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
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 The remainder of this subsection deals only with the boot blocks.
88 program is documented separately.
90 After the boot blocks have been loaded,
91 you should see a prompt similar to the following:
94 Default: 0:ad(0,a)/boot/loader
98 The automatic boot will attempt to load
102 of either the floppy or the hard disk.
103 This boot may be aborted by typing any character on the keyboard
107 At this time, the following input will be accepted:
108 .Bl -tag -width indent
110 Give a short listing of the files in the root directory of the default
111 boot device, as a hint about available boot files.
114 may also be specified as the last segment of a path, in which case
115 the listing will be of the relevant subdirectory.)
119 .Ar bios_drive : interface ( unit , Oo Ar slice , Oc Ar part )
122 .Op Fl aCcDdghmnPprsv
125 Specify boot file and flags.
126 .Bl -tag -width indent
128 The drive number as recognized by the BIOS.
129 0 for the first drive, 1 for the second drive, etc.
131 The type of controller to boot from.
132 Note that the controller is required
133 to have BIOS support since the BIOS services are used to load the
136 The supported interfaces are:
138 .Bl -tag -width "adXX" -compact
140 ST506, IDE, ESDI, RLL disks on a WD100[2367] or lookalike
143 5 1/4" or 3 1/2" High density floppies
145 SCSI disk on any supported SCSI controller
150 The unit number of the drive on the interface being used.
151 0 for the first drive, 1 for the second drive, etc.
152 .It Oo Ar slice , Oc Ns Ar part
153 The partition letter inside the
158 By convention, only partition
160 contains a bootable image.
161 If sliced disks are used
162 .Pq Dq fdisk partitions ,
165 (1 for the first slice, 2 for the second slice, etc.\&)
166 can be booted from, with the default (if not specified) being the active slice
167 or, otherwise, the first
172 is specified as 0, the first
176 slice) is booted from.
178 The pathname of the file to boot (relative to the root directory
179 on the specified partition).
181 .Pa /boot/kernel/kernel .
182 Symbolic links are not supported (hard links are).
183 .It Xo Op Fl aCcDdghmnPpqrsv
188 .Bl -tag -width "-CXX" -compact
190 during kernel initialization,
191 ask for the device to mount as the root file system.
193 try to mount root file system from a CD-ROM.
195 this flag is currently a no-op.
197 boot with the dual console configuration.
199 configuration, the console will be either the internal display
200 or the serial port, depending on the state of the
203 In the dual console configuration,
204 both the internal display and the serial port will become the console
205 at the same time, regardless of the state of the
209 enter the DDB kernel debugger
212 as early as possible in kernel initialization.
214 use the GDB remote debugging protocol.
216 force the serial console.
217 For instance, if you boot from the internal console,
220 option to force the kernel to use the serial port as its
222 The serial port driver
224 has a flag (0x20) to override this option.
225 If that flag is set, the serial port will always be used as the console,
228 option described here.
233 mute the console to suppress all console input and output during the
236 ignore key press to interrupt boot before
241 If no keyboard is found, the
245 options are automatically set.
247 pause after each attached device during the device probing phase.
250 do not write anything to the console unless automatic boot fails or
252 This option only affects second-stage bootstrap,
253 to prevent next stages from writing to the console use in
258 use the statically configured default for the device containing the
262 Normally, the root file system is on the device
263 that the kernel was loaded from.
265 boot into single-user mode; if the console is marked as
269 the root password must be entered.
271 set the speed of the serial console to
273 The default is 9600 unless it has been overridden by setting
274 .Va BOOT_COMCONSOLE_SPEED
277 and recompiling and reinstalling the boot blocks.
279 be verbose during device probing (and later).
286 file to set the default configuration options for the boot block code.
289 for more information about the
293 .Bl -tag -width /boot/loader -compact
295 parameters for the boot blocks (optional)
297 first stage bootstrap file
299 second stage bootstrap file
301 third stage bootstrap
302 .It Pa /boot/kernel/kernel
304 .It Pa /boot/kernel.old/kernel
305 typical non-default kernel (optional)
308 When disk-related errors occur, these are reported by the second-stage
309 bootstrap using the same error codes returned by the BIOS, for example
310 .Dq Disk error 0x1 (lba=0x12345678) .
311 Here is a partial list of these error codes:
313 .Bl -tag -width "0x80" -compact
317 Address mark not found
323 DMA attempt across 64K boundary
327 Uncorrectable CRC/ECC error
337 On older machines, or otherwise where EDD support (disk packet
338 interface support) is not available, all boot-related files and
339 structures (including the kernel) that need to be accessed during the
340 boot phase must reside on the disk at or below cylinder 1023 (as the
341 BIOS understands the geometry).
344 is reported by the second-stage bootstrap, it generally means that this
345 requirement has not been adhered to.
361 The bsdlabel format used by this version of
364 different from that of other architectures.
366 Due to space constraints, the keyboard probe initiated by the
368 option is simply a test that the BIOS has detected an
373 keyboard (with no F11 and F12 keys, etc.) is attached, the probe will