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LOADER(8)		  BSD System Manager's Manual		     LOADER(8)

     loader -- kernel bootstrapping final stage

     The program called	loader is the final stage of FreeBSD's kernel boot-
     strapping process.	 On IA32 (i386)	architectures, it is a BTX client.  It
     is	linked statically to libstand(3) and usually located in	the directory

     It	provides a scripting language that can be used to automate tasks, do
     pre-configuration or assist in recovery procedures.  This scripting lan-
     guage is roughly divided in two main components.  The smaller one is a
     set of commands designed for direct use by	the casual user, called
     "builtin commands"	for historical reasons.	 The main drive	behind these
     commands is user-friendliness.  The bigger	component is an	ANS Forth com-
     patible Forth interpreter based on	FICL, by John Sadler.

     During initialization, loader will	probe for a console and	set the
     console variable, or set it to serial console ("comconsole") if the pre-
     vious boot	stage used that.  If multiple consoles are selected, they will
     be	listed separated by spaces.  Then, devices are probed, currdev and
     loaddev are set, and LINES	is set to 24.  Next, FICL is initialized, the
     builtin words are added to	its vocabulary,	and /boot/boot.4th is pro-
     cessed if it exists.  No disk switching is	possible while that file is
     being read.  The inner interpreter	loader will use	with FICL is then set
     to	interpret, which is FICL's default.  After that, /boot/loader.rc is
     processed if available, and, failing that,	/boot/boot.conf	is read	for
     historical	reasons.  These	files are processed through the	include	com-
     mand, which reads all of them into	memory before processing them, making
     disk changes possible.

     At	this point, if an autoboot has not been	tried, and if autoboot_delay
     is	not set	to "NO"	(not case sensitive), then an autoboot will be tried.
     If	the system gets	past this point, prompt	will be	set and	loader will
     engage interactive	mode.  Please note that	historically even when
     autoboot_delay is set to "0" user will be able to interrupt autoboot
     process by	pressing some key on the console while kernel and modules are
     being loaded.  In some cases such behaviour may be	undesirable, to	pre-
     vent it set autoboot_delay	to "-1", in this case loader will engage in-
     teractive mode only if autoboot has failed.

     In	loader,	builtin	commands take parameters from the command line.	 Pres-
     ently, the	only way to call them from a script is by using	evaluate on a
     string.  If an error condition occurs, an exception will be generated,
     which can be intercepted using ANS	Forth exception	handling words.	 If
     not intercepted, an error message will be displayed and the interpreter's
     state will	be reset, emptying the stack and restoring interpreting	mode.

     The builtin commands available are:

     autoboot [seconds [prompt]]
	     Proceeds to bootstrap the system after a number of	seconds, if
	     not interrupted by	the user.  Displays a countdown	prompt warning
	     the user the system is about to be	booted,	unless interrupted by
	     a key press.  The kernel will be loaded first if necessary.  De-
	     faults to 10 seconds.

	     Displays statistics about disk cache usage.  For debugging	only.

     boot kernelname [...]
     boot -flag	...
	     Immediately proceeds to bootstrap the system, loading the kernel
	     if	necessary.  Any	flags or arguments are passed to the kernel,
	     but they must precede the kernel name, if a kernel	name is	pro-

	     WARNING: The behavior of this builtin is changed if loader.4th(8)
	     is	loaded.

     echo [-n] [<message>]
	     Displays text on the screen.  A new line will be printed unless
	     -n	is specified.

     heap    Displays memory usage statistics.	For debugging purposes only.

     help [topic [subtopic]]
	     Shows help	messages read from /boot/  The special
	     topic index will list the topics available.

     include file [file	...]
	     Process script files.  Each file, in turn,	is completely read
	     into memory, and then each	of its lines is	passed to the command
	     line interpreter.	If any error is	returned by the	interpreter,
	     the include command aborts	immediately, without reading any other
	     files, and	returns	an error itself	(see ERRORS).

