Table of ContentsGNU GRUB manualThis is the documentation of GNU GRUB, the GRand Unified Bootloader, a flexible and powerful boot loader program for a wide range of architectures. Show
This edition documents version 2.06. This manual is for GNU GRUB (version 2.06, 10 May 2021). Copyright © 1999,2000,2001,2002,2004,2006,2008,2009,2010,2011,2012,2013 Free Software Foundation, Inc.
1 Introduction to GRUB1.1 OverviewBriefly, 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-loading1. 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 (see Command-line interface), or a menu interface (see 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 (see 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 (see Naming convention) to GRUB, how to install GRUB on your drive (see Installation), and how to boot your OSes (see Booting), step by step. 1.2 History of GRUBGRUB 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 (see Motivation in 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. See 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. 1.3 Differences from previous versionsGRUB 2 is a rewrite of GRUB (see 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.
1.4 GRUB featuresThe primary requirement for GRUB is that it be compliant with the Multiboot Specification, which is described in Motivation in The Multiboot Specification. The other goals, listed in approximate order of importance, are:
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 formatsSupport many of the a.out variants plus ELF. Symbol tables are also loaded. Support non-Multiboot kernelsSupport many of the various free 32-bit kernels that lack Multiboot compliance (primarily FreeBSD, NetBSD2, OpenBSD, and Linux). Chain-loading of other boot loaders is also supported. Load multiples modulesFully support the Multiboot feature of loading multiple modules. Load a configuration fileSupport 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 (see Commands) are a superset of those supported on the command-line. An example configuration file is provided in Configuration. Provide a menu interfaceA menu interface listing preset boot commands, with a programmable timeout, is available. There is no fixed limit on the number of boot entries, and the current implementation has space for several hundred. Have a flexible command-line interfaceA 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 (see Commands) are a subset of those supported for configuration files. Editing commands closely resembles the Bash command-line (see Command Line Editing in Bash Features), with TAB-completion of commands, devices, partitions, and files in a directory depending on context. Support multiple filesystem typesSupport multiple filesystem types transparently, plus a useful explicit blocklist notation. The currently supported filesystem types are Amiga Fast FileSystem (AFFS), AtheOS fs, BeFS, BtrFS (including raid0, raid1, raid10, gzip and lzo), cpio (little- and big-endian bin, odc and newc variants), Linux ext2/ext3/ext4, DOS FAT12/FAT16/FAT32, exFAT, F2FS, HFS, HFS+, ISO9660 (including Joliet, Rock-ridge and multi-chunk files), JFS, Minix fs (versions 1, 2 and 3), nilfs2, NTFS (including compression), ReiserFS, ROMFS, Amiga Smart FileSystem (SFS), Squash4, tar, UDF, BSD UFS/UFS2, XFS, and ZFS (including lzjb, gzip, zle, mirror, stripe, raidz1/2/3 and encryption in AES-CCM and AES-GCM). See Filesystem, for more information. Support automatic decompressionCan decompress files which were compressed by 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 deviceSupport reading data from any or all floppies or hard disk(s) recognized by the BIOS, independent of the setting of the root device. Be independent of drive geometry translationsUnlike 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 RAMGRUB 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 (see Motivation in The Multiboot Specification), not all kernels make use of this information, but GRUB provides it for those who do. Support Logical Block Address modeIn 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 bootingGRUB is basically a disk-based boot loader but also has network support. You can load OS images from a network by using the TFTP protocol. Support remote terminalsTo 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. 1.5 The role of a boot loaderThe following is a quotation from Gordon Matzigkeit, a GRUB fanatic:
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. 2 Naming conventionThe 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: 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. 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. 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. 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 (see Command-line interface) options have argument completion. This means that, for example, you only need to type 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: 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. 3 OS-specific notes about grub toolsOn OS which have device nodes similar to Unix-like OS GRUB tools use the OS name. E.g. for GNU/Linux: On AROS we use another syntax. For volumes: E.g. 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. 4 InstallationIn order to install GRUB as your boot loader, you need to first install the GRUB system and utilities under your UNIX-like operating system (see 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 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. 4.1 Installing GRUB using grub-installFor information on where GRUB should be installed on PC BIOS platforms, see BIOS installation. In order to install GRUB under a UNIX-like OS (such as GNU), invoke the
program 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: Likewise, under GNU/Hurd, this has the same effect: But all the above examples assume that GRUB should put images under the /boot directory. If you want GRUB to put images under a directory other than /boot, you need to specify the option --boot-directory. The typical usage is that you create a GRUB boot floppy with a filesystem. Here is an example: # mke2fs /dev/fd0 # mount -t ext2 /dev/fd0 /mnt # mkdir /mnt/boot # grub-install --boot-directory=/mnt/boot /dev/fd0 # umount /mnt Some BIOSes have a bug of exposing the first partition of a USB drive as a floppy instead of exposing the USB drive as a hard disk (they call it “USB-FDD” boot). In such cases, you need to install like this: # losetup /dev/loop0 /dev/sdb1 # mount /dev/loop0 /mnt/usb # grub-install --boot-directory=/mnt/usb/bugbios --force --allow-floppy /dev/loop0 This install doesn’t conflict with standard install as long as they are in separate directories. On EFI systems for fixed disk install you have to mount EFI System Partition. If you mount it at /boot/efi then you don’t need any special arguments: Otherwise you need to specify where your EFI System partition is mounted: # grub-install --efi-directory=/mnt/efi For removable installs you have to use --removable and specify both --boot-directory and --efi-directory: # grub-install --efi-directory=/mnt/usb --boot-directory=/mnt/usb/boot --removable 4.2 Making a GRUB bootable CD-ROMGRUB supports the no emulation mode in the El Torito specification6. 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 -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’: Make a directory for GRUB: If desired, make the config file grub.cfg under iso/boot/grub (see 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. 4.3 The map between BIOS drives and OS devicesIf the device map file exists, the GRUB utilities ( device is a drive specified in the GRUB syntax (see 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 ‘#’. 4.4 BIOS installationMBRThe partition table format traditionally used on PC BIOS platforms is called the Master Boot Record (MBR) format; this is the format that allows up to four primary partitions and additional logical partitions. With this partition table format, there are two ways to install GRUB: it can be embedded in the area between the MBR and the first partition (called by various names, such as the "boot track", "MBR gap", or "embedding area", and which is usually at least 1000 KiB), or the core image can be installed in a file system and a list of the blocks that make it up can be stored in the first sector of that partition. Modern tools usually leave MBR gap of at least 1023 KiB. This amount is sufficient to cover most configurations. Hence this value is recommended by the GRUB team. Historically many tools left only 31 KiB of space. This is not enough to parse reliably difficult structures like Btrfs, ZFS, RAID or LVM, or to use difficult disk access methods like ahci. Hence GRUB will warn if attempted to install into small MBR gap except in a small number of configurations that were grandfathered. The grandfathered config must: * use biosdisk as disk access module for /boot * not use any additional partition maps to access /boot * /boot must be on one of following filesystems: * AFFS, AFS, BFS, cpio, newc, odc, ext2/3/4, FAT, exFAT, F2FS, HFS, uncompressed HFS+, ISO9660, JFS, Minix, Minix2, Minix3, NILFS2, NTFS, ReiserFS, ROMFS, SFS, tar, UDF, UFS1, UFS2, XFS MBR gap has few technical problems. There is no way to reserve space in the embedding area with complete safety, and some proprietary software is known to use it to make it difficult for users to work around licensing restrictions. GRUB works it around by detecting sectors by other software and avoiding them and protecting its own sectors using Reed-Solomon encoding. GRUB team recommends having MBR gap of at least 1000 KiB Should it be not possible GRUB has support for a fallback solution which is heavily recommended against. Installing to a filesystem means that GRUB is vulnerable to its blocks being moved around by filesystem features such as tail packing, or even by aggressive fsck implementations, so this approach is quite fragile; and this approach can only be used if the /boot filesystem is on the same disk that the BIOS boots from, so that GRUB does not have to rely on guessing BIOS drive numbers. The GRUB development team generally recommends embedding GRUB before the first partition, unless you have special requirements. You must ensure that the first partition starts at least 1000 KiB (2000 sectors) from the start of the disk; on modern disks, it is often a performance advantage to align partitions on larger boundaries anyway, so the first partition might start 1 MiB from the start of the disk. GPTSome 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. 5 BootingGRUB can load Multiboot-compliant kernels in a consistent way, but for some free operating systems you need to use some OS-specific magic. 5.1 How to boot operating systemsGRUB 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. 5.1.1 How to boot an OS directly with GRUBMultiboot (see Motivation in 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 (see Chain-loading). FIXME: this section is incomplete.
However, DOS and Windows have some deficiencies, so you might have to use more complicated instructions. See DOS/Windows, for more information. 5.1.2 Chain-loading an OSOperating 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 menuentry "Windows" { insmod chain insmod ntfs set root=(hd0,1) chainloader +1 } On systems with multiple hard disks, an additional workaround may be required. See DOS/Windows. Chain-loading is only supported on PC BIOS and EFI platforms. 5.2 Loopback bootingGRUB is able to read from an image (be it one of CD or HDD) stored on any of its accessible storages (refer to see
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 5.3 Booting from LVM cache logical volumeThe LVM cache logical volume is the logical volume consisting of the original and the cache pool logical volume. The original is usually on a larger and slower storage device while the cache pool is on a smaller and faster one. The performance of the original volume can be improved by storing the frequently used data on the cache pool to utilize the greater performance of faster device. GRUB boots from LVM cache logical volume merely by reading it’s original logical volume so that dirty data in cache pool volume is disregarded. This is not a problem for "writethrough" cache mode as it ensures that any data written will be stored both on the cache and the origin LV. For the other cache mode "writeback", which delays writing from the cache pool back to the origin LV to boost performance, GRUB may fail to boot in the wake of accidental power outage due to it’s inability to assemble the cache device for reading the required dirty data left behind. The situation will be improved after adding full support to the LVM cache logical volume in the future. 5.4 Some caveats on OS-specific issuesHere, we describe some caveats on several operating systems. 5.4.1 GNU/HurdSince 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.
