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 Some newer PCs boot using UEFI firmware, not BIOS.
60 That process is described
64 A three-stage bootstrap is employed.
65 Control is passed from the boot blocks (bootstrap stages one and two) to a
66 third-stage bootstrap program,
68 This third stage provides more sophisticated control over the booting
69 process than it is possible to achieve in the boot blocks, which are
70 constrained by occupying limited fixed space on a given disk or slice.
72 The remainder of this subsection deals only with the boot blocks.
75 program is documented separately.
77 After the boot blocks have been loaded,
78 you should see a prompt similar to the following:
81 Default: 0:ad(0,a)/boot/loader
85 The automatic boot will attempt to load
89 of either the floppy or the hard disk.
90 This boot may be aborted by typing any character on the keyboard
94 At this time, the following input will be accepted:
95 .Bl -tag -width indent
97 Give a short listing of the files in the root directory of the default
98 boot device, as a hint about available boot files.
101 may also be specified as the last segment of a path, in which case
102 the listing will be of the relevant subdirectory.)
105 .Ar bios_drive : interface ( unit , Oo Ar slice , Oc Ar part )
108 .Op Fl aCcDdghmnPprsv
111 Specify boot file and flags.
112 .Bl -tag -width indent
114 The drive number as recognized by the BIOS.
115 0 for the first drive, 1 for the second drive, etc.
117 The type of controller to boot from.
118 Note that the controller is required
119 to have BIOS support since the BIOS services are used to load the
122 The supported interfaces are:
124 .Bl -tag -width "adXX" -compact
126 ST506, IDE, ESDI, RLL disks on a WD100[2367] or lookalike
129 5 1/4" or 3 1/2" High density floppies
131 SCSI disk on any supported SCSI controller
136 The unit number of the drive on the interface being used.
137 0 for the first drive, 1 for the second drive, etc.
138 .It Oo Ar slice , Oc Ns Ar part
139 The partition letter inside the
144 By convention, only partition
146 contains a bootable image.
147 If sliced disks are used
148 .Pq Dq fdisk partitions ,
151 (1 for the first slice, 2 for the second slice, etc.\&)
152 can be booted from, with the default (if not specified) being the active slice
153 or, otherwise, the first
158 is specified as 0, the first
162 slice) is booted from.
164 The pathname of the file to boot (relative to the root directory
165 on the specified partition).
167 .Pa /boot/kernel/kernel .
168 Symbolic links are not supported (hard links are).
169 .It Xo Op Fl aCcDdghmnPpqrsv
174 .Bl -tag -width "-CXX" -compact
176 during kernel initialization,
177 ask for the device to mount as the root file system.
179 try to mount root file system from a CD-ROM.
181 this flag is currently a no-op.
183 boot with the dual console configuration.
185 configuration, the console will be either the internal display
186 or the serial port, depending on the state of the
189 In the dual console configuration,
190 both the internal display and the serial port will become the console
191 at the same time, regardless of the state of the
195 enter the DDB kernel debugger
198 as early as possible in kernel initialization.
200 use the GDB remote debugging protocol.
202 force the serial console.
203 For instance, if you boot from the internal console,
206 option to force the kernel to use the serial port as its
209 mute the console to suppress all kernel console input and output during the
212 ignore key press to interrupt boot before
217 If no keyboard is found, the
221 options are automatically set.
223 pause after each attached device during the device probing phase.
226 do not write anything to the console unless automatic boot fails or
228 This option only affects second-stage bootstrap,
229 to prevent next stages from writing to the console use in
234 use the statically configured default for the device containing the
238 Normally, the root file system is on the device
239 that the kernel was loaded from.
241 boot into single-user mode; if the console is marked as
245 the root password must be entered.
247 set the speed of the serial console to
249 The default is 9600 unless it has been overridden by setting
250 .Va BOOT_COMCONSOLE_SPEED
253 and recompiling and reinstalling the boot blocks.
255 be verbose during device probing (and later).
262 file to set the default configuration options for the boot block code.
265 for more information about the
269 .Bl -tag -width /boot/loader -compact
271 parameters for the boot blocks (optional)
273 first stage bootstrap file
275 second stage bootstrap file
277 third stage bootstrap
278 .It Pa /boot/kernel/kernel
280 .It Pa /boot/kernel.old/kernel
281 typical non-default kernel (optional)
284 When disk-related errors occur, these are reported by the second-stage
285 bootstrap using the same error codes returned by the BIOS, for example
286 .Dq Disk error 0x1 (lba=0x12345678) .
287 Here is a partial list of these error codes:
289 .Bl -tag -width "0x80" -compact
293 Address mark not found
299 DMA attempt across 64K boundary
303 Uncorrectable CRC/ECC error
313 On older machines, or otherwise where EDD support (disk packet
314 interface support) is not available, all boot-related files and
315 structures (including the kernel) that need to be accessed during the
316 boot phase must reside on the disk at or below cylinder 1023 (as the
317 BIOS understands the geometry).
320 is reported by the second-stage bootstrap, it generally means that this
321 requirement has not been adhered to.
344 The bsdlabel format used by this version of
347 different from that of other architectures.
349 Due to space constraints, the keyboard probe initiated by the
351 option is simply a test that the BIOS has detected an
356 keyboard (with no F11 and F12 keys, etc.) is attached, the probe will