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

NAME
     disklabel -- read and write disk pack label

SYNOPSIS
     disklabel [-r] [-f] disk
     disklabel -w [-r] [-n] [-f] disk disktype/auto [packid]
     disklabel -e [-r] [-n] [-f] disk
     disklabel -R [-r] [-n] [-f] disk protofile
     disklabel [-NW] [-f] disk

     disklabel -B [-b boot1 -s boot2] [-f] disk [disktype/auto]
     disklabel -w -B [-n] [-b boot1 -s boot2] [-f] disk disktype/auto [packid]
     disklabel -R -B [-n] [-b boot1 -s boot2] [-f] disk protofile
               [disktype/auto]

DESCRIPTION
     The disklabel utility installs, examines or modifies the label on a disk
     drive or pack, or a regular file representing a disk image.  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.  There are sev-
     eral forms of the command that read (display), install or edit the label
     on a disk.  In addition, disklabel can install bootstrap code.

   Raw or in-core label
     The disk label resides close to or at the beginning of each disk slice.
     For faster access, the kernel maintains a copy in core at all times.  By
     default, most disklabel access the in-core copy of the label.  To access
     the raw (on-disk) copy, use the -r option.  This option allows 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.  Note that -r is implicit when disklabel operates on
     a regular file ( -f) option.

   Disk device name
     Unless the -f option is used, all disklabel forms require a disk device
     name, which should always be the raw device name representing the disk or
     slice.  For example da0 represents the entire disk regardless of any DOS
     partitioning, and da0s1 represents a slice.  Some devices, most notably
     ccd, require that the ``whole-disk'' (or ``c'') partition be specified.
     For example ccd0c.  You do not have to include the /dev/ path prefix when
     specifying the device.  The disklabel utility will automatically prepend
     it.  If the -f option is used, disklabel will interpret the disk name
     (which must be an absolute pathname) as the name of a regular file repre-
     senting a disk image, and will work on it instead of a device.  Note that
     when it operates on a regular file, the -r option becomes implicit as the
     kernel will not cache disklabel info.

   Reading the disk label
     To examine the label on a disk drive, use disklabel without options:

     disklabel [-r] disk

     disk represents the raw disk in question, and may be in the form da0 or
     /dev/da0c.  It will display all of the parameters associated with the
     drive and its partition layout.  Unless the -r flag is given, the ker-
     nel'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, disklabel
     reads the label from the raw disk and displays it.  Both versions are
     usually identical except in the case where a label has not yet been ini-
     tialized or is corrupt.

   Writing a standard label
     To write a standard label, use the form

     disklabel -w [-r] [-n] disk disktype/auto [packid]

     disklabel -w [-r] [-n] disk auto

     The required arguments to disklabel are the drive to be labeled 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 identi-
     fication string, up to 16 characters long.  The pack id must be quoted if
     it contains blanks.

     If the -n flag is given, no data will be written to the device, and
     instead the disklabel that would have been written will be printed to
     stdout.

     If the -r flag is given, the disk sectors containing the label and boot-
     strap will be written directly.  A side-effect of this is that any exist-
     ing bootstrap code will be overwritten and the disk rendered unbootable.
     See the boot options below for a method of writing the label and the
     bootstrap at the same time.  If -r is not specified, the existing label
     will be updated via the in-core copy and any bootstrap code will be unaf-
     fected.  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 speci-
     fied 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 suc-
     ceed for all SCSI disks, most IDE disks, vnode devices, and regular
     files.  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 (full pathnames are still required when operating with
     regular files and the -f option).

     For most harddisks, a label based on percentages for most partitions (and
     one partition with a size of `*') will produce a reasonable configura-
     tion.

     PC-based systems have special requirements in order for the BIOS to prop-
     erly recognize a FreeBSD disklabel.  Older systems may require what is
     known as a ``dangerously dedicated'' disklabel, which creates a fake DOS
     partition to work around problems older BIOSes have with modern disk
     geometries.  On newer systems you generally want to create a normal DOS
     partition using fdisk and then create a FreeBSD disklabel within that
     slice.  This is described later on in this page.

     Installing a new disklabel does not in of itself allow your system to
     boot a kernel using that label.  You must also install boot blocks, which
     is described later on in this manual page.