     load [-t type] file ...
	     Loads a kernel, kernel loadable module (kld), disk	image, or file
	     of	opaque contents	tagged as being	of the type type.  Kernel and
	     modules can be either in a.out or ELF format.  Any	arguments
	     passed after the name of the file to be loaded will be passed as
	     arguments to that file.  Use the md_image type to make the	kernel
	     create a file-backed md(4)	disk.  This is useful for booting from
	     a temporary rootfs.  Currently, argument passing does not work
	     for the kernel.

     load_geli [-n keyno] prov file
	     Loads a geli(8) encryption	keyfile	for the	given provider name.
	     The key index can be specified via	keyno or will default to zero.

     ls	[-l] [path]
	     Displays a	listing	of files in the	directory path,	or the root
	     directory if path is not specified.  If -l	is specified, file
	     sizes will	be shown too.

     lsdev [-v]
	     Lists all of the devices from which it may	be possible to load
	     modules.  If -v is	specified, more	details	are printed.

     lsmod [-v]
	     Displays loaded modules.  If -v is	specified, more	details	are

     more file [file ...]
	     Display the files specified, with a pause at each LINES dis-

     pnpscan [-v]
	     Scans for Plug-and-Play devices.  This is not functional at

     read [-t seconds] [-p prompt] [variable]
	     Reads a line of input from	the terminal, storing it in variable
	     if	specified.  A timeout can be specified with -t,	though it will
	     be	canceled at the	first key pressed.  A prompt may also be dis-
	     played through the	-p flag.

     reboot  Immediately reboots the system.

     set variable
     set variable=value
	     Set loader's environment variables.

     show [variable]
	     Displays the specified variable's value, or all variables and
	     their values if variable is not specified.

     unload  Remove all	modules	from memory.

     unset variable
	     Removes variable from the environment.

     ?	     Lists available commands.

     The loader	has actually two different kinds of `environment' variables.
     There are ANS Forth's environmental queries, and a	separate space of en-
     vironment variables used by builtins, which are not directly available to
     Forth words.  It is the latter type that this section covers.

     Environment variables can be set and unset	through	the set	and unset
     builtins, and can have their values interactively examined	through	the
     use of the	show builtin.  Their values can	also be	accessed as described

     Notice that these environment variables are not inherited by any shell
     after the system has been booted.

     A few variables are set automatically by loader.  Others can affect the
     behavior of either	loader or the kernel at	boot.  Some options may	re-
     quire a value, while others define	behavior just by being set.  Both
     types of builtin variables	are described below.

	       Number of seconds autoboot will wait before booting.  If	this
	       variable	is not defined,	autoboot will default to 10 seconds.

	       If set to "NO", no autoboot will	be automatically attempted af-
	       ter processing /boot/loader.rc, though explicit autoboot's will
	       be processed normally, defaulting to 10 seconds delay.

	       If set to "0", no delay will be inserted, but user still	will
	       be able to interrupt autoboot process and escape	into the in-
	       teractive mode by pressing some key on the console while	kernel
	       and modules are being loaded.

	       If set to "-1", no delay	will be	inserted and loader will en-
	       gage interactive	mode only if autoboot has failed for some rea-

	       Instructs the kernel to prompt the user for the name of the
	       root device when	the kernel is booted.

	       Instructs the kernel to try to mount the	root file system from

     boot_ddb  Instructs the kernel to start in	the DDB	debugger, rather than
	       proceeding to initialize	when booted.

	       Instructs the kernel to mount the statically compiled-in	root
	       file system.

     boot_gdb  Selects gdb-remote mode for the kernel debugger by default.

	       Enables multiple	console	support	in the kernel early on boot.
	       In a running system, console configuration can be manipulated
	       by the conscontrol(8) utility.

	       All console output is suppressed	when console is	muted.	In a
	       running system, the state of console muting can be manipulated
	       by the conscontrol(8) utility.

	       During the device probe,	pause after each line is printed.

	       Force the use of	a serial console even when an internal console
	       is present.

	       Prevents	the kernel from	initiating a multi-user	startup; in-
	       stead, a	single-user mode will be entered when the kernel has
	       finished	device probing.

