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 By default, a three-stage bootstrap is employed, and control is
65 automatically passed from the boot blocks (bootstrap stages one and
66 two) to a separate 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 However, it is possible to dispense with the third stage altogether,
73 either by specifying a kernel name in the boot block parameter
78 is set, by hitting a key during a brief pause (while one of the characters
87 Booting will also be attempted at stage two, if the
88 third stage cannot be loaded.
90 The remainder of this subsection deals only with the boot blocks.
93 program is documented separately.
95 After the boot blocks have been loaded,
96 you should see a prompt similar to the following:
99 Default: 0:ad(0,a)/boot/loader
103 The automatic boot will attempt to load
107 of either the floppy or the hard disk.
108 This boot may be aborted by typing any character on the keyboard
112 At this time, the following input will be accepted:
113 .Bl -tag -width indent
115 Give a short listing of the files in the root directory of the default
116 boot device, as a hint about available boot files.
119 may also be specified as the last segment of a path, in which case
120 the listing will be of the relevant subdirectory.)
123 .Ar bios_drive : interface ( unit , Oo Ar slice , Oc Ar part )
126 .Op Fl aCcDdghmnPprsv
129 Specify boot file and flags.
130 .Bl -tag -width indent
132 The drive number as recognized by the BIOS.
133 0 for the first drive, 1 for the second drive, etc.
135 The type of controller to boot from.
136 Note that the controller is required
137 to have BIOS support since the BIOS services are used to load the
140 The supported interfaces are:
142 .Bl -tag -width "adXX" -compact
144 ST506, IDE, ESDI, RLL disks on a WD100[2367] or lookalike
147 5 1/4" or 3 1/2" High density floppies
149 SCSI disk on any supported SCSI controller
154 The unit number of the drive on the interface being used.
155 0 for the first drive, 1 for the second drive, etc.
156 .It Oo Ar slice , Oc Ns Ar part
157 The partition letter inside the
162 By convention, only partition
164 contains a bootable image.
165 If sliced disks are used
166 .Pq Dq fdisk partitions ,
169 (1 for the first slice, 2 for the second slice, etc.\&)
170 can be booted from, with the default (if not specified) being the active slice
171 or, otherwise, the first
176 is specified as 0, the first
180 slice) is booted from.
182 The pathname of the file to boot (relative to the root directory
183 on the specified partition).
185 .Pa /boot/kernel/kernel .
186 Symbolic links are not supported (hard links are).
187 .It Xo Op Fl aCcDdghmnPpqrsv
192 .Bl -tag -width "-CXX" -compact
194 during kernel initialization,
195 ask for the device to mount as the root file system.
197 try to mount root file system from a CD-ROM.
199 this flag is currently a no-op.
201 boot with the dual console configuration.
203 configuration, the console will be either the internal display
204 or the serial port, depending on the state of the
207 In the dual console configuration,
208 both the internal display and the serial port will become the console
209 at the same time, regardless of the state of the
213 enter the DDB kernel debugger
216 as early as possible in kernel initialization.
218 use the GDB remote debugging protocol.
220 force the serial console.
221 For instance, if you boot from the internal console,
224 option to force the kernel to use the serial port as its
227 mute the console to suppress all kernel console input and output during the
230 ignore key press to interrupt boot before
235 If no keyboard is found, the
239 options are automatically set.
241 pause after each attached device during the device probing phase.
244 do not write anything to the console unless automatic boot fails or
246 This option only affects second-stage bootstrap,
247 to prevent next stages from writing to the console use in
252 use the statically configured default for the device containing the
256 Normally, the root file system is on the device
257 that the kernel was loaded from.
259 boot into single-user mode; if the console is marked as
263 the root password must be entered.
265 set the speed of the serial console to
267 The default is 9600 unless it has been overridden by setting
268 .Va BOOT_COMCONSOLE_SPEED
271 and recompiling and reinstalling the boot blocks.
273 be verbose during device probing (and later).
280 file to set the default configuration options for the boot block code.
283 for more information about the
287 .Bl -tag -width /boot/loader -compact
289 parameters for the boot blocks (optional)
291 first stage bootstrap file
293 second stage bootstrap file
295 third stage bootstrap
296 .It Pa /boot/kernel/kernel
298 .It Pa /boot/kernel.old/kernel
299 typical non-default kernel (optional)
302 When disk-related errors occur, these are reported by the second-stage
303 bootstrap using the same error codes returned by the BIOS, for example
304 .Dq Disk error 0x1 (lba=0x12345678) .
305 Here is a partial list of these error codes:
307 .Bl -tag -width "0x80" -compact
311 Address mark not found
317 DMA attempt across 64K boundary
321 Uncorrectable CRC/ECC error
331 On older machines, or otherwise where EDD support (disk packet
332 interface support) is not available, all boot-related files and
333 structures (including the kernel) that need to be accessed during the
334 boot phase must reside on the disk at or below cylinder 1023 (as the
335 BIOS understands the geometry).
338 is reported by the second-stage bootstrap, it generally means that this
339 requirement has not been adhered to.
358 The bsdlabel format used by this version of
361 different from that of other architectures.
363 Due to space constraints, the keyboard probe initiated by the
365 option is simply a test that the BIOS has detected an
370 keyboard (with no F11 and F12 keys, etc.) is attached, the probe will