disklabel - read and write disk pack label
disklabel -r disk
disklabel -w [ -r ] disk disktype [ packid ]
disklabel -e [ -r ] disk
disklabel -R [ -r ] disk protofile
disklabel [ -NW ] disk
disklabel -B [ -b boot ] disk [ disktype ]
disklabel -w -B [ -b boot ] disk disktype [ packid ]
disklabel -R -B [ -b boot ] disk protofile [ disktype ]
Disklabel can be used to install, examine or modify the label on a disk drive or pack.
When writing the label, it can be used to change the drive identification, the disk parti-
tions on the drive, or to replace a damaged label. On some systems, disklabel can be used
to install bootstrap code as well. There are several forms of the command that read (dis-
play), install or edit the label on a disk. Each form has an additional option, -r, which
causes the label to be read from or written to the disk directly, rather than going
through the system's in-core copy of the label. This option may allow a label to be
installed on a disk without kernel support for a label, such as when labels are first
installed on a system; it must be used when first installing a label on a disk. The spe-
cific effect of -r is described under each command. The read and install forms also sup-
port the -B option to install bootstrap code. These variants are described later.
The first form of the command (read) is used to examine the label on the named disk drive
(e.g. ra0 or /dev/rra0a). It will display all of the parameters associated with the drive
and its partition layout. Unless the -r flag is given, the kernel's in-core copy of the
label is displayed; if the disk has no label, or the partition types on the disk are
incorrect, the kernel may have constructed or modified the label. If the -r flag is
given, the label from the raw disk will be displayed rather than the in-core label.
The second form of the command, with the -w flag, is used to write a standard label on the
designated drive. The required arguments to disklabel are the drive to be labelled (e.g.
sd0), and the drive type as described in the disktab(5) file. The drive parameters and
partitions are taken from that file. If different disks of the same physical type are to
have different partitions, it will be necessary to have separate disktab entries describ-
ing each, or to edit the label after installation as described below. The optional argu-
ment is a pack identification string, up to 16 characters long. The pack id must be
quoted if it contains blanks. If the -r flag is given, the disk sectors containing the
label and bootstrap will be written directly. A side-effect of this is that any existing
bootstrap code will be overwritten and the disk rendered unbootable. If -r is not speci-
fied, the existing label will be updated via the in-core copy and any bootstrap code will
be unaffected. If the disk does not already have a label, the -r flag must be used. In
either case, the kernel's in-core label is replaced.
An existing disk label may be edited by using the -e flag. The label is read from the in-
core kernel copy, or directly from the disk if the -r flag is also given. The label is
formatted and then supplied to an editor for changes. If no editor is specified in an
EDITOR environment variable, vi(1) is used. When the editor terminates, the formatted
label is reread and used to rewrite the disk label. Existing bootstrap code is unchanged
regardless of whether -r was specified.
With the -R flag, disklabel is capable of restoring a disk label that was formatted in a
prior operation and saved in an ascii file. The prototype file used to create the label
should be in the same format as that produced when reading or editing a label. Comments
are delimited by # and newline. As with -w , any existing bootstrap code will be clob-
bered if -r is specified and will be unaffected otherwise.
The -NW flags for disklabel explicitly disallow and allow, respectively, writing of the
pack label area on the selected disk.
The final three forms of disklabel are used to install bootstrap code on machines where
the bootstrap is part of the label. The bootstrap code is comprised of one or two boot
programs depending on the machine. The -B option is used to denote that bootstrap code is
to be installed. The -r flag is implied by -B and never needs to be specified. The name
of the boot program(s) to be installed can be selected in a variety of ways. First, the
names can be specified explicitly via the -b flag. If the name is not explicitly given,
standard boot blocks will be used. The boot programs are located in /mdec. The names of
the program is taken from the ``b0'' parameter of the disktab(5) entry for the disk if
disktype was given and its disktab entry exists and includes that parameter. Otherwise,
the boot program name is derived from the name of the disk. These name is of the form
basenameuboot ; for example, /usr/mdec/rauboot if the disk device is ra0.
The first of the three boot-installation forms is used to install bootstrap code without
changing the existing label. It is essentially a read command with respect to the disk
label itself and all options are related to the specification of the boot program as
described previously. The final two forms are analogous to the basic write and restore
versions except that they will install bootstrap code in addition to a new label.
Display the in-core label for ra0 as obtained via /dev/rra0a.
disklabel -w -r /dev/rra0a ra81x foo
Create a label for sd0 based on information for ``ra81x'' found in /etc/disktab. Any
existing bootstrap code will be clobbered.
disklabel -e -r ra0
Read the on-disk label for ra0, edit it and reinstall in-core as well as on-disk. Exist-
ing bootstrap code is unaffected.
disklabel -R ra0 mylabel
Restore the on-disk and in-core label for sd0 from information in mylabel. Existing boot-
strap code is unaffected.
disklabel -B ra0
Install a new bootstrap on ra0. The boot code comes from /mdec/rauboot. On-disk and in-
core labels are unchanged.
disklabel -w -B /dev/rra0a -b newboot ra81x
Install a new label and bootstrap. The label is derived from disktab information for
``ra81x'' and installed both in-core and on-disk. The bootstrap code comes from the file
The kernel device drivers will not allow the size of a disk partition to be decreased or
the offset of a partition to be changed while it is open. Some device drivers create a
label containing only a single large partition if a disk is unlabeled; thus, the label
must be written to the ``a'' partition of the disk while it is open. This sometimes
requires the desired label to be set in two steps, the first one creating at least one
other partition, and the second setting the label on the new partition while shrinking the
When a disk name is given without a full pathname, the constructed device name uses the
``a'' partition on the tahoe and pdp-11 the ``c'' partition on all others.
3rd Berkeley Distribution April 21, 1995 DISKLABEL(8)