2 .\" Copyright (c) 1999 Daniel C. Sobral
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26 .\" $FreeBSD: src/sys/boot/common/loader.8,v 1.57 2003/06/29 20:57:55 brueffer Exp $
33 .Nd kernel bootstrapping final stage
39 kernel bootstrapping process.
40 It is implemented as a
42 client and is linked statically to
52 directory exist on the boot file system, then
54 is prepended to all relative file names used by
56 This makes it possible to locate all files used by
62 directory on the boot file system.
63 If boot and root are the same file system, then files used by
67 If boot and root are different file systems, then files used by
71 on the boot file system, which is mounted as
73 on the root file system when the kernel is running.
75 During initialization,
77 will probe for a console and set the
79 variable, or set it to serial console
81 if the previous boot stage used that.
82 Then, devices are probed,
91 is processed if available, and, failing that,
93 is read for historical reasons.
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.
116 builtin commands take parameters from the command line.
118 The builtin commands available are:
120 .Bl -tag -width indent -compact
121 .It Ar variable Ns = Ns Ar value
126 The value is always assigned to a local variable
130 is in the list of known kernel environment variables or is a kernel tunable,
131 the value is also assigned to the kernel environment variable of the
133 If the variable name contains a
135 it is considered a kernel tunable.
136 Local variables are unset if
139 Kernel environment variable will have empty value.
141 In other words, the assignment above will set a local variable and
142 if applicable, also assign
144 to the kernel environment variable, even if
148 .Sx KERNEL ENVIRONMENT VARIABLES AND LOCAL VARIABLES .
151 can be a string or a string expression containing literal text and
152 kernel environment variables, like
156 Escape sequences like
162 (character with number given in octal)
164 This is actually a general facility of
166 which can be used for arguments of all commands.
168 .It Ic autoboot Op Ar delay Op Ar prompt
169 Proceeds to bootstrap the system after a number of seconds, if not
170 interrupted by the user.
171 Displays a countdown prompt
172 warning the user the system is about to be booted,
173 unless interrupted by a key press.
174 The kernel will be loaded first if necessary.
175 Defaults to 10 seconds.
178 Displays statistics about disk cache usage.
181 .It Ic boot Oo Fl Ns Ar flag ... Oc Op Ar kernelname
182 Immediately proceeds to bootstrap the system, loading the kernel
184 Any flags or arguments are passed to the kernel, but they
185 must precede the kernel name, if a kernel name is provided.
186 Flags are described in
194 .It Ic cd Op Ar directory
195 Change working directory to
199 .It Ic echo Oo Fl n Oc Op Ar message
200 Displays text on the screen.
201 A new line will be printed unless
204 See description of assignment
205 .Pq Ar variable Ns = Ns Ar value
207 for use of kernel environment variables and escape sequences in
211 Conditional if/else/endif.
213 .It Ic elseifexists Ar path
216 exists, i.e.\& file/dir present.
219 Conditional if/else/endif.
222 Displays memory usage statistics.
223 For debugging purposes only.
225 .It Ic help Op Ar topic Op Ar subtopic
226 Shows help messages read from
231 will list all topics available.
233 .It Ic ifexists Ar path
236 exists, i.e.\& file/dir present.
238 .It Ic ifset Ar kenv_variable
239 Conditional kernel environment variable
244 Process script files.
245 Each file, in turn, is completely read into memory,
246 and then each of its lines is passed to the command line interpreter.
247 If any error is returned by the interpreter, the include
248 command aborts immediately, without reading any other files, and
249 returns an error itself.
251 .It Ic load Oo Fl t Ar type Oc Ar file Op Ar argument ...
252 Loads a kernel, kernel loadable module (kld), or file of opaque
253 contents tagged as being of the type
255 Kernel and modules can be either in a.out or
258 Any arguments passed after the name of the file to be loaded
259 will be passed as arguments to that file.
262 Load the kernel and all modules specified by MODULE_load variables.
264 .It Ic local Op Ar local_variable ...
265 Displays the specified variable's value, or all local variables and their
270 .It Ic ls Oo Fl l Oc Op Ar path
271 Displays a listing of files in the directory
273 or the current directory if
278 is specified, file sizes will be shown too.
284 prefix indicates a disk slice or partition from which it may be
285 possible to load modules.
288 is specified, more details,
289 like disk slice or partition size and position, are printed.
292 Displays loaded modules.
295 is specified, more details are shown.
297 .It Ic lunset Ar local_variable
298 Unset a local variable.
299 Discards the value and removes the variable.
301 .It Ic lunsetif Ar local_variable kenv_variable
304 if kernel environment variable
306 is true, i.e.\& set to 1 or
312 .It Ic menuadd Ar command_line
313 Add script line for the current menu item.
316 Clear all menu items.
318 .It Ic menuitem Ar key description
319 Start a new menu item.
320 When running the menu system, a line with
324 is displayed, and an item is chosen by pressing
328 Display the files specified, with a pause at each
332 .It Ic optcd Op Ar directory
333 Change the working directory to
339 but ignores errors when changing the directory.