	       Setting this variable causes extra debugging information	to be
	       printed by the kernel during the	boot phase.

     bootfile  List of semicolon-separated search path for bootable kernels.
	       The default is "kernel".

	       Defines the speed of the	serial console (i386 and amd64 only).
	       If the previous boot stage indicated that a serial console is
	       in use then this	variable is initialized	to the current speed
	       of the console serial port.  Otherwise it is set	to 9600	unless
	       this was	overridden using the BOOT_COMCONSOLE_SPEED variable
	       when loader was compiled.  Changes to the comconsole_speed
	       variable	take effect immediately.

	       Defines the base	i/o port used to access	console	UART (i386 and
	       amd64 only).  If	the variable is	not set, its assumed value is
	       0x3F8, which corresponds	to PC port COM1, unless	overridden by
	       BOOT_COMCONSOLE_PORT variable during the	compilation of loader.
	       Setting the comconsole_port variable automatically set
	       hw.uart.console environment variable to provide a hint to ker-
	       nel for location	of the console.	 Loader	console	is changed im-
	       mediately after variable	comconsole_port	is set.

	       Defines the location of a PCI device of the 'simple communica-
	       tion' class to be used as the serial console UART (i386 and
	       amd64 only).  The syntax	of the variable	is
	       'bus:device:function[:bar]', where all members must be numeric,
	       with possible 0x	prefix to indicate a hexadecimal value.	 The
	       bar member is optional and assumed to be	0x10 if	omitted.  The
	       bar must	decode i/o space.  Setting the variable
	       comconsole_pcidev automatically sets the	variable
	       comconsole_port to the base of the selected bar,	and hint
	       hw.uart.console.	 Loader	console	is changed immediately after
	       variable	comconsole_pcidev is set.

     console   Defines the current console or consoles.	 Multiple consoles may
	       be specified.  In that case, the	first listed console will be-
	       come the	default	console	for userland output (e.g. from

     currdev   Selects the default device.  Syntax for devices is odd.

     dumpdev   Sets the	device for kernel dumps.  This can be used to ensure
	       that a device is	configured before the corresponding dumpdev
	       directive from rc.conf(5) has been processed, allowing kernel
	       panics that happen during the early stages of boot to be	cap-

	       If set to a valid directory in the root file system, it causes
	       init(8) to perform a chroot(2) operation	on that	directory,
	       making it the new root directory.  That happens before entering
	       single-user mode	or multi-user mode (but	after executing	the
	       init_script if enabled).

	       Sets the	list of	binaries which the kernel will try to run as
	       the initial process.  The first matching	binary is used.	 The
	       default list is "/sbin/init:/sbin/oinit:/sbin/init.bak:

	       If set to a valid file name in the root file system, instructs
	       init(8) to run that script as the very first action, before do-
	       ing anything else.  Signal handling and exit code interpreta-
	       tion is similar to running the /etc/rc script.  In particular,
	       single-user operation is	enforced if the	script terminates with
	       a non-zero exit code, or	if a SIGTERM is	delivered to the
	       init(8) process (PID 1).

	       Defines the shell binary	to be used for executing the various
	       shell scripts.  The default is "/bin/sh".  It is	used for run-
	       ning the	init_script if set, as well as for the /etc/rc and
	       /etc/rc.shutdown	scripts.  The value of the corresponding
	       kenv(2) variable	is evaluated every time	init(8)	calls a	shell
	       script, so it can be changed later on using the kenv(1) util-
	       ity.  In	particular, if a non-default shell is used for running
	       an init_script, it might	be desirable to	have that script reset
	       the value of init_shell back to the default, so that the
	       /etc/rc script is executed with the standard shell /bin/sh.

	       Has the value "OK" if the Forth's current state is interpret-

     LINES     Define the number of lines on the screen, to be used by the

	       Sets the	list of	directories which will be searched for modules
	       named in	a load command or implicitly required by a dependency.
	       The default value for this variable is

	       Sets the	number of IDE disks as a workaround for	some problems
	       in finding the root disk	at boot.  This has been	deprecated in
	       favor of	root_disk_unit.

     prompt    Value of	loader's prompt.  Defaults to "${interpret}".  If
	       variable	prompt is unset, the default prompt is `>'.

