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
168 .It Ic cd Op Ar directory
169 Change working directory to
173 .It Ic echo Oo Fl n Oc Op Ar message
174 Displays text on the screen.
175 A new line will be printed unless
180 Displays memory usage statistics.
181 For debugging purposes only.
183 .It Ic help Op Ar topic Op Ar subtopic
184 Shows help messages read from
189 will list all topics available.
192 Process script files.
193 Each file, in turn, is completely read into memory,
194 and then each of its lines is passed to the command line interpreter.
195 If any error is returned by the interpreter, the include
196 command aborts immediately, without reading any other files, and
197 returns an error itself.
199 .It Ic load Oo Fl t Ar type Oc Ar file Op Ar argument ...
200 Loads a kernel, kernel loadable module (kld), or file of opaque
201 contents tagged as being of the type
203 Kernel and modules can be either in a.out or
206 Any arguments passed after the name of the file to be loaded
207 will be passed as arguments to that file.
208 Currently, argument passing does not work for the kernel.
211 Load the kernel and all modules specified by MODULE_load variables.
213 .It Ic local Op Ar local_variable ...
214 Displays the specified variable's value, or all local variables and their
219 .It Ic ls Oo Fl l Oc Op Ar path
220 Displays a listing of files in the directory
222 or the root directory if
227 is specified, file sizes will be shown too.
233 prefix indicates a disk slice or partition from which it may be
234 possible to load modules.
237 is specified, more details,
238 like disk slice or partition size and position, are printed.
241 Displays loaded modules.
244 is specified, more details are shown.
246 .It Ic lunset Ar local_variable
247 Unset a local variable.
248 Discards the value and removes the variable.
250 .It Ic lunsetif Ar local_variable env_variable
255 is true, i.e.\& set to 1 or
261 .It Ic menuadd Ar command_line
262 Add script line for the current menu item.
265 Clear all menu items.
267 .It Ic menuitem Ar key description
268 Start a new menu item.
269 When running the menu system, a line with
273 is displayed, and an item is chosen by pressing
277 Display the files specified, with a pause at each
281 .It Ic optcd Op Ar directory
282 Change the working directory to
288 but ignores errors when changing the directory.
291 Process script files.
295 but ignores errors while executing commands in included files.
297 .It Ic pnpscan Op Fl v
298 Scans for Plug-and-Play devices.
299 This is not functional at present.
302 Prints the working directory.
304 .It Ic read Oo Fl t Ar seconds Oc Oo Fl p Ar prompt Oc Op Ar env_variable
305 Reads a line of input from the terminal, storing it in
308 A timeout can be specified with
310 though it will be canceled at the first key pressed.
311 A prompt may also be displayed through the
316 Immediately reboots the system.
318 .It Ic set Ar env_variable
319 .It Ic set Ar env_variable Ns = Ns Ar value
322 environment variables.
324 .It Ic show Op Ar env_variable
325 Displays the specified kernel environment variable's value,
326 or all variables and their values if
331 Removes all modules from memory.
333 .It Ic unset Ar env_variable
336 from the environment.
339 Lists most available commands with a short help text for each.
341 .Ss ENVIRONMENT VARIABLES AND LOCAL VARIABLES
344 has actually two different kinds of variables.
346 kernel environment variables, which are visible to the kernel when it is run,
347 and a separate space of local variables used by
349 which are not available to the kernel.
351 Environment variables can be set and unset through the
355 builtins, and can have their values interactively examined through the
360 Notice that these environment variables are not inherited by any shell
361 after the system has been booted, but can be examined by
364 A few variables are set automatically by
366 Others can affect the behavior of either
368 or the kernel at boot.
369 Some options may require a value,
370 while others define behavior just by being set.
371 Both types of variables are described below.
372 .Bl -tag -width indent
374 Unset this to disable automatic loading of the ACPI module.
375 .It Va autoboot_delay
378 will wait before booting.
379 If this variable is not defined,
381 will default to 10 seconds.
387 will be automatically attempted after processing
391 will be processed normally, defaulting to 10 seconds delay.
393 Instructs the kernel to prompt the user for the name of the root device
394 when the kernel is booted.
396 Instructs the kernel to start in the DDB debugger, rather than
397 proceeding to initialize when booted.
399 Selects gdb-remote mode for the kernel debugger by default.
401 Prevents the kernel from initiating a multi-user startup; instead single-user
402 mode will be entered when the kernel has finished device probing.
403 .It Va boot_userconfig
404 Requests that the kernel's interactive device configuration program
405 be run when the kernel is booted.
407 Setting this variable causes extra debugging information to be printed
408 by the kernel during and after the boot phase.
410 List of semicolon-separated search path for bootable kernels.
412 .Dq Li kernel;kernel.old .
414 Defines the current console.
416 Selects the default device.
417 Syntax for devices is odd.
419 Unset this to disable automatic loading of the EHCI module.
421 Sets the list of binaries which the kernel will try to run as the initial
423 The first matching binary is used.
425 .Dq Li /sbin/init:/sbin/oinit:/sbin/init.bak .
427 Define the number of lines on the screen, to be used by the pager.
429 Sets the list of directories which will be searched for modules named in a
431 command or implicitly required by a dependency.
432 The default value for this variable is
434 which first searches the current working directory and then
437 Sets the number of IDE disks as a workaround for some problems in
438 finding the root disk at boot.