342 Process script files.
346 but ignores errors while executing commands in included files.
348 .It Ic pnpscan Op Fl v
349 Scans for Plug-and-Play devices.
350 This is not functional at present.
353 Prints the working directory.
355 .It Ic read Oo Fl p Ar prompt Oc Oo Fl t Ar seconds Oc Op Ar kenv_variable
356 Reads a line of input from the terminal,
357 storing it in kernel environment variable
360 A prompt may be displayed through the
363 A timeout can be specified with
365 though it will be canceled at the first key pressed.
368 Immediately reboots the system.
370 .It Ic set Ar kenv_variable
371 .It Ic set Ar kenv_variable Ns = Ns Ar value
372 Set kernel environment variable
377 is given, the empty string is the value.
379 .It Ic show Op Ar kenv_variable
380 Displays the specified kernel environment variable's value,
381 or all variables and their values if
386 Removes all modules from memory.
388 .It Ic unset Ar kenv_variable
391 from the kernel environment.
394 Lists most available commands with a short help text for each.
396 .Ss KERNEL ENVIRONMENT VARIABLES AND LOCAL VARIABLES
399 actually has two different kinds of variables.
401 kernel environment variables,
402 which are visible to the kernel when it is started,
403 and a separate space of local variables used by
405 which are not available to the kernel.
407 Both local variable and kernel environment variable
408 of the same name are changed by assignment
409 .Pq Ar variable Ns = Ns Ar value .
411 Kernel environment variables can be set and unset through the
415 builtins, and can have their values examined through the
420 Variables in command arguments or
426 refers to kernel environment variables.
428 Local variables can be unset with
432 builtin, and can have their values examined through the
436 Notice that these environment variables are not inherited by any shell
437 after the system has been booted, but can be examined by
440 Note that a variable can have two instances with differnet values:
441 both a local variable instance and a kernel environment variable instance
442 can exist for the same name and with different values.
443 This can cause confusion and is seldom done on purpose.
445 A few variables are set automatically by
447 Others can affect the behavior of either
449 or the kernel at boot.
450 Some options may require a value,
451 while others define behavior just by being set.
452 Both types of variables are described below.
453 .Bl -tag -width indent
455 Used for handling automatic loading of the
458 To disable automatic loading of the ACPI module use:
461 .Dl set hint.acpi.0.disabled=1
462 .It Va autoboot_delay
467 will wait before booting.
468 Default value is 10 seconds.
474 will be automatically attempted after processing
478 will be processed normally, defaulting to 10 seconds delay.
480 Instructs the kernel to prompt the user for the name of the root device
481 when the kernel is booted.
483 Instructs the kernel to start in the DDB debugger, rather than
484 proceeding to initialize when booted.
486 Selects gdb-remote mode for the kernel debugger by default.
488 Prevents the kernel from initiating a multi-user startup; instead single-user
489 mode will be entered when the kernel has finished device probing.
490 .It Va boot_userconfig
491 Requests that the kernel's interactive device configuration program
492 be run when the kernel is booted.
494 Setting this variable causes extra debugging information to be printed
495 by the kernel during and after the boot phase.
497 List of semicolon-separated search path for bootable kernels.
501 Defines the current console.
503 Selects the default device.
504 Syntax for devices is odd.
505 .It Va default_kernel
506 Selects default kernel loaded by
512 The name of a device where the kernel can save a crash dump in case
514 This automatically sets the
520 Used for handling automatic loading of the
523 To disable automatic loading of the EHCI module use:
526 .Dl set hint.ehci.0.disabled=1
533 By setting this variable
535 can be run from a subdirectory of the root file system.
537 Sets the list of binaries which the kernel will try to run as the initial
539 The first matching binary is used.
541 .Dq Li /sbin/init:/sbin/oinit:/sbin/init.bak .
542 .It Va kernel_options
543 Set kernel boot flags.
548 Define the number of lines on the screen, to be used by the pager.
550 Sets the list of directories which will be searched for modules named in a
552 command or implicitly required by a dependency.
553 The default value for this variable is
555 which first searches the current working directory and then
558 Sets the number of IDE disks as a workaround for some problems in
559 finding the root disk at boot.
560 This has been deprecated in favor of
568 Kernel environment variables can be used in
579 .Dl "set prompt=\*q\e${currdev} OK\*q"
580 .It Va root_disk_unit
581 If the code which detects the disk unit number for the root disk is
582 confused, e.g.\& by a mix of
589 gaps in the sequence (e.g.\& no primary slave), the unit number can
590 be forced by setting this variable.
593 .Va vfs.root.mountfrom
596 By default the value of
598 is used to set the root file system
599 when the kernel is booted.
