DISKLABEL(8)

NAME
disklabel - read and write disk pack label

SYNOPSIS
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]

DESCRIPTION
Disklabel installs, examines or modifes 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. There are several 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 is resident close to or at the beginning of each disk partition. 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.

  Disk device name

All disklabel forms require a disk device name, which should always be the raw "complete" (or "c") partition, for example /dev/da0c. disklabel understands the abbreviation da0, which it converts internally to /dev/da0c.

  Reading the disk label

To examine or save 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 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, disklabel reads the label from the raw disk and displays it.

  Writing a standard label

To write a standard label, use the form

disklabel -w [-r] disk disktype [packid]

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 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. 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 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.

  Editing an existing disk label

To edit an existing disk label, use the form

disklabel -e [-r] 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 specified.

  Restoring a disk label from a file

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

disklabel -R [-r] disk protofile

disklabel is capable of restoring a disk label that was previously saved in a file ASCII. 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.

  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 silently ignores 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:

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

This form installs the bootstrap only. It does not change the disk label.

disklabel -w -B [ -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.

disklabel -R -B [ -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 bootstrap.

The bootstrap commands always access the disk directly, so it is not necessary to specify the -r flag.

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 specified, 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).

FILES
/etc/disktab
/boot/
/boot/boot<n>

SAVED FILE FORMAT
disklabel 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 specifications 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
    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
    This is the UNIX partition table, not the Microsoft partition table described in fdisk(8).

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

identifier
    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
    is the size of the partition in sectors.

offset
    is the offset of the start of the partition from the beginning of the drive.

fstype
    describes the purpose of the partition. The example shows most normal usages. For UFS file systems, use type 4.2BSD. See /usr/include/sys/disklabel.h for a complete list.

fsize
    For file systems only, the fragment size.

bsize
    For file systems only, the block size.

bps/cpg
    For UFS file systems, the number of cylinders in a cylinder group. For LFS file systems, the segment shift value.
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 da0

Display the in-core label for da0 as obtained via /dev/da0c.

    disklabel da0 > savedlabel

Save the in-core label for da0 into the file savedlabel. This file can be used with the -R flag to restore the label at a later date.

    disklabel -w -r /dev/da0c 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 savedlabel

Restore the on-disk and in-core label for da0 from information in savedlabel. 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/da0c -b newboot1 -s 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 files /boot/newboot1 and /boot/newboot2.

SEE ALSO
disklabel(5), disktab(5), boot0cfg(8), fdisk(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 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.

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. 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 disk.

disklabel does not perform adequate error checking. No warning is given if partitions overlap, nor if space remains unused.