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The list of available commands

In this chapter, we list all commands that are available in GRUB.

Commands belong to different groups. A few can only be used in the global section of the configuration file (or "menu"); most of them can be entered on the command-line and can be either used in the menu or in the menu entries.

The list of commands for the menu only

The semantics used in parsing the configuration file are the following:

These commands can only be used in the menu:


Command: default num
Set the default entry to the entry number num. Numbering starts from 0, and the entry number 0 is the default if the command is not used.

You can specify `saved' instead of a number. In this case, the default entry is the entry saved with the command @command{savedefault}. See section savedefault, for more information.


Command: fallback num
Go into unattended boot mode: if the default boot entry has any errors, instead of waiting for the user to do anything, immediately start over using the num entry (same numbering as the default command (see section default)). This obviously won't help if the machine was rebooted by a kernel that GRUB loaded.


Command: hiddenmenu
Don't display the menu. If the command is used, no menu will be displayed on the control terminal, and the default entry will be booted after the timeout expired. The user can still request the menu to be displayed by pressing ESC before the timeout expires. See also section The hidden menu interface.


Command: timeout sec
Set a timeout, in sec seconds, before automatically booting the default entry (normally the first entry defined).


Command: title name ...
Start a new boot entry, and set its name to the contents of the rest of the line, starting with the first non-space character.

The list of general commands

Commands usable both in the menu and in the command-line.


Command: bootp [@option{--with-configfile}]
Initialize a network device via the BOOTP protocol. This command is only available if GRUB is compiled with netboot support. See also section Downloading OS images from a network.

If you specify @option{--with-configfile} to this command, GRUB will fetch and load a configuration file specified by your BOOTP server with the vendor tag `150'.


Command: color normal [highlight]
Change the menu colors. The color normal is used for most lines in the menu (see section The simple menu interface), and the color highlight is used to highlight the line where the cursor points. If you omit highlight, then the inverted color of normal is used for the highlighted line. The format of a color is 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


Command: device drive file
In the grub shell, specify the file file as the actual drive for a BIOS drive drive. You can use this command to create a disk image, and/or to fix the drives guessed by GRUB when GRUB fails to determine them correctly, like this:

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).


Command: dhcp [--with-configfile]
Initialize a network device via the DHCP protocol. Currently, this command is just an alias for @command{bootp}, since the two protocols are very similar. This command is only available if GRUB is compiled with netboot support. See also section Downloading OS images from a network.

If you specify @option{--with-configfile} to this command, GRUB will fetch and load a configuration file specified by your DHCP server with the vendor tag `150'.


Command: hide partition
Hide the partition partition by setting the hidden bit in its partition type code. This is useful only when booting DOS or Windows and multiple primary FAT partitions exist in one disk. See also section DOS/Windows.


Command: ifconfig [@option{--server=server}] [@option{--gateway=gateway}] [@option{--mask=mask}] [@option{--address=address}]
Configure the IP address, the netmask, the gateway, and the server address of a network device manually. The values must be in dotted decimal format, like `'. The order of the options is not important. This command shows current network configuration, if no option is specified. See also section Downloading OS images from a network.


Command: partnew part type from to
Create a new primary partition. part is a partition specification in GRUB syntax (see section Naming convention); type is the partition type and must be a number in the range 0-0xff; from and to are the starting and ending sectors, expressed as an absolute sector number.


Command: parttype part type
Change the type of an existing partition. part is a partition specification in GRUB syntax (see section Naming convention); type is the new partition type and must be a number in the range 0-0xff.


Command: password [@option{--md5}] passwd [new-config-file]
If used in the first section of a menu file, disable all interactive editing control (menu entry editor and command-line) and entries protected by the command @command{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. You can also use this command in the script section, in which case it will ask for the password, before continueing. The option @option{--md5} tells GRUB that passwd is encrypted with @command{md5crypt} (see section md5crypt).


Command: rarp
Initialize a network device via the RARP protocol. This command is only available if GRUB is compiled with netboot support. See also section Downloading OS images from a network.


Command: serial [@option{--unit=unit}] [@option{--port=port}] [@option{--speed=speed}] [@option{--word=word}] [@option{--parity=parity}] [@option{--stop=stop}] [@option{--device=dev}]
Initialize a serial device. unit is a number in the range 0-3 specifying which serial port to use; default is 0, that corresponds 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 are 1 or 2. Default is 8 data bits and one stop bit. parity is one of `no', `odd', `even' and defaults to `no'. The option @option{--device} can only be used in the grub shell and is used to specify the tty device to be used in the host operating system (see section Invoking the grub shell).

The serial port is not used as a communication channel unless the @command{terminal} command is used (see section terminal).

This command is only available if GRUB is compiled with serial support. See also section Using GRUB via a serial line.