5.4.2 GNU/LinuxIt is relatively easy to boot GNU/Linux from GRUB, because it somewhat resembles to boot a Multiboot-compliant OS.
5.4.3 NetBSDBooting 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
5.4.4 DOS/WindowsGRUB cannot boot DOS or Windows directly, so you must chain-load them (see 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 This performs a virtual swap between your first and second hard drive. Caution: This is effective only if DOS (or Windows) uses BIOS to access the swapped disks. If that OS uses a special driver for the disks, this probably won’t work. Another problem arises if you installed more than one set of DOS/Windows onto one disk, because they could be confused if there are more than one primary partitions for DOS/Windows. Certainly you should avoid doing this, but there is a solution if you do want to do so. Use the partition hiding/unhiding technique. If GRUB hides a DOS (or Windows) partition (see parttool), DOS (or Windows) will ignore the partition. If GRUB unhides a DOS (or Windows) partition, DOS (or Windows) will detect the partition. Thus, if you have installed DOS (or Windows) on the first and the second partition of the first hard disk, and you want to boot the copy on the first partition, do the following: parttool (hd0,1) hidden- parttool (hd0,2) hidden+ set root=(hd0,1) chainloader +1 parttool ${root} boot+ boot 6 Writing your own configuration fileGRUB 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. 6.1 Simple configuration handlingThe program
The file /etc/default/grub controls the operation of GRUB_TERMINAL_INPUT="console serial" Valid keys in /etc/default/grub are as follows: ‘GRUB_DEFAULT’The default menu entry. This may be a number, in which case it identifies the Nth entry in the generated menu counted from zero, or the title of a menu entry, or the special string ‘saved’. Using the id may be useful if you want to set a menu entry as the default even though there may be a variable number of entries before it. For example, if you have: menuentry 'Example GNU/Linux distribution' --class gnu-linux --id example-gnu-linux { ... } then you can make this the default using: GRUB_DEFAULT=example-gnu-linux Previously it was documented the way to use entry title. While this still works it’s not recommended since titles often contain unstable device names and may be translated If you set this to ‘saved’, then the default menu entry will be that saved by ‘GRUB_SAVEDEFAULT’ or The default is ‘0’. ‘GRUB_SAVEDEFAULT’If this option is set to ‘true’, then, when an entry is selected, save it as a new default entry for use by future runs of GRUB. This is only useful if ‘GRUB_DEFAULT=saved’; it is a
separate option because ‘GRUB_DEFAULT=saved’ is useful without this option, in conjunction with Boot the default entry this many seconds after the menu is displayed, unless a key is pressed. The default is ‘5’. Set to ‘0’ to boot immediately without displaying the menu, or to ‘-1’ to wait indefinitely. If ‘GRUB_TIMEOUT_STYLE’ is set to ‘countdown’ or ‘hidden’, the timeout is instead counted before the menu is displayed. ‘GRUB_TIMEOUT_STYLE’If this option is unset or set to ‘menu’, then GRUB will display the menu and then wait for the timeout set by ‘GRUB_TIMEOUT’ to expire before booting the default entry. Pressing a key interrupts the timeout. If this option is set to ‘countdown’ or ‘hidden’, then, before displaying the menu, GRUB will wait for the timeout set by ‘GRUB_TIMEOUT’ to expire. If ESC or F4 are pressed, or SHIFT is held down during that time, it will display the menu and wait for input. If a hotkey associated with a menu entry is pressed, it will boot the associated menu entry immediately. If the timeout expires before either of these happens, it will boot the default entry. In the ‘countdown’ case, it will show a one-line indication of the remaining time. ‘GRUB_DEFAULT_BUTTON’‘GRUB_TIMEOUT_BUTTON’‘GRUB_TIMEOUT_STYLE_BUTTON’‘GRUB_BUTTON_CMOS_ADDRESS’Variants of the corresponding variables without the ‘_BUTTON’ suffix, used to support vendor-specific power buttons. See Vendor power-on keys. ‘GRUB_DISTRIBUTOR’Set by distributors of GRUB to their identifying name. This is used to generate more informative menu entry titles. ‘GRUB_TERMINAL_INPUT’Select the terminal input device. You may select multiple devices here, separated by spaces. Valid terminal input names depend on the platform, but may include ‘console’ (native platform console), ‘serial’ (serial terminal), ‘serial_<port>’ (serial terminal with explicit port selection), ‘at_keyboard’ (PC AT keyboard), or ‘usb_keyboard’ (USB keyboard using the HID Boot Protocol, for cases where the firmware does not handle this). The default is to use the platform’s native terminal input. ‘GRUB_TERMINAL_OUTPUT’Select the terminal output device. You may select multiple devices here, separated by spaces. Valid terminal output names depend on the platform, but may include ‘console’ (native platform console), ‘serial’ (serial terminal), ‘serial_<port>’ (serial terminal with explicit port selection), ‘gfxterm’ (graphics-mode output), ‘vga_text’ (VGA text output), ‘mda_text’ (MDA text output), ‘morse’ (Morse-coding using system beeper) or ‘spkmodem’ (simple data protocol using system speaker). ‘spkmodem’ is useful when no serial port is available. Connect the output of sending system (where GRUB is running) to line-in of receiving system (usually developer machine). On receiving system compile ‘spkmodem-recv’ from ‘util/spkmodem-recv.c’ and run: parecord --channels=1 --rate=48000 --format=s16le | ./spkmodem-recv The default is to use the platform’s native terminal output. ‘GRUB_TERMINAL’If this option is set, it overrides both ‘GRUB_TERMINAL_INPUT’ and ‘GRUB_TERMINAL_OUTPUT’ to the same value. ‘GRUB_SERIAL_COMMAND’A command to configure the serial port when using the serial console. See serial. Defaults to ‘serial’. ‘GRUB_CMDLINE_LINUX’Command-line arguments to add to menu entries for the Linux kernel. ‘GRUB_CMDLINE_LINUX_DEFAULT’Unless ‘GRUB_DISABLE_RECOVERY’ is set to ‘true’, two menu entries will be generated for each Linux kernel: one default entry and one entry for recovery mode. This option lists command-line arguments to add only to the default menu entry, after those listed in ‘GRUB_CMDLINE_LINUX’. ‘GRUB_CMDLINE_NETBSD’‘GRUB_CMDLINE_NETBSD_DEFAULT’As ‘GRUB_CMDLINE_LINUX’ and ‘GRUB_CMDLINE_LINUX_DEFAULT’, but for NetBSD. ‘GRUB_CMDLINE_GNUMACH’As ‘GRUB_CMDLINE_LINUX’, but for GNU Mach. ‘GRUB_CMDLINE_XEN’ ‘GRUB_CMDLINE_XEN_DEFAULT’The values of these options are passed to Xen hypervisor Xen menu entries, for all respectively normal entries. ‘GRUB_CMDLINE_LINUX_XEN_REPLACE’‘GRUB_CMDLINE_LINUX_XEN_REPLACE_DEFAULT’The values of these options replace the values of ‘GRUB_CMDLINE_LINUX’ and ‘GRUB_CMDLINE_LINUX_DEFAULT’ for Linux and Xen menu entries. ‘GRUB_EARLY_INITRD_LINUX_CUSTOM’ ‘GRUB_EARLY_INITRD_LINUX_STOCK’List of space-separated early initrd images to be loaded from ‘/boot’. This is for loading things like CPU microcode, firmware, ACPI tables, crypto keys, and so on. These early images will be loaded in the order declared, and all will be loaded before the actual functional initrd image. ‘GRUB_EARLY_INITRD_LINUX_STOCK’ is for your distribution to declare images that are provided by the distribution. It should not be modified without understanding the consequences. They will be loaded first. ‘GRUB_EARLY_INITRD_LINUX_CUSTOM’ is for your custom created images. The default stock images are as follows, though they may be overridden by your distribution: intel-uc.img intel-ucode.img amd-uc.img amd-ucode.img early_ucode.cpio microcode.cpio‘GRUB_DISABLE_LINUX_UUID’ Normally, If If this option is set to ‘true’, disable the generation of recovery mode menu entries. ‘GRUB_DISABLE_UUID’Normally, If graphical video support is required, either because the ‘gfxterm’ graphical terminal is in use or because ‘GRUB_GFXPAYLOAD_LINUX’ is set, then After 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. See gfxmode. ‘GRUB_BACKGROUND’Set a background image for use with the ‘gfxterm’ graphical terminal. The value of this option must be a file readable by GRUB at boot time, and it must end with .png, .tga, .jpg, or .jpeg. The image will be scaled if necessary to fit the screen. ‘GRUB_THEME’Set a theme for use with the ‘gfxterm’ graphical terminal. ‘GRUB_GFXPAYLOAD_LINUX’Set to ‘text’ to force the Linux kernel to boot in normal text mode, ‘keep’ to preserve the graphics mode set using ‘GRUB_GFXMODE’, ‘widthxheight’[‘xdepth’] to set a particular graphics mode, or a sequence of these separated by commas or semicolons to try several modes in sequence. See gfxpayload. Depending on your kernel, your distribution, your graphics card, and the phase of the moon, note that using this option may cause GNU/Linux to suffer from various display problems, particularly during the early part of the boot sequence. If you have problems, set this option to ‘text’ and GRUB will tell Linux to boot in normal text mode. ‘GRUB_DISABLE_OS_PROBER’The List of space-separated FS UUIDs of filesystems to be ignored from os-prober output. For efi chainloaders it’s <UUID>@<EFI FILE> ‘GRUB_DISABLE_SUBMENU’Normally, If set to ‘y’, 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 play. ‘GRUB_BADRAM’If this option is set, GRUB will issue a badram command to filter out specified regions of RAM. ‘GRUB_PRELOAD_MODULES’This option may be set to a list of GRUB module names separated by spaces. Each module will be loaded as early as possible, at the start of grub.cfg. The following options are still accepted for compatibility with existing configurations, but have better replacements: ‘GRUB_HIDDEN_TIMEOUT’Wait this many seconds before displaying the menu. If ESC or F4 are pressed, or SHIFT is held down during that time, display the menu and wait for input according to ‘GRUB_TIMEOUT’. If a hotkey associated with a menu entry is pressed, boot the associated menu entry immediately. If the timeout expires before either of these happens, display the menu for the number of seconds specified in ‘GRUB_TIMEOUT’ before booting the default entry. If you set ‘GRUB_HIDDEN_TIMEOUT’, you should also set ‘GRUB_TIMEOUT=0’ so that the menu is not displayed at all unless ESC or F4 are pressed, or SHIFT is held down. This option is unset by default, and is deprecated in favour of the less confusing ‘GRUB_TIMEOUT_STYLE=countdown’ or ‘GRUB_TIMEOUT_STYLE=hidden’. ‘GRUB_HIDDEN_TIMEOUT_QUIET’In conjunction with ‘GRUB_HIDDEN_TIMEOUT’, set this to ‘true’ to suppress the verbose countdown while waiting for a key to be pressed before displaying the menu. This option is unset by default, and is deprecated in favour of the less confusing ‘GRUB_TIMEOUT_STYLE=countdown’. ‘GRUB_HIDDEN_TIMEOUT_BUTTON’Variant of ‘GRUB_HIDDEN_TIMEOUT’, used to support vendor-specific power buttons. See Vendor power-on keys. This option is unset by default, and is deprecated in favour of the less confusing ‘GRUB_TIMEOUT_STYLE=countdown’ or ‘GRUB_TIMEOUT_STYLE=hidden’. For more detailed customisation of 6.2 Root Identifcation HeuristicsIf the target operating system uses the Linux kernel, When booting, the Linux kernel will delegate the task of mounting the root filesystem to the initrd. Most initrd images determine the root file system by checking the Linux kernel’s command-line for the ‘root’ key and use
