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BOOT(8)			 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 in-
       clude a CD-ROM drive as a boot device.

       Some newer PCs boot using UEFI firmware,	not BIOS.  That	process	is de-
       scribed 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  pro-
       gram,  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 ac-
		       tive  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,  depend-
			     ing  on the state of the -h option	below.	In the
			     dual console  configuration,  both	 the  internal
			     display  and the serial port will become the con-
			     sole 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  de-
			     vice 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 de-
			     vice  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 115200 unless it has been overrid-
			     den   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 er-
       ror 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.

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	13.2			 July 11, 2020			       BOOT(8)

NAME | DESCRIPTION | FILES | DIAGNOSTICS | SEE ALSO | BUGS

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