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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), or file of opaque
211 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.
216 Currently, argument passing does not work for the kernel.
222 Displays a listing of files in the directory
224 or the root directory if
229 is specified, file sizes will be shown too.
232 Lists all of the devices from which it may be possible to load modules.
235 is specified, more details are printed.
238 Displays loaded modules.
241 is specified, more details are shown.
243 .It Ic more Ar file Op Ar
244 Display the files specified, with a pause at each
248 .It Ic pnpscan Op Fl v
249 Scans for Plug-and-Play devices.
250 This is not functional at present.
257 Reads a line of input from the terminal, storing it in
260 A timeout can be specified with
262 though it will be canceled at the first key pressed.
263 A prompt may also be displayed through the
268 Immediately reboots the system.
270 .It Ic set Ar variable
271 .It Ic set Ar variable Ns = Ns Ar value
272 Set loader's environment variables.
274 .It Ic show Op Va variable
275 Displays the specified variable's value, or all variables and their
281 Remove all modules from memory.
283 .It Ic unset Va variable
286 from the environment.
289 Lists available commands.
291 .Ss BUILTIN ENVIRONMENT VARIABLES
294 has actually two different kinds of
297 There are ANS Forth's
298 .Em environmental queries ,
299 and a separate space of environment variables used by builtins, which
300 are not directly available to Forth words.
301 It is the latter type that this section covers.
303 Environment variables can be set and unset through the
307 builtins, and can have their values interactively examined through the
311 Their values can also be accessed as described in
314 Notice that these environment variables are not inherited by any shell
315 after the system has been booted.
317 A few variables are set automatically by
319 Others can affect the behavior of either
321 or the kernel at boot.
322 Some options may require a value,
323 while others define behavior just by being set.
324 Both types of builtin variables are described below.
325 .Bl -tag -width bootfile
327 Unset this to disable automatic loading of the ACPI module.
329 .Va hint.acpi.0.disabled
332 .It Va autoboot_delay
335 will wait before booting.
336 If this variable is not defined,
338 will default to 10 seconds.
344 will be automatically attempted after processing
345 .Pa /boot/loader.rc ,
348 will be processed normally, defaulting to 10 seconds delay.
352 no delay will be inserted, but user still will be able to interrupt
354 process and escape into the interactive mode by pressing some key
355 on the console while kernel and
356 modules are being loaded.
360 no delay will be inserted and
362 will engage interactive mode only if
364 has failed for some reason.
366 Instructs the kernel to prompt the user for the name of the root device
367 when the kernel is booted.
369 Instructs the kernel to try to mount the root file system from CD-ROM.
371 Instructs the kernel to start in the DDB debugger, rather than
372 proceeding to initialize when booted.
374 Instructs the kernel to mount the statically compiled-in root file system.
376 Selects gdb-remote mode for the kernel debugger by default.
377 .It Va boot_multicons
378 Enables multiple console support in the kernel early on boot.
379 In a running system, console configuration can be manipulated
384 All console output is suppressed when console is muted.
385 In a running system, the state of console muting can be manipulated by the
389 During the device probe, pause after each line is printed.
391 Force the use of a serial console even when an internal console
394 Prevents the kernel from initiating a multi-user startup; instead,
395 a single-user mode will be entered when the kernel has finished
398 Setting this variable causes extra debugging information to be printed
399 by the kernel during the boot phase.
401 List of semicolon-separated search path for bootable kernels.
404 .It Va comconsole_speed
405 Defines the speed of the serial console (i386 and amd64 only).
406 If the previous boot stage indicated that a serial console is in use
407 then this variable is initialized to the current speed of the console
409 Otherwise it is set to 9600 unless this was overridden using the
410 .Va BOOT_COMCONSOLE_SPEED
416 variable take effect immediately.
418 Defines the current console or consoles.
419 Multiple consoles may be specified.
420 In that case, the first listed console will become the default console for
421 userland output (e.g.\& from
424 Selects the default device.
425 Syntax for devices is odd.
427 If set to a valid directory in the root file system, it causes
431 operation on that directory, making it the new root directory.
