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.\"	@(#)disklabel.8	8.2 (Berkeley) 4/19/94
.\" $FreeBSD$
.\"
.Dd October 5, 2016
.Dt BSDLABEL 8
.Os
.Sh NAME
.Nm bsdlabel
.Nd read and write BSD label
.Sh SYNOPSIS
.Nm
.Op Fl A
.Ar disk | Fl f Ar file
.Nm
.Fl w
.Op Fl \&An
.Op Fl B Op Fl b Ar boot
.Op Fl m Ar machine
.Ar disk | Fl f Ar file
.Op Ar type
.Nm
.Fl e
.Op Fl \&An
.Op Fl B Op Fl b Ar boot
.Op Fl m Ar machine
.Ar disk | Fl f Ar file
.Nm
.Fl R
.Op Fl \&An
.Op Fl B Op Fl b Ar boot
.Op Fl m Ar machine
.Op Fl f
.Ar disk | Fl f Ar file
.Ar protofile
.Sh DESCRIPTION
The
.Nm
utility
installs, examines or modifies the
.Bx
label on a disk partition, or on a file containing a partition image.
In addition,
.Nm
can install bootstrap code.
.Ss Disk Device Name
When specifying the device (i.e., when the
.Fl f
option is not used),
the
.Pa /dev/
path prefix may be omitted;
the
.Nm
utility will automatically prepend it.
.Ss General Options
The
.Fl A
option enables processing of the historical parts of the
.Bx
label.
If the option is not given, suitable values are set for these fields.
.Pp
The
.Fl f
option tells
.Nm
that the program will operate on a file instead of a disk partition.
.Pp
The
.Fl n
option stops the
.Nm
program right before the disk would have been modified, and displays
the result instead of writing it.
.Pp
The
.Fl m Ar machine
argument forces
.Nm
to use a layout suitable for a different architecture.
Current valid values are
.Cm i386
and
.Cm amd64 .
If this option is omitted,
.Nm
will use a layout suitable for the current machine.
.Ss Reading the Disk Label
To examine the label on a disk drive, use the form
.Pp
.Nm
.Op Fl A
.Op Fl m Ar machine
.Ar disk
.Pp
.Ar disk
represents the disk in question, and may be in the form
.Pa da0
or
.Pa /dev/da0 .
It will display the partition layout.
.Ss Writing a Standard Label
To write a standard label, use the form
.Pp
.Nm
.Fl w
.Op Fl \&An
.Op Fl m Ar machine
.Ar disk
.Op Ar type
.Pp
If the drive
.Ar type
is specified, the entry of that name in the
.Xr disktab 5
file is used; otherwise, or if the type is specified as 'auto', a default
layout is used.
.Ss Editing an Existing Disk Label
To edit an existing disk label, use the form
.Pp
.Nm
.Fl e
.Op Fl \&An
.Op Fl m Ar machine
.Ar disk
.Pp
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.
.Ss Restoring a Disk Label From a File
To restore a disk label from a file, use the form
.Pp
.Nm
.Fl R
.Op Fl \&An
.Op Fl m Ar machine
.Ar disk protofile
.Pp
The
.Nm
utility
is capable of restoring a disk label that was previously saved in a file in
.Tn 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
.Ql #
and newline.
.Ss Installing Bootstraps
If the
.Fl B
option is specified, bootstrap code will be read from the file
.Pa /boot/boot
and written to the disk.
The
.Fl b Ar boot
option allows a different file to be used.
.Sh FILES
.Bl -tag -width ".Pa /etc/disktab" -compact
.It Pa /boot/boot
Default boot image.
.It Pa /etc/disktab
Disk description file.
.El
.Sh SAVED FILE FORMAT
The
.Nm
utility
uses an
.Tn ASCII
version of the label when examining, editing, or restoring a disk
label.
The format is:
.Bd -literal -offset 4n

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
.Ed
.Pp
If the
.Fl A
option is specified, the format is:
.Bd -literal -offset 4n
# /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
.Ed
.Pp
Lines starting with a
.Ql #
mark are comments.
.Pp
The partition table can have up to 8 entries.
