grub/docs/commands.txt

Listing of commands available in the configuration files, a subset of
which is usable on the command-line.

The interpretation of the config file represents a simple state-machine,
where:

  (1) Config-file specific commands have to be used before any others.
  (2) A multiboot kernel must be loaded before modules can be.
  (3) A kernel must be loaded before either the config-file entry ends,
        or any "boot" command is issued in any case.

Semantics are as follows:

  -- The files *must* be in plain-text format!!

  -- "#" at the beginning of a line means it is a comment line in a config
     file only.

  -- Options are separated by spaces.

  -- All numbers can be either decimal or hexidecimal.  A hexidecimal number
     must be preceeded by "0x", and is case insensitive.

  -- Extra options/text at the end of the line is ignored unless otherwise
     specified.

  -- Bad commands generally get included in the current entry being added
     to, except before entries start, where they are ignored.


Notes for interpreting commands described in double-quotes below:

  -- "literal_string" : means use the string "literal_string".
  -- "<name>" : means the whole name "<name>" represents some variable
		quantity that is interpreted at runtime (like a number
		or device/file name).
  -- "[option]" : means "option" is may be omitted.
  -- "..." : means extra text included at the end of the line is used for
		some purpose.


Commands usable in config files only.

  --  "timeout= <sec>"
	Sets a timeout, in <sec> seconds, before automatically booting the
	default entry (normally the first entry defined).

  --  "default= <num>"
	Sets the default entry to entry number <num> (otherwise it is 0,
	the first entry).

  --  "fallback= <num>"
	Goes into unattended boot mode:  if the default boot entry has any
	errors, instead of waiting for the user to do anything, it
	immediately starts over using the <num> entry (same numbering
	as the "default=" command).  This obviously doesn't help if the
	machine was in the middle of the boot process (after leaving GRUBs
	code) and rebooted.

  --  "password= <passwd> <new_config_file>"
	Disables all interactive editing control (menu entry editor
	and command-line).  If the password <passwd> is entered, it
	loads the <new_config_file> as a new config file and restarts
	the GRUB Stage 2.

  --  "title= ..."
	Starts a new menu entry, and sets it's name to the contents of the
	rest of the line, starting with the first non-space character.


Commands usable in config files and interactively.

  --  "pause= ..."
	Prints the entirety of "pause= ..." to the end of it's line, then
	waits until a key is pressed.

	NOTE that placing a ^G in it will cause the speaker to emit the
	standard beep sound, which is useful when asking the user to change
	floppies, etc.

  --  "uppermem= <kbytes>"
	Forces GRUB to ignore what it found during the autoprobe of the
	memory available to the system, and to use <kbytes> as the number
	of kilobytes of upper memory installed.  Any address range maps
	of the system are discarded.

	NOTE:  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.

  --  "root= <device> [<hdbias>]"
	Sets the current "root partition" to the device <device>, then
	attempts to mount it to get the partition size (for passing the
	partition descriptor in ES:ESI, used by some chainloaded
	bootloaders), the BSD drive-type (for booting BSD kernels using
	their native boot format), and fixup automatic determination of
	the PC partition where a BSD sub-partition is located.  The optional
	<hdbias> parameter is a number to tell a kernel which is using
	one of the BSD boot methodologies how many BIOS drive numbers
	are on controllers before the current one.  An example is if there
	is an IDE disk and a SCSI disk, then set the root partition
	normally, except for a kernel using a BSD boot methodology
	(FreeBSD or NetBSD), then use a "1" for <hdbias>.

  --  "rootnoverify= <device> [<hdbias>]"
	Similar to "root=", but doesn'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 partition is still
	desired.

	NOTE: the items mentioned in "root=" above which are derived from
	attempting the mount will NOT work correctly.

  --  "chainloader= <file>"
	Loads <file> as a chainloader.

	NOTE: 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".

  --  "kernel= <file> ..."
	Attempts to load the primary boot image (Multiboot a.out or ELF,
	Linux zImage or bzImage, FreeBSD-a.out, or NetBSD-a.out) from
	<file>.  This command ignores the rest of the contents of the line,
	except that the entire line starting with the kernel filename is
	passed verbatim as the "kernel command-line".  The module state is
	reset by this (i.e. reload any modules).

  --  "module= <file> ..."
	Loads a boot module for a Multiboot format boot image (no
	interpretation of the file contents are made, so the user of this
	command/writer of the config file must know what the kernel in
	question works with).  The rest of the line is passed as the "module
	command-line" much like with the "kernel=" command.

  --  "modulenounzip= <file> ..."
	Exactly like "module", except that automatic decompression is
	disabled.

  --  "initrd= <file> ..."
	Loads an initial ramdisk for a Linux format boot image and sets
	the appropriate parameters in the Linux setup area in memory.

  --  "install= <stage1_file> [d] <dest_dev> <file> <addr> [p] [<config_file>]"
	This command is fairly complex, and for detailed examples one
	should look at the install documentation.  In short, it will
	perform a full install presuming the stage1.5 or stage2 (they're
	loaded the same way, I'll just refer to it as a stage2 from now on)
	is in it's final install location (pretty much all other edits are
	performed by the "install=" command).

	In slightly more detail, it will load <stage1_file>, validate
	that it is a GRUB stage1 of the right version number, install
	blocklists for loading <file> (if the option "d" is present,
	the stage1 will always look for the actual disk <file> was
	installed on, rather than using the booting drive) as a stage2
	into memory at address <addr> (for a stage1.5, an address of
	0x2000 should be used, and for a stage2, an address of 0x8000
	should be used), then write the completed stage1 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 <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.  Finally, it
	preserves the DOS BPB (and for hard disks, the partition table) of
	the sector the stage1 is to be installed into.

  --  "makeactive"
	Sets the active partition on the root disk to GRUB's root partition
	(on a floppy this is a NO-OP).  This is limited to working with
	"primary" PC partitions.

  --  "boot"
	This boots the OS/chainloader which has been loaded.  Only necessary
	if running the fully interactive command-line (it is implicit at the
	end of a config-file entry).


Commands usable in config files and interactively which are only available
in the debug version of the GRUB Stage 2.

  --  "testload= <file>"
	Reads the entire contents of <file> in several different ways and
	compares them, to test the filesystem code.  The output is somewhat
	cryptic (see the "T" subcommand of "syscmd=" below), but if no
	errors are reported and the part right at the end which reads
	"i=<X>, filepos=<Y>" has <X> and <Y> equal, then it is definitely
	consistent, and very likely works correctly subject to a consistent
	offset error.  A good idea if this works is then to try loading a
	kernel with your code.

  --  "read= <addr>"
	Reads a 32-bit unsigned value at address <addr> and displays it
	in hex format.

  --  "displaymem"
	Displays what GRUB thinks the system address space map of the
	machine is, including all regions of physical RAM installed.
	The "upper/lower memory" thing GRUB has 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).

  --  "impsprobe"
	Probes Intel MPS spec 1.1 or 1.4 configuration table and boots
	the various other CPUs which are found into a tight loop.

  --  "fstest"
	Toggles filesystem test mode.

	Filesytem 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:

		"<sector, byte_offset, byte_len>"  for high-level reads
			inside a partition (so "sector" is an offset from
			the start of the partition).
		"[sector]"  for low-level sector requests from the disk
			(so "sector" is offset from the start of the disk).

	Filesystem test mode is turned off by any uses of the "install=" or
	"testload=" commands.