13. The list of available commands

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

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

13.1 The list of commands for the menu only

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

• The menu-specific commands have to be used before any others.
• The files must be in plain-text format.
• ‘#’ at the beginning of a line in a configuration file means it is only a comment.
• Options are separated by spaces.
• All numbers can be either decimal or hexadecimal. A hexadecimal number must be preceded by ‘0x’, and is case-insensitive.
• Extra options or text at the end of the line are ignored unless otherwise specified.
• Unrecognized commands are added to the current entry, except before entries start, where they are ignored.

These commands can only be used in the menu:

13.1.1 default

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 savedefault. See section savedefault, for more information.

13.1.2 fallback

Command: fallback num...

Go into unattended boot mode: if the default boot entry has any errors, instead of waiting for the user to do something, 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. You can specify multiple fallback entry numbers.

13.1.3 hiddenmenu

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 The hidden menu interface.

13.1.4 timeout

Command: timeout sec

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

13.1.5 title

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.

13.2 The list of general commands

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

13.2.1 bootp

Command: bootp [‘--with-configfile’]

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

If you specify ‘--with-configfile’ to this command, GRUB will fetch and load a configuration file specified by your BOOTP server with the vendor tag ‘150’.

13.2.2 color

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:

• black
• blue
• green
• cyan
• red
• magenta
• brown
• light-gray

  These below can be specified only for the foreground.

• dark-gray
• light-blue
• light-green
• light-cyan
• light-red
• light-magenta
• yellow
• white

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

13.2.3 device

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).

13.2.4 dhcp

Command: dhcp [--with-configfile]

Initialize a network device via the DHCP protocol. Currently, this command is just an alias for bootp, since the two protocols are very similar. This command is only available if GRUB is compiled with netboot support. See also Downloading OS images from a network.

If you specify ‘--with-configfile’ to this command, GRUB will fetch and load a configuration file specified by your DHCP server with the vendor tag ‘150’.

13.2.5 hide

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 DOS/Windows.

13.2.6 ifconfig

Command: ifconfig [‘--server=server’] [‘--gateway=gateway’] [‘--mask=mask’] [‘--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 ‘192.168.11.178’. The order of the options is not important. This command shows current network configuration, if no option is specified. See also Downloading OS images from a network.

13.2.7 pager

Command: pager [flag]

Toggle or set the state of the internal pager. If flag is ‘on’, the internal pager is enabled. If flag is ‘off’, it is disabled. If no argument is given, the state is toggled.

13.2.8 partnew

Command: partnew part type from len

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 is the starting address and len is the length, both in sector units.

13.2.9 parttype

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.

13.2.10 password

Command: password [‘--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 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 continuing. The option ‘--md5’ tells GRUB that passwd is encrypted with md5crypt (see section md5crypt).

13.2.11 rarp

Command: rarp

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

13.2.12 serial

Command: serial [‘--unit=unit’] [‘--port=port’] [‘--speed=speed’] [‘--word=word’] [‘--parity=parity’] [‘--stop=stop’] [‘--device=dev’]

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 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 terminal command is used (see section terminal).

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

13.2.13 setkey

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 letter, 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:

‘exclam’

‘!’

‘at’

‘@’

‘numbersign’

‘#’

‘dollar’

‘$’

‘percent’

‘%’

‘caret’

‘^’

‘ampersand’

‘&’

‘asterisk’

‘*’

‘parenleft’

‘(’

‘parenright’

‘)’

‘minus’

‘-’

‘underscore’

‘_’

‘equal’

‘=’

‘plus’

‘+’

‘bracketleft’

‘[’

‘braceleft’

‘{’

‘bracketright’

‘]’

‘braceright’

‘}’

‘semicolon’

‘;’

‘colon’

‘:’

‘quote’

‘'’

‘doublequote’

‘"’

‘backquote’

‘`’

‘tilde’

‘~’

‘backslash’

‘\’

‘bar’

‘|’

‘comma’

‘,’

‘less’

‘<’

‘period’

‘.’

‘greater’

‘>’

‘slash’

‘/’

‘question’

‘?’

‘space’

‘ ’

13.2.14 splashimage

Command: splashimage file

Select an image to use as the background image. This should be specified using normal GRUB device naming syntax. The format of the file is a gzipped xpm which is 640x480 with a 14 color palette.

13.2.15 terminal

Command: terminal [‘--dumb’] [‘--no-echo’] [‘--no-edit’] [‘--timeout=secs’] [‘--lines=lines’] [‘--silent’] [‘console’] [‘serial’] [‘hercules’]

Select a terminal for user interaction. The terminal is assumed to be VT100-compatible unless ‘--dumb’ is specified. If both ‘console’ and ‘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 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 ‘hercules’ as the argument.

The option ‘--lines’ defines the number of lines in your terminal, and it is used for the internal pager function. If you don’t specify this option, the number is assumed as 24.

The option ‘--silent’ suppresses the message to prompt you to hit any key. This might be useful if your system has no terminal device.

The option ‘--no-echo’ has GRUB not to echo back input characters. This implies the option ‘--no-edit’.

The option ‘--no-edit’ disables the BASH-like editing feature.

13.2.16 terminfo

Command: terminfo ‘--name=name’ ‘--cursor-address=seq’ [‘--clear-screen=seq’] [‘--enter-standout-mode=seq’] [‘--exit-standout-mode=seq’]

Define the capabilities of your terminal. Use this command to define escape sequences, if it is not vt100-compatible. You may use ‘\e’ for <ESC> and ‘^X’ for a control character.

