1.\" Copyright (c) 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This code is derived from software written and contributed 5.\" to Berkeley by William Jolitz. 6.\" 7.\" Almost completely rewritten for FreeBSD 2.1 by Joerg Wunsch. 8.\" 9.\" Substantially revised for FreeBSD 3.1 by Robert Nordier. 10.\" 11.\" Redistribution and use in source and binary forms, with or without 12.\" modification, are permitted provided that the following conditions 13.\" are met: 14.\" 1. Redistributions of source code must retain the above copyright 15.\" notice, this list of conditions and the following disclaimer. 16.\" 2. Redistributions in binary form must reproduce the above copyright 17.\" notice, this list of conditions and the following disclaimer in the 18.\" documentation and/or other materials provided with the distribution. 19.\" 3. Neither the name of the University nor the names of its contributors 20.\" may be used to endorse or promote products derived from this software 21.\" without specific prior written permission. 22.\" 23.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 24.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 26.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 27.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33.\" SUCH DAMAGE. 34.\" 35.\" @(#)boot_i386.8 8.2 (Berkeley) 4/19/94 36.\" 37.\" $FreeBSD$ 38.\" 39.Dd July 11, 2020 40.Dt BOOT 8 i386 41.Os 42.Sh NAME 43.Nm boot 44.Nd system bootstrapping procedures 45.Sh DESCRIPTION 46.Sy Power fail and crash recovery . 47Normally, the system will reboot itself at power-up or after crashes. 48An automatic consistency check of the file systems will be performed, 49and unless this fails, the system will resume multi-user operations. 50.Pp 51.Sy Cold starts . 52Most i386 PCs attempt to boot first from floppy disk drive 0 (sometimes 53known as drive A:) and, failing that, from hard disk drive 0 (sometimes 54known as drive C:, or as drive 0x80 to the BIOS). 55Some BIOSes allow 56you to change this default sequence, and may also include a CD-ROM 57drive as a boot device. 58.Pp 59Some newer PCs boot using UEFI firmware, not BIOS. 60That process is described 61in 62.Xr uefi 8 . 63.Pp 64A three-stage bootstrap is employed. 65Control is passed from the boot blocks (bootstrap stages one and two) to a 66third-stage bootstrap program, 67.Xr loader 8 . 68This third stage provides more sophisticated control over the booting 69process than it is possible to achieve in the boot blocks, which are 70constrained by occupying limited fixed space on a given disk or slice. 71.Pp 72The remainder of this subsection deals only with the boot blocks. 73The 74.Xr loader 8 75program is documented separately. 76.Pp 77After the boot blocks have been loaded, 78you should see a prompt similar to the following: 79.Bd -literal 80>> FreeBSD/x86 BOOT 81Default: 0:ad(0,a)/boot/loader 82boot: 83.Ed 84.Pp 85The automatic boot will attempt to load 86.Pa /boot/loader 87from partition 88.Ql a 89of either the floppy or the hard disk. 90This boot may be aborted by typing any character on the keyboard 91at the 92.Ql boot\&: 93prompt. 94At this time, the following input will be accepted: 95.Bl -tag -width indent 96.It Ic \&? 97Give a short listing of the files in the root directory of the default 98boot device, as a hint about available boot files. 99(A 100.Ic ?\& 101may also be specified as the last segment of a path, in which case 102the listing will be of the relevant subdirectory.) 103.It Xo 104.Sm off 105.Ar bios_drive : interface ( unit , Oo Ar slice , Oc Ar part ) 106.Ar filename 107.Sm on 108.Op Fl aCcDdghmnPprsv 109.Op Fl S Ns Ar speed 110.Xc 111Specify boot file and flags. 112.Bl -tag -width indent 113.It Ar bios_drive 114The drive number as recognized by the BIOS. 1150 for the first drive, 1 for the second drive, etc. 116.It Ar interface 117The type of controller to boot from. 118Note that the controller is required 119to have BIOS support since the BIOS services are used to load the 120boot file image. 121.Pp 122The supported interfaces are: 123.Pp 124.Bl -tag -width "adXX" -compact 125.It ad 126ST506, IDE, ESDI, RLL disks on a WD100[2367] or lookalike 127controller 128.It fd 1295 1/4" or 3 1/2" High density floppies 130.It da 131SCSI disk on any supported SCSI controller 132.\".It cd 133.\"boot from CDROM 134.El 135.It Ar unit 136The unit number of the drive on the interface being used. 1370 for the first drive, 1 for the second drive, etc. 138.It Oo Ar slice , Oc Ns Ar part 139The partition letter inside the 140.Bx 141portion of the disk. 142See 143.Xr bsdlabel 8 . 144By convention, only partition 145.Ql a 146contains a bootable image. 147If sliced disks are used 148.Pq Dq fdisk partitions , 149any 150.Ar slice 151(1 for the first slice, 2 for the second slice, etc.\&) 152can be booted from, with the default (if not specified) being the active slice 153or, otherwise, the first 154.Fx 155slice. 156If 157.Ar slice 158is specified as 0, the first 159.Fx 160slice (also known as 161.Dq compatibility 162slice) is booted from. 163.It Ar filename 164The pathname of the file to boot (relative to the root directory 165on the specified partition). 