Command: setkey [to_key from_key]
Change the keyboard map. The key from_key is mapped to the key to_key. If no argument is specified, reset key mappings. Note 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:

` '


Command: terminal [@option{--dumb}] [@option{--timeout=secs}] [@option{console}] [@option{serial}] [@option{hercules}]
Select a terminal for user interaction. The terminal is assumed to be VT100-compatible unless @option{--dumb} is specified. If both @option{console} and @option{serial} are specified, then GRUB will use the one where a key is entered first or the first when the timeout expires. If neither are specified, the current setting is reported. This command is only available if GRUB is compiled with serial support. See also section Using GRUB via a serial line.

This may not make sense for most users, but GRUB supports Hercules console as well. Hercules console is usable like the ordinary console, and the usage is quite similar to that for serial terminals: specify @option{hercules} as the argument.


Command: tftpserver ipaddr
Caution: This command exists only for backward compatibility. Use @command{ifconfig} (see section ifconfig) instead.

Override a TFTP server address returned by a BOOTP/DHCP/RARP server. The argument ipaddr must be in dotted decimal format, like `'. This command is only available if GRUB is compiled with netboot support. See also section Downloading OS images from a network.


Command: unhide partition
Unhide the partition partition by clearing the hidden bit in its partition type code. This is useful only when booting DOS or Windows and multiple primary partitions exist in one disk. See also section DOS/Windows.

The list of command-line and menu entry commands

These commands are usable in the command-line and in menu entries. If you forget a command, you can run the command @command{help} (see section help).


Command: blocklist file
Print the block list notation of the file file. See section How to specify block lists.


Command: boot
Boot the OS/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).


Command: cat file
Display the contents of the file file. This command may be useful to remind you of your OS's root partition:

grub> cat /etc/fstab


Command: chainloader [@option{--force}] file
Load file as a chain-loader. Like any other file loaded by the filesystem code, it can use the blocklist notation to grab the first sector of the current partition with `+1'. If you specify the option @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 (see section SCO UnixWare).


Command: cmp file1 file2
Compare the file file1 with the file file2. If they differ in size, print the sizes like this:

Differ in size: 0x1234 [foo], 0x4321 [bar]

If the sizes are equal but the bytes at an offset differ, then print the bytes like this:

Differ at the offset 777: 0xbe [foo], 0xef [bar]

If they are completely identical, nothing will be printed.


Command: configfile file
Load file as a configuration file.


Command: debug
Toggle debug mode (by default it is off). When debug mode is on, some extra messages are printed to show disk activity. This global debug flag is mainly useful for GRUB developers when testing new code.


Command: displayapm
Display APM BIOS information.


Command: displaymem
Display what GRUB thinks the system address space map of the machine is, including all regions of physical RAM installed. GRUB's upper/lower memory display uses the standard BIOS interface for the available memory in the first megabyte, or lower memory, and a synthesized number from various BIOS interfaces of the memory starting at 1MB and going up to the first chipset hole for upper memory (the standard PC upper memory interface is limited to reporting a maximum of 64MB).


Command: embed stage1_5 device
Embed the Stage 1.5 stage1_5 in the sectors after the MBR if device is a drive, or in the boot loader area if device is a FFS partition or a ReiserFS partition.(8) Print the number of sectors which stage1_5 occupies, if successful.

Usually, you don't need to run this command directly. See section setup.


Command: find filename
Search for the file name filename in all of partitions and print the list of the devices which contain the file. The file name filename should be an absolute file name like /boot/grub/stage1.


Command: fstest
Toggle filesystem test mode. Filesystem test mode, when turned on, prints out data corresponding to all the device reads and what values are being sent to the low-level routines. The format is `<partition-offset-sector, byte-offset, byte-length>' for high-level reads inside a partition, and `[disk-offset-sector]' for low-level sector requests from the disk. Filesystem test mode is turned off by any use of the @command{install} (see section install) or @command{testload} (see section testload) commands.


Command: geometry drive [cylinder head sector [total_sector]]
Print the information for the drive drive. In the grub shell, you can set the geometry of the drive arbitrarily. The number of the cylinders, the one of the heads, the one of the sectors and the one of the total sectors are set to CYLINDER, HEAD, SECTOR and TOTAL_SECTOR, respectively. If you omit TOTAL_SECTOR, then it will be calculated based on the C/H/S values automatically.


Command: halt @option{--no-apm}
The command halts the computer. If the @option{--no-apm} option is specified, no APM BIOS call is performed. Otherwise, the computer is shut down using APM.


Command: help [pattern ...]
Display helpful information about builtin commands. If you do not specify pattern, this command shows short descriptions of all available commands. If you specify any patterns, it displays longer information about each of the commands which match those patterns.


Command: impsprobe
Probe the Intel Multiprocessor Specification 1.1 or 1.4 configuration table and boot the various CPUs which are found into a tight loop. This command can be used only in the Stage 2.


Command: initrd file ...
Load an initial ramdisk for a Linux format boot image and set the appropriate parameters in the Linux setup area in memory. See also section GNU/Linux.


Command: install [@option{--force-lba}] [@option{--stage2=os_stage2_file}] stage1_file [@option{d}] dest_dev stage2_file [addr] [@option{p}] [config_file] [real_config_file]
This command is fairly complex, and you should not use this command unless you are familiar with GRUB. Use @command{setup} (see section setup) instead.

