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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,
248 as well as ZFS pools.
251 is specified, more details are printed, including ZFS pool information
252 in a format that resembles
257 Displays loaded modules.
260 is specified, more details are shown.
262 .It Ic lszfs Ar filesystem
263 A ZFS extended command that can be used to explore the ZFS filesystem
265 Lists the immediate children of the
267 The filesystem hierarchy is rooted at a filesystem with the same name
270 .It Ic more Ar file Op Ar
271 Display the files specified, with a pause at each
275 .It Ic pnpscan Op Fl v
276 Scans for Plug-and-Play devices.
277 This is not functional at present.
284 Reads a line of input from the terminal, storing it in
287 A timeout can be specified with
289 though it will be canceled at the first key pressed.
290 A prompt may also be displayed through the
295 Immediately reboots the system.
297 .It Ic set Ar variable
298 .It Ic set Ar variable Ns = Ns Ar value
299 Set loader's environment variables.
301 .It Ic show Op Va variable
302 Displays the specified variable's value, or all variables and their
308 Remove all modules from memory.
310 .It Ic unset Va variable
313 from the environment.
316 Lists available commands.
318 .Ss BUILTIN ENVIRONMENT VARIABLES
321 has actually two different kinds of
324 There are ANS Forth's
325 .Em environmental queries ,
326 and a separate space of environment variables used by builtins, which
327 are not directly available to Forth words.
328 It is the latter type that this section covers.
330 Environment variables can be set and unset through the
334 builtins, and can have their values interactively examined through the
338 Their values can also be accessed as described in
341 Notice that these environment variables are not inherited by any shell
342 after the system has been booted.
344 A few variables are set automatically by
346 Others can affect the behavior of either
348 or the kernel at boot.
349 Some options may require a value,
350 while others define behavior just by being set.
351 Both types of builtin variables are described below.
352 .Bl -tag -width bootfile
353 .It Va autoboot_delay
356 will wait before booting.
357 Configuration options are described in
360 Instructs the kernel to prompt the user for the name of the root device
361 when the kernel is booted.
363 Instructs the kernel to try to mount the root file system from CD-ROM.
365 Instructs the kernel to start in the DDB debugger, rather than
366 proceeding to initialize when booted.
368 Instructs the kernel to mount the statically compiled-in root file system.
370 Selects gdb-remote mode for the kernel debugger by default.
371 .It Va boot_multicons
372 Enables multiple console support in the kernel early on boot.
373 In a running system, console configuration can be manipulated
378 All kernel console output is suppressed when console is muted.
379 In a running system, the state of console muting can be manipulated by the
383 During the device probe, pause after each line is printed.
385 Force the use of a serial console even when an internal console
388 Prevents the kernel from initiating a multi-user startup; instead,
389 a single-user mode will be entered when the kernel has finished
392 Setting this variable causes extra debugging information to be printed
393 by the kernel during the boot phase.
395 List of semicolon-separated search path for bootable kernels.
398 .It Va comconsole_speed
399 Defines the speed of the serial console (i386 and amd64 only).
400 If the previous boot stage indicated that a serial console is in use
401 then this variable is initialized to the current speed of the console
403 Otherwise it is set to 9600 unless this was overridden using the
404 .Va BOOT_COMCONSOLE_SPEED
410 variable take effect immediately.
411 .It Va comconsole_port
412 Defines the base i/o port used to access console UART
413 (i386 and amd64 only).
414 If the variable is not set, its assumed value is 0x3F8, which
415 corresponds to PC port COM1, unless overridden by
416 .Va BOOT_COMCONSOLE_PORT
417 variable during the compilation of
421 variable automatically set
423 environment variable to provide a hint to kernel for location of the console.
424 Loader console is changed immediately after variable
427 .It Va comconsole_pcidev
428 Defines the location of a PCI device of the 'simple communication'
429 class to be used as the serial console UART (i386 and amd64 only).
430 The syntax of the variable is
431 .Li 'bus:device:function[:bar]' ,
432 where all members must be numeric, with possible
434 prefix to indicate a hexadecimal value.
437 member is optional and assumed to be 0x10 if omitted.
438 The bar must decode i/o space.
440 .Va comconsole_pcidev
441 automatically sets the variable
443 to the base of the selected bar, and hint
444 .Va hw.uart.console .
