*nix Documentation Project
·  Home
 +   man pages
·  Linux HOWTOs
·  FreeBSD Tips
·  *niX Forums

  man pages->OpenBSD man pages -> disklabel (5)              



NAME    [Toc]    [Back]

     disklabel - disk pack label

SYNOPSIS    [Toc]    [Back]

     #include <sys/disklabel.h>

DESCRIPTION    [Toc]    [Back]

     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(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.

     The  label  is  located  in sector number LABELSECTOR of the
drive, usually
     sector 0 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(2),
     which  is done as needed by the disklabel(8) program, allows
     of the label sector.

     A copy of the in-core label for a disk can be obtained  with
     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 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 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
     Thus, the initial label for a disk or disk pack must be  installed by
     writing  to  the  raw disk.  The DIOCGPDINFO 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 DIOCRLDINFO 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 disklabel(8).

     Note that when a disk has no real BSD 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 fdisk(8)
     the default label will also include  DOS  and  Linux  partitions.  However,
     these  entries  are  not dynamic, they are fixed at the time
disklabel(8) is
     run.  That means that subsequent changes  that  affect  nonOpenBSD partitions
  will  not be present in the default label, though you
may update
     them by hand.  To see the default  label,  run  disklabel(8)
with the -d
     flag.   You  can  then run disklabel(8) with the -e flag and
paste any entries
 you want from the default label into the real one.

SEE ALSO    [Toc]    [Back]

     disktab(5), disklabel(8)

CAVEATS    [Toc]    [Back]

     disklabel only supports up to a maximum  of  15  partitions,
`a' through
     `p',  excluding  `c'.  The `c' partition is reserved for the
entire physical
 disk.  By convention, the `a' partition of the boot disk
is the root
     partition,  and  the  `b'  partition of the boot disk is the
swap partition,
     but all other letters can be used in any order for any other
     as desired.

OpenBSD      3.6                          August      6,     2001
[ Back ]
 Similar pages
Name OS Title
disklabel Tru64 Reads and writes a disk pack label and formats disk partitions
disklabel OpenBSD read and write disk pack label
bsdlabel FreeBSD read and write disk pack label
disklabel FreeBSD read and write disk pack label
createlabel Tru64 creates a disk label structure for a disk device
set_usage Tru64 checks whether a disk partition is in use and sets the fstype of the partition in the disk label
disklabel OpenBSD disk label management routines
readdisklabel OpenBSD disk label management routines
writedisklabel OpenBSD disk label management routines
disklabel NetBSD disk label management routines
Copyright © 2004-2005 DeniX Solutions SRL
newsletter delivery service