   Editing an existing disk label
     To edit an existing disk label, use the form

     disklabel -e [-r] [-n] disk

     This command reads the label from the in-core kernel copy, or directly
     from the disk if the -r flag is also specified.  The label is written to
     a file in ASCII 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 label file is used to rewrite the disk label.
     Existing bootstrap code is unchanged regardless of whether -r was speci-
     fied.  If -n is specified, no data will be written to the device, and
     instead the disklabel that would have been written will be printed to
     stdout.  This is useful to see how a partitioning scheme will work out
     for a specific disk.

   Restoring a disk label from a file
     To restore a disk label from a file, use the form

     disklabel -R [-r] [-n] disk protofile

     disklabel is capable of restoring a disk label that was previously saved
     in a file in ASCII format.  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 when writing a new
     label, any existing bootstrap code will be clobbered if -r is specified
     and will be unaffected otherwise.  See the boot options below for a
     method of restoring the label and writing the bootstrap at the same time.
     If -n is used, no data will be written to the device, and instead the
     disklabel that would have been written will be printed to stdout.  This
     is useful to see how a partitioning scheme will work out for a specific
     disk.

   Enabling and disabling writing to the disk label area
     By default, it is not possible to write to the disk label area at the
     beginning of a disk.  The disk driver arranges for write(2) and similar
     system calls to return EROFS on any attempt to do so.  If you need to
     write to this area (for example, to obliterate the label), use the form

     disklabel -W disk

     To disallow writing to the label area after previously allowing it, use
     the command

     disklabel -N disk

   Installing bootstraps
     The final three forms of disklabel are used to install bootstrap code.
     If you are creating a ``dangerously-dedicated'' slice for compatibility
     with older PC systems, you generally want to specify the raw disk name
     such as da0.  If you are creating a label within an existing DOS slice,
     you should specify the partition name such as da0s1a.  Making a slice
     bootable can be tricky.  If you are using a normal DOS slice you typi-
     cally install (or leave) a standard MBR on the base disk and then install
     the FreeBSD bootblocks in the slice.

     disklabel -B [-b boot1 -s boot2] disk [disktype]

     This form installs the bootstrap only.  It does not change the disk
     label.  You should never use this command on a base disk unless you
     intend to create a ``dangerously-dedicated'' disk, such as da0.  This
     command is typically run on a slice such as da0s1.

     disklabel -w -B [-n] [-b boot1 -s boot2] disk disktype [packid]

     This form corresponds to the ``write label'' command described above.  In
     addition to writing a new volume label, it also installs the bootstrap.
     If run on a base disk this command will create a
     ``dangerously-dedicated'' label.  This command is normally run on a slice
     rather than a base disk.  If -n is used, no data will be written to the
     device, and instead the disklabel that would have been written will be
     printed to stdout.

     disklabel -R -B [-n] [-b boot1 -s boot2] disk protofile [disktype]

     This form corresponds to the ``restore label'' command described above.
     In addition to restoring the volume label, it also installs the boot-
     strap.  If run on a base disk this command will create a
     ``dangerously-dedicated'' label.  This command is normally run on a slice
     rather than a base disk.

     The bootstrap commands always access the disk directly, so it is not nec-
     essary to specify the -r flag.  If -n is used, no data will be written to
     the device, and instead the disklabel that would have been written will
     be printed to stdout.

     The bootstrap code is comprised of two boot programs.  Specify the name
     of the boot programs to be installed in one of these ways:

     1.   Specify the names explicitly with the -b and -s flags.  -b indicates
          the primary boot program and -s the secondary boot program.  The
          boot programs are located in /boot.

     2.   If the -b and -s flags are not specified, but disktype was speci-
          fied, the names of the programs are taken from the ``b0'' and ``b1''
          parameters of the disktab(5) entry for the disk if the disktab entry
          exists and includes those parameters.

     3.   Otherwise, the default boot image names are used: /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).

   Initializing/Formatting a bootable disk from scratch
     To initialize a disk from scratch the following sequence is recommended.
     Please note that this will wipe everything that was previously on the
     disk, including any non-FreeBSD slices.

     1.   Use fdisk(8) to initialize the hard disk, and create a slice table,
          referred to as the ``partition table'' in DOS.

     2.   Use disklabel to define partitions on FreeBSD slices created in the
          previous step.

     3.   Finally use newfs(8) to create file systems on new partitions.

     A typical partitioning scheme would be to have an `a' partition of
     approximately 128MB to hold the root file system, a `b' partition for
     swap, a `d' partition for /var (usually 128MB), an `e' partition for
     /var/tmp (usually 128MB), an `f' partition for /usr (usually around 2GB),
     and finally a `g' partition for /home (usually all remaining space).
     Your mileage may vary.

     fdisk -BI da0

     disklabel -w -B da0s1 auto

     disklabel -e da0s1

FILES
     /boot/boot    Default boot image.
     /etc/disktab  Disk description file.

