BOOT(8) FreeBSD System Manager's Manual (i386) BOOT(8)
NAME
boot - system bootstrapping procedures
DESCRIPTION
Power fail and crash recovery. Normally, the system will reboot itself
at power-up or after crashes. An automatic consistency check of the file
systems will be performed, and unless this fails, the system will resume
multi-user operations.
Cold starts. Most i386 PCs attempt to boot first from floppy disk drive
0 (sometimes known as drive A:) and, failing that, from hard disk drive 0
(sometimes known as drive C:, or as drive 0x80 to the BIOS). Some BIOSes
allow you to change this default sequence, and may also include a CD-ROM
drive as a boot device.
Some newer PCs boot using UEFI firmware, not BIOS. That process is
described in uefi(8).
A three-stage bootstrap is employed. Control is passed from the boot
blocks (bootstrap stages one and two) to a third-stage bootstrap program,
loader(8). This third stage provides more sophisticated control over the
booting process than it is possible to achieve in the boot blocks, which
are constrained by occupying limited fixed space on a given disk or
slice.
The remainder of this subsection deals only with the boot blocks. The
loader(8) program is documented separately.
After the boot blocks have been loaded, you should see a prompt similar
to the following:
>> FreeBSD/x86 BOOT
Default: 0:ad(0,a)/boot/loader
boot:
The automatic boot will attempt to load /boot/loader from partition `a'
of either the floppy or the hard disk. This boot may be aborted by
typing any character on the keyboard at the `boot:' prompt. At this
time, the following input will be accepted:
? Give a short listing of the files in the root directory of the
default boot device, as a hint about available boot files. (A ?
may also be specified as the last segment of a path, in which
case the listing will be of the relevant subdirectory.)
bios_drive:interface(unit,[slice,]part)filename [-aCcDdghmnPprsv]
[-Sspeed]
Specify boot file and flags.
bios_drive
The drive number as recognized by the BIOS. 0 for the
first drive, 1 for the second drive, etc.
interface
The type of controller to boot from. Note that the
controller is required to have BIOS support since the
BIOS services are used to load the boot file image.
The supported interfaces are:
ad ST506, IDE, ESDI, RLL disks on a WD100[2367] or
lookalike controller
fd 5 1/4" or 3 1/2" High density floppies
da SCSI disk on any supported SCSI controller
unit The unit number of the drive on the interface being used.
0 for the first drive, 1 for the second drive, etc.
[slice,]part
The partition letter inside the BSD portion of the disk.
See bsdlabel(8). By convention, only partition `a'
contains a bootable image. If sliced disks are used
("fdisk partitions"), any slice (1 for the first slice, 2
for the second slice, etc.) can be booted from, with the
default (if not specified) being the active slice or,
otherwise, the first FreeBSD slice. If slice is
specified as 0, the first FreeBSD slice (also known as
"compatibility" slice) is booted from.
filename
The pathname of the file to boot (relative to the root
directory on the specified partition). Defaults to
/boot/kernel/kernel. Symbolic links are not supported
(hard links are).
[-aCcDdghmnPpqrsv] [-Sspeed]
Boot flags:
-a during kernel initialization, ask for the device to
mount as the root file system.
-C try to mount root file system from a CD-ROM.
-c this flag is currently a no-op.
-D boot with the dual console configuration. In the
single configuration, the console will be either
the internal display or the serial port, depending
on the state of the -h option below. In the dual
console configuration, both the internal display
and the serial port will become the console at the
same time, regardless of the state of the -h
option.
-d enter the DDB kernel debugger (see ddb(4)) as early
as possible in kernel initialization.
-g use the GDB remote debugging protocol.
-h force the serial console. For instance, if you
boot from the internal console, you can use the -h
option to force the kernel to use the serial port
as its console device.
-m mute the console to suppress all kernel console
input and output during the boot.
-n ignore key press to interrupt boot before loader(8)
is invoked.
-P probe the keyboard. If no keyboard is found, the
-D and -h options are automatically set.
-p pause after each attached device during the device
probing phase.
-q be quiet, do not write anything to the console
unless automatic boot fails or is disabled. This
option only affects second-stage bootstrap, to
prevent next stages from writing to the console use
in combination with the -m option.
-r use the statically configured default for the
device containing the root file system (see
config(8)). Normally, the root file system is on
the device that the kernel was loaded from.
-s boot into single-user mode; if the console is
marked as "insecure" (see ttys(5)), the root
password must be entered.
-Sspeed
set the speed of the serial console to speed. The
default is 9600 unless it has been overridden by
setting BOOT_COMCONSOLE_SPEED in make.conf(5) and
recompiling and reinstalling the boot blocks.
-v be verbose during device probing (and later).
Use the /boot.config file to set the default configuration options for
the boot block code. See boot.config(5) for more information about the
/boot.config file.
FILES
/boot.config parameters for the boot blocks (optional)
/boot/boot1 first stage bootstrap file
/boot/boot2 second stage bootstrap file
/boot/loader third stage bootstrap
/boot/kernel/kernel
default kernel
/boot/kernel.old/kernel
typical non-default kernel (optional)
DIAGNOSTICS
When disk-related errors occur, these are reported by the second-stage
bootstrap using the same error codes returned by the BIOS, for example
"Disk error 0x1 (lba=0x12345678)". Here is a partial list of these error
codes:
0x1 Invalid argument
0x2 Address mark not found
0x4 Sector not found
0x8 DMA overrun
0x9 DMA attempt across 64K boundary
0xc Invalid media
0x10 Uncorrectable CRC/ECC error
0x20 Controller failure
0x40 Seek failed
0x80 Timeout
NOTE: On older machines, or otherwise where EDD support (disk packet
interface support) is not available, all boot-related files and
structures (including the kernel) that need to be accessed during the
boot phase must reside on the disk at or below cylinder 1023 (as the BIOS
understands the geometry). When a "Disk error 0x1" is reported by the
second-stage bootstrap, it generally means that this requirement has not
been adhered to.
SEE ALSO
ddb(4), boot.config(5), make.conf(5), mount.conf(5), ttys(5),
boot0cfg(8), btxld(8), config(8), efibootmgr(8), efivar(8), gpart(8),
gptboot(8), gptzfsboot(8), halt(8), loader(8), nextboot(8), reboot(8),
shutdown(8), uefi(8), zfsbootcfg(8)
BUGS
The bsdlabel format used by this version of BSD is quite different from
that of other architectures.
Due to space constraints, the keyboard probe initiated by the -P option
is simply a test that the BIOS has detected an "extended" keyboard. If
an "XT/AT" keyboard (with no F11 and F12 keys, etc.) is attached, the
probe will fail.
FreeBSD 13.1-RELEASE-p6 July 11, 2020 FreeBSD 13.1-RELEASE-p6
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