FreeBSD 7.0 manual page repository

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boot - system bootstrapping procedures



      boot - system bootstrapping procedures


      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.
      By default, a three-stage bootstrap is employed, and control is automati‐
      cally passed from the boot blocks (bootstrap stages one and two) to a
      separate third-stage bootstrap program, loader(8).  This third stage pro‐
      vides more sophisticated control over the booting process than it is pos‐
      sible 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/i386 BOOT
      Default: 0:ad(0,a)/boot/loader
      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 typ‐
      ing 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]
              Specify boot file and flags.
                      The drive number as recognized by the BIOS.  0 for the
                      first drive, 1 for the second drive, etc.
                      The type of controller to boot from.  Note that the con‐
                      troller 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.
                      The partition letter inside the BSD portion of the disk.
                      See bsdlabel(8).  By convention, only partition ‘a’ con‐
                      tains 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.
                      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
                      -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) 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.  See the man page for sio(4) for
                            more details.
                      -m    mute the console to suppress all 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 pre‐
                            vent 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 pass‐
                            word must be entered.
                            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.


      /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
                    default kernel
                    typical non-default kernel (optional)


      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
      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 struc‐
      tures (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.
      ddb(4), boot.config(5), make.conf(5), ttys(5), boot0cfg(8), bsdlabel(8),
      btxld(8), config(8), halt(8), loader(8), nextboot(8), reboot(8),


      The bsdlabel(5) 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.


Based on BSD UNIX
FreeBSD is an advanced operating system for x86 compatible (including Pentium and Athlon), amd64 compatible (including Opteron, Athlon64, and EM64T), UltraSPARC, IA-64, PC-98 and ARM architectures. It is derived from BSD, the version of UNIX developed at the University of California, Berkeley. It is developed and maintained by a large team of individuals. Additional platforms are in various stages of development.