] [@option{--alt}] Return true if the Shift, Control, or Alt modifier keys are held down, as requested by options. This is useful in scripting, to allow some user control over behaviour without having to wait for a keypress. Checking key modifier status is only supported on some platforms. If invoked without any options, the @command{keystatus} command returns true if and only if checking key modifier status is supported. @end deffn @node ls @subsection ls @deffn 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 (@pxref{Device syntax}), then list all files at the root directory of that device. If the argument is a directory given as an absolute file name (@pxref{File name syntax}), then list the contents of that directory. @end deffn @node parttool @subsection parttool @deffn Command parttool partition commands Make various modifications to partition table entries. Each @var{command} is either a boolean option, in which case it must be followed with @samp{+} or @samp{-} (with no intervening space) to enable or disable that option, or else it takes a value in the form @samp{@var{command}=@var{value}}. Currently, @command{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: @table @asis @item @samp{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 @emph{primary} partitions. @item @samp{type} (value) Change the type of an existing partition. The value must be a number in the range 0-0xFF (prefix with @samp{0x} to enter it in hexadecimal). @item @samp{hidden} (boolean) When enabled, this hides the selected partition by setting the @dfn{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 @ref{DOS/Windows}. @end table @end deffn @node password @subsection password @deffn Command password user clear-password Define a user named @var{user} with password @var{clear-password}. @xref{Security}. @end deffn @node password_pbkdf2 @subsection password_pbkdf2 @deffn Command password_pbkdf2 user hashed-password Define a user named @var{user} with password hash @var{hashed-password}. Use @command{grub-mkpasswd-pbkdf2} (@pxref{Invoking grub-mkpasswd-pbkdf2}) to generate password hashes. @xref{Security}. @end deffn @node play @subsection play @deffn Command play file | tempo [pitch1 duration1] [pitch2 duration2] ... Plays a tune If the argument is a file name (@pxref{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. @end deffn @node pxe_unload @subsection pxe_unload @deffn Command pxe_unload Unload the PXE environment (@pxref{Network}). This command is only available on PC BIOS systems. @end deffn @node reboot @subsection reboot @deffn Command reboot Reboot the computer. @end deffn @node search @subsection search @deffn Command search @ [@option{--file}|@option{--label}|@option{--fs-uuid}] @ [@option{--set} var] [@option{--no-floppy}] name Search devices by file (@option{-f}, @option{--file}), filesystem label (@option{-l}, @option{--label}), or filesystem UUID (@option{-u}, @option{--fs-uuid}). If the @option{--set} option is used, the first device found is set as the value of environment variable @var{var}. The default variable is @samp{root}. The @option{--no-floppy} option prevents searching floppy devices, which can be slow. The @samp{search.file}, @samp{search.fs_label}, and @samp{search.fs_uuid} commands are aliases for @samp{search --file}, @samp{search --label}, and @samp{search --fs-uuid} respectively. @end deffn @node set @subsection set @deffn Command set [envvar=value] Set the environment variable @var{envvar} to @var{value}. If invoked with no arguments, print all environment variables with their values. @end deffn @node unset @subsection unset @deffn Command unset envvar Unset the environment variable @var{envvar}. @end deffn @node uppermem @subsection uppermem This command is not yet implemented for GRUB 2, although it is planned. @node Security @chapter Authentication and authorisation By default, the boot loader interface is accessible to anyone with physical access to the console: anyone can select and edit any menu entry, and anyone can get direct access to a GRUB shell prompt. For most systems, this is reasonable since anyone with direct physical access has a variety of other ways to gain full access, and requiring authentication at the boot loader level would only serve to make it difficult to recover broken systems. However, in some environments, such as kiosks, it may be appropriate to lock down the boot loader to require authentication before performing certain operations. The @samp{password} (@pxref{password}) and @samp{password_pbkdf2} (@pxref{password_pbkdf2}) commands can be used to define users, each of which has an associated password. @samp{password} sets the password in plain text, requiring @file{grub.cfg} to be secure; @samp{password_pbkdf2} sets the password hashed using the Password-Based Key Derivation Function (RFC 2898), requiring the use of @command{grub-mkpasswd-pbkdf2} (@pxref{Invoking grub-mkpasswd-pbkdf2}) to generate password hashes. In order to enable authentication support, the @samp{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 @samp{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 @option{--users} option to the @samp{menuentry} command (@pxref{menuentry}). If the @option{--users} option is not used for a menu entry, then that entry is unrestricted. Putting this together, a typical @file{grub.cfg} fragment might look like this: @example @group set superusers="root" password_pbkdf2 root grub.pbkdf2.sha512.10000.biglongstring password user1 insecure menuentry "May be run by any user" @{ set root=(hd0,1) linux /vmlinuz @} menuentry "Superusers only" --users "" @{ set root=(hd0,1) linux /vmlinuz single @} menuentry "May be run by user1 or a superuser" --users user1 @{ set root=(hd0,2) chainloader +1 @} @end group @end example The @command{grub-mkconfig} program does not yet have built-in support for generating configuration files with