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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
490 This functionality has generally been eclipsed by rerooting.
496 Sets the list of binaries which the kernel will try to run as the initial
498 The first matching binary is used.
500 .Dq Li /sbin/init:/sbin/oinit:/sbin/init.bak:\:/rescue/init .
502 If set to a valid file name in the root file system,
505 to run that script as the very first action,
506 before doing anything else.
507 Signal handling and exit code interpretation is similar to
511 In particular, single-user operation is enforced
512 if the script terminates with a non-zero exit code,
513 or if a SIGTERM is delivered to the
516 This functionality has generally been eclipsed by rerooting.
522 Defines the shell binary to be used for executing the various shell scripts.
525 It is used for running the
527 if set, as well as for the
532 The value of the corresponding
534 variable is evaluated every time
536 calls a shell script, so it can be changed later on using the
539 In particular, if a non-default shell is used for running an
541 it might be desirable to have that script reset the value of
543 back to the default, so that the
545 script is executed with the standard shell
550 if the Forth's current state is interpreting.
552 Define the number of lines on the screen, to be used by the pager.
554 Sets the list of directories which will be searched for modules
555 named in a load command or implicitly required by a dependency.
556 The default value for this variable is
557 .Dq Li /boot/kernel;/boot/modules .
559 Sets the number of IDE disks as a workaround for some problems in
560 finding the root disk at boot.
561 This has been deprecated in favor of
568 .Dq Li "${interpret}" .
571 is unset, the default prompt is
573 .It Va root_disk_unit
574 If the code which detects the disk unit number for the root disk is
575 confused, e.g.\& by a mix of SCSI and IDE disks, or IDE disks with
576 gaps in the sequence (e.g.\& no primary slave), the unit number can
577 be forced by setting this variable.
579 By default the value of
581 is used to set the root file system
582 when the kernel is booted.
583 This can be overridden by setting
588 Other variables are used to override kernel tunable parameters.
589 The following tunables are available:
591 .It Va efi.rt.disabled
592 Disable UEFI runtime services in the kernel, if applicable.
593 Runtime services are only available and used if the kernel is booted in a UEFI
596 Limit the amount of physical memory the system will use.
597 By default the size is in bytes, but the
598 .Cm k , K , m , M , g
602 are also accepted and indicate kilobytes, megabytes and gigabytes
604 An invalid suffix will result in the variable being ignored by the
606 .It Va hw.pci.host_start_mem , hw.acpi.host_start_mem
607 When not otherwise constrained, this limits the memory start
609 The default is 0x80000000 and should be set to at least size of the
610 memory and not conflict with other resources.
611 Typically, only systems without PCI bridges need to set this variable
612 since PCI bridges typically constrain the memory starting address
613 (and the variable is only used when bridges do not constrain this
615 .It Va hw.pci.enable_io_modes
616 Enable PCI resources which are left off by some BIOSes or are not
617 enabled correctly by the device driver.
618 Tunable value set to ON (1) by default, but this may cause problems
619 with some peripherals.
621 Set the size of a number of statically allocated system tables; see
623 for a description of how to select an appropriate value for this
625 When set, this tunable replaces the value declared in the kernel
626 compile-time configuration file.
627 .It Va kern.ipc.nmbclusters
628 Set the number of mbuf clusters to be allocated.
629 The value cannot be set below the default
630 determined when the kernel was compiled.
631 .It Va kern.ipc.nsfbufs
634 buffers to be allocated.
637 Not all architectures use such buffers; see
640 .It Va kern.maxswzone
641 Limits the amount of KVM to be used to hold swap
642 metadata, which directly governs the
643 maximum amount of swap the system can support,
644 at the rate of approximately 200 MB of swap space
645 per 1 MB of metadata.
646 This value is specified in bytes of KVA space.
647 If no value is provided, the system allocates
648 enough memory to handle an amount of swap
649 that corresponds to eight times the amount of
650 physical memory present in the system.
652 Note that swap metadata can be fragmented,
653 which means that the system can run out of
654 space before it reaches the theoretical limit.
655 Therefore, care should be taken to not configure
656 more swap than approximately half of the
659 Running out of space for swap metadata can leave
660 the system in an unrecoverable state.
661 Therefore, you should only change
662 this parameter if you need to greatly extend the
663 KVM reservation for other resources such as the
665 .Va kern.ipc.nmbclusters .