432 That happens before entering single-user mode or multi-user
433 mode (but after executing the
437 Sets the list of binaries which the kernel will try to run as the initial
439 The first matching binary is used.
441 .Dq Li /sbin/init:/sbin/oinit:/sbin/init.bak:\:/rescue/init:/stand/sysinstall .
443 If set to a valid file name in the root file system,
446 to run that script as the very first action,
447 before doing anything else.
448 Signal handling and exit code interpretation is similar to
452 In particular, single-user operation is enforced
453 if the script terminates with a non-zero exit code,
454 or if a SIGTERM is delivered to the
458 Defines the shell binary to be used for executing the various shell scripts.
461 It is used for running the
463 if set, as well as for the
468 The value of the corresponding
470 variable is evaluated every time
472 calls a shell script, so it can be changed later on using the
475 In particular, if a non-default shell is used for running an
477 it might be desirable to have that script reset the value of
479 back to the default, so that the
481 script is executed with the standard shell
486 if the Forth's current state is interpreting.
488 Define the number of lines on the screen, to be used by the pager.
490 Sets the list of directories which will be searched for modules
491 named in a load command or implicitly required by a dependency.
492 The default value for this variable is
493 .Dq Li /boot/kernel;/boot/modules .
495 Sets the number of IDE disks as a workaround for some problems in
496 finding the root disk at boot.
497 This has been deprecated in favor of
504 .Dq Li "${interpret}" .
507 is unset, the default prompt is
509 .It Va root_disk_unit
510 If the code which detects the disk unit number for the root disk is
511 confused, e.g.\& by a mix of SCSI and IDE disks, or IDE disks with
512 gaps in the sequence (e.g.\& no primary slave), the unit number can
513 be forced by setting this variable.
515 By default the value of
517 is used to set the root file system
518 when the kernel is booted.
519 This can be overridden by setting
524 Other variables are used to override kernel tunable parameters.
525 The following tunables are available:
528 Limit the amount of physical memory the system will use.
529 By default the size is in bytes, but the
530 .Cm k , K , m , M , g
534 are also accepted and indicate kilobytes, megabytes and gigabytes
536 An invalid suffix will result in the variable being ignored by the
538 .It Va hw.pci.host_start_mem , hw.acpi.host_start_mem
539 When not otherwise constrained, this limits the memory start
541 The default is 0x80000000 and should be set to at least size of the
542 memory and not conflict with other resources.
543 Typically, only systems without PCI bridges need to set this variable
544 since PCI bridges typically constrain the memory starting address
545 (and the variable is only used when bridges do not constrain this
547 .It Va hw.pci.enable_io_modes
548 Enable PCI resources which are left off by some BIOSes or are not
549 enabled correctly by the device driver.
550 Tunable value set to ON (1) by default, but this may cause problems
551 with some peripherals.
553 Set the size of a number of statically allocated system tables; see
555 for a description of how to select an appropriate value for this
557 When set, this tunable replaces the value declared in the kernel
558 compile-time configuration file.
559 .It Va kern.ipc.nmbclusters
560 Set the number of mbuf clusters to be allocated.
561 The value cannot be set below the default
562 determined when the kernel was compiled.
563 .It Va kern.ipc.nsfbufs
566 buffers to be allocated.
569 Not all architectures use such buffers; see
572 .It Va kern.maxswzone
573 Limits the amount of KVM to be used to hold swap
574 meta information, which directly governs the
575 maximum amount of swap the system can support.
576 This value is specified in bytes of KVA space
577 and defaults to 32MBytes on i386 and amd64.
579 to not reduce this value such that the actual
580 amount of configured swap exceeds 1/2 the
581 kernel-supported swap.
582 The default of 32MB allows
583 the kernel to support a maximum of ~7GB of swap.
585 this parameter if you need to greatly extend the
586 KVM reservation for other resources such as the
588 .Va kern.ipc.nmbclusters .
