BSDLABEL(8) BSD System Manager’s Manual BSDLABEL(8)


bsdlabel — read and write disk pack label


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


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 instructs bsdlabel to use the layout suitable for the specified machine.

Reading the Disk Label
To examine the label on a disk drive, use bsdlabel without options:

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 [−An] [−m machine] disk [type]

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

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

bsdlabel −e [−An] [−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 [−An] [−m machine] disk protofile

bsdlabel 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 argument is specified, bootstrap code will be read from the file /boot/boot and written to the disk. The −b boot argument allows a different file to be used.


Default boot image.


Disk description file.


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 0 4.2BSD 1024 8192 16
b: 160000 81920 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
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
b: 160000 81920 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.


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 K, M, and G are allowed. Size and type should be specified without any spaces between them.

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


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.


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 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.)


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


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.


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.


bsdlabel da0s1

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

bsdlabel 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.

bsdlabel -w /dev/da0s1

Create a label for da0s1.

bsdlabel -e da0s1

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

bsdlabel -e -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.

bsdlabel -w da0s1

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

bsdlabel -R da0s1 savedlabel

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

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

bsdlabel -B da0s1

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

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

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

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
bsdlabel -w -B da0s1
bsdlabel -e 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.

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 ad0s1c new_label_file’’:

# /dev/ad0s1c:

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


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.


Due to the use of an u_int32_t to store the number of sectors, bsdlabels 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 gpt(8).

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


ccd(4), geom(4), md(4), disktab(5), boot0cfg(8), fdisk(8), gpt(8)

BSD March 15, 2003 BSD