its value as the identification method of the root file system. To improve the reliability of booting, most initrd images also allow the root file system to be identified by its UUID. Because of this behavior, the If no initrd is detected or ‘GRUB_DISABLE_LINUX_UUID’ is set to ‘true’ then The following table summarizes the behavior of the
Remember, ‘GRUB_DISABLE_LINUX_PARTUUID’ and ‘GRUB_DISABLE_LINUX_UUID’ are also considered to be set to ‘false’ when they are unset. 6.3 Writing full configuration files directlygrub.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. WordsA 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 wordsReserved 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 ! [[ ]] { } 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. QuotingQuoting 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: ‘$’, ‘"’, ‘\’, or newline. A backslash-newline pair is treated as a line continuation (that is, it is removed from the input stream and effectively ignored7). A double quote may be quoted within double quotes by preceding it with a backslash. Variable expansionThe ‘$’ 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 (see 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. CommentsA word beginning with ‘#’ causes that word and all remaining characters on that line to be ignored. Simple commandsA 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
Compound commandsA compound command is one of the following: for name in word …; do list; doneThe list of words following The The 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 See menuentry. Built-in CommandsSome 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 n ]Resume the next iteration of the enclosing n ]Causes a function to exit with the return value specified by arg ] …Replace positional parameters starting with n ]The positional parameters from 6.4 Multi-boot manual configCurrently autogenerating config files for multi-boot environments depends on os-prober and has several shortcomings. Due to that it is disabled by default. It is advised to use the power of GRUB syntax and do it yourself. A possible configuration is detailed here, feel free to adjust to your needs. First create a separate GRUB partition, big enough to hold GRUB. Some of the following entries show how to load OS installer images from this same partition, for that you obviously need to make the partition large enough to hold those images as well. Mount this partition on/mnt/boot and disable GRUB in all OSes and manually install self-compiled latest GRUB with:
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=ftp://mirror.switch.ch/mirror/fedora/linux/development/rawhide/x86_64 lang=en_US keymap=sg resolution=1280x800 initrd /fedora/initrd.img } menuentry "Debian sid installer" { search --set=root --label GRUB --hint hd0,msdos5 linux /debian/dists/sid/main/installer-amd64/current/images/hd-media/vmlinuz initrd /debian/dists/sid/main/installer-amd64/current/images/hd-media/initrd.gz } Notes:
6.5 Embedding a configuration file into GRUBGRUB 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. To embed a configuration file, use the -c option to After the embedded configuration file (if any) is executed, GRUB will load the ‘normal’ module (see
normal), which will then read the real configuration file from $prefix/grub.cfg. By this point, the search.fs_uuid 01234567-89ab-cdef-0123-456789abcdef root set prefix=($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 search.fs_label grub root if [ -e /boot/grub/example/test1.cfg ]; then set prefix=($root)/boot/grub configfile /boot/grub/example/test1.cfg else if [ -e /boot/grub/example/test2.cfg ]; then set prefix=($root)/boot/grub configfile /boot/grub/example/test2.cfg else echo "Could not find an example configuration file!" fi fi The embedded configuration file may not contain menu entries directly, but may only read them from elsewhere using 7 Theme file format7.1 IntroductionThe 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 Elements7.2.1 ColorsColors can be specified in several ways:
7.2.2 FontsThe 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 (loadfont). To see the list of loaded fonts, execute the “lsfonts” command (lsfonts). If there are too many fonts to fit on screen, do “set pager=1” before executing “lsfonts”. 7.2.3 Progress BarProgress 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 IndicatorThe 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 LabelsText 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 MenuThe 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 BoxesOne 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:
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:
As an example of how an image might be sliced up, consider the styled box used for a terminal view. 7.2.8 Creating Styled Box ImagesThe 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:
7.3 Theme File ManualThe 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:
7.3.1 Global Properties7.3.2 FormatGlobal properties are specified with the simple format:
In this example, name3 is assigned a color value. 7.3.3 Global Property List
7.3.4 Component ConstructionGreater 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:
properties of a component are specified as "name = value" (whitespace surrounding tokens is optional and is ignored) where *value* may be:
7.3.5 Component ListThe following is a list of the components and the properties they support.
7.3.6 Common propertiesThe 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:
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:
8 Booting GRUB from the networkThe following instructions don’t work for *-emu, i386-qemu, i386-coreboot, i386-multiboot, mips_loongson, mips-arc and mips_qemu_mips To generate a netbootable directory, run: grub-mknetdir --net-directory=/srv/tftp --subdir=/boot/grub -d /usr/lib/grub/<platform> E.g. for i386-pc: grub-mknetdir --net-directory=/srv/tftp --subdir=/boot/grub -d /usr/lib/grub/i386-pc Then follow instructions printed out by grub-mknetdir on configuring your DHCP server. The grub.cfg file is placed in the same directory as the path output by grub-mknetdir hereafter referred to as FWPATH. GRUB will search for its configuration files in order using the following rules where the appended value corresponds to a value on the client machine. ‘(FWPATH)’/grub.cfg-‘(UUID OF MACHINE)’ ‘(FWPATH)’/grub.cfg-‘(MAC ADDRESS OF NIC)’ ‘(FWPATH)’/grub.cfg-‘(IPv4 OR IPv6 ADDRESS)’ ‘(FWPATH)’/grub.cfg The UUID is the Client Machine Identifier Option Definition as specified in RFC 4578. The client will only attempt to loouk up a UUID config file if it was provided by the DHCP server. The client will only attempt to look up an IPv6 address config once, however, it will try the IPv4 multiple times. The concrete example below shows what would happen under the IPv4 case. UUID: 7726a678-7fc0-4853-a4f6-c85ac36a120a MAC: 52:54:00:ec:33:81 IPV4: 10.0.0.130 (0A000082) ‘(FWPATH)’/grub.cfg-7726a678-7fc0-4853-a4f6-c85ac36a120a ‘(FWPATH)’/grub.cfg-52-54-00-ec-33-81 ‘(FWPATH)’/grub.cfg-0A000082 ‘(FWPATH)’/grub.cfg-0A00008 ‘(FWPATH)’/grub.cfg-0A0000 ‘(FWPATH)’/grub.cfg-0A000 ‘(FWPATH)’/grub.cfg-0A00 ‘(FWPATH)’/grub.cfg-0A0 ‘(FWPATH)’/grub.cfg-0A ‘(FWPATH)’/grub.cfg-0 ‘(FWPATH)’/grub.cfg This feature is enabled by default but it can be disabled by setting the ‘feature_net_search_cfg’ to ‘n’. Since this happens before the configuration file is read by GRUB, this option has to be disabled in an embedded configuration file (see Embedded configuration). After GRUB has started, files on the TFTP server will be accessible via the ‘(tftp)’ device. The server IP address can be controlled by changing the ‘(tftp)’ device name to ‘(tftp,server-ip)’. Note that this should be changed both in the prefix and in any references to the device name in the configuration file. GRUB provides several environment variables which may be used to inspect or change the behaviour of the PXE device. In the following description <interface> is placeholder for the name of network interface (platform dependent): ‘net_<interface>_ip’The network interface’s IP address. Read-only. ‘net_<interface>_mac’The network interface’s MAC address. Read-only. ‘net_<interface>_hostname’The client host name provided by DHCP. Read-only. ‘net_<interface>_domain’The client domain name provided by DHCP. Read-only. ‘net_<interface>_rootpath’The path to the client’s root disk provided by DHCP. Read-only. ‘net_<interface>_extensionspath’The path to additional DHCP vendor extensions provided by DHCP. Read-only. ‘net_<interface>_boot_file’The boot file name provided by DHCP. Read-only. ‘net_<interface>_dhcp_server_name’The name of the DHCP server responsible for these boot parameters. Read-only. ‘net_<interface>_next_server’The IP address of the next (usually, TFTP) server provided by DHCP. Read-only. ‘net_default_interface’Initially set to name of network interface that was used to load grub. Read-write, although setting it affects only interpretation of ‘net_default_ip’ and ‘net_default_mac’ ‘net_default_ip’The IP address of default interface. Read-only. This is alias for the ‘net_${net_default_interface}_ip’. ‘net_default_mac’The default interface’s MAC address. Read-only. This is alias for the ‘net_${net_default_interface}_mac’. ‘net_default_server’The default server used by network drives (see Device syntax). Read-write, although setting this is only useful before opening a network device. 9 Using GRUB via a serial lineThis 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 The commands 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. 10 Using GRUB with vendor power-on keysSome 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 (see 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 M1330M121:3 Dell XPS M153085:3 Dell Latitude E430085:3 Asus EeePC 1005PE84:1 (unconfirmed) LENOVO ThinkPad T410s (2912W1C)101:3 To take full advantage of this function, install GRUB into the MBR (see 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:
Then compare these text files and find where a bit was toggled. E.g. in case of Dell XPS it was: It’s a bit number 3 as seen from following table:
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 11 GRUB image filesGRUB 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.imgOn 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 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.imgThis 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.imgThis image is used as the start of the core image when booting from the network using PXE. See Network. lnxboot.imgThis 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.imgThis 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.imgThis is the core image of GRUB. It is