In short, it will perform a full install presuming the Stage 2 or Stage 1.5(9) is in its final install location.

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 file name 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:

Fujitsu LifeBook 400 BIOS version 31J0103A
HP Vectra XU 6/200 BIOS version GG.06.11

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.

Caution3: You must specify the option @option{--stage2} in the grub shell, if you cannot unmount the filesystem where your stage2 file resides. The argument should be the file name in your operating system.


Command: ioprobe drive
Probe I/O ports used for the drive drive. This command will list the I/O ports on the screen. For technical information, See section Hacking GRUB.


Command: kernel [@option{--type=type}] [@option{--no-mem-option}] file ...
Attempt to load the primary boot image (Multiboot a.out or ELF, Linux zImage or bzImage, FreeBSD a.out, NetBSD a.out, etc.) from file. The rest of the line is passed verbatim as the kernel command-line. Any modules must be reloaded after using this command.

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.

The option @option{--no-mem-option} is effective only for Linux. If the option is specified, GRUB doesn't pass the option @option{mem=} to the kernel.


Command: lock
Prevent normal users from executing arbitrary menu entries. You must use the command @command{password} if you really want this command to be useful (see section password).

This command is used in a menu, as shown in this example:

title This entry is too dangerous to be executed by normal users
root (hd0,a)
kernel /no-security-os

See also section Protecting your computer from cracking.


Command: makeactive
Set the active partition on the root disk to GRUB's root device. This command is limited to primary PC partitions on a hard disk.


Command: map to_drive from_drive
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. Here is an example:

grub> map (hd0) (hd1)
grub> map (hd1) (hd0)

The example exchanges the order between the first hard disk and the second hard disk. See also section DOS/Windows.


Command: md5crypt
Prompt to enter a password, and encrypt it in MD5 format. The encrypted password can be used with the command @command{password} (see section password). See also section Protecting your computer from cracking.


Command: module file ...
Load a boot module file for a Multiboot format boot image (no interpretation of the file contents are made, so that user of this command must know what the kernel in question expects). The rest of the line is passed as the module command-line, like the @command{kernel} command. You must load a Multiboot kernel image before loading any module. See also section modulenounzip.


Command: modulenounzip file ...
The same as @command{module} (see section module), except that automatic decompression is disabled.


Command: pause message ...
Print the message, then wait until a key is pressed. Note that placing ^G (ASCII code 7) in the message will cause the speaker to emit the standard beep sound, which is useful when prompting the user to change floppies.


Command: quit
Exit from the grub shell @command{grub} (see section Invoking the grub shell). This command can be used only in the grub shell.


Command: reboot
Reboot the computer.


Command: read addr
Read a 32-bit value from memory at address addr and display it in hex format.


Command: root device [hdbias]
Set the current root device to the device device, then attempt to mount it to get the partition size (for passing the partition descriptor in 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.

See also section rootnoverify.


Command: rootnoverify device [hdbias]
Similar to @command{root} (see section 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 @command{root} above which derived from attempting the mount will not work correctly.


Command: savedefault
Save the current menu entry as a default entry. Here is an example:

default saved
timeout 10

title GNU/Linux
root (hd0,0)
kernel /boot/vmlinuz root=/dev/sda1 vga=ext
initrd /boot/initrd

title FreeBSD
root (hd0,a)
kernel /boot/loader

With this configuration, GRUB will choose the entry booted previously as the default entry. See also section default.


Command: setup [@option{--force-lba}] [@option{--stage2=os_stage2_file}] [@option{--prefix=dir}] install_device [image_device]
Set up the installation of GRUB automatically. This command uses the more flexible command @command{install} (see section install) in the backend and installs GRUB into the device install_device. If image_device is specified, then find the GRUB images (see section GRUB image files) in the device image_device, otherwise use the current root device, which can be set by the command @command{root}. If install_device is a hard disk, then embed a Stage 1.5 in the disk if possible.

The option @option{--prefix} specifies the directory under which GRUB images are put. If it is not specified, GRUB automatically searches them in `/boot/grub' and `/grub'.

The options @option{--force-lba} and @option{--stage2} are just passed to @command{install} if specified. See section install, for more information.


Command: testload file
Read the entire contents of file in several different ways and compares them, to test the filesystem code. The output is somewhat cryptic, but if no errors are reported and the final `i=X, filepos=Y' reading has X and Y equal, then it is definitely consistent, and very likely works correctly subject to a consistent offset error. If this test succeeds, then a good next step is to try loading a kernel.


Command: testvbe mode
Test the VESA BIOS EXTENSION mode mode. This command will switch your video card to the graphics mode, and show an endless animation. Hit any key to return. See also section vbeprobe.


Command: uppermem kbytes
Force GRUB to assume that only kbytes kilobytes of upper memory are installed. Any system address range maps are discarded.

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.


Command: vbeprobe [mode]
Probe VESA BIOS EXTENSION information. If the mode mode is specified, show only the information about mode. Otherwise, this command lists up available VBE modes on the screen. See also section testvbe.

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