SAVED FILE FORMAT
     The disklabel utility uses an ASCII version of the label when examining,
     editing, or restoring a disk label.  The format is:

         # /dev/da1c:
         type: SCSI
         disk: da0s1
         label:
         flags:
         bytes/sector: 512
         sectors/track: 51
         tracks/cylinder: 19
         sectors/cylinder: 969
         cylinders: 1211
         sectors/unit: 1173930
         rpm: 3600
         interleave: 1
         trackskew: 0
         cylinderskew: 0
         headswitch: 0           # milliseconds
         track-to-track seek: 0  # milliseconds
         drivedata: 0

         8 partitions:
         #        size   offset    fstype   [fsize bsize bps/cpg]
           a:    81920        0    4.2BSD     1024  8192    16   # (Cyl.    0 - 84*)
           b:   160000    81920      swap                        # (Cyl.   84* - 218*)
           c:  1173930        0    unused        0     0         # (Cyl.    0 - 1211*)
           h:   962010   211920     vinum                        # (Cyl.  218*- 1211*)

     Lines starting with a `#' mark are comments.  Most of the other specifi-
     cations are no longer used.  The ones which must still be set correctly
     are:

     label is an optional label, set by the packid option when writing a
     label.

     flags may be removable, ecc or badsect.  removable is set for removable
     media drives, but no current FreeBSD driver evaluates this flag.  ecc is
     no longer supported; badsect specifies that the drive can perform bad
     sector remapping.

     sectors/unit describes the total size of the disk.  This value must be
     correct.

     the partition table is the UNIX partition table, not the DOS partition
     table described in fdisk(8).

     The partition table can have up to 8 entries.  It contains the following
     information:

     #       The partition identifier is a single letter in the range `a' to
             `h'.  By convention, partition `c' is reserved to describe the
             entire disk.

     size    The size of the partition in sectors, K (kilobytes - 1024), M
             (megabytes - 1024*1024), G (gigabytes - 1024*1024*1024), % (per-
             centage of free space after removing any fixed-size partitions
             other than partition `c'), or * (all remaining free space after
             fixed-size and percentage partitions).  For partition `c', a size
             of * indicates the entire disk.  Lowercase versions of K, M, and
             G are allowed.  Size and type should be specifed without any spa-
             ces between them.

             Example: 2097152, 1G, 1024M and 1048576K are all the same size
             (assuming 512-byte sectors).

     offset  The offset of the start of the partition from the beginning of
             the drive in sectors, or * to have disklabel calculate the cor-
             rect offset to use (the end of the previous partition plus one,
             ignoring partition `c'.  For partition `c', * will be interpreted
             as an offset of 0.

     fstype  Describes the purpose of the partition.  The example shows all
             currently used partition types.  For UFS file systems and ccd(4)
             partitions, use type 4.2BSD.  For Vinum drives, use type vinum.
             Other common types are swap and unused.  By convention, partition
             `c' represents the entire slice and should be of type unused,
             though disklabel does not enforce this convention.  The disklabel
             utility also knows about a number of other partition types, none
             of which are in current use.  (See the definitions starting with
             FS_UNUSED in <sys/disklabel.h> for more details).

     fsize   For 4.2BSD and LFS file systems only, the fragment size.
             Defaults to 1024 for partitions smaller than 1GB, 4096 for parti-
             tions 1GB or larger.

     bsize   For 4.2BSD and LFS file systems only, the block size.  Defaults
             to 8192 for partitions smaller than 1GB, 16384 for partitions 1GB
             or larger.

     bps/cpg
             For 4.2BSD file systems, the number of cylinders in a cylinder
             group.  For LFS file systems, the segment shift value.  Defaults
             to 16 for partitions smaller than 1GB, 64 for partitions 1GB or
             larger.

     The remainder of the line is a comment and shows the cylinder allocations
     based on the obsolete (but possibly correct) geometry information about
     the drive.  The asterisk (`*') indicates that the partition does not
     begin or end exactly on a cylinder boundary.

