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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, and, failing that,
95 is read for historical reasons.
96 These files are processed through the
98 command, which reads all of them into memory before processing them,
99 making disk changes possible.
103 has not been tried, and if
107 (not case sensitive), then an
110 If the system gets past this point,
114 will engage interactive mode.
115 Please note that historically even when
119 user will be able to interrupt autoboot process by pressing some key
120 on the console while kernel and modules are being loaded.
122 cases such behaviour may be undesirable, to prevent it set
128 will engage interactive mode only if
134 builtin commands take parameters from the command line.
136 the only way to call them from a script is by using
139 If an error condition occurs, an exception will be generated,
140 which can be intercepted using
142 Forth exception handling
144 If not intercepted, an error message will be displayed and
145 the interpreter's state will be reset, emptying the stack and restoring
148 The builtin commands available are:
150 .Bl -tag -width Ds -compact
151 .It Ic autoboot Op Ar seconds Op Ar prompt
152 Proceeds to bootstrap the system after a number of seconds, if not
153 interrupted by the user.
154 Displays a countdown prompt
155 warning the user the system is about to be booted,
156 unless interrupted by a key press.
157 The kernel will be loaded first if necessary.
158 Defaults to 10 seconds.
161 Displays statistics about disk cache usage.
165 .It Ic boot Ar kernelname Op Cm ...
166 .It Ic boot Fl flag Cm ...
167 Immediately proceeds to bootstrap the system, loading the kernel
169 Any flags or arguments are passed to the kernel, but they
170 must precede the kernel name, if a kernel name is provided.
173 The behavior of this builtin is changed if
181 Displays text on the screen.
182 A new line will be printed unless
187 Displays memory usage statistics.
188 For debugging purposes only.
190 .It Ic help Op topic Op subtopic
191 Shows help messages read from
192 .Pa /boot/loader.help .
195 will list the topics available.
197 .It Ic include Ar file Op Ar
198 Process script files.
199 Each file, in turn, is completely read into memory,
200 and then each of its lines is passed to the command line interpreter.
201 If any error is returned by the interpreter, the include
202 command aborts immediately, without reading any other files, and
203 returns an error itself (see
210 Loads a kernel, kernel loadable module (kld), disk image,
211 or file of opaque contents tagged as being of the type
213 Kernel and modules can be either in a.out or ELF format.
214 Any arguments passed after the name of the file to be loaded
215 will be passed as arguments to that file.
218 type to make the kernel create a file-backed
221 This is useful for booting from a temporary rootfs.
222 Currently, argument passing does not work for the kernel.
230 encryption keyfile for the given provider name.
231 The key index can be specified via
233 or will default to zero.
239 Displays a listing of files in the directory
241 or the root directory if
246 is specified, file sizes will be shown too.
249 Lists all of the devices from which it may be possible to load modules.
252 is specified, more details are printed.
255 Displays loaded modules.
258 is specified, more details are shown.
260 .It Ic more Ar file Op Ar
261 Display the files specified, with a pause at each
265 .It Ic pnpscan Op Fl v
266 Scans for Plug-and-Play devices.
267 This is not functional at present.
274 Reads a line of input from the terminal, storing it in
277 A timeout can be specified with
279 though it will be canceled at the first key pressed.
280 A prompt may also be displayed through the
285 Immediately reboots the system.
287 .It Ic set Ar variable
288 .It Ic set Ar variable Ns = Ns Ar value
289 Set loader's environment variables.
291 .It Ic show Op Va variable
292 Displays the specified variable's value, or all variables and their
298 Remove all modules from memory.
300 .It Ic unset Va variable
303 from the environment.
306 Lists available commands.
308 .Ss BUILTIN ENVIRONMENT VARIABLES
311 has actually two different kinds of
314 There are ANS Forth's
315 .Em environmental queries ,
316 and a separate space of environment variables used by builtins, which
317 are not directly available to Forth words.
318 It is the latter type that this section covers.
320 Environment variables can be set and unset through the
324 builtins, and can have their values interactively examined through the
328 Their values can also be accessed as described in
331 Notice that these environment variables are not inherited by any shell
332 after the system has been booted.
