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 Local variables are unset if
136 Kernel environment variables may have empty values.
138 In other words, the assignment above will set a local variable and
139 if it is applicable, also assign
141 to the kernel environment variable, even if
145 .Sx ENVIRONMENT VARIABLES AND LOCAL VARIABLES .
147 .It Ic autoboot Op Ar delay Op Ar prompt
148 Proceeds to bootstrap the system after a number of seconds, if not
149 interrupted by the user.
150 Displays a countdown prompt
151 warning the user the system is about to be booted,
152 unless interrupted by a key press.
153 The kernel will be loaded first if necessary.
154 Defaults to 10 seconds.
157 Displays statistics about disk cache usage.
160 .It Ic boot Oo Fl Ns Ar flag ... Oc Op Ar kernelname
161 Immediately proceeds to bootstrap the system, loading the kernel
163 Any flags or arguments are passed to the kernel, but they
164 must precede the kernel name, if a kernel name is provided.
165 Flags are described in
173 .It Ic cd Op Ar directory
174 Change working directory to
178 .It Ic echo Oo Fl n Oc Op Ar message
179 Displays text on the screen.
180 A new line will be printed unless
185 Conditional if/else/endif.
187 .It Ic elseifexists Ar path
190 exists, i.e.\& file/dir present.
193 Conditional if/else/endif.
196 Displays memory usage statistics.
197 For debugging purposes only.
199 .It Ic help Op Ar topic Op Ar subtopic
200 Shows help messages read from
205 will list all topics available.
207 .It Ic ifexists Ar path
210 exists, i.e.\& file/dir present.
212 .It Ic ifset Ar env_variable
218 Process script files.
219 Each file, in turn, is completely read into memory,
220 and then each of its lines is passed to the command line interpreter.
221 If any error is returned by the interpreter, the include
222 command aborts immediately, without reading any other files, and
223 returns an error itself.
225 .It Ic load Oo Fl t Ar type Oc Ar file Op Ar argument ...
226 Loads a kernel, kernel loadable module (kld), or file of opaque
227 contents tagged as being of the type
229 Kernel and modules can be either in a.out or
232 Any arguments passed after the name of the file to be loaded
233 will be passed as arguments to that file.
234 Currently, argument passing does not work for the kernel.
237 Load the kernel and all modules specified by MODULE_load variables.
239 .It Ic local Op Ar local_variable ...
240 Displays the specified variable's value, or all local variables and their
245 .It Ic ls Oo Fl l Oc Op Ar path
246 Displays a listing of files in the directory
248 or the root directory if
253 is specified, file sizes will be shown too.
259 prefix indicates a disk slice or partition from which it may be
260 possible to load modules.
263 is specified, more details,
264 like disk slice or partition size and position, are printed.
267 Displays loaded modules.
270 is specified, more details are shown.
272 .It Ic lunset Ar local_variable
273 Unset a local variable.
274 Discards the value and removes the variable.
276 .It Ic lunsetif Ar local_variable env_variable
281 is true, i.e.\& set to 1 or
287 .It Ic menuadd Ar command_line
288 Add script line for the current menu item.
291 Clear all menu items.
293 .It Ic menuitem Ar key description
294 Start a new menu item.
295 When running the menu system, a line with
299 is displayed, and an item is chosen by pressing
303 Display the files specified, with a pause at each
307 .It Ic optcd Op Ar directory
308 Change the working directory to
314 but ignores errors when changing the directory.
317 Process script files.
321 but ignores errors while executing commands in included files.
323 .It Ic pnpscan Op Fl v
324 Scans for Plug-and-Play devices.
325 This is not functional at present.
328 Prints the working directory.
330 .It Ic read Oo Fl t Ar seconds Oc Oo Fl p Ar prompt Oc Op Ar env_variable
331 Reads a line of input from the terminal, storing it in
334 A timeout can be specified with
336 though it will be canceled at the first key pressed.
337 A prompt may also be displayed through the
342 Immediately reboots the system.
344 .It Ic set Ar env_variable
345 .It Ic set Ar env_variable Ns = Ns Ar value
348 environment variables.