589 Modifies kernel option
590 .Dv VM_SWZONE_SIZE_MAX .
591 .It Va kern.maxbcache
592 Limits the amount of KVM reserved for use by the
593 buffer cache, specified in bytes.
594 The default maximum is 200MB on i386,
595 and 400MB on amd64, sparc64, and sun4v.
596 This parameter is used to
597 prevent the buffer cache from eating too much
598 KVM in large-memory machine configurations.
599 Only mess around with this parameter if you need to
600 greatly extend the KVM reservation for other resources
601 such as the swap zone or
602 .Va kern.ipc.nmbclusters .
604 the NBUF parameter will override this limit.
606 .Dv VM_BCACHE_SIZE_MAX .
607 .It Va machdep.disable_mtrrs
608 Disable the use of i686 MTRRs (x86 only).
609 .It Va net.inet.tcp.tcbhashsize
610 Overrides the compile-time set value of
612 or the preset default of 512.
613 Must be a power of 2.
615 Sets the size of kernel memory (bytes).
616 This overrides the value determined when the kernel was compiled.
619 .It Va vm.kmem_size_min
620 .It Va vm.kmem_size_max
621 Sets the minimum and maximum (respectively) amount of kernel memory
622 that will be automatically allocated by the kernel.
623 These override the values determined when the kernel was compiled.
627 .Dv VM_KMEM_SIZE_MAX .
630 When a builtin command is executed, the rest of the line is taken
631 by it as arguments, and it is processed by a special parser which
632 is not used for regular Forth commands.
634 This special parser applies the following rules to the parsed text:
638 All backslash characters are preprocessed.
641 \eb , \ef , \er , \en and \et are processed as in C.
643 \es is converted to a space.
650 Useful for things like
653 \e0xN and \e0xNN are replaced by the hex N or NN.
655 \eNNN is replaced by the octal NNN
659 \e" , \e' and \e$ will escape these characters, preventing them from
660 receiving special treatment in Step 2, described below.
662 \e\e will be replaced with a single \e .
664 In any other occurrence, backslash will just be removed.
667 Every string between non-escaped quotes or double-quotes will be treated
668 as a single word for the purposes of the remaining steps.
674 with the value of the environment variable
677 Space-delimited arguments are passed to the called builtin command.
678 Spaces can also be escaped through the use of \e\e .
681 An exception to this parsing rule exists, and is described in
682 .Sx BUILTINS AND FORTH .
683 .Ss BUILTINS AND FORTH
684 All builtin words are state-smart, immediate words.
685 If interpreted, they behave exactly as described previously.
686 If they are compiled, though,
687 they extract their arguments from the stack instead of the command line.
689 If compiled, the builtin words expect to find, at execution time, the
690 following parameters on the stack:
691 .D1 Ar addrN lenN ... addr2 len2 addr1 len1 N
694 are strings which will compose the command line that will be parsed
695 into the builtin's arguments.
696 Internally, these strings are concatenated in from 1 to N,
697 with a space put between each one.
699 If no arguments are passed, a 0
701 be passed, even if the builtin accepts no arguments.
703 While this behavior has benefits, it has its trade-offs.
704 If the execution token of a builtin is acquired (through
712 the builtin behavior will depend on the system state
720 This is particularly annoying for programs that want or need to
722 In this case, the use of a proxy is recommended.
727 is a Forth interpreter written in C, in the form of a forth
728 virtual machine library that can be called by C functions and vice
733 each line read interactively is then fed to
737 back to execute the builtin words.
744 The words available to
746 can be classified into four groups.
749 Forth standard words, extra
753 words, and the builtin commands;
754 the latter were already described.
757 Forth standard words are listed in the
760 The words falling in the two other groups are described in the
761 following subsections.
763 .Bl -tag -width wid-set-super
771 This is the STRING word set's
778 This is the STRING word set's
788 .Ss FREEBSD EXTRA WORDS
789 .Bl -tag -width XXXXXXXX
791 Evaluates the remainder of the input buffer, after having printed it first.
793 Evaluates the remainder of the input buffer under a
799 but without outputting a trailing space.