authentication. You can use @file{/etc/grub.d/40_custom} to add simple superuser authentication, by adding @kbd{set superusers=} and @kbd{password} or @kbd{password_pbkdf2} commands. @node Troubleshooting @chapter Error messages produced by GRUB @menu * GRUB only offers a rescue shell:: @end menu @node GRUB only offers a rescue shell @section GRUB only offers a rescue shell GRUB's normal start-up procedure involves setting the @samp{prefix} environment variable to a value set in the core image by @command{grub-install}, setting the @samp{root} variable to match, loading the @samp{normal} module from the prefix, and running the @samp{normal} command. This command is responsible for reading @file{/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 @samp{normal} module for some reason. It may be possible to work around this temporarily: for instance, if the reason for the failure is that @samp{prefix} is wrong (perhaps it refers to the wrong device, or perhaps the path to @file{/boot/grub} was not correctly made relative to the device), then you can correct this and enter normal mode manually: @example @group # Inspect the current prefix (and other preset variables): set # Set to the correct value, which might be something like this: set prefix=(hd0,1)/grub set root=(hd0,1) insmod normal normal @end group @end example 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 @kbd{grub-install @var{device}} (@pxref{Invoking grub-install}). When doing this, there are a few things to remember: @itemize @bullet{} @item 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. @samp{/dev/sda}) is the one that your firmware will boot from. @item At least on BIOS systems, if you tell @command{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. @item 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. @item Check that GRUB actually knows how to read from the device and file system containing @file{/boot/grub}. It will not be able to read from encrypted devices, nor from file systems for which support has not yet been added to GRUB. @end itemize @node Invoking grub-install @chapter Invoking grub-install The program @command{grub-install} installs GRUB on your drive using @command{grub-mkimage} and (on some platforms) @command{grub-setup}. You must specify the device name on which you want to install GRUB, like this: @example grub-install @var{install_device} @end example The device name @var{install_device} is an OS device name or a GRUB device name. @command{grub-install} accepts the following options: @table @option @item --help Print a summary of the command-line options and exit. @item --version Print the version number of GRUB and exit. @item --root-directory=@var{dir} Install GRUB images under the directory @var{dir} instead of the root directory. This option is useful when you want to install GRUB into a separate partition or a removable disk. Here is an example in which you have a separate @dfn{boot} partition which is mounted on @file{/boot}: @example @kbd{grub-install --root-directory=/boot hd0} @end example @item --recheck Recheck the device map, even if @file{/boot/grub/device.map} already exists. You should use this option whenever you add/remove a disk into/from your computer. @end table @node Invoking grub-mkconfig @chapter Invoking grub-mkconfig The program @command{grub-mkconfig} generates a configuration file for GRUB (@pxref{Simple configuration}). @example grub-mkconfig -o /boot/grub/grub.cfg @end example @command{grub-mkconfig} accepts the following options: @table @option @item --help Print a summary of the command-line options and exit. @item --version Print the version number of GRUB and exit. @item -o @var{file} @itemx --output=@var{file} Send the generated configuration file to @var{file}. The default is to send it to standard output. @end table @node Invoking grub-mkpasswd-pbkdf2 @chapter Invoking grub-mkpasswd-pbkdf2 The program @command{grub-mkpasswd-pbkdf2} generates password hashes for GRUB (@pxref{Security}). @example grub-mkpasswd-pbkdf2 @end example @command{grub-mkpasswd-pbkdf2} accepts the following options: @table @option @item -c @var{number} @itemx --iteration-count=@var{number} Number of iterations of the underlying pseudo-random function. Defaults to 10000. @item -l @var{number} @itemx --buflen=@var{number} Length of the generated hash. Defaults to 64. @item -s @var{number} @itemx --salt=@var{number} Length of the salt. Defaults to 64. @end table @node Obtaining and Building GRUB @appendix How to obtain and build GRUB @quotation @strong{Caution:} GRUB requires binutils-2.9.1.0.23 or later because the GNU assembler has been changed so that it can produce real 16bits machine code between 2.9.1 and 2.9.1.0.x. See @uref{http://sources.redhat.com/binutils/}, to obtain information on how to get the latest version. @end quotation GRUB is available from the GNU alpha archive site @uref{ftp://alpha.gnu.org/gnu/grub} or any of its mirrors. The file will be named grub-version.tar.gz. The current version is @value{VERSION}, so the file you should grab is: @uref{ftp://alpha.gnu.org/gnu/grub/grub-@value{VERSION}.tar.gz} To unbundle GRUB use the instruction: @example @kbd{zcat grub-@value{VERSION}.tar.gz | tar xvf -} @end example which will create a directory called @file{grub-@value{VERSION}} with all the sources. You can look at the file @file{INSTALL} for detailed instructions on how to build and install GRUB, but you should be able to just do: @example @group @kbd{cd grub-@value{VERSION}} @kbd{./configure} @kbd{make install} @end group @end example Also, the latest version is available using Bazaar. See @uref{http://www.gnu.org/software/grub/grub-download.en.html} for more information. @node Reporting bugs @appendix Reporting bugs These are the guideline for how to report bugs. Take a look at this list below before you submit bugs: @enumerate @item Before getting unsettled, read