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32 .Nd kernel bootstrapping final stage
38 kernel bootstrapping process.
39 On IA32 (i386) architectures, it is a
42 It is linked statically to
44 and usually located in the directory
47 It provides a scripting language that can be used to
48 automate tasks, do pre-configuration or assist in recovery
50 This scripting language is roughly divided in
52 The smaller one is a set of commands
53 designed for direct use by the casual user, called "builtin
54 commands" for historical reasons.
55 The main drive behind these commands is user-friendliness.
56 The bigger component is an
58 Forth compatible Forth interpreter based on FICL, by
61 During initialization,
63 will probe for a console and set the
65 variable, or set it to serial console
67 if the previous boot stage used that.
68 If multiple consoles are selected, they will be listed separated by spaces.
69 Then, devices are probed,
78 is initialized, the builtin words are added to its vocabulary, and
80 is processed if it exists.
81 No disk switching is possible while that file is being read.
93 is processed if available.
94 These files are processed through the
96 command, which reads all of them into memory before processing them,
97 making disk changes possible.
101 has not been tried, and if
105 (not case sensitive), then an
108 If the system gets past this point,
112 will engage interactive mode.
113 Please note that historically even when
117 user will be able to interrupt autoboot process by pressing some key
118 on the console while kernel and modules are being loaded.
120 cases such behaviour may be undesirable, to prevent it set
126 will engage interactive mode only if
132 builtin commands take parameters from the command line.
134 the only way to call them from a script is by using
137 If an error condition occurs, an exception will be generated,
138 which can be intercepted using
140 Forth exception handling
142 If not intercepted, an error message will be displayed and
143 the interpreter's state will be reset, emptying the stack and restoring
146 The builtin commands available are:
148 .Bl -tag -width Ds -compact
149 .It Ic autoboot Op Ar seconds Op Ar prompt
150 Proceeds to bootstrap the system after a number of seconds, if not
151 interrupted by the user.
152 Displays a countdown prompt
153 warning the user the system is about to be booted,
154 unless interrupted by a key press.
155 The kernel will be loaded first if necessary.
156 Defaults to 10 seconds.
159 Displays statistics about disk cache usage.
163 .It Ic boot Ar kernelname Op Cm ...
164 .It Ic boot Fl flag Cm ...
165 Immediately proceeds to bootstrap the system, loading the kernel
167 Any flags or arguments are passed to the kernel, but they
168 must precede the kernel name, if a kernel name is provided.
171 The behavior of this builtin is changed if
179 Displays text on the screen.
180 A new line will be printed unless
185 Displays memory usage statistics.
186 For debugging purposes only.
188 .It Ic help Op topic Op subtopic
189 Shows help messages read from
190 .Pa /boot/loader.help .
193 will list the topics available.
195 .It Ic include Ar file Op Ar
196 Process script files.
197 Each file, in turn, is completely read into memory,
198 and then each of its lines is passed to the command line interpreter.
199 If any error is returned by the interpreter, the include
200 command aborts immediately, without reading any other files, and
201 returns an error itself (see
208 Loads a kernel, kernel loadable module (kld), disk image,
209 or file of opaque contents tagged as being of the type
211 Kernel and modules can be either in a.out or ELF format.
212 Any arguments passed after the name of the file to be loaded
213 will be passed as arguments to that file.
216 type to make the kernel create a file-backed
219 This is useful for booting from a temporary rootfs.
220 Currently, argument passing does not work for the kernel.
228 encryption keyfile for the given provider name.
229 The key index can be specified via
231 or will default to zero.
237 Displays a listing of files in the directory
239 or the root directory if
244 is specified, file sizes will be shown too.
247 Lists all of the devices from which it may be possible to load modules.
250 is specified, more details are printed.
253 Displays loaded modules.
256 is specified, more details are shown.
258 .It Ic more Ar file Op Ar
259 Display the files specified, with a pause at each
263 .It Ic pnpscan Op Fl v
264 Scans for Plug-and-Play devices.
265 This is not functional at present.
272 Reads a line of input from the terminal, storing it in
275 A timeout can be specified with
277 though it will be canceled at the first key pressed.