666 Modifies kernel option
667 .Dv VM_SWZONE_SIZE_MAX .
668 .It Va kern.maxbcache
669 Limits the amount of KVM reserved for use by the
670 buffer cache, specified in bytes.
671 The default maximum is 200MB on i386,
672 and 400MB on amd64 and sparc64.
673 This parameter is used to
674 prevent the buffer cache from eating too much
675 KVM in large-memory machine configurations.
676 Only mess around with this parameter if you need to
677 greatly extend the KVM reservation for other resources
678 such as the swap zone or
679 .Va kern.ipc.nmbclusters .
681 the NBUF parameter will override this limit.
683 .Dv VM_BCACHE_SIZE_MAX .
684 .It Va kern.msgbufsize
685 Sets the size of the kernel message buffer.
686 The default limit of 64KB is usually sufficient unless
687 large amounts of trace data need to be collected
688 between opportunities to examine the buffer or
690 Overrides kernel option
692 .It Va machdep.disable_mtrrs
693 Disable the use of i686 MTRRs (x86 only).
694 .It Va net.inet.tcp.tcbhashsize
695 Overrides the compile-time set value of
697 or the preset default of 512.
698 Must be a power of 2.
699 .It Va twiddle_divisor
700 Throttles the output of the
702 I/O progress indicator displayed while loading the kernel and modules.
703 This is useful on slow serial consoles where the time spent waiting for
704 these characters to be written can add up to many seconds.
705 The default is 1 (full speed); a value of 2 spins half as fast, and so on.
707 Sets the size of kernel memory (bytes).
708 This overrides the value determined when the kernel was compiled.
711 .It Va vm.kmem_size_min
712 .It Va vm.kmem_size_max
713 Sets the minimum and maximum (respectively) amount of kernel memory
714 that will be automatically allocated by the kernel.
715 These override the values determined when the kernel was compiled.
719 .Dv VM_KMEM_SIZE_MAX .
722 When a builtin command is executed, the rest of the line is taken
723 by it as arguments, and it is processed by a special parser which
724 is not used for regular Forth commands.
726 This special parser applies the following rules to the parsed text:
729 All backslash characters are preprocessed.
732 \eb , \ef , \er , \en and \et are processed as in C.
734 \es is converted to a space.
741 Useful for things like
744 \e0xN and \e0xNN are replaced by the hex N or NN.
746 \eNNN is replaced by the octal NNN
750 \e" , \e' and \e$ will escape these characters, preventing them from
751 receiving special treatment in Step 2, described below.
753 \e\e will be replaced with a single \e .
755 In any other occurrence, backslash will just be removed.
758 Every string between non-escaped quotes or double-quotes will be treated
759 as a single word for the purposes of the remaining steps.
765 with the value of the environment variable
768 Space-delimited arguments are passed to the called builtin command.
769 Spaces can also be escaped through the use of \e\e .
772 An exception to this parsing rule exists, and is described in
773 .Sx BUILTINS AND FORTH .
774 .Ss BUILTINS AND FORTH
775 All builtin words are state-smart, immediate words.
776 If interpreted, they behave exactly as described previously.
777 If they are compiled, though,
778 they extract their arguments from the stack instead of the command line.
780 If compiled, the builtin words expect to find, at execution time, the
781 following parameters on the stack:
782 .D1 Ar addrN lenN ... addr2 len2 addr1 len1 N
785 are strings which will compose the command line that will be parsed
786 into the builtin's arguments.
787 Internally, these strings are concatenated in from 1 to N,
788 with a space put between each one.
790 If no arguments are passed, a 0
792 be passed, even if the builtin accepts no arguments.
794 While this behavior has benefits, it has its trade-offs.
795 If the execution token of a builtin is acquired (through
803 the builtin behavior will depend on the system state
811 This is particularly annoying for programs that want or need to
813 In this case, the use of a proxy is recommended.
818 is a Forth interpreter written in C, in the form of a forth
819 virtual machine library that can be called by C functions and vice
824 each line read interactively is then fed to
828 back to execute the builtin words.
835 The words available to
837 can be classified into four groups.
840 Forth standard words, extra
844 words, and the builtin commands;
845 the latter were already described.
848 Forth standard words are listed in the
851 The words falling in the two other groups are described in the
852 following subsections.