built dynamically from the kernel image and an arbitrary list of modules by the See BIOS installation, for details on where the core image can be installed on PC systems. *.modEverything 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 For GRUB Legacy usersGRUB 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. stage1Stage 1 from GRUB Legacy was very similar to boot.img in GRUB 2, and they serve the same function. *_stage1_5In 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. stage2GRUB 2 has no single Stage 2 image. Instead, it loads modules from /boot/grub at run-time. stage2_eltoritoIn 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 There is as yet no equivalent for nbgrub in GRUB 2; it was used by Etherboot and some other network boot loaders. pxegrubIn 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. See Network. 12 Core image size limitationHeavily limited platforms:
Lightly limited platforms:
13 Filesystem syntax and semanticsGRUB 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 13.1 How to specify devicesThe 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 (fd0) (hd0) (cd) (ahci0) (ata0) (crypto0) (usb0) (cryptouuid/123456789abcdef0123456789abcdef0) (mduuid/123456789abcdef0123456789abcdef0) (lvm/system-root) (lvmid/F1ikgD-2RES-306G-il9M-7iwa-4NKW-EbV1NV/eLGuCQ-L4Ka-XUgR-sjtJ-ffch-bajr-fCNfz5) (md/myraid) (md/0) (ieee1275/disk2) (ieee1275//pci@1f\,0/ide@d/disk@2) (nand) (memdisk) (host) (myloop) (hostdisk//dev/sda) part-num represents the partition number of device, starting from one. partname is optional but is recommended since disk may have several top-level partmaps. Specifying third and later component you can access to subpartitions. The syntax ‘(hd0)’ represents using the entire disk (or the MBR when installing GRUB), while the syntax ‘(hd0,1)’ represents using the first partition of the disk (or the boot sector of the partition when installing GRUB). (hd0,msdos1) (hd0,msdos1,msdos5) (hd0,msdos1,bsd3) (hd0,netbsd1) (hd0,gpt1) (hd0,1,3) If you enabled the network support, the special drives If you boot GRUB from a CD-ROM, ‘(cd)’ is available. See Making a GRUB bootable CD-ROM, for details. 13.2 How to specify filesThere 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)’ (see set),
then 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. 13.3 How to specify block listsA block list is used for specifying a file that doesn’t appear in the filesystem, like a chainloader. The syntax is 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 (see
File name syntax), if a blocklist does not contain a device name, then GRUB uses GRUB’s root device. So 14 GRUB’s user interfaceGRUB 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. 14.1 The flexible command-line interfaceThe 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 entered8. The commands (see 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-fPC right keyMove forward one character. C-bPC left keyMove back one character. C-aHOMEMove to the start of the line. C-eENDMove the the end of the line. C-dDELDelete the character underneath the cursor. C-hBSDelete the character to the left of the cursor. C-kKill the text from the current cursor position to the end of the line. C-uKill backward from the cursor to the beginning of the line. C-yYank the killed text back into the buffer at the cursor. C-pPC up keyMove up through the history list. C-nPC down keyMove 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 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. 14.2 The simple menu interfaceThe 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 (see Security), all you can do is choose an entry by pressing RET, or press p to enter the password. 14.3 Editing a menu entryThe 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. 15 GRUB environment variablesGRUB 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 (see set), unset (see unset), or looked up (see 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. 15.1 Special environment variablesThese variables have special meaning to GRUB. 15.1.1 biosnumWhen chain-loading another boot loader (see Chain-loading), GRUB may need to know what BIOS drive number corresponds to the root device (see 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, see drivemap. 15.1.2 check_signaturesThis variable controls whether GRUB enforces digital signature validation on loaded files. See Using digital signatures. 15.1.3 chosenWhen 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 ‘>’. 15.1.4 cmdpathThe location from which core.img was loaded as an absolute directory name (see 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. 15.1.5 color_highlightThis variable contains the “highlight” foreground and background terminal colors, separated by a slash (‘/’). Setting this variable changes those colors. For the available color names, see color_normal. The default is ‘black/light-gray’. 15.1.6 color_normalThis 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:
The default is ‘light-gray/black’. The color support support varies from terminal to terminal. ‘morse’ has no color support at all. ‘mda_text’ color support is limited to highlighting by black/white reversal. ‘console’ on ARC, EMU and IEEE1275, ‘serial_*’ and ‘spkmodem’ are governed by terminfo and support only 8 colors if in modes ‘vt100-color’ (default for console on emu), ‘arc’ (default for console on ARC), ‘ieee1275’ (default for console on IEEE1275). When in mode ‘vt100’ then the color support is limited to highlighting by black/white reversal. When in mode ‘dumb’ there is no color support. When console supports no colors this setting is ignored. When console supports 8 colors, then the colors from the second half of the previous list are mapped to the matching colors of first half. ‘console’ on EFI and BIOS and ‘vga_text’ support all 16 colors. ‘gfxterm’ supports all 16 colors and would be theoretically extendable to support whole rgb24 palette but currently there is no compelling reason to go beyond the current 16 colors. 15.1.7 config_directoryThis variable is automatically set by GRUB to the directory part of current configuration file name (see config_file). 15.1.8 config_fileThis variable is automatically set by GRUB to the name of configuration file that is being processed by commands 15.1.9 debugThis 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. 15.1.10 defaultIf this variable is set, it identifies a menu entry that should be selected by default, possibly after a timeout (see timeout). The entry may be identified by number (starting from 0 at each level of the hierarchy), by title, or by id. For example, if you have: menuentry 'Example GNU/Linux distribution' --class gnu-linux --id example-gnu-linux { ... } then you can make this the default using: default=example-gnu-linux If the entry is in a submenu, then it must be identified using the number, title, or id of each of the submenus starting from the top level, followed by the number, title, or id of the menu entry itself, with each element separated by ‘>’. For example, take the following menu structure: GNU/Hurd --id gnu-hurd Standard Boot --id=gnu-hurd-std Rescue shell --id=gnu-hurd-rescue Other platforms --id=other Minix --id=minix Version 3.4.0 --id=minix-3.4.0 Version 3.3.0 --id=minix-3.3.0 GRUB Invaders --id=grub-invaders The more recent release of Minix would then be identified as ‘Other platforms>Minix>Version 3.4.0’, or as ‘1>0>0’, or as ‘other>minix>minix-3.4.0’. This variable is often set by ‘GRUB_DEFAULT’ (see Simple configuration), 15.1.11 fallbackIf 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’ (see default). 15.1.12 gfxmodeIf 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’. 15.1.13 gfxpayloadIf this variable is set, it controls the video mode in which the Linux kernel starts up, replacing the ‘vga=’ boot option (see 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 (see 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’ (see Simple configuration). 15.1.14 gfxterm_fontIf this variable is set, it names a font to use for text on the ‘gfxterm’ graphical terminal. Otherwise, ‘gfxterm’ may use any available font. 15.1.15 grub_cpuIn normal mode (see normal), GRUB sets the ‘grub_cpu’ variable to the CPU type for which GRUB was built (e.g. ‘i386’ or ‘powerpc’). 15.1.16 grub_platformIn normal mode (see normal), GRUB sets the ‘grub_platform’ variable to the platform for which GRUB was built (e.g. ‘pc’ or ‘efi’). 15.1.17 icondirIf 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. See Theme file format. 15.1.18 langIf this variable is set, it names the language code that the
15.1.19 locale_dirIf this variable is set, it names the directory where translation files may be found (see gettext), usually /boot/grub/locale. Otherwise, internationalization is disabled.
15.1.20 menu_color_highlightThis 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, see color_normal. The default is the value of ‘color_highlight’ (see color_highlight). 15.1.21 menu_color_normalThis 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, see color_normal. The default is the value of ‘color_normal’ (see color_normal). 15.1.22 net_<interface>_boot_fileSee Network. 15.1.23 net_<interface>_dhcp_server_nameSee Network. 15.1.24 net_<interface>_domainSee Network. 15.1.25 net_<interface>_extensionspathSee Network. 15.1.26 net_<interface>_hostnameSee Network. 15.1.27 net_<interface>_ipSee Network. 15.1.28 net_<interface>_macSee Network. 15.1.29 net_<interface>_next_serverSee Network. 15.1.30 net_<interface>_rootpathSee Network. 15.1.31 net_default_interfaceSee Network. 15.1.32 net_default_ipSee Network. 15.1.33 net_default_macSee Network. 15.1.34 net_default_serverSee Network. 15.1.35 pagerIf set to ‘1’, pause output after each screenful and wait for keyboard input. The default is not to pause output. 15.1.36 prefixThe location of the ‘/boot/grub’ directory as an absolute file name (see
File name syntax). This is normally set by GRUB at startup based on information provided by 15.1.37 pxe_blksizeSee Network. 15.1.38 pxe_default_gatewaySee Network. 15.1.39 pxe_default_serverSee Network. 15.1.40 rootThe root device name (see 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’ (see 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’. 15.1.41 superusersThis variable may be set to a list of superuser names to enable authentication support. See Security. 15.1.42 themeThis variable may be set to a directory containing a GRUB graphical menu theme. See Theme file format. This variable is often set by ‘GRUB_THEME’ (see Simple configuration). 15.1.43 timeoutIf 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’ (see 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’ (see Simple configuration). 15.1.44 timeout_styleThis variable may be set to ‘menu’, ‘countdown’, or ‘hidden’ to control the way in which the timeout (see timeout) interacts with displaying the menu. See the documentation of ‘GRUB_TIMEOUT_STYLE’ (see Simple configuration) for details. 15.2 The GRUB environment blockIt 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 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).
