boot0cfg(8)

NAME

boot0cfg - boot manager installation/configuration utility

SYNOPSIS

boot0cfg [-Bv] [-b boot0] [-d drive] [-f file] [-m mask] [-o
options]
         [-s slice] [-t ticks] disk

DESCRIPTION

The FreeBSD `boot0' boot manager permits the operator to se

lect from
which disk and slice an i386 machine (PC) is booted.

Note that what are referred to here as ``slices'' are typi

cally 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 embed

ded table of
defined slices).

The options are:

-B Install the `boot0' boot manager. This option caus

es 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, alterna

tively
/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 ref

erencing 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.

-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.

-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 op

tions may be
specified (with ``no'' prepended as necessary):

packet Use the disk packet (BIOS INT 0x13 exten

sions) 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 man

ager. (The

MBR may be updated to flag slices as `ac

tive', and to
save slice selection information.) This is

the default;
a `noupdate' option causes the MBR to be

treated as readonly.

-s slice

Set the default boot selection to slice. Values be

tween 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 approxi

mately 18.2
ticks per second.)

-v Verbose: display information about the slices de

fined, etc.

FILES

/boot/boot0 The default `boot0' image
/boot/boot0sio Image for serial consoles

(COM1,9600,8,N,1,MODEM)

EXIT STATUS 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

SEE ALSO

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

AUTHORS

Robert Nordier <rnordier@FreeBSD.org>.

BUGS

Protection mechanisms in the geom(4) subsystem might prevent

boot0cfg
from being able to update the MBR on a mounted disk. In

structions for
temporarily disabling these protection mechanisms can be

found in the
geom(4) manpage.

Use of the `packet' option may cause `boot0' to fail, de

pending 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!

BSD February 21, 1999

BSD