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disklabel(4)


NAME

  disklabel - Disk pack label


SYNOPSIS

  #include <sys/disklabel.h>


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 disklabel 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.

  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
  containing 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
  modification 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.


SEE ALSO

  Files: disktab(4)

  Commands: disklabel(8)

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