home | help 
BOOT0CFG(8)		     System Manager's Manual		     BOOT0CFG(8)

NAME
     boot0cfg -- boot manager installation/configuration utility

SYNOPSIS
     boot0cfg [-Bv] [-b boot0] [-d drive] [-e bell character] [-f file]
	      [-i volume-id] [-m mask] [-o options] [-s slice] [-t ticks] disk

DESCRIPTION
     The  FreeBSD `boot0' boot manager permits the operator to select from which
     disk and slice an i386 machine (PC) is booted.

     Note that what are referred  to  here  as	"slices"  are  typically  called
     "partitions"  in non-BSD documentation relating to the PC.  Typically, only
     non-removable disks are sliced.

     The boot0cfg utility optionally installs the `boot0' boot	manager  on  the
     specified disk; and allows various operational parameters to be configured.

     On  PCs,  a  boot	manager  typically occupies sector 0 of a disk, which is
     known as the Master Boot Record (MBR).  The  MBR  contains  both  code  (to
     which  control is passed by the PC BIOS) and data (an embedded table of de-
     fined slices).

     The options are:

     -B      Install the `boot0' boot manager.	This option causes MBR	code  to
	     be replaced, without affecting the embedded slice table.

     -b boot0
	     Specify  which  `boot0'  image  to use.  The default is /boot/boot0
	     which  will  use  the   video   card   as	 output,   alternatively
	     /boot/boot0sio  can be used for output to the COM1 port.  (Be aware
	     that nothing will be output to the COM1 port unless the modem  sig-
	     nals DSR and CTS are active.)

     -d drive
	     Specify  the  drive  number  used by the PC BIOS in referencing the
	     drive which contains the specified disk.  Typically  this	will  be
	     0x80  for the first hard drive, 0x81 for the second hard drive, and
	     so on; however any integer between 0 and 0xff is acceptable here.

     -e bell character
	     Set the character to be printed in case of input error.

     -f file
	     Specify that a backup copy of the preexisting MBR should be written
	     to file.  This file is created if it does not exist,  and	replaced
	     if it does.

     -i volume-id
	     Specifies	a volume-id (in the form XXXX-XXXX) to be saved at loca-
	     tion 0x1b8 in the MBR. This information is sometimes used by NT, XP
	     and Vista to identify the disk drive. The option is only compatible
	     with version 2.00 of the 512-byte boot block.

     -m mask
	     Specify slices to be enabled/disabled, where mask is an integer be-
	     tween 0 (no slices enabled) and 0xf (all four slices enabled).

     -o options
	     A comma-separated string of any of the  following	options  may  be
	     specified (with "no" prepended as necessary):

	     packet  Use  the  disk packet (BIOS INT 0x13 extensions) interface,
		     as opposed to the legacy (CHS) interface, when  doing  disk
		     I/O.  This allows booting above cylinder 1023, but requires
		     specific BIOS support.  The default is `packet'.

	     setdrv  Forces the drive containing the disk to be referenced using
		     drive  number definable by means of the -d option.  The de-
		     fault is `nosetdrv'.

	     update  Allow the MBR to be updated by the boot manager.  (The  MBR
		     may  be  updated  to  flag  slices as `active', and to save
		     slice selection  information.)   This  is	the  default;  a
		     `noupdate'  option  causes  the  MBR to be treated as read-
		     only.

     -s slice
	     Set the default boot selection to slice.  Values between  1  and  4
	     refer  to slices; a value of 5 refers to the option of booting from
	     a second disk.

     -t ticks
	     Set the timeout value to  ticks.	(There	are  approximately  18.2
	     ticks per second.)

     -v      Verbose: display information about the slices defined, etc.

NOTE
     Protection  mechanisms in the geom(4) subsystem might prevent boot0cfg from
     being able to update the MBR on a mounted disk.  Instructions for temporar-
     ily disabling these protection mechanisms can be found in the geom(4)  man-
     page. Specifically, do a

	   sysctl kern.geom.debugflags=0x10

     to allow writing to the MBR, and restore it to 0 afterwards.

FILES
     /boot/boot0     The default `boot0' image
     /boot/boot0sio  Image for serial consoles (COM1,9600,8,N,1,MODEM)

EXIT STATUS
     The boot0cfg utility exits 0 on success, and >0 if an error occurs.

EXAMPLES
     To boot slice 2 on the next boot:

	   boot0cfg -s 2 ad0

     To enable just slices 1 and 2 in the menu:

	   boot0cfg -m 0x3 ad0

     To  go back to non-interactive booting, use fdisk(8) to install the default
     MBR:

	   fdisk -B ad0

SEE ALSO
     geom(4), boot(8), fdisk(8)

AUTHORS
     Robert Nordier <rnordier@FreeBSD.org>.

BUGS
     Use of the `packet' option may cause `boot0' to fail, depending on the  na-
     ture of BIOS support.

     Use of the `setdrv' option with an incorrect -d operand may cause the boot0
     code  to  write  the MBR to the wrong disk, thus trashing its previous con-
     tent.  Be careful.

FreeBSD 7.2			January 13, 2009		     BOOT0CFG(8)
home | help