16 The list of available commandsIn 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 16.1 The list of commands for the menu onlyThe semantics used in parsing the configuration file are the following:
These commands can only be used in the menu: 16.1.1 menuentryCommand: 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 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. See Security. The --unrestricted option grants all users access to specific menu entries. See 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 16.1.2 submenuCommand: 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 16.2 The list of general commandsCommands usable anywhere in the menu and in the command-line. 16.2.1 serialCommand: 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 See also Serial terminal. 16.2.2 terminal_inputCommand: 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. 16.2.3 terminal_outputCommand: 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. 16.2.4 terminfoCommand: terminfo [-a|-u|-v] [-g WxH] [term] [type]Define the capabilities of your terminal by giving the name of an entry in the terminfo database, which should correspond roughly to a ‘TERM’ environment variable in Unix. The currently available terminal types are ‘vt100’, ‘vt100-color’, ‘ieee1275’, and ‘dumb’. If you need other terminal types, please contact us to discuss the best way to include support for these in GRUB. The -a (--ascii), -u (--utf8), and -v (--visual-utf8) options control how non-ASCII text is displayed. -a specifies an ASCII-only terminal; -u specifies logically-ordered UTF-8; and -v specifies "visually-ordered UTF-8" (in other words, arranged such that a terminal emulator without bidirectional text support will display right-to-left text in the proper order; this is not really proper UTF-8, but a workaround). The -g (--geometry) can be used to specify terminal geometry. If no option or terminal type is specified, the current terminal type is printed. 16.3 The list of command-line and menu entry commandsThese commands are usable in the command-line and in menu entries. If you forget a command, you can run the command 16.3.1 [Command:[ expression ] Alias for 16.3.2 acpiCommand: acpi [-1|-2] [--exclude=table1,…|--load-only=table1,…] [--oemid=id] [--oemtable=table] [--oemtablerev=rev] [--oemtablecreator=creator] [--oemtablecreatorrev=rev] [--no-ebda] filename …Modern BIOS systems normally implement the Advanced Configuration and Power Interface (ACPI), and define various tables that describe the interface between an ACPI-compliant operating system and the firmware. In some cases, the tables provided by default only work well with certain operating systems, and it may be necessary to replace some of them. Normally, this command will replace the Root System Description Pointer (RSDP) in the Extended BIOS Data Area to point to the new tables. If the --no-ebda option is used, the new tables will be known only to GRUB, but may be used by GRUB’s EFI emulation. Note: The command is not allowed when lockdown is enforced (see Lockdown). Otherwise an attacker can instruct the GRUB to load an SSDT table to overwrite the kernel lockdown configuration and later load and execute unsigned code. 16.3.3 authenticateCommand: authenticate [userlist]Check whether user is in userlist or listed in the value of variable ‘superusers’. See see superusers for valid user list format. If ‘superusers’ is empty, this command returns true. See Security. 16.3.4 background_colorCommand: background_color colorSet background color for active terminal. For valid color specifications see see Colors. Background color can be changed only when using ‘gfxterm’ for terminal output. This command sets color of empty areas without text. Text background color is controlled by environment variables color_normal, color_highlight, menu_color_normal, menu_color_highlight. See Special environment variables. 16.3.5 background_imageCommand: background_image [[--mode ‘stretch’|‘normal’] file]Load background image for active terminal from file. Image is stretched to fill up entire screen unless option --mode ‘normal’ is given. Without arguments remove currently loaded background image. Background image can be changed only when using ‘gfxterm’ for terminal output. 16.3.6 badramCommand: 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. The command is similar to Note: The command is not allowed when lockdown is enforced (see Lockdown). This prevents removing EFI memory regions to potentially subvert the security mechanisms provided by the UEFI secure boot. 16.3.7 blocklistCommand: blocklist filePrint a block list (see Block list syntax) for file. 16.3.8 bootCommand: bootBoot 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). 16.3.9 catCommand: cat [--dos] fileDisplay the contents of the file file. This command may be useful to remind you of your OS’s root partition: 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. 16.3.10 chainloaderCommand: chainloader [--force] fileLoad file as a chain-loader. Like any other file loaded by the filesystem code, it can use the blocklist notation (see 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. 16.3.11 clearCommand: clearClear the screen. 16.3.12 cmoscleanCommand: cmosclean byte:bitClear value of bit in CMOS at location byte:bit. This command is available only on platforms that support CMOS. 16.3.13 cmosdumpDump: CMOS contentsDump full CMOS contents as hexadecimal values. This command is available only on platforms that support CMOS. 16.3.14 cmostestCommand: cmostest byte:bitTest 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. 16.3.15 cmpCommand: cmp file1 file2Compare 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. 16.3.16 configfileCommand: configfile fileLoad 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 16.3.17 cpuidCommand: cpuid [-l] [-p]Check for CPU features. This command is only available on x86 systems. With the -l option, return true if the CPU supports long mode (64-bit). With the -p option, return true if the CPU supports Physical Address Extension (PAE). If invoked without options, this command currently behaves as if it had been invoked with -l. This may change in the future. 16.3.18 crcCommand: crc arg …Alias for 16.3.19 cryptomountCommand: cryptomount device|-u uuid|-a|-bSetup access to encrypted device. If necessary, passphrase is requested interactively. Option device configures specific grub device (see Naming convention); option -u uuid configures device with specified uuid; option -a configures all detected encrypted devices; option -b configures all geli containers that have boot flag set. GRUB suports devices encrypted using LUKS, LUKS2 and geli. Note that necessary modules (luks, luks2 and geli) have to be loaded manually before this command can be used. For LUKS2 only the PBKDF2 key derivation function is supported, as Argon2 is not yet supported. Also, note that, unlike filesystem UUIDs, UUIDs for encrypted devices must be specified without dash separators. 16.3.20 cutmemCommand: cutmem from[K|M|G] to[K|M|G]Remove any memory regions in specified range. This command notifies the memory manager that specified regions of RAM ought to be filtered out. This remains in effect after a payload kernel has been loaded by GRUB, as long as the loaded kernel obtains its memory map from GRUB. Kernels that support this include Linux, GNU Mach, the kernel of FreeBSD and Multiboot kernels in general. The command is similar to Note: The command is not allowed when lockdown is enforced (see Lockdown). This prevents removing EFI memory regions to potentially subvert the security mechanisms provided by the UEFI secure boot. 16.3.21 dateCommand: 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. 16.3.22 devicetreeCommand: devicetree fileLoad a device tree blob (.dtb) from a filesystem, for later use by a Linux kernel. Does not perform merging with any device tree supplied by firmware, but rather replaces it completely. Note: The command is not allowed when lockdown is enforced (see Lockdown). This is done to prevent subverting various security mechanisms. 16.3.23 distrustCommand: distrust pubkey_idRemove 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 16.3.24 drivemapCommand: drivemap -l|-r|[-s] from_drive to_driveWithout 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 ${root} as a drive specification. With the -s option, perform the reverse mapping as well, swapping the two drives. With the -l option, list the current mappings. With the -r option, reset all mappings to the default values. For example: 16.3.25 echoCommand: echo [-n] [-e] string …Display the requested text and, unless the -n option is used, a trailing new line. If there is more than one string, they are separated by spaces in the output. As usual in GRUB commands, variables may be substituted using ‘${var}’. The -e option enables interpretation of backslash escapes. The following sequences are recognised: \\ backslash \a alert (BEL) \c suppress trailing new line \f form feed \n new line \r carriage return \t horizontal tab \v vertical tab When interpreting backslash escapes, backslash followed by any other character will print that character. 16.3.26 evalCommand: eval string ...Concatenate arguments together using single space as separator and evaluate result as sequence of GRUB commands. 16.3.27 exportCommand: export envvarExport the
environment variable envvar. Exported variables are visible to subsidiary configuration files loaded using 16.3.28 falseCommand: falseDo nothing, unsuccessfully. This is mainly useful in control constructs such as 16.3.29 gettextCommand: gettext stringTranslate string into the current language. The current language code is stored in the ‘lang’ variable in GRUB’s environment (see lang). Translation files in MO format are read from ‘locale_dir’ (see locale_dir), usually /boot/grub/locale. 16.3.30 gptsyncCommand: 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. 16.3.31 haltCommand: halt --no-apmThe 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. 16.3.32 hashsumCommand: 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 16.3.33 helpCommand: 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. 16.3.34 initrdCommand: initrd file [file …]Load, in order, all initial ramdisks for a Linux kernel image, and set
the appropriate parameters in the Linux setup area in memory. This may only be used after the 16.3.35 initrd16Command: initrd16 file [file …]Load, in order, all initial ramdisks for a Linux kernel image to be booted in 16-bit mode, and set the appropriate parameters in the Linux setup area in memory. This may only be used after the This command is only available on x86 systems. 16.3.36 insmodCommand: insmod moduleInsert the dynamic GRUB module called module. 16.3.37 keystatusCommand: keystatus [--shift] [--ctrl] [--alt]Return true if the Shift, Control, or Alt modifier keys are held down, as requested by options. This is useful in scripting, to allow some user control over behaviour without having to wait for a keypress. Checking key modifier status is only supported on some platforms. If invoked without any options, the 16.3.38 linuxCommand: 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 (see 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 16.3.39 linux16Command: 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 (see initrd16). The kernel will be booted using the traditional 16-bit boot protocol. As well as bypassing problems with ‘vga=’ described in 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. 16.3.40 list_envCommand: list_env [--file file]List all variables in the environment block file. See Environment block. The --file option overrides the default location of the environment block. 16.3.41 list_trustedCommand: list_trustedList all public keys trusted by GRUB for validating signatures. The output
is in GPG’s v4 key fingerprint format (i.e., the output of 16.3.42 load_envCommand: load_env [--file file] [--skip-sig] [whitelisted_variable_name] …Load all variables from the environment block file into the environment. See 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 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 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. See Using digital signatures, for more information. 16.3.43 loadfontCommand: loadfont file …Load specified font files. Unless absolute pathname is given, file is assumed to be in directory ‘$prefix/fonts’ with suffix ‘.pf2’ appended. See Fonts. 16.3.44 loopbackCommand: loopback [-d] device fileMake the device named device correspond to the contents of the filesystem image in file. For example: loopback loop0 /path/to/image ls (loop0)/ With the -d option, delete a device previously created using this command. 16.3.45 lsCommand: 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 (see Device syntax), then print the name of the filesystem of that device. If the argument is a directory given as an absolute file name (see File name syntax), then list the contents of that directory. 16.3.46 lsfontsCommand: lsfontsList loaded fonts. 16.3.47 lsmodCommand: lsmodShow list of loaded modules. 16.3.48 md5sumCommand: md5sum arg …Alias for 16.3.49 moduleCommand: module [--nounzip] file [arguments]Load a module for multiboot kernel image. The rest of the line is passed verbatim as the module command line. 16.3.50 multibootCommand: 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 (see module). Some kernels have known problems. You need to specify –quirk-* for those. –quirk-bad-kludge is a problem seen in several products that they include loading kludge information with invalid data in ELF file. GRUB prior to 0.97 and some custom builds preferred ELF information while 0.97 and GRUB 2 use kludge. Use this option to ignore kludge. Known affected systems: old Solaris, SkyOS. –quirk-modules-after-kernel is needed for kernels which load at relatively high address e.g. 16MiB mark and can’t cope with modules stuffed between 1MiB mark and beginning of the kernel. Known afftected systems: VMWare. 16.3.51 nativediskCommand: nativediskSwitch from firmware disk drivers to native ones. Really useful only on platforms where both firmware and native disk drives are available. Currently i386-pc, i386-efi, i386-ieee1275 and x86_64-efi. 16.3.52 normalCommand: 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 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.
