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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35 .\" @(#)boot_i386.8 8.2 (Berkeley) 4/19/94
37 .\" $FreeBSD: src/sbin/reboot/boot_i386.8,v 1.23.2.11 2002/04/24 17:47:58 rnordier Exp $
44 .Nd system bootstrapping procedures
46 .Sy Power fail and crash recovery .
47 Normally, the system will reboot itself at power-up or after crashes.
48 An automatic consistency check of the file systems will be performed,
49 and unless this fails, the system will resume multi-user operations.
52 Most i386 PCs attempt to boot first from floppy disk drive 0 (sometimes
53 known as drive A:) and, failing that, from hard disk drive 0 (sometimes
54 known as drive C:, or as drive 0x80 to the BIOS). Some BIOSes allow
55 you to change this default sequence, and may also include a CD-ROM
56 drive as a boot device.
58 By default, a three-stage bootstrap is employed, and control is
59 automatically passed from the boot blocks (bootstrap stages one and
60 two) to a separate third-stage bootstrap program,
62 This third stage provides more sophisticated control over the booting
63 process than it is possible to achieve in the boot blocks, which are
64 constrained by occupying limited fixed space on a given disk or slice.
66 However, it is possible to dispense with the third stage altogether,
67 either by specifying a kernel name in the boot block parameter
72 is set, by hitting a key during a brief pause (while one of the characters
80 is invoked. Booting will also be attempted at stage two, if the
81 third stage cannot be loaded.
83 The remainder of this subsection deals only with the boot blocks. The
85 program is documented separately.
87 After the boot blocks have been loaded,
88 you should see a prompt similar to the following:
91 0:ad(0,a)/boot/loader:
94 The automatic boot will attempt to load
100 of either the floppy or the hard disk.
101 This boot may be aborted by typing any character on the keyboard
104 prompt. At this time, the following input will be accepted:
105 .Bl -tag -width indent
107 Give a short listing of the files in the root directory of the default
108 boot device, as a hint about available boot files. (A
110 may also be specified as the last segment of a path, in which case
111 the listing will be of the relevant subdirectory.)
113 .Ar bios_drive : Ns Ar interface Ns Po
114 .Ar unit , Ns Ar part Pc
116 .Op Fl aCcDdghmnPprsVv
118 Specify boot file and flags.
119 .Bl -tag -width indent
121 The drive number as recognized by the BIOS.
122 0 for the first drive, 1 for the second drive, etc.
124 The type of controller to boot from. Note that the controller is required
125 to have BIOS support since the BIOS services are used to load the
128 The supported interfaces are:
130 .Bl -tag -width "adXX" -compact
132 ST506, IDE, ESDI, RLL disks on a WD100[2367] or lookalike
135 5 \(14" or 3 \(12" High density floppies
137 SCSI disk on any supported SCSI controller
142 The unit number of the drive on the interface being used.
143 0 for the first drive, 1 for the second drive, etc.
145 The partition letter inside the
147 portion of the disk. See
149 By convention, only partition
151 contains a bootable image. If sliced disks are used
152 .Pq Dq fdisk partitions ,
153 any slice can be booted from, with the default being the active slice
154 or, otherwise, the first
158 The pathname of the file to boot (relative to the root directory
159 on the specified partition). Defaults to
161 Symbolic links are not supported (hard links are).
162 .It Fl aCcDdghmnPprsVv
165 .Bl -tag -width "-CXX" -compact
167 during kernel initialization,
168 ask for the device to mount as the root file system.
172 Use all available consoles as the system console. Input will be accepted
173 on any console and output will be routed to all of them. This is the
176 Use the serial console as the system console.
178 Use the video console as the system console.
180 Mute the system console. None of the console devices will be used for the
183 enter the DDB kernel debugger
186 as early as possible in kernel initialization.
188 use the GDB remote debugging protocol.
190 ignore key press to interrupt boot before
194 probe the keyboard. If no keyboard is found, the
198 options are automatically set.
200 pause after each attached device during the device probing phase.
202 use the statically configured default for the device containing the
206 Normally, the root file system is on the device
207 that the kernel was loaded from.
209 boot into single-user mode; if the console is marked as
213 the root password must be entered.
215 be verbose during device probing (and later).
220 You may put a BIOS drive number, a controller type, a unit number,
221 a partition, a kernel file name, and any valid option in
223 to set defaults. Enter them in one line just as you type at the
227 .Bl -tag -width /boot/loader -compact
229 parameters for the boot blocks (optional)
231 first stage bootstrap file
233 second stage bootstrap file
235 third stage bootstrap
238 .It Pa /boot/kernel.old
239 typical non-default kernel (optional)
242 When disk-related errors occur, these are reported by the second-stage
243 bootstrap using the same error codes returned by the BIOS, for example
244 .Dq Disk error 0x1 (lba=0x12345678) .
245 Here is a partial list of these error codes:
247 .Bl -tag -width "0x80" -compact
251 Address mark not found
257 DMA attempt across 64K boundary
261 Uncorrectable CRC/ECC error
271 On older machines, or otherwise where EDD support (disk packet
272 interface support) is not available, all boot-related files and
273 structures (including the kernel) that need to be accessed during the
274 boot phase must reside on the disk at or below cylinder 1023 (as the
275 BIOS understands the geometry). When a
277 is reported by the second-stage bootstrap, it generally means that this
278 requirement has not been adhered to.
293 format used by this version of
296 different from that of other architectures.
298 Due to space constraints, the keyboard probe initiated by the
300 option is simply a test that the BIOS has detected an
304 keyboard (with no F11 and F12 keys, etc.) is attached, the probe will
307 Some features are not yet documented.