445 Loader console is changed immediately after variable
446 .Va comconsole_pcidev
449 Defines the current console or consoles.
450 Multiple consoles may be specified.
451 In that case, the first listed console will become the default console for
452 userland output (e.g.\& from
455 Selects the default device to loader the kernel from.
457 .Dl Ic loader_device:
462 .Dl Ic zfs:zroot/ROOT/default:
464 Sets the device for kernel dumps.
465 This can be used to ensure that a device is configured before the corresponding
469 has been processed, allowing kernel panics that happen during the early stages
470 of boot to be captured.
478 Sets the list of binaries which the kernel will try to run as the initial
480 The first matching binary is used.
482 .Dq Li /sbin/init:/sbin/oinit:/sbin/init.bak:\:/rescue/init .
492 if the Forth's current state is interpreting.
494 Define the number of lines on the screen, to be used by the pager.
496 Sets the list of directories which will be searched for modules
497 named in a load command or implicitly required by a dependency.
498 The default value for this variable is
499 .Dq Li /boot/kernel;/boot/modules .
501 Sets the number of IDE disks as a workaround for some problems in
502 finding the root disk at boot.
503 This has been deprecated in favor of
510 .Dq Li "${interpret}" .
513 is unset, the default prompt is
515 .It Va root_disk_unit
516 If the code which detects the disk unit number for the root disk is
517 confused, e.g.\& by a mix of SCSI and IDE disks, or IDE disks with
518 gaps in the sequence (e.g.\& no primary slave), the unit number can
519 be forced by setting this variable.
521 By default the value of
523 is used to set the root file system
524 when the kernel is booted.
525 This can be overridden by setting
530 Other variables are used to override kernel tunable parameters.
531 The following tunables are available:
533 .It Va efi.rt.disabled
534 Disable UEFI runtime services in the kernel, if applicable.
535 Runtime services are only available and used if the kernel is booted in a UEFI
538 Limit the amount of physical memory the system will use.
539 By default the size is in bytes, but the
540 .Cm k , K , m , M , g
544 are also accepted and indicate kilobytes, megabytes and gigabytes
546 An invalid suffix will result in the variable being ignored by the
548 .It Va hw.pci.host_start_mem , hw.acpi.host_start_mem
549 When not otherwise constrained, this limits the memory start
551 The default is 0x80000000 and should be set to at least size of the
552 memory and not conflict with other resources.
553 Typically, only systems without PCI bridges need to set this variable
554 since PCI bridges typically constrain the memory starting address
555 (and the variable is only used when bridges do not constrain this
557 .It Va hw.pci.enable_io_modes
558 Enable PCI resources which are left off by some BIOSes or are not
559 enabled correctly by the device driver.
560 Tunable value set to ON (1) by default, but this may cause problems
561 with some peripherals.
563 Set the size of a number of statically allocated system tables; see
565 for a description of how to select an appropriate value for this
567 When set, this tunable replaces the value declared in the kernel
568 compile-time configuration file.
569 .It Va kern.ipc.nmbclusters
570 Set the number of mbuf clusters to be allocated.
571 The value cannot be set below the default
572 determined when the kernel was compiled.
573 .It Va kern.ipc.nsfbufs
576 buffers to be allocated.
579 Not all architectures use such buffers; see
582 .It Va kern.maxswzone
583 Limits the amount of KVM to be used to hold swap
584 metadata, which directly governs the
585 maximum amount of swap the system can support,
586 at the rate of approximately 200 MB of swap space
587 per 1 MB of metadata.
588 This value is specified in bytes of KVA space.
589 If no value is provided, the system allocates
590 enough memory to handle an amount of swap
591 that corresponds to eight times the amount of
592 physical memory present in the system.
594 Note that swap metadata can be fragmented,
595 which means that the system can run out of
596 space before it reaches the theoretical limit.
597 Therefore, care should be taken to not configure
598 more swap than approximately half of the
601 Running out of space for swap metadata can leave
602 the system in an unrecoverable state.
603 Therefore, you should only change
604 this parameter if you need to greatly extend the
605 KVM reservation for other resources such as the
607 .Va kern.ipc.nmbclusters .
608 Modifies kernel option
609 .Dv VM_SWZONE_SIZE_MAX .
610 .It Va kern.maxbcache
611 Limits the amount of KVM reserved for use by the
612 buffer cache, specified in bytes.
613 The default maximum is 200MB on i386,
614 and 400MB on amd64 and sparc64.
615 This parameter is used to
616 prevent the buffer cache from eating too much
617 KVM in large-memory machine configurations.
618 Only mess around with this parameter if you need to
619 greatly extend the KVM reservation for other resources
620 such as the swap zone or
621 .Va kern.ipc.nmbclusters .
623 the NBUF parameter will override this limit.
