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.\" $OpenBSD: disklabel.5,v 1.16 2003/06/21 23:14:23 jmc Exp $
.\" $NetBSD: disklabel.5,v 1.3 1995/03/18 14:54:36 cgd Exp $
.\"
.\" Copyright (c) 1987, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" Symmetric Computer Systems.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)disklabel.5.5 8.1 (Berkeley) 6/5/93
.\"
.Dd August 6, 2001
.Dt DISKLABEL 5
.Os
.Sh NAME
.Nm disklabel
.Nd disk pack label
.Sh SYNOPSIS
.Fd #include <sys/disklabel.h>
.Sh DESCRIPTION
Each disk or disk pack on a system may contain a disk label
which provides detailed information
about the geometry of the disk and the partitions into which the disk
is divided.
It should be initialized when the disk is formatted,
and may be changed later with the
.Xr disklabel 8
program.
This information is used by the system disk driver and by the bootstrap
program to determine how to program the drive
and where to find the filesystems on the disk partitions.
Additional information is used by the filesystem in order
to use the disk most efficiently and to locate important filesystem information.
The description of each partition contains an identifier for the partition
type (standard filesystem, swap area, etc.).
The filesystem updates the in-core copy of the label if it contains
incomplete information about the filesystem.
.Pp
The label is located in sector number
.Dv LABELSECTOR
of the drive, usually sector 0 where it may be found
without any information about the disk geometry.
It is at an offset
.Dv LABELOFFSET
from the beginning of the sector, to allow room for the initial bootstrap.
The disk sector containing the label is normally made read-only
so that it is not accidentally overwritten by pack-to-pack copies
or swap operations;
the
.Dv DIOCWLABEL
.Xr ioctl 2 ,
which is done as needed by the
.Em disklabel
program, allows modification of the label sector.
.Pp
A copy of the in-core label for a disk can be obtained with the
.Dv DIOCGDINFO
.Em ioctl ;
this works with a file descriptor for a block or character
.Pq Dq raw
device for any partition of the disk.
The in-core copy of the label is set by the
.Dv DIOCSDINFO
.Em ioctl .
The offset of a partition cannot generally be changed while it is open,
nor can it be made smaller while it is open.
One exception is that any change is allowed if no label was found
on the disk, and the driver was able to construct only a skeletal label
without partition information.
The
.Dv DIOCWDINFO
.Em ioctl
operation sets the in-core label and then updates the on-disk label;
there must be an existing label on the disk for this operation to succeed.
Thus, the initial label for a disk or disk pack must be installed
by writing to the raw disk.
The
.Dv DIOCGPDINFO
.Em ioctl
operation gets the default label for a disk.
This simulates the case
where there is no physical label on the disk itself and can be used to
see the label the kernel would construct in that case.
The
.Dv DIOCRLDINFO
.Em ioctl
operation causes the kernel to update its copy of label based on the
physical label on the disk.
It can be used when the on-disk version
of the label was changed directly or, if there is no physical label,
to update the kernel's skeletal label if some variable affecting label
generation has changed (e.g. the fdisk partition table).
All of these operations are normally done using
.Em disklabel .
.Sh SEE ALSO
.Xr disktab 5 ,
.Xr disklabel 8
.Sh CAVEATS
.Nm
only supports up to a maximum of 15 partitions,
.Sq a
through
.Sq p ,
excluding
.Sq c .
The
.Sq c
partition is reserved for the entire physical disk.
By convention, the
.Sq a
partition of the boot disk is the root partition, and the
.Sq b
partition of the boot disk is the swap partition,
but all other letters can be used in any order for any other
partitions as desired.
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