.\" $OpenBSD: disklabel.5,v 1.21 2013/08/14 08:39:30 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 $Mdocdate: August 14 2013 $ .Dt DISKLABEL 5 .Os .Sh NAME .Nm disklabel .Nd disk pack label .Sh SYNOPSIS .Fd #include .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. .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 the 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 .Xr disklabel 8 . .Pp Note that when a disk has no real .Bx disklabel the kernel creates a default label so that the disk can be used. This default label will include other partitions found on the disk if they are supported on your architecture. For example, on systems that support .Xr fdisk 8 partitions the default label will also include DOS and Linux partitions. However, these entries are not dynamic, they are fixed at the time .Xr disklabel 8 is run. That means that subsequent changes that affect .Pf non- Ox partitions will not be present in the default label, though you may update them by hand. To see the default label, run .Xr disklabel 8 with the .Fl d flag. You can then run .Xr disklabel 8 with the .Fl e flag and paste any entries you want from the default label into the real one. .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.