boot

BOOT(8)                 BSD/i386 System Manager's Manual                 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).

     By default, a three-stage bootstrap is employed, and control is
     automatically passed from the boot blocks (bootstrap stages one and two) to
     a separate 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.

     However, it is possible to dispense with the third stage altogether, either
     by specifying a kernel name in the boot block parameter file, /boot.config,
     or, unless option -n is set, by hitting a key during a brief pause (while
     one of the characters -, \, |, or / is displayed) before loader(8) is
     invoked.  Booting will also be attempted at stage two, if the third stage
     cannot be loaded.

     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.  The serial port driver sio(4) (but
                           not uart(4)) has a flag (0x20) to override this
                           option.  If that flag is set, the serial port will
                           always be used as the console, regardless of the -h
                           option described here.
                     -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), gpart(8), gptboot(8), halt(8), loader(8), nextboot(8),
     reboot(8), shutdown(8), uefi(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.

BSD                              April 30, 2019                              BSD