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
89 partition. As a result, slices which are missing an
91 parition require user intervention during the boot process.
93 The remainder of this subsection deals only with the boot blocks.
96 program is documented separately.
98 After the boot blocks have been loaded,
99 you should see a prompt similar to the following:
102 Default: 0:ad(0,a)/boot/loader
106 The automatic boot will attempt to load
110 of either the floppy or the hard disk.
111 This boot may be aborted by typing any character on the keyboard
115 At this time, the following input will be accepted:
116 .Bl -tag -width indent
118 Give a short listing of the files in the root directory of the default
119 boot device, as a hint about available boot files.
122 may also be specified as the last segment of a path, in which case
123 the listing will be of the relevant subdirectory.)
127 .Ar bios_drive : interface ( unit , Oo Ar slice , Oc Ar part )
130 .Op Fl aCcDdghmnPprsv
132 Specify boot file and flags.
133 .Bl -tag -width indent
135 The drive number as recognized by the BIOS.
136 0 for the first drive, 1 for the second drive, etc.
138 The type of controller to boot from.
139 Note that the controller is required
140 to have BIOS support since the BIOS services are used to load the
143 The supported interfaces are:
145 .Bl -tag -width "adXX" -compact
147 ST506, IDE, ESDI, RLL disks on a WD100[2367] or lookalike
150 5 1/4" or 3 1/2" High density floppies
152 SCSI disk on any supported SCSI controller
157 The unit number of the drive on the interface being used.
158 0 for the first drive, 1 for the second drive, etc.
159 .It Oo Ar slice , Oc Ns Ar part
160 The partition letter inside the
165 By convention, only partition
167 contains a bootable image.
168 If sliced disks are used
169 .Pq Dq fdisk partitions ,
172 (1 for the first slice, 2 for the second slice, etc.\&)
173 can be booted from, with the default (if not specified) being the active slice
174 or, otherwise, the first
179 is specified as 0, the first
183 slice) is booted from.
185 The pathname of the file to boot (relative to the root directory
186 on the specified partition).
189 Symbolic links are not supported (hard links are).
190 .It Fl aCcDdghmnPprsv
193 .Bl -tag -width "-CXX" -compact
195 during kernel initialization,
196 ask for the device to mount as the root file system.
198 try to mount root file system from a CD-ROM.
200 this flag is currently a no-op.
202 boot with the dual console configuration.
204 configuration, the console will be either the internal display
205 or the serial port, depending on the state of the
208 In the dual console configuration,
209 both the internal display and the serial port will become the console
210 at the same time, regardless of the state of the
214 enter the DDB kernel debugger
217 as early as possible in kernel initialization.
219 use the GDB remote debugging protocol.
221 force the serial console.
222 For instance, if you boot from the internal console,
225 option to force the kernel to use the serial port as its
227 The serial port driver
229 has a flag (0x20) to override this option.
230 If that flag is set, the serial port will always be used as the console,
233 option described here.
240 ignore key press to interrupt boot before
245 If no keyboard is found, the
249 options are automatically set.
251 pause after each attached device during the device probing phase.
253 use the statically configured default for the device containing the
257 Normally, the root file system is on the device
258 that the kernel was loaded from.
260 boot into single-user mode; if the console is marked as
264 the root password must be entered.
266 be verbose during device probing (and later).
271 You may put a BIOS drive number, a controller type, a unit number,
272 a partition, a kernel file name, and any valid option in
275 Enter them in one line just as you type at the
279 .Bl -tag -width /boot/loader -compact
281 parameters for the boot blocks (optional)
283 first stage bootstrap file
285 second stage bootstrap file
287 third stage bootstrap
288 .It Pa /boot/kernel/kernel
290 .It Pa /boot/kernel.old/kernel
291 typical non-default kernel (optional)
305 When disk-related errors occur, these are reported by the second-stage
306 bootstrap using the same error codes returned by the BIOS, for example
307 .Dq Disk error 0x1 (lba=0x12345678) .
308 Here is a partial list of these error codes:
310 .Bl -tag -width "0x80" -compact
314 Address mark not found
320 DMA attempt across 64K boundary
324 Uncorrectable CRC/ECC error
334 On older machines, or otherwise where EDD support (disk packet
335 interface support) is not available, all boot-related files and
336 structures (including the kernel) that need to be accessed during the
337 boot phase must reside on the disk at or below cylinder 1023 (as the
338 BIOS understands the geometry).
341 is reported by the second-stage bootstrap, it generally means that this
342 requirement has not been adhered to.
346 format used by this version of
349 different from that of other architectures.
351 Due to space constraints, the keyboard probe initiated by the
353 option is simply a test that the BIOS has detected an
358 keyboard (with no F11 and F12 keys, etc.) is attached, the probe will