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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12 .\" modification, are permitted provided that the following conditions
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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 PCs attempt to boot first from hard disk drive 0 (sometimes
53 known as drive C:) and, failing that, from various other mass storage
56 you to change this default sequence, and typically also include a CD-ROM
57 drive as a boot device.
59 Newer PCs boot using UEFI firmware, not legacy BIOS.
60 That process is described in
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 0:ad(0,a)/boot/loader:
99 The automatic boot will attempt to load
105 of either the floppy or the hard disk.
106 This boot may be aborted by typing any character on the keyboard
109 prompt. At this time, the following input will be accepted:
110 .Bl -tag -width indent
112 Give a short listing of the files in the root directory of the default
113 boot device, as a hint about available boot files. (A
115 may also be specified as the last segment of a path, in which case
116 the listing will be of the relevant subdirectory.)
118 .Ar bios_drive : Ns Ar interface Ns Po
119 .Ar unit , Ns Ar part Pc
121 .Op Fl aCcDdghmnPprsVv
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 \(14" or 3 \(12" 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).
167 .It Fl aCcDdghmnPprsVv
170 .Bl -tag -width "-CXX" -compact
172 during kernel initialization,
173 ask for the device to mount as the root file system.
177 Use all available consoles as the system console. Input will be accepted
178 on any console and output will be routed to all of them. This is the
181 Use the serial console as the system console.
183 Use the video console as the system console.
185 Mute the system console. None of the console devices will be used for the
188 enter the DDB kernel debugger
191 as early as possible in kernel initialization.
193 use the GDB remote debugging protocol.
195 ignore key press to interrupt boot before
199 probe the keyboard. If no keyboard is found, the
203 options are automatically set.
205 pause after each attached device during the device probing phase.
207 use the statically configured default for the device containing the
211 Normally, the root file system is on the device
212 that the kernel was loaded from.
214 boot into single-user mode; if the console is marked as
218 the root password must be entered.
220 be verbose during device probing (and later).
225 You may put a BIOS drive number, a controller type, a unit number,
226 a partition, a kernel file name, and any valid option in
228 to set defaults. Enter them in one line just as you type at the
232 .Bl -tag -width /boot/loader -compact
234 parameters for the boot blocks (optional)
236 first stage bootstrap file
238 second stage bootstrap file
240 third stage bootstrap
243 .It Pa /boot/kernel.old
244 typical non-default kernel (optional)
247 When disk-related errors occur, these are reported by the second-stage
248 bootstrap using the same error codes returned by the BIOS, for example
249 .Dq Disk error 0x1 (lba=0x12345678) .
250 Here is a partial list of these error codes:
252 .Bl -tag -width "0x80" -compact
256 Address mark not found
262 DMA attempt across 64K boundary
266 Uncorrectable CRC/ECC error
276 On older machines, or otherwise where EDD support (disk packet
277 interface support) is not available, all boot-related files and
278 structures (including the kernel) that need to be accessed during the
279 boot phase must reside on the disk at or below cylinder 1023 (as the
280 BIOS understands the geometry). When a
282 is reported by the second-stage bootstrap, it generally means that this
283 requirement has not been adhered to.
299 format used by this version of
302 different from that of other architectures.
304 Due to space constraints, the keyboard probe initiated by the
306 option is simply a test that the BIOS has detected an
310 keyboard (with no F11 and F12 keys, etc.) is attached, the probe will
313 Some features are not yet documented.