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disklabel(4)							 disklabel(4)

  disklabel - Disk pack	label


  #include <&lt;sys/disklabel.h>&gt;

  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	for-
  matted, and may be changed later with	the disklabel program.	This informa-
  tion 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	sys-
  tem updates the in-core copy of the label if it contains incomplete infor-
  mation about the file	system.

  The label is located in sector number	LABELSECTOR of the drive, usually
  sector 0 (zero) where	it may be found	without	any information	about the
  disk geometry.  It is	at an offset LABELOFFSET from the beginning of the
  sector, to allow room	for the	initial	bootstrap.  The	disk sector contain-
  ing the label	is normally made read-only so that it is not accidentally
  overwritten by pack-to-pack copies or	swap operations; the DIOCWLABEL
  ioctl, which is done as needed by the	disklabel program, allows modifica-
  tion of the label sector.

  A copy of the	in-core	label for a disk can be	obtained with the DIOCGDINFO
  ioctl; 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 DIOCSDINFO ioctl.  The	offset of a partition cannot generally be
  changed, nor 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 DIOCWDINFO 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.	 All of	these operations are
  normally done	using the disklabel program.


  Files: disktab(4)

  Commands: disklabel(8)