278 A prompt may also be displayed through the
283 Immediately reboots the system.
285 .It Ic set Ar variable
286 .It Ic set Ar variable Ns = Ns Ar value
287 Set loader's environment variables.
289 .It Ic show Op Va variable
290 Displays the specified variable's value, or all variables and their
296 Remove all modules from memory.
298 .It Ic unset Va variable
301 from the environment.
304 Lists available commands.
306 .Ss BUILTIN ENVIRONMENT VARIABLES
309 has actually two different kinds of
312 There are ANS Forth's
313 .Em environmental queries ,
314 and a separate space of environment variables used by builtins, which
315 are not directly available to Forth words.
316 It is the latter type that this section covers.
318 Environment variables can be set and unset through the
322 builtins, and can have their values interactively examined through the
326 Their values can also be accessed as described in
329 Notice that these environment variables are not inherited by any shell
330 after the system has been booted.
332 A few variables are set automatically by
334 Others can affect the behavior of either
336 or the kernel at boot.
337 Some options may require a value,
338 while others define behavior just by being set.
339 Both types of builtin variables are described below.
340 .Bl -tag -width bootfile
341 .It Va autoboot_delay
344 will wait before booting.
345 If this variable is not defined,
347 will default to 10 seconds.
353 will be automatically attempted after processing
354 .Pa /boot/loader.rc ,
357 will be processed normally, defaulting to 10 seconds delay.
361 no delay will be inserted, but user still will be able to interrupt
363 process and escape into the interactive mode by pressing some key
364 on the console while kernel and
365 modules are being loaded.
369 no delay will be inserted and
371 will engage interactive mode only if
373 has failed for some reason.
375 Instructs the kernel to prompt the user for the name of the root device
376 when the kernel is booted.
378 Instructs the kernel to try to mount the root file system from CD-ROM.
380 Instructs the kernel to start in the DDB debugger, rather than
381 proceeding to initialize when booted.
383 Instructs the kernel to mount the statically compiled-in root file system.
385 Selects gdb-remote mode for the kernel debugger by default.
386 .It Va boot_multicons
387 Enables multiple console support in the kernel early on boot.
388 In a running system, console configuration can be manipulated
393 All console output is suppressed when console is muted.
394 In a running system, the state of console muting can be manipulated by the
398 During the device probe, pause after each line is printed.
400 Force the use of a serial console even when an internal console
403 Prevents the kernel from initiating a multi-user startup; instead,
404 a single-user mode will be entered when the kernel has finished
407 Setting this variable causes extra debugging information to be printed
408 by the kernel during the boot phase.
410 List of semicolon-separated search path for bootable kernels.
413 .It Va comconsole_speed
414 Defines the speed of the serial console (i386 and amd64 only).
415 If the previous boot stage indicated that a serial console is in use
416 then this variable is initialized to the current speed of the console
418 Otherwise it is set to 9600 unless this was overridden using the
419 .Va BOOT_COMCONSOLE_SPEED
425 variable take effect immediately.
426 .It Va comconsole_port
427 Defines the base i/o port used to access console UART
428 (i386 and amd64 only).
429 If the variable is not set, its assumed value is 0x3F8, which
430 corresponds to PC port COM1, unless overridden by
431 .Va BOOT_COMCONSOLE_PORT
432 variable during the compilation of
436 variable automatically set
438 environment variable to provide a hint to kernel for location of the console.
439 Loader console is changed immediately after variable
442 .It Va comconsole_pcidev
443 Defines the location of a PCI device of the 'simple communication'
444 class to be used as the serial console UART (i386 and amd64 only).
445 The syntax of the variable is
446 .Li 'bus:device:function[:bar]' ,
447 where all members must be numeric, with possible
449 prefix to indicate a hexadecimal value.
452 member is optional and assumed to be 0x10 if omitted.
453 The bar must decode i/o space.
455 .Va comconsole_pcidev
456 automatically sets the variable
458 to the base of the selected bar, and hint
459 .Va hw.uart.console .
460 Loader console is changed immediately after variable
461 .Va comconsole_pcidev
464 Defines the current console or consoles.
465 Multiple consoles may be specified.
466 In that case, the first listed console will become the default console for
467 userland output (e.g.\& from
470 Selects the default device.
471 Syntax for devices is odd.
473 Sets the device for kernel dumps.
474 This can be used to ensure that a device is configured before the corresponding
478 has been processed, allowing kernel panics that happen during the early stages
479 of boot to be captured.
