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.\"     @(#)disklabel.5.5	8.1 (Berkeley) 6/5/93
.\" $FreeBSD: src/sbin/disklabel/disklabel.5,v 1.7.2.4 2002/08/21 18:58:16 trhodes Exp $
.\" $DragonFly: src/sbin/disklabel/disklabel.5,v 1.6 2008/08/21 21:08:08 thomas Exp $
.\"
.Dd August 21, 2008
.Dt DISKLABEL32 5
.Os
.Sh NAME
.Nm disklabel32
.Nd 32 bit disk pack label
.Sh SYNOPSIS
.In 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 disklabel32 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 file systems on the disk partitions.
Additional information is used by the file system in order
to use the disk most efficiently and to locate important file system information.
The description of each partition contains an identifier for the partition
type (standard file system, swap area, etc.).
The file system updates the in-core copy of the label if it contains
incomplete information about the file system.
.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
.Xr disklabel32 8
program.
.Pp
A copy of the in-core label for a disk can be obtained with the
.Dv DIOCGDINFO
.Xr ioctl 2 ;
this works with a file descriptor for a block or character (``raw'') device
for any partition of the disk.
The in-core copy of the label is set by the
.Dv DIOCSDINFO
.Xr ioctl 2 .
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.
Finally, the
.Dv DIOCWDINFO
.Xr ioctl 2
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.
All of these operations are normally done using
.Xr disklabel32 8 .
.Pp
The format of the disk label is specified in
.In sys/disklabel32.h .
.Sh SEE ALSO
.Xr disklabel64 5 ,
.Xr disktab 5 ,
.Xr disklabel32 8