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

     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
			   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.  See the man page for uart(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.

BSD				 July 4, 2010				   BSD

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