boot0cfg man page on FreeBSD

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BOOT0CFG(8)		  BSD System Manager's Manual		   BOOT0CFG(8)

     boot0cfg — boot manager installation/configuration utility

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

     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 config‐

     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
     defined 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 signals 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

     -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 writ‐
	     ten 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
	     location 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
	     between 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 default 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-

     -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.

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

	   sysctl kern.geom.debugflags=0x10

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

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

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

     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

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

     Robert Nordier ⟨⟩.

     Use of the ‘packet’ option may cause ‘boot0’ to fail, depending on the
     nature 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
     content.  Be careful.

BSD			       January 13, 2009				   BSD

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