BSDLABEL(8)

NAME
bsdlabel - read and write BSD label

SYNOPSIS
bsdlabel [-A] disk | -f file
bsdlabel -w [-] [-B [-b boot]] [-m machine] disk | -f file [type]
bsdlabel -e [-] [-B [-b boot]] [-m machine] disk | -f file
bsdlabel -R [-] [-B [-b boot]] [-m machine] [-f] disk | -f file protofile

DESCRIPTION
The bsdlabel utility installs, examines or modifies the BSD label on a disk partition, or on a file containing a partition image. In addition, bsdlabel can install bootstrap code.

  Disk Device Name
When specifying the device (i.e., when the -f option is not used), the /dev/ path prefix may be omitted; the bsdlabel utility will automatically prepend it.

  General Options
The -A option enables processing of the historical parts of the BSD label. If the option is not given, suitable values are set for these fields.

The -f option tells bsdlabel that the program will operate on a file instead of a disk partition.

The -n option stops the bsdlabel program right before the disk would have been modified, and displays the result instead of writing it.

The -m machine argument forces bsdlabel to use a layout suitable for a different architecture. Current valid values are i386, amd64, and pc98. If this option is omitted, bsdlabel will use a layout suitable for the current machine.

  Reading the Disk Label
To examine the label on a disk drive, use the form

bsdlabel [-A] [-m machine] disk

disk represents the disk in question, and may be in the form da0 or /dev/da0. It will display the partition layout.

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

bsdlabel -w [-] [-m machine] disk [type]

If the drive type is specified, the entry of that name in the disktab(5) file is used; otherwise, or if the type is specified as 'auto', a default layout is used.

  Editing an Existing Disk Label
To edit an existing disk label, use the form

bsdlabel -e [-] [-m machine] disk

This command opens the disk label in the default editor, and when the editor exits, the label is validated and if OK written to disk.

  Restoring a Disk Label From a File
To restore a disk label from a file, use the form

bsdlabel -R [-] [-m machine] disk protofile

The bsdlabel utility 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.

  Installing Bootstraps
If the -B option is specified, bootstrap code will be read from the file /boot/boot and written to the disk. The -b boot option allows a different file to be used.

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

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

    8 partitions:
    #        size   offset    fstype   [fsize bsize bps/cpg]
      a:    81920       16    4.2BSD     2048 16384  5128
      b:  1091994    81936      swap
      c:  1173930        0    unused        0     0         # "raw" part, don't edit

If the -A option is specified, 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       16    4.2BSD     1024  8192    16
      b:   160000    81936      swap
      c:  1173930        0    unused        0     0         # "raw" part, don't edit

Lines starting with a ‘#’ mark are comments.

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), % (percentage 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 suffixes K, M, and G are allowed. Size and suffix should be specified without any spaces 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 bsdlabel calculate the correct 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. The first partition should start at offset 16, because the first 16 sectors are reserved for metadata.

fstype
    Describes the purpose of the partition. The above 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 bsdlabel does not enforce this convention. The bsdlabel 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 file systems only, the fragment size; see newfs(8).

bsize
    For 4.2BSD file systems only, the block size; see newfs(8).

bps/cpg
    For 4.2BSD file systems, the number of cylinders in a cylinder group; see newfs(8).

EXAMPLES
Display the label for the first slice of the da0 disk, as obtained via /dev/da0s1:

    bsdlabel da0s1

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:

    bsdlabel da0s1 > savedlabel

Create a label for da0s1:

    bsdlabel -w /dev/da0s1

Read the label for da0s1, edit it, and install the result:

    bsdlabel -e 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:

    bsdlabel -e -n da0s1

Write a default label on da0s1. Use another bsdlabel -e command to edit the partitioning and file system information:

    bsdlabel -w da0s1

Restore the on-disk and in-core label for da0s1 from information in savedlabel:

    bsdlabel -R da0s1 savedlabel

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 allotted for various partitions with a labeling scheme using %-based or * partition sizes:

    bsdlabel -R -n da0s1 label_layout

Install a new bootstrap on da0s1. The boot code comes from /boot/boot:

    bsdlabel -B da0s1

Install a new label and bootstrap. The bootstrap code comes from the file newboot in the current working directory:

    bsdlabel -w -B -b newboot /dev/da0s1

Completely wipe any prior information on the disk, creating a new bootable disk with a DOS partition table containing one slice, covering the whole disk. Initialize the label on this slice, then edit it. The dd(1) commands are optional, but may be necessary for some BIOSes to properly recognize the disk:

    dd if=/dev/zero of=/dev/da0 bs=512 count=32
    gpart create -s MBR da0
    gpart add -t freebsd da0
    gpart set -a active -i 1 da0
    gpart bootcode -b /boot/mbr da0
    dd if=/dev/zero of=/dev/da0s1 bs=512 count=32
    bsdlabel -w -B da0s1
    bsdlabel -e da0s1

This is an example disk label that uses some of the new partition size types such as %, M, G, and *, which could be used as a source file for “bsdlabel -R ada0s1 new_label_file”:

    # /dev/ada0s1:
    8 partitions:
    #        size   offset    fstype   [fsize bsize bps/cpg]
      a:   400M       16    4.2BSD     4096 16384    75    # (Cyl.    0 - 812*)
      b:     1G        *      swap
      c:      *        *    unused
      e: 204800        *    4.2BSD
      f:     5g        *    4.2BSD
      g:      *        *    4.2BSD

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.

COMPATIBILITY
Due to the use of an uint32_t to store the number of sectors, BSD labels are restricted to a maximum of 2^32-1 sectors. This usually means 2TB of disk space. Larger disks should be partitioned using another method such as gpart(8).

The various BSDs all use slightly different versions of BSD labels and are not generally compatible.

SEE ALSO
ccd(4), geom(4), md(4), disktab(5), boot0cfg(8), gpart(8), newfs(8)

HISTORY
The disklabel utility appeared in 4.3BSD Tahoe.