439 This has been deprecated in favor of
447 .It Va root_disk_unit
448 If the code which detects the disk unit number for the root disk is
449 confused, e.g.\& by a mix of
456 gaps in the sequence (e.g.\& no primary slave), the unit number can
457 be forced by setting this variable.
459 By default the value of
461 is used to set the root file system
462 when the kernel is booted.
463 This can be overridden by setting
467 The name of a device where the kernel can save a crash dump in case
469 This automatically sets the
476 Other variables are used to override kernel tunable parameters.
479 tunables are available:
480 .Bl -tag -width indent
482 Set irqX's destination to the given
485 If the specified value is larger than the last
490 This variable should not be used if
492 support is not compiled into kernel.
494 Limit the amount of physical memory the system will use.
495 By default the size is in bytes, but the
496 .Cm k , K , m , M , g
500 are also accepted and indicate kilobytes, megabytes and gigabytes
502 An invalid suffix will result in the variable being ignored by the
504 .It Va hw.usb.hack_defer_exploration
505 The USB keyboard will sometimes not attach properly unless you set this
507 .It Va kern.emergency_intr_enable
508 Setting this to 1 enables emergency interrupt polling.
509 All interrupt handlers are executed periodically.
510 This mode is very expensive and should
511 only be used to get a system accessible when interrupt routing is
513 It is primarily used by kernel developers to debug new systems.
514 .It Va kern.emergency_intr_freq
515 Set the polling rate for the emergency interrupt polling code.
516 The default is 10 (hz) to dissuade casual use.
517 If you are doing real work
518 with emergency interrupt polling mode enabled, it is recommended
519 that you use a frequency between 100hz and 300hz.
521 Set the size of a number of statically allocated system tables; see
523 for a description of how to select an appropriate value for this tunable.
524 When set, this tunable replaces the value declared in the kernel
525 compile-time configuration file.
526 .It Va kern.ipc.nmbclusters
527 Set the number of mbuf clusters to be allocated.
528 The value cannot be set below the default
529 determined when the kernel was compiled.
533 Toggles the mmx optimizations for the bcopy/copyin/copyout routines
534 .It Va kern.vm.kmem.size
535 Sets the size of kernel memory (bytes).
536 This overrides the value determined when the kernel was compiled.
537 .It Va kern.maxswzone
540 to be used to hold swap
541 meta information, which directly governs the
542 maximum amount of swap the system can support.
543 This value is specified in bytes of KVA space
544 and defaults to around 70MBytes.
546 to not reduce this value such that the actual
547 amount of configured swap exceeds \(12 the
548 kernel-supported swap.
549 The default 70MB allows
550 the kernel to support a maximum of (approximately)
551 14GB of configured swap.
552 Only mess around with
553 this parameter if you need to greatly extend the
555 reservation for other resources such as the
559 .Va VM_SWZONE_SIZE_MAX .
560 .It Va kern.maxbcache
561 Limits the amount of KVM reserved for use by the
562 buffer cache, specified in bytes.
563 The default maximum is 200MB.
564 This parameter is used to
565 prevent the buffer cache from eating too much
567 in large-memory machine configurations.
568 Only mess around with this parameter if you need to
571 reservation for other resources
572 such as the swap zone or
575 the NBUF parameter will override this limit.
577 .Va VM_BCACHE_SIZE_MAX .
578 .It Va machdep.disable_mtrrs
583 .It Va net.inet.tcp.tcbhashsize
584 Overrides the compile-time set value of
586 or the preset default of 512.
587 Must be a power of 2.
588 .It Va vfs.root.mountfrom
589 Specify root file system.
590 A semicolon separated list of file systems to try
591 as the kernel root file system.
592 File system format is file system type and disk store,
594 This variable needs to be set when using a boot-only partition, which is
595 typically mounted on root file system as
598 One file system example:
603 multi volume example:
604 .Dl hammer:da8s1a:da9s1a
606 Several file systems, boot list, example:
607 .Dl ufs:da0s1a;hammer:ad1s1d
609 Each file system in the list will be tried in the order specified
610 until the mount succeeds.
613 prompt is displayed for manual entry.
615 You may not specify devtab labels here but you can specify paths available to
618 .Dl hammer:serno/L41JYE0G.s1d
621 .Bl -tag -width /boot/defaults/dloader.menu -compact
622 .It Pa /boot/boot.conf
624 bootstrapping script.
629 .It Pa /boot/defaults/dloader.menu
631 menu setup commands -- do not change this file.
632 .It Pa /boot/defaults/loader.conf
634 configuration file, see
636 -- do not change this file.
637 .It Pa /boot/dloader.menu
640 .It Pa /boot/dloader.rc
642 bootstrapping script.
643 .It Pa /boot/loader.conf
644 .It Pa /boot/loader.conf.local
646 configuration files, see
648 .It Pa /boot/loader.help
649 help messages, used by the
654 Boot in single user mode:
659 Load kernel's user configuration file.
660 Notice that a kernel must be loaded before any other
662 command is attempted.
663 .Bd -literal -offset indent
665 load -t userconfig_script kernel.conf
668 Load the kernel, a splash screen, and then autoboot in five seconds.
669 .Bd -literal -offset indent
672 load -t splash_image_data chuckrulez.bmp
676 Set the disk unit of the root device to 2, and then boot.
677 This would be needed in a system with two IDE disks,
678 with the second IDE disk hardwired to
682 .Bd -literal -offset indent
710 .An Michael Smith Aq msmith@FreeBSD.org .
714 .An Matthew Dillon Aq dillon@backplane.com .