481 If set to a valid directory in the root file system, it causes
485 operation on that directory, making it the new root directory.
486 That happens before entering single-user mode or multi-user
487 mode (but after executing the
491 Sets the list of binaries which the kernel will try to run as the initial
493 The first matching binary is used.
495 .Dq Li /sbin/init:/sbin/oinit:/sbin/init.bak:\:/rescue/init .
497 If set to a valid file name in the root file system,
500 to run that script as the very first action,
501 before doing anything else.
502 Signal handling and exit code interpretation is similar to
506 In particular, single-user operation is enforced
507 if the script terminates with a non-zero exit code,
508 or if a SIGTERM is delivered to the
512 Defines the shell binary to be used for executing the various shell scripts.
515 It is used for running the
517 if set, as well as for the
522 The value of the corresponding
524 variable is evaluated every time
526 calls a shell script, so it can be changed later on using the
529 In particular, if a non-default shell is used for running an
531 it might be desirable to have that script reset the value of
533 back to the default, so that the
535 script is executed with the standard shell
540 if the Forth's current state is interpreting.
542 Define the number of lines on the screen, to be used by the pager.
544 Sets the list of directories which will be searched for modules
545 named in a load command or implicitly required by a dependency.
546 The default value for this variable is
547 .Dq Li /boot/kernel;/boot/modules .
549 Sets the number of IDE disks as a workaround for some problems in
550 finding the root disk at boot.
551 This has been deprecated in favor of
558 .Dq Li "${interpret}" .
561 is unset, the default prompt is
563 .It Va root_disk_unit
564 If the code which detects the disk unit number for the root disk is
565 confused, e.g.\& by a mix of SCSI and IDE disks, or IDE disks with
566 gaps in the sequence (e.g.\& no primary slave), the unit number can
567 be forced by setting this variable.
569 By default the value of
571 is used to set the root file system
572 when the kernel is booted.
573 This can be overridden by setting
578 Other variables are used to override kernel tunable parameters.
579 The following tunables are available:
582 Limit the amount of physical memory the system will use.
583 By default the size is in bytes, but the
584 .Cm k , K , m , M , g
588 are also accepted and indicate kilobytes, megabytes and gigabytes
590 An invalid suffix will result in the variable being ignored by the
592 .It Va hw.pci.host_start_mem , hw.acpi.host_start_mem
593 When not otherwise constrained, this limits the memory start
595 The default is 0x80000000 and should be set to at least size of the
596 memory and not conflict with other resources.
597 Typically, only systems without PCI bridges need to set this variable
598 since PCI bridges typically constrain the memory starting address
599 (and the variable is only used when bridges do not constrain this
601 .It Va hw.pci.enable_io_modes
602 Enable PCI resources which are left off by some BIOSes or are not
603 enabled correctly by the device driver.
604 Tunable value set to ON (1) by default, but this may cause problems
605 with some peripherals.
607 Set the size of a number of statically allocated system tables; see
609 for a description of how to select an appropriate value for this
611 When set, this tunable replaces the value declared in the kernel
612 compile-time configuration file.
613 .It Va kern.ipc.nmbclusters
614 Set the number of mbuf clusters to be allocated.
615 The value cannot be set below the default
616 determined when the kernel was compiled.
617 .It Va kern.ipc.nsfbufs
620 buffers to be allocated.
623 Not all architectures use such buffers; see
626 .It Va kern.maxswzone
627 Limits the amount of KVM to be used to hold swap
628 metadata, which directly governs the
629 maximum amount of swap the system can support,
630 at the rate of approximately 200 MB of swap space
631 per 1 MB of metadata.
632 This value is specified in bytes of KVA space.
633 If no value is provided, the system allocates
634 enough memory to handle an amount of swap
635 that corresponds to eight times the amount of
636 physical memory present in the system.
638 Note that swap metadata can be fragmented,
639 which means that the system can run out of
640 space before it reaches the theoretical limit.
641 Therefore, care should be taken to not configure
642 more swap than approximately half of the
645 Running out of space for swap metadata can leave
646 the system in an unrecoverable state.
647 Therefore, you should only change
648 this parameter if you need to greatly extend the
649 KVM reservation for other resources such as the
651 .Va kern.ipc.nmbclusters .
