disklabel[32,64] utilities - Change the default disklabel program
[dragonfly.git] / sbin / disklabel32 / disklabel32.5
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35.\" @(#)disklabel.5.5 8.1 (Berkeley) 6/5/93
36.\" $FreeBSD: src/sbin/disklabel/disklabel.5,v 1.7.2.4 2002/08/21 18:58:16 trhodes Exp $
7d65714f 37.\" $DragonFly: src/sbin/disklabel/disklabel.5,v 1.6 2008/08/21 21:08:08 thomas Exp $
984263bc 38.\"
7d65714f 39.Dd August 21, 2008
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40.Dt DISKLABEL 5
41.Os
42.Sh NAME
43.Nm disklabel
7d65714f 44.Nd 32 bit disk pack label
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45.Sh SYNOPSIS
46.In sys/disklabel.h
47.Sh DESCRIPTION
48Each disk or disk pack on a system may contain a disk label
49which provides detailed information
50about the geometry of the disk and the partitions into which the disk
51is divided.
52It should be initialized when the disk is formatted,
53and may be changed later with the
54.Xr disklabel 8
55program.
56This information is used by the system disk driver and by the bootstrap
57program to determine how to program the drive
58and where to find the file systems on the disk partitions.
59Additional information is used by the file system in order
60to use the disk most efficiently and to locate important file system information.
61The description of each partition contains an identifier for the partition
62type (standard file system, swap area, etc.).
63The file system updates the in-core copy of the label if it contains
64incomplete information about the file system.
65.Pp
66The label is located in sector number
67.Dv LABELSECTOR
68of the drive, usually sector 0 where it may be found
69without any information about the disk geometry.
70It is at an offset
71.Dv LABELOFFSET
72from the beginning of the sector, to allow room for the initial bootstrap.
73The disk sector containing the label is normally made read-only
74so that it is not accidentally overwritten by pack-to-pack copies
75or swap operations;
76the
77.Dv DIOCWLABEL
78.Xr ioctl 2 ,
79which is done as needed by the
80.Xr disklabel 8
81program.
82.Pp
83A copy of the in-core label for a disk can be obtained with the
84.Dv DIOCGDINFO
85.Xr ioctl 2 ;
86this works with a file descriptor for a block or character (``raw'') device
87for any partition of the disk.
88The in-core copy of the label is set by the
89.Dv DIOCSDINFO
90.Xr ioctl 2 .
91The offset of a partition cannot generally be changed while it is open,
92nor can it be made smaller while it is open.
93One exception is that any change is allowed if no label was found
94on the disk, and the driver was able to construct only a skeletal label
95without partition information.
96Finally, the
97.Dv DIOCWDINFO
98.Xr ioctl 2
99operation sets the in-core label and then updates the on-disk label;
100there must be an existing label on the disk for this operation to succeed.
101Thus, the initial label for a disk or disk pack must be installed
102by writing to the raw disk.
103All of these operations are normally done using
104.Xr disklabel 8 .
105.Pp
5c1eb2a8 106The format of the disk label is specified in
7d65714f 107.In sys/disklabel32.h .
984263bc 108.Sh SEE ALSO
7d65714f 109.Xr disklabel64 5 ,
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110.Xr disktab 5 ,
111.Xr disklabel 8