EXAMPLES
           disklabel da0s1

     Display the in-core label for the first slice of the da0 disk, as
     obtained via /dev/da0s1.  (If the disk is ``dangerously-dedicated'', the
     base disk name should be specified, such as da0.)

           disklabel da0s1 > savedlabel

     Save the in-core label for da0s1 into the file savedlabel.  This file can
     be used with the -R option to restore the label at a later date.

           disklabel -w -r /dev/da0s1 da2212 foo

     Create a label for da0s1 based on information for ``da2212'' found in
     /etc/disktab.  Any existing bootstrap code will be clobbered and the disk
     rendered unbootable.

           disklabel -e -r da0s1

     Read the on-disk label for da0s1, edit it, and reinstall in-core as well
     as on-disk.  Existing bootstrap code is unaffected.

           disklabel -e -r -n da0s1

     Read the on-disk label for da0s1, edit it, and display what the new label
     would be (in sectors).  It does not install the new label either in-core
     or on-disk.

           disklabel -r -w da0s1 auto

     Try to auto-detect the required information from da0s1, and write a new
     label to the disk.  Use another disklabel -e command to edit the parti-
     tioning and file system information.

           disklabel -R da0s1 savedlabel

     Restore the on-disk and in-core label for da0s1 from information in
     savedlabel.  Existing bootstrap code is unaffected.

           disklabel -R -n da0s1 label_layout

     Display what the label would be for da0s1 using the partition layout in
     label_layout.  This is useful for determining how much space would be
     alloted for various partitions with a labelling scheme using %-based or *
     partition sizes.

           disklabel -B da0s1

     Install a new bootstrap on da0s1.  The boot code comes from /boot/boot1
     and possibly /boot/boot2.  On-disk and in-core labels are unchanged.

           disklabel -w -B /dev/da0s1 -b newboot1 -s newboot2 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 files /boot/newboot1 and /boot/newboot2.

           dd if=/dev/zero of=/dev/da0 bs=512 count=32
           fdisk -BI da0
           dd if=/dev/zero of=/dev/da0s1 bs=512 count=32
           disklabel -w -B da0s1 auto
           disklabel -e da0s1

     Completely wipe any prior information on the disk, creating a new
     bootable disk with a DOS partition table containing one ``whole-disk''
     slice.  Then initialize the slice, then edit it to your needs.  The dd
     commands are optional, but may be necessary for some BIOSes to properly
     recognize the disk.

     This is an example disklabel that uses some of the new partition size
     types such as %, M, G, and *, which could be used as a source file for

           disklabel -R ad0s1c new_label_file

         # /dev/ad0s1c:
         type: ESDI
         disk: ad0s1
         label:
         flags:
         bytes/sector: 512
         sectors/track: 63
         tracks/cylinder: 16
         sectors/cylinder: 1008
         cylinders: 40633
         sectors/unit: 40959009
         rpm: 3600
         interleave: 1
         trackskew: 0
         cylinderskew: 0
         headswitch: 0           # milliseconds
         track-to-track seek: 0  # milliseconds
         drivedata: 0

         8 partitions:
         #        size   offset    fstype   [fsize bsize bps/cpg]
           a:   400M        0    4.2BSD     4096 16384    75     # (Cyl.    0 - 812*)
           b:     1G        *      swap
           c:      *        *    unused
           e: 204800        *    4.2BSD
           f:     5g        *    4.2BSD
           g:      *        *    4.2BSD

SEE ALSO
     ccd(4), disklabel(5), disktab(5), boot0cfg(8), fdisk(8), vinum(8)

DIAGNOSTICS
     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 parti-
     tion 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 file systems.  As a result, it may not be possi-
     ble to have file systems 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
     file systems on FS_BOOT partitions.  Conversely, if a partition has a
     type other than FS_UNUSED or FS_BOOT, disklabel will not install boot-
     strap code that overlaps it.

BUGS
     When a disk name is given without a full pathname, the constructed device
     name uses the ``c'' partition.

     For the i386 architecture, the primary bootstrap sector contains an
     embedded fdisk table.  The disklabel utility 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 ded-
     icated, so that the BSD disklabel starts at absolute block 0 on the disk.

     The disklabel utility does not perform all possible error checking.
     Warning *is* given if partitions overlap; if an absolute offset does not
     match the expected offset; if the ``c'' partition does not start at 0 or
     does not cover the entire slice; if a partition runs past the end of the
     device; and a number of other errors; but no warning is given if space
     remains unused.

FreeBSD 4.10                     July 30, 1999                    FreeBSD 4.10

NAME | SYNOPSIS | DESCRIPTION | FILES | SAVED FILE FORMAT | EXAMPLES | SEE ALSO | DIAGNOSTICS | BUGS

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