In this chapter, we list all commands that are available in GRUB.
Commands belong to different groups. A few can only be used in the global section of the configuration file (or "menu"); most of them can be entered on the command line and can be either used in the menu or in the menu entries.
The semantics used in parsing the configuration file are the following:
These commands can only be used in the menu:
default
command). This obviously won't help if the machine was rebooted by a
kernel that GRUB loaded.
lock
. If
the password passwd is entered, it loads the new-config-file
as a new config file and restarts the GRUB Stage 2, if
new-config-file is specified. Otherwise, GRUB will just unlock the
privileged instructions.
Commands usable both in the menu and in the command line.
foreground/background
. foreground and
background are symbolic color names. A symbolic color name must be
one of these:
But only the first eight names can be used for background. You can
prefix blink-
to foreground if you want a blinking
foreground color.
This command can be used in the configuration file and on the command line, so you may write something like this in your configuration file:
# Set default colors. color light-gray/blue black/light-gray # Change the colors. title OS-BS like color magenta/blue black/magenta
grub> device (fd0) /floppy-image grub> device (hd0) /dev/sd0
This command can be used only in the grub shell (see section Invoking the grub shell).
bootp
, since the two
protocols are very similar. This command
is only available if GRUB is compiled with netboot support.
0-0xff
; from and
to are the starting and ending sectors, expressed as an absolute
sector number.
The serial port is not used as a communication channel unless the terminal command is used.
This command is only available if GRUB is compiled with serial support.
Note also that this command does not exchange the keys. If you want to exchange the keys, run this command again with the arguments exchanged, like this:
grub> setkey capslock control grub> setkey control capslock
A key must be an alphabet, a digit, or one of these symbols: `escape', `exclam', `at', `numbersign', `dollar', `percent', `caret', `ampersand', `asterisk', `parenleft', `parenright', `minus', `underscore', `equal', `plus', `backspace', `tab', `bracketleft', `braceleft', `bracketright', `braceright', `enter', `control', `semicolon', `colon', `quote', `doublequote', `backquote', `tilde', `shift', `backslash', `bar', `comma', `less', `period', `greater', `slash', `question', `alt', `space', `capslock', `FX' (`X' is a digit), and `delete'. This table describes to which character each of the symbols corresponds:
These commands are usable in the command line and in menu entries. If
you forget a command, you can run the command help
.
grub> cat /etc/fstab
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.
/boot/grub/stage1
.
install
or testload
commands.
In slightly more detail, it will load stage1_file, validate that it is a GRUB Stage 1 of the right version number, install a blocklist for loading stage2_file as a Stage 2. If the option @option{d} is present, the Stage 1 will always look for the actual disk stage2_file was installed on, rather than using the booting drive. The Stage 2 will be loaded at address addr, which must be `0x8000' for a true Stage 2, and `0x2000' for a Stage 1.5. If addr is not present, GRUB will determine the address automatically. It then writes the completed Stage 1 to the first block of the device dest_dev. If the options @option{p} or config_file are present, then it reads the first block of stage2, modifies it with the values of the partition stage2_file was found on (for @option{p}) or places the string config_file into the area telling the stage2 where to look for a configuration file at boot time. Likewise, if real_config_file is present and stage2_file is a Stage 1.5, then the Stage 2 config_file is patched with the configuration filename real_config_file. This command preserves the DOS BPB (and for hard disks, the partition table) of the sector the Stage 1 is to be installed into.
Caution: Several buggy BIOSes don't pass a booting drive properly when booting from a hard disk drive. Therefore, you will have to specify the option @option{d}, whether your Stage2 resides at the booting drive or not, if you have such a BIOS unfortunately. We know these are defective in that:
Caution2: A number of BIOSes don't return a correct LBA support bitmap even if they do have the support. So GRUB provides a solution to ignore the wrong bitmap, that is, the option @option{--force-lba}. Don't use this option if you know that your BIOS doesn't have LBA support.
This command also accepts the option @option{--type} so that you can specify the kernel type of file explicitly. The argument type must be one of these: `netbsd', `freebsd', `openbsd', `linux', `biglinux', and `multiboot'. However, you need to specify it only if you want to load a NetBSD ELF kernel, because GRUB can automatically determine a kernel type in the other cases, quite safely.
password
if you really want this command to be
useful.
This command is used in a menu, as shown in this this example:
title This entry is too dangerous to be executed by normal users lock root (hd0,a) kernel /no-security-os
grub> map (hd0) (hd1) grub> map (hd1) (hd0)
The example exchanges the order between the first hard disk and the second hard disk.
kernel
command. You must load a Multiboot kernel image before
loading any module.
module
, except that automatic decompression is
disabled.
grub
(see section Invoking the grub shell). This command can be used only in the GRUB shell.
ES:ESI
, used by some chain-loaded boot loaders), the
BSD drive-type (for booting BSD kernels using their native boot format),
and correctly determine the PC partition where a BSD sub-partition is
located. The optional hdbias parameter is a number to tell a BSD
kernel how many BIOS drive numbers are on controllers before the current
one. For example, if there is an IDE disk and a SCSI disk, and your
FreeBSD root partition is on the SCSI disk, then use a `1' for
hdbias.
root
, but don't attempt to mount the
partition. This is useful for when an OS is outside of the area of the
disk that GRUB can read, but setting the correct root device is still
desired. Note that the items mentioned in root
above which
derived from attempting the mount will not work correctly.
install
in the backend and installs GRUB
into the device install_device. If image_device is
specified, then find the GRUB images in the device image_device,
otherwise use the current root device, which can be set by the
command root
. If install_device is a hard disk, then
embed a Stage 1.5 in the disk if possible.
The option @option{--force-lba} is just passed to install
if
specified. See the description on install
, for more
information.
Caution: This should be used with great caution, and should only be necessary on some old machines. GRUB's BIOS probe can pick up all RAM on all new machines the author has ever heard of. It can also be used for debugging purposes to lie to an OS.
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