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     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
     previous boot stage used that.  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.


     In loader, builtin commands take parameters from the command line.
     Presently, 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 gener-
     ated, which can be intercepted using ANS Forth exception handling words.
     If not intercepted, an error message will be displayed and the inter-
     preter's state will be reset, emptying the stack and restoring interpret-
     ing 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.
	     Defaults to 10 seconds.

	     Displays statistics about disk cache usage.  For depuration only.

	     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/loader.help.  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), 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.  Currently, argument passing does not work for the

     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
     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
     environment 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
     require a value, while others define behavior just by being set.  Both
     types of builtin variables are described below.

	       Unset this to disable automatic loading of the ACPI module.
	       See also hint.acpi.0.disabled in device.hints(5).

	       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
	       after processing /boot/loader.rc, though explicit autoboot's
	       will be processed normally, defaulting to 10 seconds delay.

	       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.

     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.

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

	       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''.

     console   Defines the current console.

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

	       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

	       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.

		   tables; 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.  Modifies NMBCLUSTERS.

		   Set the number of sendfile(2) buffers to be allocated.
		   Overrides NSFBUFS.

		   Limits the amount of KVM to be used to hold swap meta
		   information, which directly governs the maximum amount of
		   swap the system can support.  This value is specified in
		   bytes of KVA space and defaults to around 70MBytes.	Care
		   should be taken to not reduce this value such that the
		   actual amount of configured swap exceeds 1/2 the kernel-
		   supported swap.  The default 70MB allows the kernel to sup-
		   port a maximum of (approximately) 14GB of configured swap.
		   Only mess around with this parameter if you need to greatly
		   extend the KVM reservation for other resources such as the
		   buffer cache or NMBCLUSTERS.  Modifies VM_SWZONE_SIZE_MAX.

		   Limits the amount of KVM reserved for use by the buffer
		   cache, specified in bytes.  The default maximum is 200MB.
		   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 NMBCLUSTERS.  Note that the NBUF parameter
		   will override this limit.  Modifies VM_BCACHE_SIZE_MAX.

		   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.

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

     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   \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
     accepts 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
	       exception 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.

	       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.

	     TRUE if the architecture is AXP.

	     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/loader.help		 Loaded by help.  Contains the help messages.


     Boot in single user mode:

	   boot -s

     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 wd2 instead of wd1.

	   set root_disk_unit=2
	   boot /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
     extension word set, Providing the Search-Order extensions word set.


     The loader first appeared in FreeBSD 3.1.


     The loader was written by Michael Smith <msmith@FreeBSD.org>.

     FICL was written by John Sadler <john_sadler@alum.mit.edu>.


     The expect and accept words will read from the input buffer instead of


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