334 A few variables are set automatically by
336 Others can affect the behavior of either
338 or the kernel at boot.
339 Some options may require a value,
340 while others define behavior just by being set.
341 Both types of builtin variables are described below.
342 .Bl -tag -width bootfile
343 .It Va autoboot_delay
346 will wait before booting.
347 If this variable is not defined,
349 will default to 10 seconds.
355 will be automatically attempted after processing
356 .Pa /boot/loader.rc ,
359 will be processed normally, defaulting to 10 seconds delay.
363 no delay will be inserted, but user still will be able to interrupt
365 process and escape into the interactive mode by pressing some key
366 on the console while kernel and
367 modules are being loaded.
371 no delay will be inserted and
373 will engage interactive mode only if
375 has failed for some reason.
377 Instructs the kernel to prompt the user for the name of the root device
378 when the kernel is booted.
380 Instructs the kernel to try to mount the root file system from CD-ROM.
382 Instructs the kernel to start in the DDB debugger, rather than
383 proceeding to initialize when booted.
385 Instructs the kernel to mount the statically compiled-in root file system.
387 Selects gdb-remote mode for the kernel debugger by default.
388 .It Va boot_multicons
389 Enables multiple console support in the kernel early on boot.
390 In a running system, console configuration can be manipulated
395 All console output is suppressed when console is muted.
396 In a running system, the state of console muting can be manipulated by the
400 During the device probe, pause after each line is printed.
402 Force the use of a serial console even when an internal console
405 Prevents the kernel from initiating a multi-user startup; instead,
406 a single-user mode will be entered when the kernel has finished
409 Setting this variable causes extra debugging information to be printed
410 by the kernel during the boot phase.
412 List of semicolon-separated search path for bootable kernels.
415 .It Va comconsole_speed
416 Defines the speed of the serial console (i386 and amd64 only).
417 If the previous boot stage indicated that a serial console is in use
418 then this variable is initialized to the current speed of the console
420 Otherwise it is set to 9600 unless this was overridden using the
421 .Va BOOT_COMCONSOLE_SPEED
427 variable take effect immediately.
428 .It Va comconsole_port
429 Defines the base i/o port used to access console UART
430 (i386 and amd64 only).
431 If the variable is not set, its assumed value is 0x3F8, which
432 corresponds to PC port COM1, unless overridden by
433 .Va BOOT_COMCONSOLE_PORT
434 variable during the compilation of
438 variable automatically set
440 environment variable to provide a hint to kernel for location of the console.
441 Loader console is changed immediately after variable
444 .It Va comconsole_pcidev
445 Defines the location of a PCI device of the 'simple communication'
446 class to be used as the serial console UART (i386 and amd64 only).
447 The syntax of the variable is
448 .Li 'bus:device:function[:bar]' ,
449 where all members must be numeric, with possible
451 prefix to indicate a hexadecimal value.
454 member is optional and assumed to be 0x10 if omitted.
455 The bar must decode i/o space.
457 .Va comconsole_pcidev
458 automatically sets the variable
460 to the base of the selected bar, and hint
461 .Va hw.uart.console .
462 Loader console is changed immediately after variable
463 .Va comconsole_pcidev
466 Defines the current console or consoles.
467 Multiple consoles may be specified.
468 In that case, the first listed console will become the default console for
469 userland output (e.g.\& from
472 Selects the default device.
473 Syntax for devices is odd.
475 If set to a valid directory in the root file system, it causes
479 operation on that directory, making it the new root directory.
480 That happens before entering single-user mode or multi-user
481 mode (but after executing the
485 Sets the list of binaries which the kernel will try to run as the initial
487 The first matching binary is used.
489 .Dq Li /sbin/init:/sbin/oinit:/sbin/init.bak:\:/rescue/init .
491 If set to a valid file name in the root file system,
494 to run that script as the very first action,
495 before doing anything else.
