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

     loader - kernel bootstrapping final stage

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

     It provides a scripting language that can be used to automate tasks, do
     pre-configuration or assist in recovery procedures.  This scripting
     language 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-friendlyness.  The bigger component is an ANS Forth
     compatible 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 will be
     processed 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 will be read
     for historical reasons.  These files are processed through the include
     command, which read 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.

     Loader's builtin commands take its 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
     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]
             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.

     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

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

     echo [-n] [<message>]
             Displays a 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 is, at a turn, completely read
             into memory, and then have each of its lines passed to the
             command line interpreter.  If any error is returned by the
             interpreter, the include commands aborts immediately, without
             reading any other files, and returns an error itself (see

     load [-t type] file ...
             Loads a kernel, kernel loadable module (kld), or a 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.  Notice, though, that, at the present, this does not
             work for the kernel.

     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

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

     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
             displayed 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.

     ?       Same as ``help index''.

     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 later ones that this session covers.

     Environment variables can be set and unset through the use of the set and
     unset builtins, and have their value 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
     either loader or kernel's behavior at boot.  While some of these may
     require a value, others define behavior just by being set.  These 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
               after processing /boot/loader.rc, though explict 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.

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

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

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

               Requests that the kernel's interactive device configuration
               program be run when the kernel is booted.

               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;kernel.old''.

     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
               initial process.  The default is

               Has the value ``ok'' if the Forth's current state is

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

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

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

     prompt    Value of loader's prompt.  Defaults to ``${currdev}>''.

               If the code which detects the disk unit number for the root
               disk is confused, eg. by a mix of SCSI and IDE disks, or IDE
               disks with gaps in the sequence (eg. 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
               filesystem when the kernel is booted.  This can be overridden
               by setting rootdev explicitly.

     dumpdev   A name of device where the kernel can save a crash dump in the
               case of a panic.  This automatically sets kern.dumpdev
               sysctl(3) MIB variable.

     Other variables are used to override kernel tunable parameters.  The
     following tunables are available:

                   Set the size of a number of statically allocated system
                   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
                   configuration 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.

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

                   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
                   support 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

                   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.

                   Overrides the IRQ normally assigned to a PCCARD controller.
                   Typically the first available interrupt will be allocated,
                   which may conflict with other hardware.  If this value is
                   set to 0, an interrupt will not be assigned and the
                   controller will operate in polled mode only.

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

     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 semantics on the step 2 described below.

          +o   \\ will be replaced with a single \ .

          +o   In any other occurance, 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
          environemnt variable VARIABLE.

     4.   Passes multiple space-delimited arguments to the builtin command
          called.  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
     execution 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
     particular annoying for programs that want or need to treat exceptions.
     In this case, it is recommended the use of a proxy.  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 in four groups.  The ANS
     Forth standard words, extra FICL words, extra FreeBSD words, and the
     builtin commands.  The later were already described.  The ANS Forth
     standard 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 --)
               Process file fd.

     fopen (addr len -- fd)
               Open a file.  Returns a file descriptor, or -1 in case of

     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
               allocation 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/           Loaded by help.  Contains the help messages.

     Boot in single user mode:

           boot -s

     Loads kernel's user configuration file.  Notice that a kernel must be
     loaded before any other load command is attempted.

           load kernel
           load -t userconfig_script /boot/kernel.conf

     Loads the kernel, a splash screen, and then autoboots in five seconds.

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

     Sets the disk unit of the root device to 2, and then boots.  This would
     be needed in the case of a two IDE disks system, with the second IDE
     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
     Exception Extensions word set, Providing the Locals Extensions word set,
     Providing the Memory-Allocation Extensions word set, Providing .s, bye,
     forget, see, words, [if], [else] and [then] from the Programming-Tools
     extension word set, Providing the Search-Order extensions word set.

     loader first appeared in FreeBSD 3.1.

     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.

FreeBSD 11.0-PRERELEASE         March 14, 1999         FreeBSD 11.0-PRERELEASE


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