16.3.53 normal_exitCommand: normal_exitExit normal mode (see normal). If this instance of normal mode was not nested within another one, then return to rescue mode. 16.3.54 parttoolCommand: parttool partition commandsMake various modifications to partition table entries. Each command is either a boolean option, in which case it must be followed with ‘+’ or ‘-’ (with no intervening space) to enable or disable that option, or else it takes a value in the form ‘command=value’. Currently, When enabled, this makes the selected partition be the active (bootable) partition on its disk, clearing the active flag on all other partitions. This command is limited to primary partitions. ‘type’ (value)Change the type of an existing partition. The value must be a number in the range 0-0xFF (prefix with ‘0x’ to enter it in hexadecimal). ‘hidden’ (boolean)When enabled, this hides the selected partition by setting the hidden bit in its partition type code; when disabled, unhides the selected partition by clearing this bit. This is useful only when booting DOS or Windows and multiple primary FAT partitions exist in one disk. See also DOS/Windows. 16.3.55 passwordCommand: password user clear-passwordDefine a user named user with password clear-password. See Security. 16.3.56 password_pbkdf2Command: password_pbkdf2 user hashed-passwordDefine a user named user with password hash hashed-password. Use 16.3.57 playCommand: play file | tempo [pitch2 duration1] [pitch2 duration2] …Plays a tune If the argument is a file name (see 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. 16.3.58 probeCommand: probe [--set var] --driver|--partmap|--fs|--fs-uuid|--label|--part-uuid deviceRetrieve device information. If option --set is given, assign result to variable var, otherwise print information on the screen. The option --part-uuid is currently only implemented for MSDOS and GPT formatted disks. 16.3.59 rdmsrCommand:: rdmsr 0xADDR [-v VARNAME]Read a model-specific register at address 0xADDR. If the parameter -v is used and an environment variable VARNAME is given, set that environment variable to the value that was read. Please note that on SMP systems, reading from a MSR that has a scope per hardware thread, implies that the value that is returned only applies to the particular cpu/core/thread that runs the command. Also, if you specify a reserved or unimplemented MSR address, it will cause a general protection exception (which is not currently being handled) and the system will reboot. 16.3.60 readCommand: 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. 16.3.61 rebootCommand: rebootReboot the computer. 16.3.62 regexpCommand: regexp [--set [number:]var] regexp stringTest 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’. 16.3.63 rmmodCommand: rmmod moduleRemove a loaded module. 16.3.64 save_envCommand: save_env [--file file] var …Save the named variables from the environment to the environment block file. See Environment block. The --file option overrides the default location of the environment block. This command will operate successfully even when environment variable 16.3.65 searchCommand: search [--file|--label|--fs-uuid] [--set [var]] [--no-floppy] nameSearch 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. 16.3.66 sendkeyCommand: sendkey [--num|--caps|--scroll|--insert|--pause|--left-shift|--right-shift|--sysrq|--numkey|--capskey|--scrollkey|--insertkey|--left-alt|--right-alt|--left-ctrl|--right-ctrl ‘on’|‘off’]… [no-led] keystrokeInsert 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:
As well as keystrokes, the If the --no-led option is given, the status flag options will have no effect on keyboard LEDs. If the Since This command is only available on PC BIOS systems. 16.3.67 setCommand: set [envvar=value]Set the environment variable envvar to value. If invoked with no arguments, print all environment variables with their values. 16.3.68 sha1sumCommand: sha1sum arg …Alias for 16.3.69 sha256sumCommand: sha256sum arg …Alias for 16.3.70 sha512sumCommand: sha512sum arg …Alias for 16.3.71 sleepCommand: sleep [--verbose] [--interruptible] countSleep for count seconds. If option --interruptible is given, allow pressing ESC, F4 or holding down SHIFT to interrupt sleep. With --verbose show countdown of remaining seconds. Exit code is set to 0 if timeout expired and to 1 if timeout was interrupted using any of the mentioned keys. 16.3.72 smbiosCommand: smbios [--type type] [--handle handle] [--match match] (--get-byte | --get-word | --get-dword | --get-qword | --get-string | --get-uuid) offset [--set variable]Retrieve SMBIOS information. The
The remaining options determine which field in the selected SMBIOS structure to return. Only one of these options may be specified at a time.
The default action is to print the value of the requested field to the console, but a variable name can be specified with --set to store the value instead of printing it. For example, this will store and then display the system manufacturer’s name. smbios --type 1 --get-string 4 --set system_manufacturer echo $system_manufacturer 16.3.73 sourceCommand: source fileRead file as a configuration file, as if its contents had been incorporated directly into the sourcing file. Unlike 16.3.74 testCommand: test expressionEvaluate expression and return zero exit status if result is true, non zero status otherwise. expression is one of: string1== string2the strings are equal string1!= string2the strings are not equal string1< string2string1 is lexicographically less than string2 string1<= string2string1 is lexicographically less or equal than string2 string1> string2string1 is lexicographically greater than string2 string1>= string2string1 is lexicographically greater or equal than string2 integer1-eq integer2integer1 is equal to integer2 integer1-ge integer2integer1 is greater than or equal to integer2 integer1-gt
integer2integer1 is greater than integer2 integer1-le integer2integer1 is less than or equal to integer2 integer1-lt integer2integer1 is less than integer2 integer1-ne integer2integer1 is not equal to integer2 prefixinteger1-pgt prefixinteger2integer1 is greater than integer2 after stripping off common non-numeric prefix. prefixinteger1-plt prefixinteger2integer1 is less than integer2 after stripping off common non-numeric prefix. file1-nt file2file1 is newer than
file2 (modification time). Optionally numeric bias may be directly appended to -ot file2file1 is older than file2 (modification time). Optionally numeric bias may be directly appended to -d filefile exists and is a directory -e filefile exists -f filefile exists and is not a directory -s filefile exists and has a size greater than zero -n stringthe length of string is nonzero stringstring is equivalent to -z
stringthe length of string is zero ( expression ) expression is true ! expressionexpression is false expression1-a expression2both expression1 and expression2 are true expression1 expression2both expression1 and expression2 are true. This syntax is not POSIX-compliant and is not recommended. expression1-o expression2either expression1 or expression2 is true 16.3.75 trueCommand: trueDo nothing, successfully. This is mainly useful in control constructs such as 16.3.76 trustCommand: trust [--skip-sig] pubkey_fileRead 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 16.3.77 unsetCommand: unset envvarUnset the environment variable envvar. 16.3.78 verify_detachedCommand: verify_detached [--skip-sig] file signature_file [pubkey_file]Verifies a GPG-style detached signature, where the signed file is file, and the signature itself is in file signature_file. Optionally, a specific public key to use can be specified using pubkey_file. When environment variable Exit code 16.3.79 videoinfoCommand: videoinfo [[WxH]xD]List available video modes. If resolution is given, show only matching modes. 16.3.80 wrmsrCommand:: wrmsr 0xADDR 0xVALUEWrite a 0xVALUE to a model-specific register at address 0xADDR. Please note that on SMP systems, writing to a MSR that has a scope per hardware thread, implies that the value that is written only applies to the particular cpu/core/thread that runs the command. Also, if you specify a reserved or unimplemented MSR address, it will cause a general protection exception (which is not currently being handled) and the system will reboot. Note: The command is not allowed when lockdown is enforced (see Lockdown). This is done to prevent subverting various security mechanisms. 16.3.81 xen_hypervisorCommand: xen_hypervisor file [arguments] …Load a Xen hypervisor binary from file. The rest of the line is passed verbatim as the kernel command-line. Any other binaries must be reloaded after using this command. This command is only available on AArch64 systems. 16.3.82 xen_moduleCommand: xen_module [--nounzip] file [arguments]Load a module for xen hypervisor at the booting process of xen. The rest of the line is passed verbatim as the module command line. Modules should be loaded in the following order: - dom0 kernel image - dom0 ramdisk if present - XSM policy if present This command is only available on AArch64 systems. 16.4 The list of networking commands16.4.1 net_add_addrCommand: net_add_addr interface card addressConfigure 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. 16.4.2 net_add_dnsCommand: net_add_dns serverResolve server IP address and add to the list of DNS servers used during name lookup. 16.4.3 net_add_routeCommand: net_add_route shortname ip[/prefix] [interface | ‘gw’ gateway]Add route to network with address ip as modified by prefix via either local interface or gateway. prefix is optional and defaults to 32 for IPv4 address and 128 for IPv6 address. Route is identified by shortname which can be used to remove it (see net_del_route). 