166Defaults to 167.Pa /boot/kernel/kernel . 168Symbolic links are not supported (hard links are). 169.It Xo Op Fl aCcDdghmnPpqrsv 170.Op Fl S Ns Ar speed 171.Xc 172Boot flags: 173.Pp 174.Bl -tag -width "-CXX" -compact 175.It Fl a 176during kernel initialization, 177ask for the device to mount as the root file system. 178.It Fl C 179try to mount root file system from a CD-ROM. 180.It Fl c 181this flag is currently a no-op. 182.It Fl D 183boot with the dual console configuration. 184In the single 185configuration, the console will be either the internal display 186or the serial port, depending on the state of the 187.Fl h 188option below. 189In the dual console configuration, 190both the internal display and the serial port will become the console 191at the same time, regardless of the state of the 192.Fl h 193option. 194.It Fl d 195enter the DDB kernel debugger 196(see 197.Xr ddb 4 ) 198as early as possible in kernel initialization. 199.It Fl g 200use the GDB remote debugging protocol. 201.It Fl h 202force the serial console. 203For instance, if you boot from the internal console, 204you can use the 205.Fl h 206option to force the kernel to use the serial port as its 207console device. 208.It Fl m 209mute the console to suppress all kernel console input and output during the 210boot. 211.It Fl n 212ignore key press to interrupt boot before 213.Xr loader 8 214is invoked. 215.It Fl P 216probe the keyboard. 217If no keyboard is found, the 218.Fl D 219and 220.Fl h 221options are automatically set. 222.It Fl p 223pause after each attached device during the device probing phase. 224.It Fl q 225be quiet, 226do not write anything to the console unless automatic boot fails or 227is disabled. 228This option only affects second-stage bootstrap, 229to prevent next stages from writing to the console use in 230combination with the 231.Fl m 232option. 233.It Fl r 234use the statically configured default for the device containing the 235root file system 236(see 237.Xr config 8 ) . 238Normally, the root file system is on the device 239that the kernel was loaded from. 240.It Fl s 241boot into single-user mode; if the console is marked as 242.Dq insecure 243(see 244.Xr ttys 5 ) , 245the root password must be entered. 246.It Fl S Ns Ar speed 247set the speed of the serial console to 248.Ar speed . 249The default is 9600 unless it has been overridden by setting 250.Va BOOT_COMCONSOLE_SPEED 251in 252.Xr make.conf 5 253and recompiling and reinstalling the boot blocks. 254.It Fl v 255be verbose during device probing (and later). 256.El 257.El 258.El 259.Pp 260Use the 261.Pa /boot.config 262file to set the default configuration options for the boot block code. 263See 264.Xr boot.config 5 265for more information about the 266.Pa /boot.config 267file. 268.Sh FILES 269.Bl -tag -width /boot/loader -compact 270.It Pa /boot.config 271parameters for the boot blocks (optional) 272.It Pa /boot/boot1 273first stage bootstrap file 274.It Pa /boot/boot2 275second stage bootstrap file 276.It Pa /boot/loader 277third stage bootstrap 278.It Pa /boot/kernel/kernel 279default kernel 280.It Pa /boot/kernel.old/kernel 281typical non-default kernel (optional) 282.El 283.Sh DIAGNOSTICS 284When disk-related errors occur, these are reported by the second-stage 285bootstrap using the same error codes returned by the BIOS, for example 286.Dq Disk error 0x1 (lba=0x12345678) . 287Here is a partial list of these error codes: 288.Pp 289.Bl -tag -width "0x80" -compact 290.It 0x1 291Invalid argument 292.It 0x2 293Address mark not found 294.It 0x4 295Sector not found 296.It 0x8 297DMA overrun 298.It 0x9 299DMA attempt across 64K boundary 300.It 0xc 301Invalid media 302.It 0x10 303Uncorrectable CRC/ECC error 304.It 0x20 305Controller failure 306.It 0x40 307Seek failed 308.It 0x80 309Timeout 310.El 311.Pp 312.Sy "NOTE" : 313On older machines, or otherwise where EDD support (disk packet 314interface support) is not available, all boot-related files and 315structures (including the kernel) that need to be accessed during the 316boot phase must reside on the disk at or below cylinder 1023 (as the 317BIOS understands the geometry). 318When a 319.Dq Disk error 0x1 320is reported by the second-stage bootstrap, it generally means that this 321requirement has not been adhered to. 322.Sh SEE ALSO 323.Xr ddb 4 , 324.Xr boot.config 5 , 325.Xr make.conf 5 , 326.Xr mount.conf 5 , 327.Xr ttys 5 , 328.Xr boot0cfg 8 , 329.Xr btxld 8 , 330.Xr config 8 , 331.Xr efibootmgr 8 , 332.Xr efivar 8 , 333.Xr gpart 8 , 334.Xr gptboot 8 , 335.Xr gptzfsboot 8 , 336.Xr halt 8 , 337.Xr loader 8 , 338.Xr nextboot 8 , 339.Xr reboot 8 , 340.Xr shutdown 8 , 341.Xr uefi 8 , 342.Xr zfsbootcfg 8 343.Sh BUGS 344The bsdlabel format used by this version of 345.Bx 346is quite 347different from that of other architectures. 348.Pp 349Due to space constraints, the keyboard probe initiated by the 350.Fl P 351option is simply a test that the BIOS has detected an 352.Dq extended 353keyboard. 354If an 355.Dq XT/AT 356keyboard (with no F11 and F12 keys, etc.) is attached, the probe will 357fail. 358