652 Modifies kernel option
653 .Dv VM_SWZONE_SIZE_MAX .
654 .It Va kern.maxbcache
655 Limits the amount of KVM reserved for use by the
656 buffer cache, specified in bytes.
657 The default maximum is 200MB on i386,
658 and 400MB on amd64 and sparc64.
659 This parameter is used to
660 prevent the buffer cache from eating too much
661 KVM in large-memory machine configurations.
662 Only mess around with this parameter if you need to
663 greatly extend the KVM reservation for other resources
664 such as the swap zone or
665 .Va kern.ipc.nmbclusters .
667 the NBUF parameter will override this limit.
669 .Dv VM_BCACHE_SIZE_MAX .
670 .It Va kern.msgbufsize
671 Sets the size of the kernel message buffer.
672 The default limit of 64KB is usually sufficient unless
673 large amounts of trace data need to be collected
674 between opportunities to examine the buffer or
676 Overrides kernel option
678 .It Va machdep.disable_mtrrs
679 Disable the use of i686 MTRRs (x86 only).
680 .It Va net.inet.tcp.tcbhashsize
681 Overrides the compile-time set value of
683 or the preset default of 512.
684 Must be a power of 2.
685 .It Va twiddle_divisor
686 Throttles the output of the
688 I/O progress indicator displayed while loading the kernel and modules.
689 This is useful on slow serial consoles where the time spent waiting for
690 these characters to be written can add up to many seconds.
691 The default is 1 (full speed); a value of 2 spins half as fast, and so on.
693 Sets the size of kernel memory (bytes).
694 This overrides the value determined when the kernel was compiled.
697 .It Va vm.kmem_size_min
698 .It Va vm.kmem_size_max
699 Sets the minimum and maximum (respectively) amount of kernel memory
700 that will be automatically allocated by the kernel.
701 These override the values determined when the kernel was compiled.
705 .Dv VM_KMEM_SIZE_MAX .
708 When a builtin command is executed, the rest of the line is taken
709 by it as arguments, and it is processed by a special parser which
710 is not used for regular Forth commands.
712 This special parser applies the following rules to the parsed text:
715 All backslash characters are preprocessed.
718 \eb , \ef , \er , \en and \et are processed as in C.
720 \es is converted to a space.
727 Useful for things like
730 \e0xN and \e0xNN are replaced by the hex N or NN.
732 \eNNN is replaced by the octal NNN
736 \e" , \e' and \e$ will escape these characters, preventing them from
737 receiving special treatment in Step 2, described below.
739 \e\e will be replaced with a single \e .
741 In any other occurrence, backslash will just be removed.
744 Every string between non-escaped quotes or double-quotes will be treated
745 as a single word for the purposes of the remaining steps.
751 with the value of the environment variable
754 Space-delimited arguments are passed to the called builtin command.
755 Spaces can also be escaped through the use of \e\e .
758 An exception to this parsing rule exists, and is described in
759 .Sx BUILTINS AND FORTH .
760 .Ss BUILTINS AND FORTH
761 All builtin words are state-smart, immediate words.
762 If interpreted, they behave exactly as described previously.
763 If they are compiled, though,
764 they extract their arguments from the stack instead of the command line.
766 If compiled, the builtin words expect to find, at execution time, the
767 following parameters on the stack:
768 .D1 Ar addrN lenN ... addr2 len2 addr1 len1 N
771 are strings which will compose the command line that will be parsed
772 into the builtin's arguments.
773 Internally, these strings are concatenated in from 1 to N,
774 with a space put between each one.
776 If no arguments are passed, a 0
778 be passed, even if the builtin accepts no arguments.
780 While this behavior has benefits, it has its trade-offs.
781 If the execution token of a builtin is acquired (through
789 the builtin behavior will depend on the system state
797 This is particularly annoying for programs that want or need to
799 In this case, the use of a proxy is recommended.
804 is a Forth interpreter written in C, in the form of a forth
805 virtual machine library that can be called by C functions and vice
810 each line read interactively is then fed to
814 back to execute the builtin words.
821 The words available to
823 can be classified into four groups.
826 Forth standard words, extra
830 words, and the builtin commands;
831 the latter were already described.
834 Forth standard words are listed in the
837 The words falling in the two other groups are described in the
838 following subsections.