16.4.4 net_bootpCommand: net_bootp [card]Alias for net_dhcp, for compatibility with older Grub versions. Will perform the same DHCP handshake with potential fallback to BOOTP as the net_dhcp command (see net_dhcp). 16.4.5 net_del_addrCommand: net_del_addr interfaceRemove configured interface with associated address. 16.4.6 net_del_dnsCommand: net_del_dns addressRemove address from list of servers used during name lookup. 16.4.7 net_del_routeCommand: net_del_route shortnameRemove route entry identified by shortname. 16.4.8 net_dhcpCommand: net_dhcp [card]Perform configuration of card using DHCP protocol. If no card name is specified, try to configure all existing cards. Falls back to the BOOTP protocol, if needed. If configuration was successful, interface with name card‘:dhcp’ and configured address is added to card. Additionally the following DHCP options are recognized and processed: ‘1 (Subnet Mask)’Used to calculate network local routing entry for interface card‘:dhcp’. ‘3 (Router)’Adds default route entry with the name card‘:dhcp:default’ via gateway from DHCP option. Note that only option with single route is accepted. ‘6 (Domain Name Server)’Adds all servers from option value to the list of servers used during name resolution. ‘12 (Host Name)’Sets environment variable ‘net_’<card>‘_dhcp_hostname’ (see net_<interface>_hostname) to the value of option. ‘15 (Domain Name)’Sets environment variable ‘net_’<card>‘_dhcp_domain’ (see net_<interface>_domain) to the value of option. ‘17 (Root Path)’Sets environment variable ‘net_’<card>‘_dhcp_rootpath’ (see net_<interface>_rootpath) to the value of option. ‘18 (Extensions Path)’Sets environment variable ‘net_’<card>‘_dhcp_extensionspath’ (see net_<interface>_extensionspath) to the value of option. ‘66 (TFTP Server Name)’Sets environment variable ‘net_’<card>‘_dhcp_server_name’ (see net_<interface>_dhcp_server_name) to the value of option. ‘67 (Filename)’Sets environment variable ‘net_’<card>‘_boot_file’ (see net_<interface>_boot_file) to the value of option. 16.4.9 net_get_dhcp_optionCommand: net_get_dhcp_option var interface number typeRequest 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. 16.4.10 net_ipv6_autoconfCommand: 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. 16.4.11 net_ls_addrCommand: net_ls_addrList all configured interfaces with their MAC and IP addresses. 16.4.12 net_ls_cardsCommand: net_ls_cardsList all detected network cards with their MAC address. 16.4.13 net_ls_dnsCommand: net_ls_dnsList addresses of DNS servers used during name lookup. 16.4.14 net_ls_routesCommand: net_ls_routesList routing entries. 16.4.15 net_nslookupCommand: net_nslookup name [server]Resolve address of name using DNS server server. If no server is given, use default list of servers. 17 Internationalisation17.1 CharsetGRUB 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 FilesystemsNTFS, JFS, UDF, HFS+, exFAT, long filenames in FAT, Joliet part of ISO9660 are treated as UTF-16 as per specification. AFS and BFS are read as UTF-8, again according to specification. BtrFS, cpio, tar, squash4, minix, minix2, minix3, ROMFS, ReiserFS, XFS, ext2, ext3, ext4, FAT (short names), F2FS, RockRidge part of ISO9660, nilfs2, UFS1, UFS2 and ZFS are assumed to be UTF-8. This might be false on systems configured with legacy charset but as long as the charset used is superset of ASCII you should be able to access ASCII-named files. And it’s recommended to configure your system to use UTF-8 to access the filesystem, convmv may help with migration. ISO9660 (plain) filenames are specified as being ASCII or being described with unspecified escape sequences. GRUB assumes that the ISO9660 names are UTF-8 (since any ASCII is valid UTF-8). There are some old CD-ROMs which use CP437 in non-compliant way. You’re still able to access files with names containing only ASCII characters on such filesystems though. You’re also able to access any file if the filesystem contains valid Joliet (UTF-16) or RockRidge (UTF-8). AFFS, SFS and HFS never use unicode and GRUB assumes them to be in Latin1, Latin1 and MacRoman respectively. GRUB handles filesystem case-insensitivity however no attempt is performed at case conversion of international characters so e.g. a file named lowercase greek alpha is treated as different from the one named as uppercase alpha. The filesystems in questions are NTFS (except POSIX namespace), HFS+ (configurable at mkfs time, default insensitive), SFS (configurable at mkfs time, default insensitive), JFS (configurable at mkfs time, default sensitive), HFS, AFFS, FAT, exFAT and ZFS (configurable on per-subvolume basis by property “casesensitivity”, default sensitive). On ZFS subvolumes marked as case insensitive files containing lowercase international characters are inaccessible. Also like all supported filesystems except HFS+ and ZFS (configurable on per-subvolume basis by property “normalization”, default none) GRUB makes no attempt at check of canonical equivalence so a file name u-diaresis is treated as distinct from u+combining diaresis. This however means that in order to access file on HFS+ its name must be specified in normalisation form D. On normalized ZFS subvolumes filenames out of normalisation are inaccessible. 17.3 Output terminalFirmware 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 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 terminalFirmware 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 GettextGRUB supports being translated. For this you need to have language *.mo files in $prefix/locale, load gettext module and set “lang” variable. 17.6 RegexpRegexps 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 OtherCurrently 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. 18 Security18.1 Authentication and authorisation in GRUBBy 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’ (see password)
and ‘password_pbkdf2’ (see 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 In order to enable authentication support, the ‘superusers’ environment variable must be set to a list of usernames, separated by any of spaces, commas, semicolons, pipes, or ampersands. Superusers are permitted to use the GRUB command line, edit menu entries, and execute any menu entry. If ‘superusers’ is set, then use of the command line and editing of menu entries are automatically restricted to superusers. Setting ‘superusers’ to empty string effectively disables both access to CLI and editing of menu entries. Note: The environment variable needs to be exported to also affect the section defined by the ‘submenu’ command (see submenu). Other users may be allowed to execute specific menu entries by giving a list of usernames (as above) using the --users option to the ‘menuentry’ command (see menuentry). If the --unrestricted option is used for a menu entry, then that entry is unrestricted. If the --users option is not used for a menu entry, then that only superusers are able to use it. Putting this together, a typical grub.cfg fragment might look like this: set superusers="root" password_pbkdf2 root grub.pbkdf2.sha512.10000.biglongstring password user1 insecure menuentry "May be run by any user" --unrestricted { set root=(hd0,1) linux /vmlinuz } menuentry "Superusers only" --users "" { set root=(hd0,1) linux /vmlinuz single } menuentry "May be run by user1 or a superuser" --users user1 { set root=(hd0,2) chainloader +1 } The 18.2 Using digital signatures in GRUBGRUB’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 An initial trusted public key can be embedded within the GRUB core.img using the 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: 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 # Edit /dev/shm/passphrase.txt to contain your signing key's passphrase for i in `find /boot -name "*.cfg" -or -name "*.lst" -or \ -name "*.mod" -or -name "vmlinuz*" -or -name "initrd*" -or \ -name "grubenv"`; do gpg --batch --detach-sign --passphrase-fd 0 $i < \ /dev/shm/passphrase.txt done shred /dev/shm/passphrase.txt See also: check_signatures, verify_detached, trust, list_trusted, distrust, load_env, save_env. Note that internally signature enforcement is controlled by setting the environment variable Note that signature checking does not prevent an attacker with (serial, physical, ...) console access from dropping manually to the GRUB console and executing: To prevent this, password-protection (see 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. 18.3 UEFI secure boot and shim supportThe GRUB, except the All GRUB modules not stored in the core.img, OS kernels, ACPI tables, Device Trees, etc. have to be signed, e.g, using PGP. Additionally, the commands that can be used to subvert the UEFI secure boot mechanism, such as 18.4 Embedded information for generation number based revocationThe Secure Boot Advanced Targeting (SBAT) is a mechanism to allow the revocation of components in the boot path by using generation numbers embedded into the EFI binaries. The SBAT metadata is located in an .sbat data section that has set of UTF-8 strings as comma-separated values (CSV). See https://github.com/rhboot/shim/blob/main/SBAT.md for more details. To add a data section containing the SBAT information into the binary, the --sbat option of grub-mkimage -O x86_64-efi -o grubx64.efi -p '(tftp)/grub' --sbat sbat.csv efinet tftp 18.5 Measuring boot componentsIf the tpm module is loaded and the platform has a Trusted Platform Module installed, GRUB will log each command executed and each file loaded into the TPM event log and extend the PCR values in the TPM correspondingly. All events will be logged into the PCR described below with a type of EV_IPL and an event description as described below.