496 Signal handling and exit code interpretation is similar to
500 In particular, single-user operation is enforced
501 if the script terminates with a non-zero exit code,
502 or if a SIGTERM is delivered to the
506 Defines the shell binary to be used for executing the various shell scripts.
509 It is used for running the
511 if set, as well as for the
516 The value of the corresponding
518 variable is evaluated every time
520 calls a shell script, so it can be changed later on using the
523 In particular, if a non-default shell is used for running an
525 it might be desirable to have that script reset the value of
527 back to the default, so that the
529 script is executed with the standard shell
534 if the Forth's current state is interpreting.
536 Define the number of lines on the screen, to be used by the pager.
538 Sets the list of directories which will be searched for modules
539 named in a load command or implicitly required by a dependency.
540 The default value for this variable is
541 .Dq Li /boot/kernel;/boot/modules .
543 Sets the number of IDE disks as a workaround for some problems in
544 finding the root disk at boot.
545 This has been deprecated in favor of
552 .Dq Li "${interpret}" .
555 is unset, the default prompt is
557 .It Va root_disk_unit
558 If the code which detects the disk unit number for the root disk is
559 confused, e.g.\& by a mix of SCSI and IDE disks, or IDE disks with
560 gaps in the sequence (e.g.\& no primary slave), the unit number can
561 be forced by setting this variable.
563 By default the value of
565 is used to set the root file system
566 when the kernel is booted.
567 This can be overridden by setting
572 Other variables are used to override kernel tunable parameters.
573 The following tunables are available:
576 Limit the amount of physical memory the system will use.
577 By default the size is in bytes, but the
578 .Cm k , K , m , M , g
582 are also accepted and indicate kilobytes, megabytes and gigabytes
584 An invalid suffix will result in the variable being ignored by the
586 .It Va hw.pci.host_start_mem , hw.acpi.host_start_mem
587 When not otherwise constrained, this limits the memory start
589 The default is 0x80000000 and should be set to at least size of the
590 memory and not conflict with other resources.
591 Typically, only systems without PCI bridges need to set this variable
592 since PCI bridges typically constrain the memory starting address
593 (and the variable is only used when bridges do not constrain this
595 .It Va hw.pci.enable_io_modes
596 Enable PCI resources which are left off by some BIOSes or are not
597 enabled correctly by the device driver.
598 Tunable value set to ON (1) by default, but this may cause problems
599 with some peripherals.
601 Set the size of a number of statically allocated system tables; see
603 for a description of how to select an appropriate value for this
605 When set, this tunable replaces the value declared in the kernel
606 compile-time configuration file.
607 .It Va kern.ipc.nmbclusters
608 Set the number of mbuf clusters to be allocated.
609 The value cannot be set below the default
610 determined when the kernel was compiled.
611 .It Va kern.ipc.nsfbufs
614 buffers to be allocated.
617 Not all architectures use such buffers; see
620 .It Va kern.maxswzone
621 Limits the amount of KVM to be used to hold swap
622 metadata, which directly governs the
623 maximum amount of swap the system can support,
624 at the rate of approximately 200 MB of swap space
625 per 1 MB of metadata.
626 This value is specified in bytes of KVA space.
627 If no value is provided, the system allocates
628 enough memory to handle an amount of swap
629 that corresponds to eight times the amount of
630 physical memory present in the system.
632 Note that swap metadata can be fragmented,
633 which means that the system can run out of
634 space before it reaches the theoretical limit.
635 Therefore, care should be taken to not configure
636 more swap than approximately half of the
639 Running out of space for swap metadata can leave
640 the system in an unrecoverable state.
641 Therefore, you should only change
642 this parameter if you need to greatly extend the
643 KVM reservation for other resources such as the
645 .Va kern.ipc.nmbclusters .
646 Modifies kernel option
647 .Dv VM_SWZONE_SIZE_MAX .
648 .It Va kern.maxbcache
649 Limits the amount of KVM reserved for use by the
650 buffer cache, specified in bytes.
651 The default maximum is 200MB on i386,
652 and 400MB on amd64 and sparc64.
653 This parameter is used to
654 prevent the buffer cache from eating too much
655 KVM in large-memory machine configurations.
656 Only mess around with this parameter if you need to
657 greatly extend the KVM reservation for other resources
658 such as the swap zone or
659 .Va kern.ipc.nmbclusters .
