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.
491 Setting this variable causes extra debugging information to be printed
492 by the kernel during and after the boot phase.
494 List of semicolon-separated search path for bootable kernels.
498 Defines the current console.
500 Selects the default device.
501 Syntax for devices is odd.
502 .It Va default_kernel
503 Selects default kernel loaded by
509 The name of a device where the kernel can save a crash dump in case
511 This automatically sets the
517 Used for handling automatic loading of the
520 To disable automatic loading of the EHCI module use:
523 .Dl set hint.ehci.0.disabled=1
525 Used for handling automatic loading of the
528 To disable automatic loading of the XHCI module use:
531 .Dl set hint.xhci.0.disabled=1
538 By setting this variable
540 can be run from a subdirectory of the root file system.
542 Sets the list of binaries which the kernel will try to run as the initial
544 The first matching binary is used.
546 .Dq Li /sbin/init:/sbin/oinit:/sbin/init.bak .
547 .It Va kernel_options
548 Set kernel boot flags.
553 Define the number of lines on the screen, to be used by the pager.
555 Setting this variable to
558 .Pa /boot/modules.local
561 directories list and passed to kernel for
564 Sets the list of directories which will be searched for modules named in a
566 command or implicitly required by a dependency.
567 The default value for this variable is
569 which first searches the current working directory and then
572 Sets the number of IDE disks as a workaround for some problems in
573 finding the root disk at boot.
574 This has been deprecated in favor of
582 Kernel environment variables can be used in
593 .Dl "set prompt=\*q\e${currdev} OK\*q"
594 .It Va root_disk_unit
595 If the code which detects the disk unit number for the root disk is
596 confused, e.g.\& by a mix of
603 gaps in the sequence (e.g.\& no primary slave), the unit number can
604 be forced by setting this variable.
607 .Va vfs.root.mountfrom
610 By default the value of
612 is used to set the root file system
613 when the kernel is booted.
614 This can be overridden by setting
619 .Va vfs.root.mountfrom
623 Other variables are used to override kernel tunable parameters.
626 tunables are available:
627 .Bl -tag -width indent
628 .It Va hw.ioapic_enable
631 Set to 1 to enable, 0 to disable.
634 Set irqX's destination to the given
637 If the specified value is larger than the last
642 This variable should not be used if
646 Limit the amount of physical memory the system will use.
647 By default the size is in bytes, but the
648 .Cm k , K , m , M , g
652 are also accepted and indicate kilobytes, megabytes and gigabytes
654 An invalid suffix will result in the variable being ignored by the
656 .It Va hw.usb.hack_defer_exploration
657 The USB keyboard will sometimes not attach properly unless you set this
659 .It Va kern.emergency_intr_enable
660 Setting this to 1 enables emergency interrupt polling.
661 All interrupt handlers are executed periodically.
662 This mode is very expensive and should
663 only be used to get a system accessible when interrupt routing is
665 It is primarily used by kernel developers to debug new systems.
666 .It Va kern.emergency_intr_freq
667 Set the polling rate for the emergency interrupt polling code.
668 The default is 10 (hz) to dissuade casual use.
669 If you are doing real work
670 with emergency interrupt polling mode enabled, it is recommended
671 that you use a frequency between 100hz and 300hz.
673 Set the size of a number of statically allocated system tables; see
675 for a description of how to select an appropriate value for this tunable.
676 When set, this tunable replaces the value declared in the kernel
677 compile-time configuration file.
678 .It Va kern.ipc.nmbclusters
679 Set the number of mbuf clusters to be allocated.
680 The value cannot be set below the default
681 determined when the kernel was compiled.
685 Toggles the mmx optimizations for the bcopy/copyin/copyout routines
686 .It Va kern.user_scheduler
687 Default userland scheduler (usched).
688 If set, values can be
694 .It Va kern.vm.kmem.size
695 Sets the size of kernel memory (bytes).
696 This overrides the value determined when the kernel was compiled.
697 .It Va kern.maxswzone
700 to be used to hold swap
701 meta information, which directly governs the
702 maximum amount of swap the system can support.
