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
39 .Dd September 30, 2004
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).
56 you to change this default sequence, and may also include a CD-ROM
57 drive as a boot device.
59 By default, a three-stage bootstrap is employed, and control is
60 automatically passed from the boot blocks (bootstrap stages one and
61 two) to a separate third-stage bootstrap program,
63 This third stage provides more sophisticated control over the booting
64 process than it is possible to achieve in the boot blocks, which are
65 constrained by occupying limited fixed space on a given disk or slice.
67 However, it is possible to dispense with the third stage altogether,
68 either by specifying a kernel name in the boot block parameter
73 is set, by hitting a key during a brief pause (while one of the characters
82 Booting will also be attempted at stage two, if the
83 third stage cannot be loaded.
85 Make note of the fact that
90 As a result, slices which are missing an
92 parition require user intervention during the boot process.
94 The remainder of this subsection deals only with the boot blocks.
97 program is documented separately.
99 After the boot blocks have been loaded,
100 you should see a prompt similar to the following:
103 Default: 0:ad(0,a)/boot/loader
107 The automatic boot will attempt to load
111 of either the floppy or the hard disk.
112 This boot may be aborted by typing any character on the keyboard
116 At this time, the following input will be accepted:
117 .Bl -tag -width indent
119 Give a short listing of the files in the root directory of the default
120 boot device, as a hint about available boot files.
123 may also be specified as the last segment of a path, in which case
124 the listing will be of the relevant subdirectory.)
128 .Ar bios_drive : interface ( unit , Oo Ar slice , Oc Ar part )
131 .Op Fl aCcDdghmnPprsv
133 Specify boot file and flags.
134 .Bl -tag -width indent
136 The drive number as recognized by the BIOS.
137 0 for the first drive, 1 for the second drive, etc.
139 The type of controller to boot from.
140 Note that the controller is required
141 to have BIOS support since the BIOS services are used to load the
144 The supported interfaces are:
146 .Bl -tag -width "adXX" -compact
148 ST506, IDE, ESDI, RLL disks on a WD100[2367] or lookalike
151 5 1/4" or 3 1/2" High density floppies
153 SCSI disk on any supported SCSI controller
158 The unit number of the drive on the interface being used.
159 0 for the first drive, 1 for the second drive, etc.
160 .It Oo Ar slice , Oc Ns Ar part
161 The partition letter inside the
166 By convention, only partition
168 contains a bootable image.
169 If sliced disks are used
170 .Pq Dq fdisk partitions ,
173 (1 for the first slice, 2 for the second slice, etc.\&)
174 can be booted from, with the default (if not specified) being the active slice
175 or, otherwise, the first
180 is specified as 0, the first
184 slice) is booted from.
186 The pathname of the file to boot (relative to the root directory
187 on the specified partition).
190 Symbolic links are not supported (hard links are).
191 .It Fl aCcDdghmnPprsv
194 .Bl -tag -width "-CXX" -compact
196 during kernel initialization,
197 ask for the device to mount as the root file system.
199 try to mount root file system from a CD-ROM.
201 this flag is currently a no-op.
203 boot with the dual console configuration.
205 configuration, the console will be either the internal display
206 or the serial port, depending on the state of the
209 In the dual console configuration,
210 both the internal display and the serial port will become the console
211 at the same time, regardless of the state of the
215 enter the DDB kernel debugger
218 as early as possible in kernel initialization.
220 use the GDB remote debugging protocol.
222 force the serial console.
223 For instance, if you boot from the internal console,
226 option to force the kernel to use the serial port as its
228 The serial port driver
230 has a flag (0x20) to override this option.
231 If that flag is set, the serial port will always be used as the console,
234 option described here.
241 ignore key press to interrupt boot before
246 If no keyboard is found, the
250 options are automatically set.
252 pause after each attached device during the device probing phase.
254 use the statically configured default for the device containing the
258 Normally, the root file system is on the device
259 that the kernel was loaded from.
261 boot into single-user mode; if the console is marked as
265 the root password must be entered.
267 be verbose during device probing (and later).
272 You may put a BIOS drive number, a controller type, a unit number,
273 a partition, a kernel file name, and any valid option in
276 Enter them in one line just as you type at the
280 .Bl -tag -width /boot/loader -compact
282 parameters for the boot blocks (optional)
284 first stage bootstrap file
286 second stage bootstrap file
288 third stage bootstrap
289 .It Pa /boot/kernel/kernel
291 .It Pa /boot/kernel.old/kernel
292 typical non-default kernel (optional)
295 When disk-related errors occur, these are reported by the second-stage
296 bootstrap using the same error codes returned by the BIOS, for example
297 .Dq Disk error 0x1 (lba=0x12345678) .
298 Here is a partial list of these error codes:
300 .Bl -tag -width "0x80" -compact
304 Address mark not found
310 DMA attempt across 64K boundary
314 Uncorrectable CRC/ECC error
324 On older machines, or otherwise where EDD support (disk packet
325 interface support) is not available, all boot-related files and
326 structures (including the kernel) that need to be accessed during the
327 boot phase must reside on the disk at or below cylinder 1023 (as the
328 BIOS understands the geometry).
331 is reported by the second-stage bootstrap, it generally means that this
332 requirement has not been adhered to.
347 format used by this version of
350 different from that of other architectures.
352 Due to space constraints, the keyboard probe initiated by the
354 option is simply a test that the BIOS has detected an
359 keyboard (with no F11 and F12 keys, etc.) is attached, the probe will