| blob | 6b9d2dfa13352bf8086d6f872bc90255e31428a6 |
1 .\" $NetBSD: boot.8,v 1.51 2009/09/01 21:30:17 ahoka Exp $
2 .\"
3 .\" Copyright (c) 1991, 1993
4 .\" The Regents of the University of California. All rights reserved.
5 .\"
6 .\" This code is derived from software written and contributed
7 .\" to Berkeley by William Jolitz.
8 .\"
9 .\" Redistribution and use in source and binary forms, with or without
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17 .\" 3. Neither the name of the University nor the names of its contributors
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32 .\"
33 .\" @(#)boot_i386.8 8.2 (Berkeley) 4/19/94
34 .\"
35 .Dd September 4, 2009
36 .Dt BOOT 8 i386
37 .Os
38 .Sh NAME
39 .Nm boot
40 .Nd
41 system bootstrapping procedures
42 .Sh DESCRIPTION
43 .Tn IA-32
44 computers
45 .Po
46 the
47 .Tn IBM PC
48 and its clones
49 .Pc
50 that can run
51 .Nx Ns /i386
52 can use any of the following boot procedures, depending on what the hardware and
53 .Tn BIOS
54 support:
55 .Pp
56 .Bl -tag -width "pxeboot(8)"
57 .It boot
58 bootstrap
59 .Nx
60 from the system
61 .Tn BIOS
62 .It Xr dosboot 8
63 bootstrap
64 .Nx
65 from
66 .Tn MS-DOS
67 .It Xr w95boot 8
68 bootstrap
69 .Nx
70 from
71 .Tn Windows 95
72 .It Xr pxeboot 8
73 network bootstrap
74 .Nx
75 from a
76 .Tn TCP/IP
77 .Tn LAN
78 with
79 .Tn DHCP ,
80 .Tn TFTP ,
81 and
82 .Tn NFS .
83 .El
84 .Ss Power fail and crash recovery
85 Normally, the system will reboot itself at power-up or after crashes.
86 An automatic consistency check of the file systems will be performed,
87 and unless this fails, the system will resume multi-user operations.
88 .Ss Cold starts
89 The 386
90 .Tn "PC AT"
91 clones attempt to boot the floppy disk drive A (otherwise known as drive
92 0) first, and failing that, attempt to boot the hard disk C (otherwise
93 known as hard disk controller 1, drive 0).
94 The
95 .Nx
96 bootblocks are loaded and started either by the
97 .Tn BIOS ,
98 or by a boot selector program (such as OS-BS, BOOTEASY, the OS/2 Boot Menu or
99 .Nx Ns 's
100 .No boot-selecting
101 master boot record - see
102 .Xr mbr 8 ) .
103 .Ss Normal Operation
104 Once running, a banner similar to the following will appear:
105 .Bd -unfilled -offset indent
106 \*[Gt]\*[Gt] NetBSD BIOS Boot, revision 3.0
107 \*[Gt]\*[Gt] (user@buildhost, builddate)
108 \*[Gt]\*[Gt] Memory: 637/15360 k
109 Press return to boot now, any other key for boot menu
110 booting hd0a:netbsd - starting in 5
111 .Ed
112 .Pp
113 After a countdown, the system image listed will be loaded.
114 In the example above, it will be
115 .Dq Li hd0a:netbsd
116 which is the file
117 .Nm netbsd
118 on partition
119 .Dq a
120 of the
121 .Nx
122 .Tn MBR
123 partition of the first hard disk known to the
124 .Tn BIOS
125 .Po
126 which is an
127 .Tn IDE
128 or similar device - see the
129 .Sx BUGS
130 section
131 .Pc .
132 .Pp
133 Pressing a key within the time limit, or before the boot program starts, will
134 enter interactive mode.
135 When using a short or 0 timeout, it is often useful to interrupt the boot
136 by holding down a shift key, as some BIOSes and BIOS extensions will drain the
137 keystroke buffer at various points during POST.
138 .Pp
139 If present, the file
140 .Pa /boot.cfg
141 will be used to configure the behaviour of the boot loader including
142 setting the timeout, choosing a console device, altering the banner
143 text and displaying a menu allowing boot commands to be easily chosen.