350 .It Ic show Op Ar env_variable
351 Displays the specified kernel environment variable's value,
352 or all variables and their values if
357 Removes all modules from memory.
359 .It Ic unset Ar env_variable
362 from the environment.
365 Lists most available commands with a short help text for each.
367 .Ss ENVIRONMENT VARIABLES AND LOCAL VARIABLES
370 has actually two different kinds of variables.
372 kernel environment variables, which are visible to the kernel when it is run,
373 and a separate space of local variables used by
375 which are not available to the kernel.
377 Environment variables can be set and unset through the
381 builtins, and can have their values interactively examined through the
386 Notice that these environment variables are not inherited by any shell
387 after the system has been booted, but can be examined by
390 A few variables are set automatically by
392 Others can affect the behavior of either
394 or the kernel at boot.
395 Some options may require a value,
396 while others define behavior just by being set.
397 Both types of variables are described below.
398 .Bl -tag -width indent
400 Unset this to disable automatic loading of the ACPI module.
401 .It Va autoboot_delay
406 will wait before booting.
407 Default value is 10 seconds.
413 will be automatically attempted after processing
417 will be processed normally, defaulting to 10 seconds delay.
419 Instructs the kernel to prompt the user for the name of the root device
420 when the kernel is booted.
422 Instructs the kernel to start in the DDB debugger, rather than
423 proceeding to initialize when booted.
425 Selects gdb-remote mode for the kernel debugger by default.
427 Prevents the kernel from initiating a multi-user startup; instead single-user
428 mode will be entered when the kernel has finished device probing.
429 .It Va boot_userconfig
430 Requests that the kernel's interactive device configuration program
431 be run when the kernel is booted.
433 Setting this variable causes extra debugging information to be printed
434 by the kernel during and after the boot phase.
436 List of semicolon-separated search path for bootable kernels.
440 Defines the current console.
442 Selects the default device.
443 Syntax for devices is odd.
444 .It Va default_kernel
445 Selects default kernel loaded by
449 Unset this to disable automatic loading of the EHCI module.
451 Sets the list of binaries which the kernel will try to run as the initial
453 The first matching binary is used.
455 .Dq Li /sbin/init:/sbin/oinit:/sbin/init.bak .
456 .It Va kernel_options
457 Set kernel boot flags.
462 Define the number of lines on the screen, to be used by the pager.
464 Sets the list of directories which will be searched for modules named in a
466 command or implicitly required by a dependency.
467 The default value for this variable is
469 which first searches the current working directory and then
472 Sets the number of IDE disks as a workaround for some problems in
473 finding the root disk at boot.
474 This has been deprecated in favor of
482 .It Va root_disk_unit
483 If the code which detects the disk unit number for the root disk is
484 confused, e.g.\& by a mix of
491 gaps in the sequence (e.g.\& no primary slave), the unit number can
492 be forced by setting this variable.
494 By default the value of
496 is used to set the root file system
497 when the kernel is booted.
498 This can be overridden by setting
502 The name of a device where the kernel can save a crash dump in case
504 This automatically sets the
511 Other variables are used to override kernel tunable parameters.
514 tunables are available:
515 .Bl -tag -width indent
517 Set irqX's destination to the given
520 If the specified value is larger than the last
525 This variable should not be used if
527 support is not compiled into kernel.
529 Limit the amount of physical memory the system will use.
530 By default the size is in bytes, but the
531 .Cm k , K , m , M , g
535 are also accepted and indicate kilobytes, megabytes and gigabytes
537 An invalid suffix will result in the variable being ignored by the
539 .It Va hw.usb.hack_defer_exploration
540 The USB keyboard will sometimes not attach properly unless you set this
542 .It Va kern.emergency_intr_enable
543 Setting this to 1 enables emergency interrupt polling.
544 All interrupt handlers are executed periodically.
545 This mode is very expensive and should
546 only be used to get a system accessible when interrupt routing is
548 It is primarily used by kernel developers to debug new systems.
549 .It Va kern.emergency_intr_freq
550 Set the polling rate for the emergency interrupt polling code.
551 The default is 10 (hz) to dissuade casual use.
552 If you are doing real work
553 with emergency interrupt polling mode enabled, it is recommended
554 that you use a frequency between 100hz and 300hz.
