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BSDLABEL(8) FreeBSD System Manager's Manual BSDLABEL(8)
NAME bsdlabel - read and write BSD label
SYNOPSIS 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
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 and amd64. 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 [-An] [-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 [-An] [-m machine] disk bsdlabel -R [-An] [-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:
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
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).
HISTORY The disklabel utility appeared in 4.3BSD-Tahoe.
FreeBSD 14.0-RELEASE-p6 October 5, 2016 FreeBSD 14.0-RELEASE-p6