840 .Bl -tag -width wid-set-super
848 This is the STRING word set's
855 This is the STRING word set's
865 .Ss FREEBSD EXTRA WORDS
866 .Bl -tag -width XXXXXXXX
868 Evaluates the remainder of the input buffer, after having printed it first.
870 Evaluates the remainder of the input buffer under a
876 but without outputting a trailing space.
877 .It Ic fclose Pq Ar fd --
879 .It Ic fkey Pq Ar fd -- char
880 Reads a single character from a file.
881 .It Ic fload Pq Ar fd --
884 .It Ic fopen Pq Ar addr len mode Li -- Ar fd
886 Returns a file descriptor, or \-1 in case of failure.
889 parameter selects whether the file is to be opened for read access, write
892 .Dv O_RDONLY , O_WRONLY ,
896 .Pa /boot/support.4th ,
897 indicating read only, write only, and read-write access, respectively.
900 .Pq Ar fd addr len -- len'
908 Returns the actual number of bytes read, or -1 in case of error or end of
910 .It Ic heap? Pq -- Ar cells
911 Return the space remaining in the dictionary heap, in cells.
912 This is not related to the heap used by dynamic memory allocation words.
913 .It Ic inb Pq Ar port -- char
914 Reads a byte from a port.
915 .It Ic key Pq -- Ar char
916 Reads a single character from the console.
917 .It Ic key? Pq -- Ar flag
920 if there is a character available to be read from the console.
925 .It Ic outb Pq Ar port char --
926 Writes a byte to a port.
927 .It Ic seconds Pq -- Ar u
928 Returns the number of seconds since midnight.
929 .It Ic tib> Pq -- Ar addr len
930 Returns the remainder of the input buffer as a string on the stack.
931 .It Ic trace! Pq Ar flag --
932 Activates or deactivates tracing.
936 .Ss FREEBSD DEFINED ENVIRONMENTAL QUERIES
940 if the architecture is IA32.
943 version at compile time.
948 .Ss SYSTEM DOCUMENTATION
950 .Bl -tag -width /boot/defaults/loader.conf -compact
954 .It Pa /boot/boot.4th
958 .It Pa /boot/defaults/loader.conf
959 .It Pa /boot/loader.conf
960 .It Pa /boot/loader.conf.local
962 configuration files, as described in
964 .It Pa /boot/loader.rc
966 bootstrapping script.
967 .It Pa /boot/loader.help
970 Contains the help messages.
973 Boot in single user mode:
977 Load the kernel, a splash screen, and then autoboot in five seconds.
978 Notice that a kernel must be loaded before any other
980 command is attempted.
981 .Bd -literal -offset indent
984 load -t splash_image_data /boot/chuckrulez.bmp
988 Set the disk unit of the root device to 2, and then boot.
989 This would be needed in a system with two IDE disks,
990 with the second IDE disk hardwired to ada2 instead of ada1.
991 .Bd -literal -offset indent
993 boot /boot/kernel/kernel
997 .Bl -tag -width /usr/share/examples/bootforth/X
998 .It Pa /boot/loader.4th
999 Extra builtin-like words.
1000 .It Pa /boot/support.4th
1003 .It Pa /usr/share/examples/bootforth/
1007 The following values are thrown by
1009 .Bl -tag -width XXXXX -offset indent
1011 Any type of error in the processing of a builtin.
1022 Out of interpreting text.
1024 Need more text to succeed -- will finish on next run.
1038 For the purposes of ANS Forth compliance, loader is an
1040 ANS Forth System with Environmental Restrictions, Providing
1046 parse, pick, roll, refill, to, value, \e, false, true,
1049 compile\&, , erase, nip, tuck
1054 from the Core Extensions word set, Providing the Exception Extensions
1055 word set, Providing the Locals Extensions word set, Providing the
1056 Memory-Allocation Extensions word set, Providing
1060 bye, forget, see, words,
1067 from the Programming-Tools extension word set, Providing the
1068 Search-Order extensions word set.
1080 .An Michael Smith Aq msmith@FreeBSD.org .
1084 .An John Sadler Aq john_sadler@alum.mit.edu .
1090 words will read from the input buffer instead of the console.
1091 The latter will be fixed, but the former will not.
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