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 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.
-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-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. 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
<
rnordier@FreeBSD.org>
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.