703 This value is specified in bytes of KVA space
704 and defaults to around 70MBytes.
706 to not reduce this value such that the actual
707 amount of configured swap exceeds \(12 the
708 kernel-supported swap.
709 The default 70MB allows
710 the kernel to support a maximum of (approximately)
711 14GB of configured swap.
712 Only mess around with
713 this parameter if you need to greatly extend the
715 reservation for other resources such as the
719 .Va VM_SWZONE_SIZE_MAX .
720 .It Va kern.maxbcache
721 Limits the amount of KVM reserved for use by the
722 buffer cache, specified in bytes.
723 The default maximum is 200MB on 32-bit and
724 unspecified on 64-bit.
725 This parameter is used to
726 prevent the buffer cache from eating too much
728 in large-memory machine configurations.
729 Only mess around with this parameter if you need to
732 reservation for other resources
733 such as the swap zone or
736 the NBUF parameter will override this limit.
738 .Va VM_BCACHE_SIZE_MAX .
739 .It Va machdep.disable_mtrrs
744 .It Va net.inet.tcp.tcbhashsize
745 Overrides the compile-time set value of
747 or the preset default of 512.
748 Must be a power of 2.
749 .It Va vfs.root.wakedelay
750 Specify an additional delay (default is 2 seconds if unspecified)
751 before trying to mount root.
752 .It Va vfs.root.mountfrom
753 Specify root file system.
754 A semicolon separated list of file systems to try
755 as the kernel root file system.
756 File system format is file system type and disk store,
758 This variable needs to be set when using a boot-only partition, which is
759 typically mounted on root file system as
762 One file system example:
767 multi volume example:
768 .Dl hammer2:da8s1a:da9s1a
770 Several file systems, boot list, example:
771 .Dl ufs:da0s1a;hammer2:ad1s1d
773 Each file system in the list will be tried in the order specified
774 until the mount succeeds.
777 prompt is displayed for manual entry.
779 You may not specify devtab labels here but you can specify paths available to
782 .Dl hammer:serno/L41JYE0G.s1d
783 .It Va vfs.root.realroot
784 Root file system and extra options for
788 .It Va nfsroot.iosize
789 Override the default NFS netbooted root mount io block size.
790 The default is 8192 which works with most servers.
791 suggested values are 8192, 16384, or 32768.
792 .It Va nfsroot.rahead
793 Override the default read-ahead used by netbooted root mounts.
794 The default is 4 which is reasonable. Suggested values are 1 through 8.
797 .Bl -tag -width /boot/defaults/dloader.menu -compact
798 .It Pa /boot/boot.conf
800 bootstrapping script.
802 .It Pa /boot/defaults/dloader.menu
804 menu setup commands -- do not change this file
805 .It Pa /boot/defaults/loader.conf
807 configuration file, see
809 -- do not change this file
810 .It Pa /boot/dloader.menu
813 .It Pa /boot/dloader.rc
819 .It Pa /boot/loader.conf
820 .It Pa /boot/loader.conf.local
822 configuration files, see
824 .It Pa /boot/loader.help
825 help messages, used by the
830 Boot in single user mode:
835 Load the kernel, a splash screen, and then autoboot in five seconds.
836 .Bd -literal -offset indent
839 load -t splash_image_data chuckrulez.bmp
843 Set the disk unit of the root device to 2, and then boot.
844 This would be needed in a system with two IDE disks,
845 with the second IDE disk hardwired to
849 .Bd -literal -offset indent
883 .An Michael Smith Aq Mt msmith@FreeBSD.org .
887 .An Matthew Dillon Aq Mt dillon@backplane.com .
889 A variable can have two instances: local & kernel environment,
890 this can cause confusion.