556 Set the size of a number of statically allocated system tables; see
558 for a description of how to select an appropriate value for this tunable.
559 When set, this tunable replaces the value declared in the kernel
560 compile-time configuration file.
561 .It Va kern.ipc.nmbclusters
562 Set the number of mbuf clusters to be allocated.
563 The value cannot be set below the default
564 determined when the kernel was compiled.
568 Toggles the mmx optimizations for the bcopy/copyin/copyout routines
569 .It Va kern.vm.kmem.size
570 Sets the size of kernel memory (bytes).
571 This overrides the value determined when the kernel was compiled.
572 .It Va kern.maxswzone
575 to be used to hold swap
576 meta information, which directly governs the
577 maximum amount of swap the system can support.
578 This value is specified in bytes of KVA space
579 and defaults to around 70MBytes.
581 to not reduce this value such that the actual
582 amount of configured swap exceeds \(12 the
583 kernel-supported swap.
584 The default 70MB allows
585 the kernel to support a maximum of (approximately)
586 14GB of configured swap.
587 Only mess around with
588 this parameter if you need to greatly extend the
590 reservation for other resources such as the
594 .Va VM_SWZONE_SIZE_MAX .
595 .It Va kern.maxbcache
596 Limits the amount of KVM reserved for use by the
597 buffer cache, specified in bytes.
598 The default maximum is 200MB.
599 This parameter is used to
600 prevent the buffer cache from eating too much
602 in large-memory machine configurations.
603 Only mess around with this parameter if you need to
606 reservation for other resources
607 such as the swap zone or
610 the NBUF parameter will override this limit.
612 .Va VM_BCACHE_SIZE_MAX .
613 .It Va machdep.disable_mtrrs
618 .It Va net.inet.tcp.tcbhashsize
619 Overrides the compile-time set value of
621 or the preset default of 512.
622 Must be a power of 2.
623 .It Va vfs.root.mountfrom
624 Specify root file system.
625 A semicolon separated list of file systems to try
626 as the kernel root file system.
627 File system format is file system type and disk store,
629 This variable needs to be set when using a boot-only partition, which is
630 typically mounted on root file system as
633 One file system example:
638 multi volume example:
639 .Dl hammer:da8s1a:da9s1a
641 Several file systems, boot list, example:
642 .Dl ufs:da0s1a;hammer:ad1s1d
644 Each file system in the list will be tried in the order specified
645 until the mount succeeds.
648 prompt is displayed for manual entry.
650 You may not specify devtab labels here but you can specify paths available to
653 .Dl hammer:serno/L41JYE0G.s1d
656 .Bl -tag -width /boot/defaults/dloader.menu -compact
657 .It Pa /boot/boot.conf
659 bootstrapping script.
664 .It Pa /boot/defaults/dloader.menu
666 menu setup commands -- do not change this file.
667 .It Pa /boot/defaults/loader.conf
669 configuration file, see
671 -- do not change this file.
672 .It Pa /boot/dloader.menu
675 .It Pa /boot/dloader.rc
677 bootstrapping script.
678 .It Pa /boot/loader.conf
679 .It Pa /boot/loader.conf.local
681 configuration files, see
683 .It Pa /boot/loader.help
684 help messages, used by the
689 Boot in single user mode:
694 Load kernel's user configuration file.
695 Notice that a kernel must be loaded before any other
697 command is attempted.
698 .Bd -literal -offset indent
700 load -t userconfig_script kernel.conf
703 Load the kernel, a splash screen, and then autoboot in five seconds.
704 .Bd -literal -offset indent
707 load -t splash_image_data chuckrulez.bmp
711 Set the disk unit of the root device to 2, and then boot.
712 This would be needed in a system with two IDE disks,
713 with the second IDE disk hardwired to
717 .Bd -literal -offset indent
745 .An Michael Smith Aq msmith@FreeBSD.org .
749 .An Matthew Dillon Aq dillon@backplane.com .