this manual through and through. Also, see the @uref{http://www.gnu.org/software/grub/grub-faq.html, GNU GRUB FAQ}. @item 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. @item If you have trouble with the installation, inform us of how you installed GRUB. Don't omit error messages, if any. Just @samp{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. @item If GRUB cannot boot your operating system, write down @emph{everything} you see on the screen. Don't paraphrase them, like @samp{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. @item Explain what you wanted to do. It is very useful to know your purpose and your wish, and how GRUB didn't satisfy you. @item 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. @item Write down anything that you think might be related. Please understand that we often need to reproduce the same problem you encounterred in our environment. So your information should be sufficient for us to do the same thing---Don't forget that we cannot see your computer directly. If you are not sure whether to state a fact or leave it out, state it! Reporting too many things is much better than omitting something important. @end enumerate If you follow the guideline above, submit a report to the @uref{http://savannah.gnu.org/bugs/?group=grub, Bug Tracking System}. Alternatively, you can submit a report via electronic mail to @email{bug-grub@@gnu.org}, but we strongly recommend that you use the Bug Tracking System, because e-mail can be passed over easily. Once we get your report, we will try to fix the bugs. @node Future @appendix Where GRUB will go We started the next generation of GRUB, GRUB 2. GRUB 2 includes internationalization, dynamic module loading, real memory management, multiple architecture support, a scripting language, and many other nice feature. If you are interested in the development of GRUB 2, take a look at @uref{http://www.gnu.org/software/grub/grub.html, the homepage}. @node Internals @appendix Hacking GRUB @menu * Getting the source code:: * Finding your way around:: @end menu @node Getting the source code @section Getting the source code GRUB is maintained using the @uref{http://bazaar-vcs.org/, Bazaar revision control system}. To fetch the primary development branch: @example bzr get http://bzr.savannah.gnu.org/r/grub/trunk/grub @end example The GRUB developers maintain several other branches with work in progress. Of these, the most interesting is the experimental branch, which is a staging area for new code which we expect to eventually merge into trunk but which is not yet ready: @example bzr get http://bzr.savannah.gnu.org/r/grub/branches/experimental @end example Once you have used @kbd{bzr get} to fetch an initial copy of a branch, you can use @kbd{bzr pull} to keep it up to date. If you have modified your local version, you may need to resolve conflicts when pulling. @node Finding your way around @section Finding your way around Here is a brief map of the GRUB code base. GRUB uses Autoconf, but not (yet) Automake. The top-level build rules are in @file{configure.ac}, @file{Makefile.in}, and @file{conf/*.rmk}. Each @file{conf/*.rmk} file represents a particular target configuration, and is processed into GNU Make rules by @file{genmk.rb} (which you only need to look at if you are extending the build system). If you are adding a new module which follows an existing pattern, such as a new command or a new filesystem implementation, it is usually easiest to grep @file{conf/*.rmk} for an existing example of that pattern to find out where it should be added. Low-level boot code, such as the MBR implementation on PC BIOS systems, is in the @file{boot/} directory. The GRUB kernel is in @file{kern/}. This contains core facilities such as the device, disk, and file frameworks, environment variable handling, list processing, and so on. The kernel should contain enough to get up to a rescue prompt. Header files for kernel facilities, among others, are in @file{include/}. Terminal implementations are in @file{term/}. Disk access code is spread across @file{disk/} (for accessing the disk devices themselves), @file{partmap/} (for interpreting partition table data), and @file{fs/} (for accessing filesystems). Note that, with the odd specialised exception, GRUB only contains code to @emph{read} from filesystems and tries to avoid containing any code to @emph{write} to filesystems; this lets us confidently assure users that GRUB cannot be responsible for filesystem corruption. PCI and USB bus handling is in @file{bus/}. Video handling code is in @file{video/}. The graphical menu system uses this heavily, but is in a separate directory, @file{gfxmenu/}. Most commands are implemented by files in @file{commands/}, with the following exceptions: @itemize @item A few core commands live in @file{kern/corecmd.c}. @item Commands related to normal mode live under @file{normal/}. @item Commands that load and boot kernels live under @file{loader/}. @item The @samp{loopback} command is really a disk device, and so lives in @file{disk/loopback.c}. @item The @samp{gettext} command lives under @file{gettext/}. @item The @samp{loadfont} and @samp{lsfonts} commands live under @file{font/}. @item The @samp{serial}, @samp{terminfo}, and @samp{background_image} commands live under @file{term/}. @item The @samp{efiemu_*} commands live under @file{efiemu/}. @end itemize There are a few other special-purpose exceptions; grep for them if they matter to you. @node Copying This Manual @appendix Copying This Manual @menu * GNU Free Documentation License:: License for copying this manual. @end menu @include fdl.texi @node Index @unnumbered Index @c Currently, we use only the Concept Index. @printindex cp @bye Some notes: This is an attempt to make a manual for GRUB 2. The contents are copied from the GRUB manual in GRUB Legacy, so they are not always appropriate yet for GRUB 2.