661 the NBUF parameter will override this limit.
663 .Dv VM_BCACHE_SIZE_MAX .
664 .It Va kern.msgbufsize
665 Sets the size of the kernel message buffer.
666 The default limit of 64KB is usually sufficient unless
667 large amounts of trace data need to be collected
668 between opportunities to examine the buffer or
670 Overrides kernel option
672 .It Va machdep.disable_mtrrs
673 Disable the use of i686 MTRRs (x86 only).
674 .It Va net.inet.tcp.tcbhashsize
675 Overrides the compile-time set value of
677 or the preset default of 512.
678 Must be a power of 2.
679 .It Va twiddle_divisor
680 Throttles the output of the
682 I/O progress indicator displayed while loading the kernel and modules.
683 This is useful on slow serial consoles where the time spent waiting for
684 these characters to be written can add up to many seconds.
685 The default is 1 (full speed); a value of 2 spins half as fast, and so on.
687 Sets the size of kernel memory (bytes).
688 This overrides the value determined when the kernel was compiled.
691 .It Va vm.kmem_size_min
692 .It Va vm.kmem_size_max
693 Sets the minimum and maximum (respectively) amount of kernel memory
694 that will be automatically allocated by the kernel.
695 These override the values determined when the kernel was compiled.
699 .Dv VM_KMEM_SIZE_MAX .
702 When a builtin command is executed, the rest of the line is taken
703 by it as arguments, and it is processed by a special parser which
704 is not used for regular Forth commands.
706 This special parser applies the following rules to the parsed text:
709 All backslash characters are preprocessed.
712 \eb , \ef , \er , \en and \et are processed as in C.
714 \es is converted to a space.
721 Useful for things like
724 \e0xN and \e0xNN are replaced by the hex N or NN.
726 \eNNN is replaced by the octal NNN
730 \e" , \e' and \e$ will escape these characters, preventing them from
731 receiving special treatment in Step 2, described below.
733 \e\e will be replaced with a single \e .
735 In any other occurrence, backslash will just be removed.
738 Every string between non-escaped quotes or double-quotes will be treated
739 as a single word for the purposes of the remaining steps.
745 with the value of the environment variable
748 Space-delimited arguments are passed to the called builtin command.
749 Spaces can also be escaped through the use of \e\e .
752 An exception to this parsing rule exists, and is described in
753 .Sx BUILTINS AND FORTH .
754 .Ss BUILTINS AND FORTH
755 All builtin words are state-smart, immediate words.
756 If interpreted, they behave exactly as described previously.
757 If they are compiled, though,
758 they extract their arguments from the stack instead of the command line.
760 If compiled, the builtin words expect to find, at execution time, the
761 following parameters on the stack:
762 .D1 Ar addrN lenN ... addr2 len2 addr1 len1 N
765 are strings which will compose the command line that will be parsed
766 into the builtin's arguments.
767 Internally, these strings are concatenated in from 1 to N,
768 with a space put between each one.
770 If no arguments are passed, a 0
772 be passed, even if the builtin accepts no arguments.
774 While this behavior has benefits, it has its trade-offs.
775 If the execution token of a builtin is acquired (through
783 the builtin behavior will depend on the system state
791 This is particularly annoying for programs that want or need to
793 In this case, the use of a proxy is recommended.
798 is a Forth interpreter written in C, in the form of a forth
799 virtual machine library that can be called by C functions and vice
804 each line read interactively is then fed to
808 back to execute the builtin words.
815 The words available to
817 can be classified into four groups.
820 Forth standard words, extra
824 words, and the builtin commands;
825 the latter were already described.
828 Forth standard words are listed in the
831 The words falling in the two other groups are described in the
832 following subsections.
834 .Bl -tag -width wid-set-super
842 This is the STRING word set's
849 This is the STRING word set's
859 .Ss FREEBSD EXTRA WORDS
860 .Bl -tag -width XXXXXXXX
862 Evaluates the remainder of the input buffer, after having printed it first.
864 Evaluates the remainder of the input buffer under a
870 but without outputting a trailing space.