600 This can be overridden by setting
605 .Va vfs.root.mountfrom
609 Other variables are used to override kernel tunable parameters.
612 tunables are available:
613 .Bl -tag -width indent
614 .It Va hw.ioapic_enable
617 Set to 1 to enable, 0 to disable.
620 Set irqX's destination to the given
623 If the specified value is larger than the last
628 This variable should not be used if
632 Limit the amount of physical memory the system will use.
633 By default the size is in bytes, but the
634 .Cm k , K , m , M , g
638 are also accepted and indicate kilobytes, megabytes and gigabytes
640 An invalid suffix will result in the variable being ignored by the
642 .It Va hw.usb.hack_defer_exploration
643 The USB keyboard will sometimes not attach properly unless you set this
645 .It Va kern.emergency_intr_enable
646 Setting this to 1 enables emergency interrupt polling.
647 All interrupt handlers are executed periodically.
648 This mode is very expensive and should
649 only be used to get a system accessible when interrupt routing is
651 It is primarily used by kernel developers to debug new systems.
652 .It Va kern.emergency_intr_freq
653 Set the polling rate for the emergency interrupt polling code.
654 The default is 10 (hz) to dissuade casual use.
655 If you are doing real work
656 with emergency interrupt polling mode enabled, it is recommended
657 that you use a frequency between 100hz and 300hz.
659 Set the size of a number of statically allocated system tables; see
661 for a description of how to select an appropriate value for this tunable.
662 When set, this tunable replaces the value declared in the kernel
663 compile-time configuration file.
664 .It Va kern.ipc.nmbclusters
665 Set the number of mbuf clusters to be allocated.
666 The value cannot be set below the default
667 determined when the kernel was compiled.
671 Toggles the mmx optimizations for the bcopy/copyin/copyout routines
672 .It Va kern.vm.kmem.size
673 Sets the size of kernel memory (bytes).
674 This overrides the value determined when the kernel was compiled.
675 .It Va kern.maxswzone
678 to be used to hold swap
679 meta information, which directly governs the
680 maximum amount of swap the system can support.
681 This value is specified in bytes of KVA space
682 and defaults to around 70MBytes.
684 to not reduce this value such that the actual
685 amount of configured swap exceeds \(12 the
686 kernel-supported swap.
687 The default 70MB allows
688 the kernel to support a maximum of (approximately)
689 14GB of configured swap.
690 Only mess around with
691 this parameter if you need to greatly extend the
693 reservation for other resources such as the
697 .Va VM_SWZONE_SIZE_MAX .
698 .It Va kern.maxbcache
699 Limits the amount of KVM reserved for use by the
700 buffer cache, specified in bytes.
701 The default maximum is 200MB.
702 This parameter is used to
703 prevent the buffer cache from eating too much
705 in large-memory machine configurations.
706 Only mess around with this parameter if you need to
709 reservation for other resources
710 such as the swap zone or
713 the NBUF parameter will override this limit.
715 .Va VM_BCACHE_SIZE_MAX .
716 .It Va machdep.disable_mtrrs
721 .It Va net.inet.tcp.tcbhashsize
722 Overrides the compile-time set value of
724 or the preset default of 512.
725 Must be a power of 2.
726 .It Va vfs.root.mountfrom
727 Specify root file system.
728 A semicolon separated list of file systems to try
729 as the kernel root file system.
730 File system format is file system type and disk store,
732 This variable needs to be set when using a boot-only partition, which is
733 typically mounted on root file system as
736 One file system example:
741 multi volume example:
742 .Dl hammer:da8s1a:da9s1a
744 Several file systems, boot list, example:
745 .Dl ufs:da0s1a;hammer:ad1s1d
747 Each file system in the list will be tried in the order specified
748 until the mount succeeds.
751 prompt is displayed for manual entry.
753 You may not specify devtab labels here but you can specify paths available to
756 .Dl hammer:serno/L41JYE0G.s1d
757 .It Va vfs.root.realroot
758 Root file system and extra options for
764 .Bl -tag -width /boot/defaults/dloader.menu -compact
765 .It Pa /boot/boot.conf
767 bootstrapping script.
769 .It Pa /boot/defaults/dloader.menu
771 menu setup commands -- do not change this file
772 .It Pa /boot/defaults/loader.conf
774 configuration file, see
776 -- do not change this file
777 .It Pa /boot/dloader.menu
780 .It Pa /boot/dloader.rc
786 .It Pa /boot/loader.conf
787 .It Pa /boot/loader.conf.local
789 configuration files, see
791 .It Pa /boot/loader.help
792 help messages, used by the
797 Boot in single user mode:
802 Load kernel's user configuration file.
803 Notice that a kernel must be loaded before any other
805 command is attempted.
806 .Bd -literal -offset indent
808 load -t userconfig_script kernel.conf
811 Load the kernel, a splash screen, and then autoboot in five seconds.
812 .Bd -literal -offset indent
815 load -t splash_image_data chuckrulez.bmp
819 Set the disk unit of the root device to 2, and then boot.
820 This would be needed in a system with two IDE disks,
821 with the second IDE disk hardwired to
825 .Bd -literal -offset indent
858 .An Michael Smith Aq msmith@FreeBSD.org .
862 .An Matthew Dillon Aq dillon@backplane.com .
864 A variable can have two instances: local & kernel environment,
865 this can cause confusion.