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

     boot0cfg -- boot manager installation/configuration utility

     boot0cfg [-Bv] [-b boot0] [-d drive] [-f file] [-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.

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

     -b boot0
             Specify which `boot0' image to use.  The default is /boot/boot0.

     -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

     -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.

     -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 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

             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.  This would normally be used in conjunction
             with the `noupdate' option.

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

     /boot/boot0  The default `boot0' image

     The following is an example of a typical usage of the boot0cfg utility to
     affect the next boot:

           boot0cfg -s 2 ad0

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

     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 MBR
     to be written to the wrong disk.  Be careful!

FreeBSD 4.10                   February 21, 1999                  FreeBSD 4.10


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