871 .It Ic fclose Pq Ar fd --
873 .It Ic fkey Pq Ar fd -- char
874 Reads a single character from a file.
875 .It Ic fload Pq Ar fd --
878 .It Ic fopen Pq Ar addr len mode Li -- Ar fd
880 Returns a file descriptor, or \-1 in case of failure.
883 parameter selects whether the file is to be opened for read access, write
886 .Dv O_RDONLY , O_WRONLY ,
890 .Pa /boot/support.4th ,
891 indicating read only, write only, and read-write access, respectively.
894 .Pq Ar fd addr len -- len'
902 Returns the actual number of bytes read, or -1 in case of error or end of
904 .It Ic heap? Pq -- Ar cells
905 Return the space remaining in the dictionary heap, in cells.
906 This is not related to the heap used by dynamic memory allocation words.
907 .It Ic inb Pq Ar port -- char
908 Reads a byte from a port.
909 .It Ic key Pq -- Ar char
910 Reads a single character from the console.
911 .It Ic key? Pq -- Ar flag
914 if there is a character available to be read from the console.
919 .It Ic outb Pq Ar port char --
920 Writes a byte to a port.
921 .It Ic seconds Pq -- Ar u
922 Returns the number of seconds since midnight.
923 .It Ic tib> Pq -- Ar addr len
924 Returns the remainder of the input buffer as a string on the stack.
925 .It Ic trace! Pq Ar flag --
926 Activates or deactivates tracing.
930 .Ss FREEBSD DEFINED ENVIRONMENTAL QUERIES
934 if the architecture is IA32.
937 version at compile time.
942 .Ss SYSTEM DOCUMENTATION
944 .Bl -tag -width /boot/defaults/loader.conf -compact
948 .It Pa /boot/boot.4th
952 .It Pa /boot/boot.conf
954 bootstrapping script.
956 .It Pa /boot/defaults/loader.conf
957 .It Pa /boot/loader.conf
958 .It Pa /boot/loader.conf.local
960 configuration files, as described in
962 .It Pa /boot/loader.rc
964 bootstrapping script.
965 .It Pa /boot/loader.help
968 Contains the help messages.
971 Boot in single user mode:
975 Load the kernel, a splash screen, and then autoboot in five seconds.
976 Notice that a kernel must be loaded before any other
978 command is attempted.
979 .Bd -literal -offset indent
982 load -t splash_image_data /boot/chuckrulez.bmp
986 Set the disk unit of the root device to 2, and then boot.
987 This would be needed in a system with two IDE disks,
988 with the second IDE disk hardwired to ada2 instead of ada1.
989 .Bd -literal -offset indent
991 boot /boot/kernel/kernel
995 .Bl -tag -width /usr/share/examples/bootforth/X
996 .It Pa /boot/loader.4th
997 Extra builtin-like words.
998 .It Pa /boot/support.4th
1001 .It Pa /usr/share/examples/bootforth/
1005 The following values are thrown by
1007 .Bl -tag -width XXXXX -offset indent
1009 Any type of error in the processing of a builtin.
1020 Out of interpreting text.
1022 Need more text to succeed -- will finish on next run.
1036 For the purposes of ANS Forth compliance, loader is an
1038 ANS Forth System with Environmental Restrictions, Providing
1044 parse, pick, roll, refill, to, value, \e, false, true,
1047 compile\&, , erase, nip, tuck
1052 from the Core Extensions word set, Providing the Exception Extensions
1053 word set, Providing the Locals Extensions word set, Providing the
1054 Memory-Allocation Extensions word set, Providing
1058 bye, forget, see, words,
1065 from the Programming-Tools extension word set, Providing the
1066 Search-Order extensions word set.
1078 .An Michael Smith Aq msmith@FreeBSD.org .
1082 .An John Sadler Aq john_sadler@alum.mit.edu .
1088 words will read from the input buffer instead of the console.
1089 The latter will be fixed, but the former will not.
projects / FreeBSD / stable / 10.git / blob