625 .Dv VM_BCACHE_SIZE_MAX .
626 .It Va kern.msgbufsize
627 Sets the size of the kernel message buffer.
628 The default limit of 96KB is usually sufficient unless
629 large amounts of trace data need to be collected
630 between opportunities to examine the buffer or
632 Overrides kernel option
634 .It Va machdep.disable_mtrrs
635 Disable the use of i686 MTRRs (x86 only).
636 .It Va net.inet.tcp.tcbhashsize
637 Overrides the compile-time set value of
639 or the preset default of 512.
640 Must be a power of 2.
641 .It Va twiddle_divisor
642 Throttles the output of the
644 I/O progress indicator displayed while loading the kernel and modules.
645 This is useful on slow serial consoles where the time spent waiting for
646 these characters to be written can add up to many seconds.
647 The default is 1 (full speed); a value of 2 spins half as fast, and so on.
649 Sets the size of kernel memory (bytes).
650 This overrides the value determined when the kernel was compiled.
653 .It Va vm.kmem_size_min
654 .It Va vm.kmem_size_max
655 Sets the minimum and maximum (respectively) amount of kernel memory
656 that will be automatically allocated by the kernel.
657 These override the values determined when the kernel was compiled.
661 .Dv VM_KMEM_SIZE_MAX .
665 supports the following format for specifying ZFS filesystems which
668 refers to a device specification:
670 .Ar zfs:pool/filesystem:
674 is a ZFS filesystem name as described in
679 does not have an entry for the root filesystem and
680 .Va vfs.root.mountfrom
683 refers to a ZFS filesystem, then
685 will instruct kernel to use that filesystem as the root filesystem.
687 When a builtin command is executed, the rest of the line is taken
688 by it as arguments, and it is processed by a special parser which
689 is not used for regular Forth commands.
691 This special parser applies the following rules to the parsed text:
694 All backslash characters are preprocessed.
697 \eb , \ef , \er , \en and \et are processed as in C.
699 \es is converted to a space.
706 Useful for things like
709 \e0xN and \e0xNN are replaced by the hex N or NN.
711 \eNNN is replaced by the octal NNN
715 \e" , \e' and \e$ will escape these characters, preventing them from
716 receiving special treatment in Step 2, described below.
718 \e\e will be replaced with a single \e .
720 In any other occurrence, backslash will just be removed.
723 Every string between non-escaped quotes or double-quotes will be treated
724 as a single word for the purposes of the remaining steps.
730 with the value of the environment variable
733 Space-delimited arguments are passed to the called builtin command.
734 Spaces can also be escaped through the use of \e\e .
737 An exception to this parsing rule exists, and is described in
738 .Sx BUILTINS AND FORTH .
739 .Ss BUILTINS AND FORTH
740 All builtin words are state-smart, immediate words.
741 If interpreted, they behave exactly as described previously.
742 If they are compiled, though,
743 they extract their arguments from the stack instead of the command line.
745 If compiled, the builtin words expect to find, at execution time, the
746 following parameters on the stack:
747 .D1 Ar addrN lenN ... addr2 len2 addr1 len1 N
750 are strings which will compose the command line that will be parsed
751 into the builtin's arguments.
752 Internally, these strings are concatenated in from 1 to N,
753 with a space put between each one.
755 If no arguments are passed, a 0
757 be passed, even if the builtin accepts no arguments.
759 While this behavior has benefits, it has its trade-offs.
760 If the execution token of a builtin is acquired (through
768 the builtin behavior will depend on the system state
776 This is particularly annoying for programs that want or need to
778 In this case, the use of a proxy is recommended.
783 is a Forth interpreter written in C, in the form of a forth
784 virtual machine library that can be called by C functions and vice
789 each line read interactively is then fed to
793 back to execute the builtin words.
800 The words available to
802 can be classified into four groups.
805 Forth standard words, extra
809 words, and the builtin commands;
810 the latter were already described.
813 Forth standard words are listed in the
816 The words falling in the two other groups are described in the
817 following subsections.
819 .Bl -tag -width wid-set-super
827 This is the STRING word set's
834 This is the STRING word set's
844 .Ss FREEBSD EXTRA WORDS
845 .Bl -tag -width XXXXXXXX
847 Evaluates the remainder of the input buffer, after having printed it first.
849 Evaluates the remainder of the input buffer under a
855 but without outputting a trailing space.
