freebsd/usr.sbin/boot0cfg/boot0cfg.8

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.Dd October 1, 2013
.Dt BOOT0CFG 8
.Os
.Sh NAME
.Nm boot0cfg
.Nd boot manager installation/configuration utility
.Sh SYNOPSIS
.Nm
.Op Fl Bv
.Op Fl b Ar boot0
.Op Fl d Ar drive
.Op Fl e Ar bell character
.Op Fl f Ar file
.Op Fl i Ar volume-id
.Op Fl m Ar mask
.Op Fl o Ar options
.Op Fl s Ar slice
.Op Fl t Ar ticks
.Ar disk
.Sh DESCRIPTION
The
.Fx
.Sq boot0
boot manager permits the operator to select from which disk and
slice an i386 machine (PC) is booted.
.Pp
Note that what are referred to here as
.Dq slices
are typically called
.Dq partitions
in
.No non- Ns Bx
documentation relating to the PC.
Typically, only non-removable disks are sliced.
.Pp
The
.Nm
utility optionally installs the
.Sq boot0
boot manager on the specified
.Ar disk ;
and allows various operational parameters to be configured.
.Pp
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).
.Pp
The options are:
.Bl -tag -width indent
.It Fl B
Install the
.Sq boot0
boot manager.
This option causes MBR code to be replaced, without
affecting the embedded slice table.
.It Fl b Ar boot0
Specify which
.Sq boot0
image to use.
The default is
.Pa /boot/boot0
which will use the video card as output, alternatively
.Pa /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.)
.It Fl d Ar drive
Specify the drive number used by the PC BIOS in referencing the drive
which contains the specified
.Ar 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.
.It Fl e Ar bell character
Set the character to be printed in case of input error.
.It Fl f Ar file
Specify that a backup copy of the preexisting MBR should be written to
.Ar file .
This file is created if it does not exist, and replaced if it does.
.It Fl i Ar 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.
.It Fl m Ar mask
Specify slices to be enabled/disabled, where
.Ar 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.
.It Fl o Ar options
A comma-separated string of any of the following options may be
specified (with
.Dq no
prepended as necessary):
.Bl -tag -width indent
.It 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
.Sq packet .
.It setdrv
Forces the drive containing the disk to be referenced using drive
number definable by means of the -d option.
The default is
.Sq nosetdrv .
.It update
Allow the MBR to be updated by the boot manager.
(The MBR may be updated to flag slices as
.Sq active ,
and to save slice selection information.)
This is the default; a
.Sq noupdate
option causes the MBR to be treated as read-only.
.El
.It Fl s Ar slice
Set the default boot selection to
.Ar 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
.Dq PXE
or a value of 6 can be used to boot via PXE.
.It Fl t Ar ticks
Set the timeout value to
.Ar ticks .
(There are approximately 18.2 ticks per second.)
.It Fl v
Verbose: display information about the slices defined, etc.
.El
.Sh FILES
.Bl -tag -width /boot/boot0sio -compact
.It Pa /boot/boot0
The default
.Sq boot0
image
.It Pa /boot/boot0sio
Image for serial consoles (COM1,9600,8,N,1,MODEM)
.El
.Sh EXIT STATUS
.Ex -std
.Sh EXAMPLES
To boot slice 2 on the next boot:
.Pp
.Dl "boot0cfg -s 2 ada0"
.Pp
To enable just slices 1 and 3 in the menu:
.Pp
.Dl "boot0cfg -m 0x5 ada0"
.Pp
To go back to non-interactive booting, use
.Xr gpart 8
to install the default MBR:
.Pp
.Dl "gpart bootcode -b /boot/mbr ada0"
.Sh SEE ALSO
.Xr geom 4 ,
.Xr boot 8 ,
.Xr gpart 8
.Sh AUTHORS
.An Robert Nordier Aq Mt rnordier@FreeBSD.org
.Sh BUGS
Use of the
.Sq packet
option may cause
.Sq boot0
to fail, depending on the nature of BIOS support.
.Pp
Use of the
.Sq 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.