144 See
145 .Xr boot.cfg 5 .
146 .Pp
147 The
148 .Nx Ns /i386
149 boot loader can boot a kernel using either the native
150 .Nx
151 boot protocol, or the
152 .Dq multiboot
153 protocol (which is compatible with some other operating systems).
154 In the native
155 .Nx
156 boot protocol, options are passed from the boot loader
157 to the kernel via flag bits in the
158 .Va boothowto
159 variable (see
160 .Xr boothowto 9 ) .
161 In the multiboot protocol, options are passed from the boot loader
162 to the kernel as strings.
163 .Ss Diagnostic Output
164 If the first stage boot fails to load the boot, it will print a terse
165 message indicating the reason for the failure.
166 The possible error messages and their cause are listed in
167 .Xr mbr 8 .
168 .Pp
169 If the first stage boot succeeds, the banner will be shown and the
170 error messages should be self-explanatory.
171 .Ss Interactive mode
172 In interactive mode, the boot loader will present a prompt, allowing
173 input of these commands:
174 .\" NOTE: much of this text is duplicated in the MI boot.8.
175 .\" Some of it is
176 .\" also duplicated in the i386-specific dosboot.8 and pxeboot.8;
177 .\" please try to keep all relevant files synchronized.
178 .Bl -tag -width 04n -offset 04n
179 .It Ic boot Oo Va device : Ns Oc Oo Va filename Oc Oo Fl 1234abcdmqsvxz Oc
180 The default
181 .Va device
182 will be set to the disk that the boot loader was
183 loaded from.
184 To boot from an alternate disk, the full name of the device should
185 be given at the prompt.
186 .Va device
187 is of the form
188 .Xo Va xd
189 .Op Va N Ns Op Va x
190 .Xc
191 where
192 .Va xd
193 is the device from which to boot,
194 .Va N
195 is the unit number, and
196 .Va x
197 is the partition letter.
198 .Pp
199 The following list of supported devices may vary from installation to
200 installation:
201 .Pp
202 .Bl -hang -compact
203 .It hd
204 Hard disks as numbered by the BIOS.
205 This includes ST506, IDE, ESDI, RLL disks on a WD100[2367] or
206 lookalike controller(s), and SCSI disks
207 on SCSI controllers recognized by the BIOS.
208 .It fd
209 Floppy drives as numbered by the BIOS.
210 .El
211 .Pp
212 The default
213 .Va filename
214 is
215 .Pa netbsd ;
216 if the boot loader fails to successfully
217 open that image, it then tries
218 .Pa netbsd.gz
219 (expected to be a kernel image compressed by gzip), followed by
220 .Pa netbsd.old ,
221 .Pa netbsd.old.gz ,
222 .Pa onetbsd ,
223 and finally
224 .Pa onetbsd.gz .
225 Alternate system images can be loaded by just specifying the name of the image.
226 .Pp
227 Options are:
228 .Bl -tag -width xxx
229 .It Fl 1
230 Sets the machine-dependent flag
231 .Sy RB_MD1
232 in
233 .Va boothowto .
234 In
235 .Nx Ns /i386 ,
236 this disables multiprocessor boot;
237 the kernel will boot in uniprocessor mode.
238 .It Fl 2
239 Sets the machine-dependent flag
240 .Sy RB_MD2
241 in
242 .Va boothowto .
243 In
244 .Nx Ns /i386 ,
245 this disables ACPI.
246 .It Fl 3
247 Sets the machine-dependent flag
248 .Sy RB_MD3
249 in
250 .Va boothowto .
251 In
252 .Nx Ns /i386 ,
253 this has no effect.
254 .It Fl 4
255 Sets the machine-dependent flag
256 .Sy RB_MD4
257 in
258 .Va boothowto .
259 In
260 .Nx Ns /i386 ,
261 this has no effect.
262 .It Fl a
263 Sets the
264 .Sy RB_ASKNAME
265 flag in
266 .Va boothowto .
267 This causes the kernel to prompt for the root file system device,
268 the system crash dump device, and the path to
269 .Xr init 8 .