856 .It Ic fclose Pq Ar fd --
858 .It Ic fkey Pq Ar fd -- char
859 Reads a single character from a file.
860 .It Ic fload Pq Ar fd --
863 .It Ic fopen Pq Ar addr len mode Li -- Ar fd
865 Returns a file descriptor, or \-1 in case of failure.
868 parameter selects whether the file is to be opened for read access, write
871 .Dv O_RDONLY , O_WRONLY ,
875 .Pa /boot/support.4th ,
876 indicating read only, write only, and read-write access, respectively.
879 .Pq Ar fd addr len -- len'
887 Returns the actual number of bytes read, or -1 in case of error or end of
889 .It Ic heap? Pq -- Ar cells
890 Return the space remaining in the dictionary heap, in cells.
891 This is not related to the heap used by dynamic memory allocation words.
892 .It Ic inb Pq Ar port -- char
893 Reads a byte from a port.
894 .It Ic key Pq -- Ar char
895 Reads a single character from the console.
896 .It Ic key? Pq -- Ar flag
899 if there is a character available to be read from the console.
904 .It Ic outb Pq Ar port char --
905 Writes a byte to a port.
906 .It Ic seconds Pq -- Ar u
907 Returns the number of seconds since midnight.
908 .It Ic tib> Pq -- Ar addr len
909 Returns the remainder of the input buffer as a string on the stack.
910 .It Ic trace! Pq Ar flag --
911 Activates or deactivates tracing.
915 .Ss FREEBSD DEFINED ENVIRONMENTAL QUERIES
919 if the architecture is IA32.
922 version at compile time.
930 command line provides several ways of compromising system security,
931 including, but not limited to:
935 Booting from removable storage, by setting the
941 Executing binary of choice, by setting the
947 Overriding ACPI DSDT to inject arbitrary code into the ACPI subsystem
950 One can prevent unauthorized access
953 command line by setting the
961 In order for this to be effective, one should also configure the firmware
962 (BIOS or UEFI) to prevent booting from unauthorized devices.
964 Memory disk (MD) can be used when the
968 The size of the memory disk is determined by
970 If MD available, a file system can be embedded into the
973 .Pa /sys/tools/embed_mfs.sh .
974 Then, MD will be probed and be set to
976 during initialization.
978 Currently, MD is only supported in
981 .Bl -tag -width /usr/share/examples/bootforth/ -compact
985 .It Pa /boot/loader.4th
989 .It Pa /boot/defaults/loader.conf
990 .It Pa /boot/loader.4th
991 Extra builtin-like words.
992 .It Pa /boot/loader.conf
993 .It Pa /boot/loader.conf.local
995 configuration files, as described in
997 .It Pa /boot/loader.rc
999 bootstrapping script.
1000 .It Pa /boot/loader.help
1003 Contains the help messages.
1004 .It Pa /boot/support.4th
1007 .It Pa /usr/share/examples/bootforth/
1011 Boot in single user mode:
1015 Load the kernel, a splash screen, and then autoboot in five seconds.
1016 Notice that a kernel must be loaded before any other
1018 command is attempted.
1019 .Bd -literal -offset indent
1022 load -t splash_image_data /boot/chuckrulez.bmp
1026 Set the disk unit of the root device to 2, and then boot.
1027 This would be needed in a system with two IDE disks,
1028 with the second IDE disk hardwired to ada2 instead of ada1.
1029 .Bd -literal -offset indent
1030 set root_disk_unit=2
1031 boot /boot/kernel/kernel
1034 Set the default device used for loading a kernel from a ZFS filesystem:
1035 .Bd -literal -offset indent
1036 set currdev=zfs:tank/ROOT/knowngood:
1040 The following values are thrown by
1042 .Bl -tag -width XXXXX -offset indent
1044 Any type of error in the processing of a builtin.
1055 Out of interpreting text.
1057 Need more text to succeed -- will finish on next run.
1071 For the purposes of ANS Forth compliance, loader is an
1073 ANS Forth System with Environmental Restrictions, Providing
1079 parse, pick, roll, refill, to, value, \e, false, true,
1082 compile\&, , erase, nip, tuck
1087 from the Core Extensions word set, Providing the Exception Extensions
1088 word set, Providing the Locals Extensions word set, Providing the
1089 Memory-Allocation Extensions word set, Providing
1093 bye, forget, see, words,
1100 from the Programming-Tools extension word set, Providing the
1101 Search-Order extensions word set.
1113 .An Michael Smith Aq msmith@FreeBSD.org .
1117 .An John Sadler Aq john_sadler@alum.mit.edu .
1123 words will read from the input buffer instead of the console.
1124 The latter will be fixed, but the former will not.
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