Command Section
BOOT0CFG(8)             FreeBSD 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

     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
             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
             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).
             Each mask bit enables corresponding slice if set to 1.  The least
             significant bit of the mask corresponds to slice 1, the most
             significant bit of the mask corresponds to slice 4.

     -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.  The special string ``PXE'' or a value of 6
             can be used to boot via PXE.

     -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.

     /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 ada0

     To enable just slices 1 and 3 in the menu:

           boot0cfg -m 0x5 ada0

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

           gpart bootcode -b /boot/mbr ada0

     geom(4), boot(8), gpart(8)

     Robert Nordier <[email protected]>

     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.

FreeBSD 11.1-RELEASE-p4         October 1, 2013        FreeBSD 11.1-RELEASE-p4
Command Section