270 .It Fl b
271 Sets the
272 .Sy RB_HALT
273 flag in
274 .Va boothowto .
275 This causes subsequent reboot attempts to halt instead of rebooting.
276 .It Fl c
277 Sets the
278 .Sy RB_USERCONF
279 flag in
280 .Va boothowto .
281 This causes the kernel to enter the
282 .Xr userconf 4
283 device configuration manager as soon as possible during the boot.
284 .Xr userconf 4
285 allows devices to be enabled or disabled, and allows device locators
286 (such as hardware addresses or bus numbers)
287 to be modified before the kernel attempts to attach the devices.
288 .It Fl d
289 Sets the
290 .Sy RB_KDB
291 flag in
292 .Va boothowto .
293 Requests the kernel to enter debug mode, in which it
294 waits for a connection from a kernel debugger; see
295 .Xr ddb 4 .
296 .It Fl m
297 Sets the
298 .Sy RB_MINIROOT
299 flag in
300 .Va boothowto .
301 Informs the kernel that a mini-root file system is present in memory.
302 .It Fl q
303 Sets the
304 .Sy AB_QUIET
305 flag in
306 .Va boothowto .
307 Boot the system in quiet mode.
308 .It Fl s
309 Sets the
310 .Sy RB_SINGLE
311 flag in
312 .Va boothowto .
313 Boot the system in single-user mode.
314 .It Fl v
315 Sets the
316 .Sy AB_VERBOSE
317 flag in
318 .Va boothowto .
319 Boot the system in verbose mode.
320 .It Fl x
321 Sets the
322 .Sy AB_DEBUG
323 flag in
324 .Va boothowto .
325 Boot the system with debug messages enabled.
326 .It Fl z
327 Sets the
328 .Sy AB_SILENT
329 flag in
330 .Va boothowto .
331 Boot the system in silent mode.
332 .El
333 .It Ic consdev Va dev
334 Immediately switch the console to the specified device
335 .Va dev
336 and reprint the banner.
337 .Va dev
338 must be one of
339 .\" .Bl -item -width com[0123]kbd -offset indent -compact
340 .Ar pc , com0 , com1 , com2 ,
341 .Ar com3 , com0kbd , com1kbd , com2kbd ,
342 .Ar com3kbd ,
343 or
344 .Ar auto .
345 See
346 .Sx Console Selection Policy
347 in
348 .Xr boot_console 8 .
349 .It Ic vesa Va modenum | on | off | enabled | disabled | list
350 Initialise the video card to the specified resolution and bit depth.
351 The
352 .Va modenum
353 should be in the form of
354 .Ar 0x100 , 800x600 , 800x600x32 .
355 The values
356 .Ar enabled , on
357 put the display into the default mode, and
358 .Ar disabled , off
359 returns the display into standard vga mode.
360 The value
361 .Ar list
362 lists all supported modes.
363 .It Ic dev Op Va device
364 Set the default drive and partition for subsequent filesystem
365 operations.
366 Without an argument, print the current setting.
367 .Va device
368 is of the form specified in
369 .Cm boot .
370 .It Ic help
371 Print an overview about commands and arguments.
372 .It Ic load Va module Op Va arguments
373 Load the specified kernel
374 .Va module ,
375 and pass it the specified
376 .Va arguments .
377 If the module name is not an absolute path,
378 .Pa /stand/ Xo Ns
379 .Aq Sy arch Ns
380 .Pa / Ns
381 .Aq Sy osversion Ns
382 .Pa /modules/ Ns
383 .Aq Sy module Ns
384 .Pa / Ns
385 .Aq Sy module Ns
386 .Pa .kmod
387 .Xc
388 is used.
389 Possible used of the
390 .Ic load
391 command include loading a memory disk image before booting a kernel,
392 or loading a Xen DOM0 kernel before booting the Xen hypervisor.
393 .It Ic ls Op Pa path
394 Print a directory listing of
395 .Pa path ,
396 containing inode number, filename, and file type.
397 .Pa path
398 can contain a device specification.
399 .It Ic multiboot Va kernel Op Va arguments
400 Boot the specified
401 .Va kernel ,
402 using the
403 .Dq multiboot
404 protocol instead of the native
405 .Nx
406 boot protocol.
