1 .\" Copyright (c) 1991, 1993
2 .\" The Regents of the University of California. All rights reserved.
4 .\" This code is derived from software written and contributed
5 .\" to Berkeley by William Jolitz.
7 .\" Almost completely rewritten for FreeBSD 2.1 by Joerg Wunsch.
9 .\" Substantially revised for FreeBSD 3.1 by Robert Nordier.
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21 .\" This product includes software developed by the University of
22 .\" California, Berkeley and its contributors.
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39 .\" @(#)boot_i386.8 8.2 (Berkeley) 4/19/94
41 .\" $FreeBSD: src/sbin/reboot/boot_i386.8,v 1.23.2.11 2002/04/24 17:47:58 rnordier Exp $
42 .\" $DragonFly: src/sbin/reboot/boot_pc32.8,v 1.2 2003/06/17 04:27:34 dillon Exp $
49 .Nd system bootstrapping procedures
51 .Sy Power fail and crash recovery .
52 Normally, the system will reboot itself at power-up or after crashes.
53 An automatic consistency check of the file systems will be performed,
54 and unless this fails, the system will resume multi-user operations.
57 Most i386 PCs attempt to boot first from floppy disk drive 0 (sometimes
58 known as drive A:) and, failing that, from hard disk drive 0 (sometimes
59 known as drive C:, or as drive 0x80 to the BIOS). Some BIOSes allow
60 you to change this default sequence, and may also include a CD-ROM
61 drive as a boot device.
63 By default, a three-stage bootstrap is employed, and control is
64 automatically passed from the boot blocks (bootstrap stages one and
65 two) to a separate third-stage bootstrap program,
67 This third stage provides more sophisticated control over the booting
68 process than it is possible to achieve in the boot blocks, which are
69 constrained by occupying limited fixed space on a given disk or slice.
71 However, it is possible to dispense with the third stage altogether,
72 either by specifying a kernel name in the boot block parameter
77 is set, by hitting a key during a brief pause (while one of the characters
85 is invoked. Booting will also be attempted at stage two, if the
86 third stage cannot be loaded.
88 The remainder of this subsection deals only with the boot blocks. The
90 program is documented separately.
92 After the boot blocks have been loaded,
93 you should see a prompt similar to the following:
96 Default: 0:ad(0,a)/kernel
100 The automatic boot will attempt to load
104 of either the floppy or the hard disk.
105 This boot may be aborted by typing any character on the keyboard
108 prompt. At this time, the following input will be accepted:
109 .Bl -tag -width indent
111 Give a short listing of the files in the root directory of the default
112 boot device, as a hint about available boot files. (A
114 may also be specified as the last segment of a path, in which case
115 the listing will be of the relevant subdirectory.)
118 .Ar bios_drive : Ns Ar interface Ns Po
119 .Ar unit , Ns Ar part Pc
123 Specify boot file and flags.
124 .Bl -tag -width indent
126 The drive number as recognized by the BIOS.
127 0 for the first drive, 1 for the second drive, etc.
129 The type of controller to boot from. Note that the controller is required
130 to have BIOS support since the BIOS services are used to load the
133 The supported interfaces are:
135 .Bl -tag -width "adXX" -compact
137 ST506, IDE, ESDI, RLL disks on a WD100[2367] or lookalike
140 5 1/4" or 3 1/2" High density floppies
142 SCSI disk on any supported SCSI controller
147 The unit number of the drive on the interface being used.
148 0 for the first drive, 1 for the second drive, etc.
150 The partition letter inside the
152 portion of the disk. See
154 By convention, only partition
156 contains a bootable image. If sliced disks are used
157 .Pq Dq fdisk partitions ,
158 any slice can be booted from, with the default being the active slice
159 or, otherwise, the first
163 The pathname of the file to boot (relative to the root directory
164 on the specified partition). Defaults to
166 Symbolic links are not supported (hard links are).
170 .Bl -tag -width "-CXX" -compact
172 during kernel initialization,
173 ask for the device to mount as the root file system.
177 run UserConfig to modify hardware parameters for the loaded
178 kernel. If the kernel was built with one of
179 .Dv USERCONFIG , INTRO_USERCONFIG , VISUAL_USERCONFIG
181 remain in UserConfig regardless of any
183 commands present in the script.
185 toggle single and dual console configurations. In the single
186 configuration the console will be either the internal display
187 or the serial port, depending on the state of the
189 option below. In the dual console configuration,
190 both the internal display and the serial port will become the console
191 at the same time, regardless of the state of the
193 option. However, the dual console configuration takes effect only during
194 the boot prompt. Once the kernel is loaded, the console specified
197 option becomes the only console.
199 enter the DDB kernel debugger
202 as early as possible in kernel initialization.
204 use the GDB remote debugging protocol.
206 toggle internal and serial consoles. You can use this to switch
207 console devices. For instance, if you boot from the internal console,
210 option to force the kernel to use the serial port as its
211 console device. Alternatively, if you boot from the serial port,
212 you can use this option to force the kernel to use the internal display
213 as the console instead.
214 The serial port driver
216 has a flag to override this option.
217 If that flag is set, the serial port will always be used as the console,
220 option described here. See the man page for
224 ignore key press to interrupt boot before loader(8) is invoked.
226 probe the keyboard. If no keyboard is found, the
230 options are automatically set.
232 pause after each attached device during the device probing phase.
234 use the statically configured default for the device containing the
238 Normally, the root file system is on the device
239 that the kernel was loaded from.
241 boot into single-user mode; if the console is marked as
245 the root password must be entered.
247 be verbose during device probing (and later).
252 You may put a BIOS drive number, a controller type, a unit number,
253 a partition, a kernel file name, and any valid option in
255 to set defaults. Enter them in one line just as you type at the
259 .Bl -tag -width /boot/loader -compact
261 parameters for the boot blocks (optional)
263 first stage bootstrap file
265 second stage bootstrap file
267 third stage bootstrap
271 typical non-default kernel (optional)
285 When disk-related errors occur, these are reported by the second-stage
286 bootstrap using the same error codes returned by the BIOS, for example
287 .Dq Disk error 0x1 (lba=0x12345678) .
288 Here is a partial list of these error codes:
290 .Bl -tag -width "0x80" -compact
294 Address mark not found
300 DMA attempt across 64K boundary
304 Uncorrectable CRC/ECC error
314 On older machines, or otherwise where EDD support (disk packet
315 interface support) is not available, all boot-related files and
316 structures (including the kernel) that need to be accessed during the
317 boot phase must reside on the disk at or below cylinder 1023 (as the
318 BIOS understands the geometry). When a
320 is reported by the second-stage bootstrap, it generally means that this
321 requirement has not been adhered to.
325 format used by this version of
328 different from that of other architectures.
330 Due to space constraints, the keyboard probe initiated by the
332 option is simply a test that the BIOS has detected an
336 keyboard (with no F11 and F12 keys, etc.) is attached, the probe will
339 Some features are not yet documented.