The
Fx `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
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 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 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 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-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.
FILES
/boot/boot0
The default
`boot0'
image
/boot/boot0sio
Image for serial consoles (COM1,9600,8,N,1,MODEM)
EXIT STATUS
Ex -std
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:
Protection mechanisms in the
geom(4)
subsystem might prevent
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.
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!