	       If the code which detects the disk unit number for the root
	       disk is confused, e.g. by a mix of SCSI and IDE disks, or IDE
	       disks with gaps in the sequence (e.g. no	primary	slave),	the
	       unit number can be forced by setting this variable.

     rootdev   By default the value of currdev is used to set the root file
	       system when the kernel is booted.  This can be overridden by
	       setting rootdev explicitly.

     Other variables are used to override kernel tunable parameters.  The fol-
     lowing tunables are available:

     hw.physmem	   Limit the amount of physical	memory the system will use.
		   By default the size is in bytes, but	the k, K, m, M,	g and
		   G suffixes are also accepted	and indicate kilobytes,
		   megabytes and gigabytes respectively.  An invalid suffix
		   will	result in the variable being ignored by	the kernel.

     hw.pci.host_start_mem, hw.acpi.host_start_mem
		   When	not otherwise constrained, this	limits the memory
		   start address.  The default is 0x80000000 and should	be set
		   to at least size of the memory and not conflict with	other
		   resources.  Typically, only systems without PCI bridges
		   need	to set this variable since PCI bridges typically con-
		   strain the memory starting address (and the variable	is
		   only	used when bridges do not constrain this	address).

		   Enable PCI resources	which are left off by some BIOSes or
		   are not enabled correctly by	the device driver.  Tunable
		   value set to	ON (1) by default, but this may	cause problems
		   with	some peripherals.

		   Set the size	of a number of statically allocated system ta-
		   bles; see tuning(7) for a description of how	to select an
		   appropriate value for this tunable.	When set, this tunable
		   replaces the	value declared in the kernel compile-time con-
		   figuration file.

		   Set the number of mbuf clusters to be allocated.  The value
		   cannot be set below the default determined when the kernel
		   was compiled.

		   Set the number of sendfile(2) buffers to be allocated.
		   Overrides NSFBUFS.  Not all architectures use such buffers;
		   see sendfile(2) for details.

		   Limits the amount of	KVM to be used to hold swap metadata,
		   which directly governs the maximum amount of	swap the sys-
		   tem can support, at the rate	of approximately 200 MB	of
		   swap	space per 1 MB of metadata.  This value	is specified
		   in bytes of KVA space.  If no value is provided, the	system
		   allocates enough memory to handle an	amount of swap that
		   corresponds to eight	times the amount of physical memory
		   present in the system.

		   Note	that swap metadata can be fragmented, which means that
		   the system can run out of space before it reaches the theo-
		   retical limit.  Therefore, care should be taken to not con-
		   figure more swap than approximately half of the theoretical

		   Running out of space	for swap metadata can leave the	system
		   in an unrecoverable state.  Therefore, you should only
		   change this parameter if you	need to	greatly	extend the KVM
		   reservation for other resources such	as the buffer cache or
		   kern.ipc.nmbclusters.  Modifies kernel option

		   Limits the amount of	KVM reserved for use by	the buffer
		   cache, specified in bytes.  The default maximum is 200MB on
		   i386, and 400MB on amd64 and	sparc64.  This parameter is
		   used	to prevent the buffer cache from eating	too much KVM
		   in large-memory machine configurations.  Only mess around
		   with	this parameter if you need to greatly extend the KVM
		   reservation for other resources such	as the swap zone or
		   kern.ipc.nmbclusters.  Note that the	NBUF parameter will
		   override this limit.	 Modifies VM_BCACHE_SIZE_MAX.

		   Sets	the size of the	kernel message buffer.	The default
		   limit of 64KB is usually sufficient unless large amounts of
		   trace data need to be collected between opportunities to
		   examine the buffer or dump it to a file.  Overrides kernel
		   option MSGBUF_SIZE.

		   Disable the use of i686 MTRRs (x86 only).