854 .Bl -tag -width wid-set-super
862 This is the STRING word set's
869 This is the STRING word set's
879 .Ss FREEBSD EXTRA WORDS
880 .Bl -tag -width XXXXXXXX
882 Evaluates the remainder of the input buffer, after having printed it first.
884 Evaluates the remainder of the input buffer under a
890 but without outputting a trailing space.
891 .It Ic fclose Pq Ar fd --
893 .It Ic fkey Pq Ar fd -- char
894 Reads a single character from a file.
895 .It Ic fload Pq Ar fd --
898 .It Ic fopen Pq Ar addr len mode Li -- Ar fd
900 Returns a file descriptor, or \-1 in case of failure.
903 parameter selects whether the file is to be opened for read access, write
906 .Dv O_RDONLY , O_WRONLY ,
910 .Pa /boot/support.4th ,
911 indicating read only, write only, and read-write access, respectively.
914 .Pq Ar fd addr len -- len'
922 Returns the actual number of bytes read, or -1 in case of error or end of
924 .It Ic heap? Pq -- Ar cells
925 Return the space remaining in the dictionary heap, in cells.
926 This is not related to the heap used by dynamic memory allocation words.
927 .It Ic inb Pq Ar port -- char
928 Reads a byte from a port.
929 .It Ic key Pq -- Ar char
930 Reads a single character from the console.
931 .It Ic key? Pq -- Ar flag
934 if there is a character available to be read from the console.
939 .It Ic outb Pq Ar port char --
940 Writes a byte to a port.
941 .It Ic seconds Pq -- Ar u
942 Returns the number of seconds since midnight.
943 .It Ic tib> Pq -- Ar addr len
944 Returns the remainder of the input buffer as a string on the stack.
945 .It Ic trace! Pq Ar flag --
946 Activates or deactivates tracing.
950 .Ss FREEBSD DEFINED ENVIRONMENTAL QUERIES
954 if the architecture is IA32.
957 version at compile time.
962 .Ss SYSTEM DOCUMENTATION
964 .Bl -tag -width /boot/defaults/loader.conf -compact
968 .It Pa /boot/boot.4th
972 .It Pa /boot/defaults/loader.conf
973 .It Pa /boot/loader.conf
974 .It Pa /boot/loader.conf.local
976 configuration files, as described in
978 .It Pa /boot/loader.rc
980 bootstrapping script.
981 .It Pa /boot/loader.help
984 Contains the help messages.
987 Boot in single user mode:
991 Load the kernel, a splash screen, and then autoboot in five seconds.
992 Notice that a kernel must be loaded before any other
994 command is attempted.
995 .Bd -literal -offset indent
998 load -t splash_image_data /boot/chuckrulez.bmp
1002 Set the disk unit of the root device to 2, and then boot.
1003 This would be needed in a system with two IDE disks,
1004 with the second IDE disk hardwired to ada2 instead of ada1.
1005 .Bd -literal -offset indent
1006 set root_disk_unit=2
1007 boot /boot/kernel/kernel
1011 .Bl -tag -width /usr/share/examples/bootforth/X
1012 .It Pa /boot/loader.4th
1013 Extra builtin-like words.
1014 .It Pa /boot/support.4th
1017 .It Pa /usr/share/examples/bootforth/
1021 The following values are thrown by
1023 .Bl -tag -width XXXXX -offset indent
1025 Any type of error in the processing of a builtin.
1036 Out of interpreting text.
1038 Need more text to succeed -- will finish on next run.
1052 For the purposes of ANS Forth compliance, loader is an
1054 ANS Forth System with Environmental Restrictions, Providing
1060 parse, pick, roll, refill, to, value, \e, false, true,
1063 compile\&, , erase, nip, tuck
1068 from the Core Extensions word set, Providing the Exception Extensions
1069 word set, Providing the Locals Extensions word set, Providing the
1070 Memory-Allocation Extensions word set, Providing
1074 bye, forget, see, words,
1081 from the Programming-Tools extension word set, Providing the
1082 Search-Order extensions word set.
1094 .An Michael Smith Aq msmith@FreeBSD.org .
1098 .An John Sadler Aq john_sadler@alum.mit.edu .
1104 words will read from the input buffer instead of the console.
1105 The latter will be fixed, but the former will not.
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