You can use the utility grub-terminfo to generate appropriate arguments to this command. See section Invoking grub-terminfo.

If no option is specified, the current settings are printed.

13.2.17 tftpserver

Command: tftpserver ipaddr

Caution: This command exists only for backward compatibility. Use 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 ‘192.168.0.15’. This command is only available if GRUB is compiled with netboot support. See also Downloading OS images from a network.

13.2.18 unhide

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 on one disk. See also DOS/Windows.

13.3 The list of command-line and menu entry commands

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

13.3.1 blocklist

Command: blocklist file

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

13.3.2 boot

Command: boot

Boot the OS or chain-loader which has been loaded. Only necessary if running the fully interactive command-line (it is implicit at the end of a menu entry).

13.3.3 cat

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

13.3.4 chainloader

Command: chainloader [‘--force’] file

Load file as a chain-loader. Like any other file loaded by the filesystem code, it can use the blocklist notation 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 (see section SCO UnixWare).

13.3.5 cmp

Command: cmp file1 file2

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

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

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

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

If they are completely identical, nothing will be printed.

13.3.6 configfile

Command: configfile file

Load file as a configuration file.

13.3.7 debug

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.

13.3.8 displayapm

Command: displayapm

Display APM BIOS information.

13.3.9 displaymem

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).

13.3.10 embed

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.(9) Print the number of sectors which stage1_5 occupies, if successful.

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

13.3.11 find

Command: find filename

Search for the file name filename in all mountable 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.

13.3.12 fstest

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 install (see section install) or testload (see section testload) commands.

13.3.13 geometry

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 cylinders, the number of heads, the number of sectors and the number of 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.

13.3.14 halt

Command: halt ‘--no-apm’

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

13.3.15 help

Command: help ‘--all’ [pattern …]

Display helpful information about builtin commands. If you do not specify pattern, this command shows short descriptions of most of available commands. If you specify the option ‘--all’ to this command, short descriptions of rarely used commands (such as testload) are displayed as well.

If you specify any patterns, it displays longer information about each of the commands which match those patterns.

13.3.16 impsprobe

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, but not in the grub shell.

13.3.17 initrd

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 GNU/Linux.

13.3.18 install

Command: install [‘--force-lba’] [‘--stage2=os_stage2_file’] stage1_file [‘d’] dest_dev stage2_file [addr] [‘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 setup (see section setup) instead.

In short, it will perform a full install presuming the Stage 2 or Stage 1.5(10) 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 in it a blocklist for loading stage2_file as a Stage 2. If the 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 ‘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 ‘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 unfortunately have to specify the option ‘d’, whether your Stage2 resides at the booting drive or not, if you have such a BIOS. We know these are defective in this way:

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 ‘--force-lba’. Don’t use this option if you know that your BIOS doesn’t have LBA support.

Caution3: You must specify the 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.

13.3.19 ioprobe

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.

13.3.20 kernel

Command: kernel [‘--type=type’] [‘--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 ‘--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 ‘--no-mem-option’ is effective only for Linux. If the option is specified, GRUB doesn’t pass the option ‘mem=’ to the kernel. This option is implied for Linux kernels 2.4.18 and newer.

13.3.21 lock

Command: lock

Prevent normal users from executing arbitrary menu entries. You must use the 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 lock root (hd0,a) kernel /no-security-os

See also Protecting your computer from cracking.

13.3.22 makeactive

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.

13.3.23 map

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 DOS/Windows.

13.3.24 md5crypt

Command: md5crypt

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

13.3.25 module

Command: module file …

Load a boot module file for a Multiboot format boot image (no interpretation of the file contents are made, so the 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 kernel command. You must load a Multiboot kernel image before loading any module. See also modulenounzip.

13.3.26 modulenounzip

Command: modulenounzip file …

The same as module (see section module), except that automatic decompression is disabled.

13.3.27 pause

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.

13.3.28 print

Command: print message …

Print the message. Note that placing <^G> (ASCII code 7) in the message will cause the speaker to emit the standard beep sound, which is useful for visually impaired people.

13.3.29 quit

Command: quit

Exit from the grub shell grub (see section Invoking the grub shell). This command can be used only in the grub shell.

13.3.30 reboot

Command: reboot

Reboot the computer.

13.3.31 read

Command: read addr

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

13.3.32 root

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 rootnoverify.

13.3.33 rootnoverify

Command: rootnoverify device [hdbias]

Similar to 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 root above which derived from attempting the mount will not work correctly.

13.3.34 savedefault

Command: savedefault num

Save the current menu entry or num if specified 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 savedefault title FreeBSD root (hd0,a) kernel /boot/loader savedefault

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

You can specify ‘fallback’ instead of a number. Then, next fallback entry is saved. Next fallback entry is chosen from fallback entries. Normally, this will be the first entry in fallback ones.

See also default and Invoking grub-set-default.

13.3.35 setup

Command: setup [‘--force-lba’] [‘--stage2=os_stage2_file’] [‘--prefix=dir’] install_device [image_device]

Set up the installation of GRUB automatically. This command uses the more flexible 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 root. If install_device is a hard disk, then embed a Stage 1.5 in the disk if possible.

The 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 ‘--force-lba’ and ‘--stage2’ are just passed to install if specified. See section install, for more information.

13.3.36 testload

Command: testload file

Read the entire contents of file in several different ways and compare 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.

13.3.37 testvbe

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 vbeprobe.

13.3.38 uppermem

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.

13.3.39 vbeprobe

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 testvbe.

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