GRUB will not measure its own core.img - it is expected that firmware will carry this out. GRUB will also not perform any measurements until the tpm module is loaded. As such it is recommended that the tpm module be built into core.img in order to avoid a potential gap in measurement between core.img being loaded and the tpm module being loaded. Measured boot is currently only supported on EFI platforms. 18.6 Lockdown when booting on a secure setupThe GRUB can be locked down when booted on a secure boot environment, for example if the UEFI secure boot is enabled. On a locked down configuration, the GRUB will be restricted and some operations/commands cannot be executed. The ‘lockdown’ variable is set to ‘y’ when the GRUB is locked down. Otherwise it does not exit. 19 Platform limitationsGRUB2 is designed to be portable and is actually ported across platforms. We try to keep all platforms at the level. Unfortunately some platforms are better supported than others. This is detailed in current and 2 following sections. All platforms have an artificially GRUB imposed disk size restriction of 1 EiB. In some cases, larger disk sizes can be used, but access will not be allowed beyond 1 EiB. LUKS2 devices with size larger than 16 EiB are currently not supported. They can not be created as crypto devices by cryptomount, so can not even be partially read from. LUKS have no limitations other than those imposed by the format. ARC platform is unable to change datetime (firmware doesn’t seem to provide a function for it). EMU has similar limitation. On EMU platform no serial port is available. Console charset refers only to firmware-assisted console. gfxterm is always Unicode (see Internationalisation section for its limitations). Serial is configurable to UTF-8 or ASCII (see Internationalisation). In case of qemu and coreboot ports the refered console is vga_text. Loongson always uses gfxterm. Most limited one is ASCII. CP437 provides additionally pseudographics. GRUB2 doesn’t use any language characters from CP437 as often CP437 is replaced by national encoding compatible only in pseudographics. Unicode is the most versatile charset which supports many languages. However the actual console may be much more limited depending on firmware On BIOS, network is supported only if the image is loaded through network. On sparc64, GRUB is unable to determine which server it was booted from. Direct ATA/AHCI support allows to circumvent various firmware limitations but isn’t needed for normal operation except on baremetal ports. AT keyboard support allows keyboard layout remapping and support for keys not available through firmware. It isn’t needed for normal operation except baremetal ports. Speaker allows morse and spkmodem communication. USB support provides benefits similar to ATA (for USB disks) or AT (for USB keyboards). In addition it allows USBserial. Chainloading refers to the ability to load another bootloader through the same protocol Hints allow faster disk discovery by already knowing in advance which is the disk in question. On some platforms hints are correct unless you move the disk between boots. On other platforms it’s just an educated guess. Note that hint failure results in just reduced performance, not a failure BadRAM is the ability to mark some of the RAM as “bad”. Note: due to protocol limitations mips-loongson (with Linux protocol) and mips-qemu_mips can use only memory up to first hole. Bootlocation is ability of GRUB to automatically detect where it boots from. “disk” means the detection is limited to detecting the disk with partition being discovered on install time. “partition” means that disk and partiton can be automatically discovered. “file” means that boot image file name as well as disk and partition can be discovered. For consistency, default install ignores partition and relies solely on disk detection. If no bootlocation discovery is available or boot and grub-root disks are different, UUID is used instead. On ARC if no device to install to is specified, UUID is used instead as well.
20 OutlineSome platforms have features which allows to implement some commands useless or not implementable on others. Quick summary: Information retrieval:
Workarounds for platform-specific issues:
Advanced operations for power users:
Miscelaneous:
21 Supported boot targetsX86 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.
PowerPC, IA64 and Sparc64 ports support only Linux. MIPS port supports Linux and multiboot2. 21.1 Boot testsAs 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:
Required files are:
22 Error messages produced by GRUB22.1 GRUB only offers a rescue shellGRUB’s normal start-up procedure involves setting the ‘prefix’ environment variable to a value set in the core image by 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 (see Invoking grub-install). When doing this, there are a few things to remember:
22.2 Firmware stalls instead of booting GRUBThe EFI implementation of some older MacBook laptops stalls when it gets presented a grub-mkrescue ISO image for x86_64-efi target on an USB stick. Affected are models of year 2010 or earlier. Workaround is to zeroize the bytes 446 to 461 of the EFI partition, where mformat has put a partition table entry which claims partition start at block 0. This change will not hamper bootability on other machines. 23 Invoking grub-installThe program grub-install install_device The device name install_device is an OS device name or a GRUB device name.
Print a summary of the command-line options and exit. --versionPrint the version number of GRUB and exit. --boot-directory=dirInstall 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 is equivalent to grub-install --boot-directory=/boot/ /dev/sda Here is an example in which you have a separate boot partition which is mounted on /mnt/boot: grub-install --boot-directory=/mnt/boot /dev/sdb--recheck Recheck the device map, even if /boot/grub/device.map already exists. You should use this option whenever you add/remove a disk into/from your computer. --no-rs-codesBy default on x86 BIOS systems, 24 Invoking grub-mkconfigThe program grub-mkconfig -o /boot/grub/grub.cfg
Print a summary of the command-line options and exit. --versionPrint the version number of GRUB and exit. -o file--output=fileSend the generated configuration file to file. The default is to send it to standard output. 25 Invoking grub-mkpasswd-pbkdf2The program
Number of iterations of the underlying pseudo-random function. Defaults to 10000. -l number--buflen=numberLength of the generated hash. Defaults to 64. -s number--salt=numberLength of the salt. Defaults to 64. 26 Invoking grub-mkrelpathThe program $ grub-mkrelpath /usr/share/grub/unicode.pf2 ‘/share/grub/unicode.pf2’ This is mainly used internally by other GRUB utilities such as
Print a summary of the command-line options and exit. --versionPrint the version number of GRUB and exit. 27 Invoking grub-mkrescueThe program grub-mkrescue -o grub.iso All arguments not explicitly listed as 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
Print a summary of the command-line options and exit. --versionPrint the version number of GRUB and exit. -o file--output=fileSave output in file. This "option" is required. --modules=modulesPre-load the named GRUB modules in the image. Multiple entries in modules should be separated by whitespace (so you will probably need to quote this for your shell). --rom-directory=dirIf generating images for the QEMU or Coreboot platforms, copy the resulting qemu.img or coreboot.elf files respectively to the dir directory as well as including them in the image. --xorriso=fileUse file as the Use file as the 28 Invoking grub-mountThe program
Using grub-mount /dev/sda1 /mnt
Print a summary of the command-line options and exit. --versionPrint the version number of GRUB and exit. -C--cryptoMount encrypted devices, prompting for a passphrase if necessary. -d string--debug=stringShow debugging output for conditions matching string. -K prompt|file --zfs-key=prompt|fileLoad a ZFS encryption key. If you use ‘prompt’ as the argument, Set the GRUB root device to device. You do not normally need to set this; 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. 29 Invoking grub-probeThe program grub-probe --target=fs /boot/grub grub-probe --target=drive --device /dev/sda1
Print a summary of the command-line options and exit. --versionPrint the version number of GRUB and exit. -d --deviceIf this option is given, then the non-option argument is a system device name (such as ‘/dev/sda1’), and Use file as the device map (see Device map) rather than the default, usually ‘/boot/grub/device.map’. -t target--target=targetPrint information about the given path or device as defined by target. The available targets and their meanings are: ‘fs’GRUB filesystem module. ‘fs_uuid’Filesystem Universally Unique Identifier (UUID). ‘fs_label’Filesystem label. ‘drive’GRUB device name. ‘device’System device name. ‘partmap’GRUB partition map module. ‘abstraction’GRUB abstraction module (e.g. ‘lvm’). ‘cryptodisk_uuid’Crypto device UUID. ‘msdos_parttype’MBR partition type code (two hexadecimal digits). ‘hints_string’A string of platform search hints suitable for passing to the Search hints for the PC BIOS platform. ‘ieee1275_hints’Search hints for the IEEE1275 platform. ‘baremetal_hints’Search hints for platforms where disks are addressed directly rather than via firmware. ‘efi_hints’Search hints for the EFI platform. ‘arc_hints’Search hints for the ARC platform. ‘compatibility_hint’A guess at
a reasonable GRUB drive name for this device, which may be used as a fallback if the System device name for the whole disk. -v--verbosePrint verbose messages. 30 Invoking grub-script-checkThe program grub-script-check /boot/grub/grub.cfg
Print a summary of the command-line options and exit. --versionPrint the version number of GRUB and exit. -v--verbosePrint each line of input after reading it. Appendix A How to obtain and build GRUB
GRUB is available from the GNU alpha archive site ftp://ftp.gnu.org/gnu/grub or any of its mirrors. The file will be named grub-version.tar.gz. The current version is 2.06, so the file you should grab is: ftp://ftp.gnu.org/gnu/grub/grub-2.06.tar.gz To unbundle GRUB use the instruction: zcat grub-2.06.tar.gz | tar xvf - which will create a directory called grub-2.06 with all the sources. You can look at the file INSTALL for detailed instructions on how to build and install GRUB, but you should be able to just do: cd grub-2.06 ./configure make install Also, the latest version is available using Git. See http://www.gnu.org/software/grub/grub-download.html for more information. Appendix B Reporting bugsThese are the guideline for how to report bugs. Take a look at this list below before you submit bugs:
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. Appendix C Where GRUB will goGRUB 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. Appendix D Copying This ManualD.1 GNU Free Documentation LicenseVersion 1.2, November 2002 Copyright © 2000,2001,2002 Free Software Foundation, Inc. 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.
D.1.1 ADDENDUM: How to use this License for your documentsTo 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. Index
Footnotes(1)chain-load is the mechanism for loading unsupported operating systems by loading another boot loader. It is typically used for loading DOS or Windows. (2)The NetBSD/i386 kernel is Multiboot-compliant, but lacks support for Multiboot modules. (3)Only CRC32 data integrity check is supported (xz default is CRC64 so one should use –check=crc32 option). LZMA BCJ filters are supported. (4)There are a few pathological cases where loading a very badly organized ELF kernel might take longer, but in practice this never happen. (5)The LInux LOader, a boot loader that everybody uses, but nobody likes. (6)El Torito is a specification for bootable CD using BIOS functions. (7)Currently a backslash-newline pair within a variable name is not handled properly, so use this feature with some care. (8)However, this behavior will be changed in the future version, in a user-invisible way. Which filename refers to the device driver that allows the OS to communicate with SCSI or ATA drives that arent related to the BIOS?sys – Device driver that allows access to SCSI or ATA drives that are not related to the BIOS. Ntoskrnl.exe – The Windows NTFS operating system kernel.
Which filename refers to a core Win32 subsystem DLL file?Which filename refers to a core Win32 subsystem DLL file? User32.sys.
Which acronym refers to the file system that was introduced when Microsoft created Windows NT?NTFS, which stands for NT file system and the New Technology File System, is the file system that the Windows NT operating system (OS) uses for storing and retrieving files on hard disk drives (HDDs) and solid-state drives (SSDs).
What specifies the Windows XP path installation and contains options for selecting the Windows version?Forensics - M Choic2. |