407 The
408 .Va kernel
409 is specified in the same way as with the
410 .Ic boot
411 command.
412 .Pp
413 The multiboot protocol may be used in the following cases:
414 .Bl -tag -width indent
415 .It Nx Ns / Ns Xen No kernels
416 The Xen DOM0 kernel must be loaded as a module using the
417 .Ic load
418 command, and the Xen hypervisor must be booted using the
419 .Ic multiboot
420 command.
421 Options for the DOM0 kernel (such as
422 .Dq -s
423 for single user mode) must be passed as options to the
424 .Ic load
425 command.
426 Options for the hypervisor (such as
427 .Dq dom0_mem=256M
428 to reserve 256 MB of memory for DOM0)
429 must be passed as options to the
430 .Ic multiboot
431 command.
432 See
433 .Xr boot.cfg 5
434 for examples of how to boot
435 .Nx Ns / Ns Xen.
436 .It Nx No multiboot kernels
437 A
438 .Nx
439 kernel that was built with
440 .Cd options MULTIBOOT
441 (see
442 .Xr multiboot 8 )
443 may be booted with either the
444 .Ic boot
445 or
446 .Ic multiboot
447 command, passing the same arguments in either case.
448 .It Non- Ns Nx No kernels
449 A kernel for a
450 .No non- Ns Nx
451 operating system that expects to be booted using the
452 multiboot protocol (such as by the GNU
453 .Dq GRUB
454 boot loader)
455 may be booted using the
456 .Ic multiboot
457 command.
458 See the foreign operating system's documentation for the available arguments.
459 .El
460 .It Ic quit
461 Reboot the system.
462 .El
463 .Pp
464 In an emergency, the bootstrap methods described in the
465 .Nx
466 installation notes for the i386 architecture
467 can be used to boot from floppy or other media,
468 or over the network.
469 .Sh FILES
470 .Bl -tag -width /usr/mdec/bootxx_fstype -compact
471 .It Pa /boot
472 boot program code loaded by the primary bootstrap
473 .It Pa /boot.cfg
474 optional configuration file
475 .It Pa /netbsd
476 system code
477 .It Pa /netbsd.gz
478 gzip-compressed system code
479 .It Pa /usr/mdec/boot
480 master copy of the boot program (copy to /boot)
481 .It Pa /usr/mdec/bootxx_fstype
482 primary bootstrap for filesystem type fstype, copied to the start of
483 the
484 .Nx
485 partition by
486 .Xr installboot 8 .
487 .El
488 .Sh SEE ALSO
489 .Xr ddb 4 ,
490 .Xr userconf 4 ,
491 .Xr boot.cfg 5 ,
492 .Xr boot_console 8 ,
493 .Xr dosboot 8 ,
494 .Xr halt 8 ,
495 .Xr installboot 8 ,
496 .Xr mbr 8 ,
497 .Xr multiboot 8 ,
498 .Xr pxeboot 8 ,
499 .Xr reboot 8 ,
500 .Xr shutdown 8 ,
501 .Xr w95boot 8 ,
502 .Xr boothowto 9
503 .Sh BUGS
504 The kernel file name must be specified before, not after, the boot options.
505 Any
506 .Ar filename
507 specified after the boot options, e.g.:
508 .Pp
509 .Bd -unfilled -offset indent -compact
510 .Cm boot -d netbsd.test
511 .Ed
512 .Pp
513 is ignored, and the default kernel is booted.
514 .Pp
515 Hard disks are always accessed by
516 .Tn BIOS
517 functions.
518 Unit numbers are
519 .Tn BIOS
520 device numbers which might differ from numbering in the
521 .Nx
522 kernel or physical parameters
523 .Po
524 e.g.,
525 .Tn SCSI
526 slave numbers
527 .Pc .
528 There isn't any distinction between
529 .Dq sd
530 and
531 .Dq wd
532 devices at the bootloader level.
533 This is less a bug of the bootloader code than
534 a shortcoming of the PC architecture.
535 The default disk device's name printed in the starting message
536 is derived from the
537 .Dq type
538 field of the
539 .Nx
540 disklabel (if it is a hard disk).