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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.

     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.

     Make note of the fact that /boot.config is read only from the `a' parti-
     tion.  As a result, slices which are missing an `a' parition require user
     intervention during the boot process.

     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
     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 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.

	     bios_drive
		     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' 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 speci-
		     fied 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
		     /kernel.  Symbolic links are not supported (hard links
		     are).

	     -aCcDdghmnPprsv
		     Boot flags:

		     -a    during kernel initialization, ask for the device to
			   mount as the root file system.
		     -C    boot from CDROM.
		     -c    run UserConfig to modify hardware parameters for
			   the loaded kernel.  If the kernel was built with
			   one of USERCONFIG, INTRO_USERCONFIG,
			   VISUAL_USERCONFIG options, remain in UserConfig
			   regardless of any quit commands present in the
			   script.
		     -D    toggle single and dual console configurations.  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.  However, the dual console configuration
			   takes effect only during the boot prompt.  Once the
			   kernel is loaded, the console specified by the -h
			   option becomes the only console.
		     -d    enter the DDB kernel debugger (see ddb(4)) as early
			   as possible in kernel initialization.
		     -g    use the GDB remote debugging protocol.
		     -h    toggle internal and serial consoles.  You can use
			   this to switch console devices.  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.	Alternatively, if you
		     -m    mute the console.
		     -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.
		     -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.
		     -v    be verbose during device probing (and later).

     You may put a BIOS drive number, a controller type, a unit number, a par-
     tition, a kernel file name, and any valid option in /boot.config to set
     defaults.	Enter them in one line just as you type at the `boot:' prompt.

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)

SEE ALSO

     ddb(4), ttys(5), boot0cfg(8), bsdlabel(8), btxld(8), config(8), halt(8),
     loader(8), reboot(8), shutdown(8)

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 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.
     probe will fail.

FreeBSD 5.4		      September 23, 2004		   FreeBSD 5.4

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