800 .It Ic fclose Pq Ar fd --
802 .It Ic fkey Pq Ar fd -- char
803 Reads a single character from a file.
804 .It Ic fload Pq Ar fd --
807 .It Ic fopen Pq Ar addr len mode Li -- Ar fd
809 Returns a file descriptor, or \-1 in case of failure.
812 parameter selects whether the file is to be opened for read access, write
815 .Dv O_RDONLY , O_WRONLY ,
819 .Pa /boot/support.4th ,
820 indicating read only, write only, and read-write access, respectively.
823 .Pq Ar fd addr len -- len'
831 Returns the actual number of bytes read, or -1 in case of error or end of
833 .It Ic heap? Pq -- Ar cells
834 Return the space remaining in the dictionary heap, in cells.
835 This is not related to the heap used by dynamic memory allocation words.
836 .It Ic inb Pq Ar port -- char
837 Reads a byte from a port.
838 .It Ic key Pq -- Ar char
839 Reads a single character from the console.
840 .It Ic key? Pq -- Ar flag
843 if there is a character available to be read from the console.
848 .It Ic outb Pq Ar port char --
849 Writes a byte to a port.
850 .It Ic seconds Pq -- Ar u
851 Returns the number of seconds since midnight.
852 .It Ic tib> Pq -- Ar addr len
853 Returns the remainder of the input buffer as a string on the stack.
854 .It Ic trace! Pq Ar flag --
855 Activates or deactivates tracing.
859 .Ss FREEBSD DEFINED ENVIRONMENTAL QUERIES
863 if the architecture is IA32.
866 version at compile time.
871 .Ss SYSTEM DOCUMENTATION
873 .Bl -tag -width /boot/defaults/loader.conf -compact
877 .It Pa /boot/boot.4th
881 .It Pa /boot/boot.conf
883 bootstrapping script.
885 .It Pa /boot/defaults/loader.conf
886 .It Pa /boot/loader.conf
887 .It Pa /boot/loader.conf.local
889 configuration files, as described in
891 .It Pa /boot/loader.rc
893 bootstrapping script.
894 .It Pa /boot/loader.help
897 Contains the help messages.
900 Boot in single user mode:
904 Load the kernel, a splash screen, and then autoboot in five seconds.
905 Notice that a kernel must be loaded before any other
907 command is attempted.
908 .Bd -literal -offset indent
911 load -t splash_image_data /boot/chuckrulez.bmp
915 Set the disk unit of the root device to 2, and then boot.
916 This would be needed in a system with two IDE disks,
917 with the second IDE disk hardwired to wd2 instead of wd1.
918 .Bd -literal -offset indent
924 .Bl -tag -width /usr/share/examples/bootforth/X
925 .It Pa /boot/loader.4th
926 Extra builtin-like words.
927 .It Pa /boot/support.4th
930 .It Pa /usr/share/examples/bootforth/
934 The following values are thrown by
936 .Bl -tag -width XXXXX -offset indent
938 Any type of error in the processing of a builtin.
949 Out of interpreting text.
951 Need more text to succeed -- will finish on next run.
965 For the purposes of ANS Forth compliance, loader is an
967 ANS Forth System with Environmental Restrictions, Providing
973 parse, pick, roll, refill, to, value, \e, false, true,
976 compile\&, , erase, nip, tuck
981 from the Core Extensions word set, Providing the Exception Extensions
982 word set, Providing the Locals Extensions word set, Providing the
983 Memory-Allocation Extensions word set, Providing
987 bye, forget, see, words,
994 from the Programming-Tools extension word set, Providing the
995 Search-Order extensions word set.
1007 .An Michael Smith Aq msmith@FreeBSD.org .
1011 .An John Sadler Aq john_sadler@alum.mit.edu .
1017 words will read from the input buffer instead of the console.
1018 The latter will be fixed, but the former will not.
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