		   Overrides the compile-time set value	of TCBHASHSIZE or the
		   preset default of 512.  Must	be a power of 2.

		   Throttles the output	of the `twiddle' I/O progress indica-
		   tor displayed while loading the kernel and modules.	This
		   is useful on	slow serial consoles where the time spent
		   waiting for these characters	to be written can add up to
		   many	seconds.  The default is 1 (full speed); a value of 2
		   spins half as fast, and so on.

     vm.kmem_size  Sets	the size of kernel memory (bytes).  This overrides the
		   value determined when the kernel was	compiled.  Modifies


		   Sets	the minimum and	maximum	(respectively) amount of ker-
		   nel memory that will	be automatically allocated by the ker-
		   nel.	 These override	the values determined when the kernel
		   was compiled.  Modifies VM_KMEM_SIZE_MIN and

     When a builtin command is executed, the rest of the line is taken by it
     as	arguments, and it is processed by a special parser which is not	used
     for regular Forth commands.

     This special parser applies the following rules to	the parsed text:

     1.	  All backslash	characters are preprocessed.

	  o   \b , \f ,	\r , \n	and \t are processed as	in C.

	  o   \s is converted to a space.

	  o   \v is converted to ASCII 11.

	  o   \z is just skipped.  Useful for things like "\0xf\z\0xf".

	  o   \0xN and \0xNN are replaced by the hex N or NN.

	  o   \NNN is replaced by the octal NNN	ASCII character.

	  o   \" , \' and \$ will escape these characters, preventing them
	      from receiving special treatment in Step 2, described below.

	  o   \\ will be replaced with a single	\ .

	  o   In any other occurrence, backslash will just be removed.

     2.	  Every	string between non-escaped quotes or double-quotes will	be
	  treated as a single word for the purposes of the remaining steps.

     3.	  Replace any $VARIABLE	or ${VARIABLE} with the	value of the environ-
	  ment variable	VARIABLE.

     4.	  Space-delimited arguments are	passed to the called builtin command.
	  Spaces can also be escaped through the use of	\\ .

     An	exception to this parsing rule exists, and is described	in BUILTINS

     All builtin words are state-smart,	immediate words.  If interpreted, they
     behave exactly as described previously.  If they are compiled, though,
     they extract their	arguments from the stack instead of the	command	line.

     If	compiled, the builtin words expect to find, at execution time, the
     following parameters on the stack:
	   addrN lenN ... addr2	len2 addr1 len1	N
     where addrX lenX are strings which	will compose the command line that
     will be parsed into the builtin's arguments.  Internally, these strings
     are concatenated in from 1	to N, with a space put between each one.

     If	no arguments are passed, a 0 must be passed, even if the builtin ac-
     cepts no arguments.

     While this	behavior has benefits, it has its trade-offs.  If the execu-
     tion token	of a builtin is	acquired (through ' or [']), and then passed
     to	catch or execute, the builtin behavior will depend on the system state
     at	the time catch or execute is processed!	 This is particularly annoying
     for programs that want or need to handle exceptions.  In this case, the
     use of a proxy is recommended.  For example:
	   : (boot) boot;

     FICL is a Forth interpreter written in C, in the form of a	forth virtual
     machine library that can be called	by C functions and vice	versa.

     In	loader,	each line read interactively is	then fed to FICL, which	may
     call loader back to execute the builtin words.  The builtin include will
     also feed FICL, one line at a time.

     The words available to FICL can be	classified into	four groups.  The ANS
     Forth standard words, extra FICL words, extra FreeBSD words, and the
     builtin commands; the latter were already described.  The ANS Forth stan-
     dard words	are listed in the STANDARDS section.  The words	falling	in the
     two other groups are described in the following subsections.







     compare	    This is the	STRING word set's compare.





     sliteral	    This is the	STRING word set's sliteral.








     $ (--)    Evaluates the remainder of the input buffer, after having
	       printed it first.

     % (--)    Evaluates the remainder of the input buffer under a catch ex-
	       ception guard.

