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DISKLABEL(8)            FreeBSD System Manager's Manual           DISKLABEL(8)

     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 boot1 [-s boot2]] disk [disktype]
     disklabel -w -B [-b boot1 [-s boot2]] disk disktype [packid]
     disklabel -R -B [-b boot1 [-s boot2]] 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 partitions 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
     (display), 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 specific effect of -r is described under each command.  The
     read and install forms also support 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. da0 or /dev/rda0c).  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 labeled (e.g. da0), 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 describing each, or to edit the label after installation
     as described below.  The optional argument 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 specified, 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.

     For a virgin disk that is not known to disktab(5), disktype can be
     specified as ``auto''.  In this case, the driver is requested to produce
     a virgin label for the disk.  This might or might not be successful,
     depending on whether the driver for the disk is able to get the required
     data without reading anything from the disk at all.  It will likely
     succeed for all SCSI disks, most IDE disks, and vnode devices.  Writing a
     label to the disk is the only supported operation, and the disk itself
     must be provided as the canonical name, i.e. not as a full path name.

     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 clobbered
     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 and -s flags.  On
     machines with only a single level of boot program, -b is the name of that
     program.  For machines with a two-level bootstrap, -b indicates the
     primary boot program and -s the secondary boot program.  If the names are
     not explicitly given, standard boot programs will be used.  The boot
     programs are located in /boot.  The names of the programs are taken from
     the ``b0'' and ``b1'' parameters of the disktab(5) entry for the disk if
     disktype was given and its disktab entry exists and includes those
     parameters.  Otherwise, the default boot image names are used, these
     being: /boot/boot1 and /boot/boot2 for the standard stage1 and stage2
     boot images (details may vary on architectures like the Alpha, where only
     a single-stage boot is used).

     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.


           disklabel da0

     Display the in-core label for da0 as obtained via /dev/rda0c.

           disklabel -w -r /dev/rda0c da2212 foo

     Create a label for da0 based on information for ``da2212'' found in
     /etc/disktab.  Any existing bootstrap code will be clobbered.

           disklabel -e -r da0

     Read the on-disk label for da0, edit it and reinstall in-core as well as
     on-disk.  Existing bootstrap code is unaffected.

           disklabel -r -w da0 auto

     Try to auto-detect the required information from da0, and write a new
     label to the disk.  Use another disklabel -e command to edit the
     partitioning and file system information.

           disklabel -R da0 mylabel

     Restore the on-disk and in-core label for da0 from information in
     mylabel.  Existing bootstrap code is unaffected.

           disklabel -B da0

     Install a new bootstrap on da0.  The boot code comes from /boot/boot1 and
     possibly /boot/boot2.  On-disk and in-core labels are unchanged.

           disklabel -w -B /dev/rda0c -b newboot da2212

     Install a new label and bootstrap.  The label is derived from disktab
     information for ``da2212'' and installed both in-core and on-disk.  The
     bootstrap code comes from the file /boot/newboot.

     disklabel(5), disktab(5)

     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 ``a'' partition.

     On some machines the bootstrap code may not fit entirely in the area
     allocated for it by some filesystems.  As a result, it may not be
     possible to have filesystems on some partitions of a ``bootable'' disk.
     When installing bootstrap code, disklabel checks for these cases.  If the
     installed boot code would overlap a partition of type FS_UNUSED it is
     marked as type FS_BOOT.  The newfs(8) utility will disallow creation of
     filesystems on FS_BOOT partitions.  Conversely, if a partition has a type
     other than FS_UNUSED or FS_BOOT, disklabel will not install bootstrap
     code that overlaps it.

     When a disk name is given without a full pathname, the constructed device
     name uses the ``a'' partition on the Tahoe, the ``c'' partition on all

     For the i386 architecture, the primary bootstrap sector contains an
     embedded fdisk table.  Disklabel takes care to not clobber it when
     installing a bootstrap only (-B), or when editing an existing label (-e),
     but it unconditionally writes the primary bootstrap program onto the disk
     for -w or -R, thus replacing the fdisk table by the dummy one in the
     bootstrap program.  This is only of concern if the disk is fully
     dedicated, so that the BSD disklabel starts at absolute block 0 on the

BSD 4.2                         April 19, 1994                         BSD 4.2


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