     .#	       Works like .  but without outputting a trailing space.

     fclose (fd	--)
	       Closes a	file.

     fkey (fd -- char)
	       Reads a single character	from a file.

     fload (fd --)
	       Processes a file	fd.

     fopen (addr len mode -- fd)
	       Opens a file.  Returns a	file descriptor, or -1 in case of
	       failure.	 The mode parameter selects whether the	file is	to be
	       opened for read access, write access, or	both.  The constants
	       O_RDONLY, O_WRONLY, and O_RDWR are defined in
	       /boot/support.4th, indicating read only,	write only, and	read-
	       write access, respectively.

     fread (fd addr len	-- len')
	       Tries to	read len bytes from file fd into buffer	addr.  Returns
	       the actual number of bytes read,	or -1 in case of error or end
	       of file.

     heap? (-- cells)
	       Return the space	remaining in the dictionary heap, in cells.
	       This is not related to the heap used by dynamic memory alloca-
	       tion words.

     inb (port -- char)
	       Reads a byte from a port.

     key (-- char)
	       Reads a single character	from the console.

     key? (-- flag)
	       Returns true if there is	a character available to be read from
	       the console.

     ms	(u --)
	       Waits u microseconds.

     outb (port	char --)
	       Writes a	byte to	a port.

     seconds (-- u)
	       Returns the number of seconds since midnight.

     tib> (-- addr len)
	       Returns the remainder of	the input buffer as a string on	the

     trace! (flag --)
	       Activates or deactivates	tracing.  Does not work	with catch.

	     TRUE if the architecture is IA32.

	     FreeBSD version at	compile	time.

	     loader version.

     /boot/loader		 loader	itself.
     /boot/boot.4th		 Additional FICL initialization.
     /boot/boot.conf		 loader	bootstrapping script.  Deprecated.
     /boot/loader.conf.local	 loader	configuration files, as	described in
     /boot/loader.rc		 loader	bootstrapping script.
     /boot/		 Loaded	by help.  Contains the help messages.

     Boot in single user mode:

	   boot	-s

     Load the kernel, a	splash screen, and then	autoboot in five seconds.  No-
     tice that a kernel	must be	loaded before any other	load command is	at-

	   load	kernel
	   load	splash_bmp
	   load	-t splash_image_data /boot/chuckrulez.bmp
	   autoboot 5

     Set the disk unit of the root device to 2,	and then boot.	This would be
     needed in a system	with two IDE disks, with the second IDE	disk hardwired
     to	ada2 instead of	ada1.

	   set root_disk_unit=2
	   boot	/boot/kernel/kernel

     See also:

     /boot/loader.4th		      Extra builtin-like words.

     /boot/support.4th		      loader.conf processing words.

     /usr/share/examples/bootforth/   Assorted examples.

     The following values are thrown by	loader:

	   100	  Any type of error in the processing of a builtin.

	   -1	  Abort	executed.

	   -2	  Abort" executed.

	   -56	  Quit executed.

	   -256	  Out of interpreting text.

	   -257	  Need more text to succeed -- will finish on next run.

	   -258	  Bye executed.

	   -259	  Unspecified error.

     libstand(3), loader.conf(5), tuning(7), boot(8), btxld(8)

     For the purposes of ANS Forth compliance, loader is an ANS	Forth System
     with Environmental	Restrictions, Providing	.(, :noname, ?do, parse, pick,
     roll, refill, to, value, \, false,	true, <>, 0<>, compile,	, erase, nip,
     tuck and marker from the Core Extensions word set,	Providing the Excep-
     tion Extensions word set, Providing the Locals Extensions word set, Pro-
     viding the	Memory-Allocation Extensions word set, Providing .s, bye, for-
     get, see, words, [if], [else] and [then] from the Programming-Tools ex-
     tension word set, Providing the Search-Order extensions word set.

     The loader	first appeared in FreeBSD 3.1.

     The loader	was written by Michael Smith <>.

     FICL was written by John Sadler <>.

     The expect	and accept words will read from	the input buffer instead of
     the console.  The latter will be fixed, but the former will not.

BSD			       November	18, 2015			   BSD


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