It contains the following information:
.Bl -tag -width indent
.It Ar #
The partition identifier is a single letter in the range
.Ql a
to
.Ql h .
By convention, partition
.Ql c
is reserved to describe the entire disk.
.It Ar size
The size of the partition in sectors,
.Cm K
(kilobytes - 1024),
.Cm M
(megabytes - 1024*1024),
.Cm G
(gigabytes - 1024*1024*1024),
.Cm %
(percentage of free space
.Em after
removing any fixed-size partitions other than partition
.Ql c ) ,
or
.Cm *
(all remaining free space
.Em after
fixed-size and percentage partitions).
For partition
.Ql c ,
a size of
.Cm *
indicates the entire disk.
Lowercase versions of suffixes
.Cm K , M ,
and
.Cm G
are allowed.
Size and suffix should be specified without any spaces between them.
.Pp
Example: 2097152, 1G, 1024M and 1048576K are all the same size
(assuming 512-byte sectors).
.It Ar offset
The offset of the start of the partition from the beginning of the
drive in sectors, or
.Cm *
to have
.Nm
calculate the correct offset to use (the end of the previous partition plus
one, ignoring partition
.Ql c ) .
For partition
.Ql c ,
.Cm *
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.
.It Ar fstype
Describes the purpose of the partition.
The above example shows all currently used partition types.
For
.Tn UFS
file systems and
.Xr ccd 4
partitions, use type
.Cm 4.2BSD .
For Vinum drives, use type
.Cm vinum .
Other common types are
.Cm swap
and
.Cm unused .
By convention, partition
.Ql c
represents the entire slice and should be of type
.Cm unused ,
though
.Nm
does not enforce this convention.
The
.Nm
utility
also knows about a number of other partition types,
none of which are in current use.
(See the definitions starting with
.Dv FS_UNUSED
in
.In sys/disklabel.h
for more details.)
.It Ar fsize
For
.Cm 4.2BSD
file systems only, the fragment size; see
.Xr newfs 8 .
.It Ar bsize
For
.Cm 4.2BSD
file systems only, the block size; see
.Xr newfs 8 .
.It Ar bps/cpg
For
.Cm 4.2BSD
file systems, the number of cylinders in a cylinder group; see
.Xr newfs 8 .
.El
.Sh EXAMPLES
Display the label for the first slice of the
.Pa da0
disk, as obtained via
.Pa /dev/da0s1 :
.Pp
.Dl "bsdlabel da0s1"
.Pp
Save the in-core label for
.Pa da0s1
into the file
.Pa savedlabel .
This file can be used with the
.Fl R
option to restore the label at a later date:
.Pp
.Dl "bsdlabel da0s1 > savedlabel"
.Pp
Create a label for
.Pa da0s1 :
.Pp
.Dl "bsdlabel -w /dev/da0s1"
.Pp
Read the label for
.Pa da0s1 ,
edit it, and install the result:
.Pp
.Dl "bsdlabel -e da0s1"
.Pp
Read the on-disk label for
.Pa da0s1 ,
edit it, and display what the new label would be (in sectors).
It does
.Em not
install the new label either in-core or on-disk:
.Pp
.Dl "bsdlabel -e -n da0s1"
.Pp
Write a default label on
.Pa da0s1 .
Use another
.Nm Fl e
command to edit the
partitioning and file system information:
.Pp
.Dl "bsdlabel -w da0s1"
.Pp
Restore the on-disk and in-core label for
.Pa da0s1
from information in
.Pa savedlabel :
.Pp
.Dl "bsdlabel -R da0s1 savedlabel"
.Pp
Display what the label would be for
.Pa da0s1
using the partition layout in
.Pa label_layout .
This is useful for determining how much space would be allotted for various
partitions with a labeling scheme using
.Cm % Ns -based
or
.Cm *
partition sizes:
.Pp
.Dl "bsdlabel -R -n da0s1 label_layout"
.Pp
Install a new bootstrap on
.Pa da0s1 .
The boot code comes from
.Pa /boot/boot :
.Pp
.Dl "bsdlabel -B da0s1"
.Pp
Install a new label and bootstrap.
The bootstrap code comes from the file
.Pa newboot
in the current working directory:
.Pp
.Dl "bsdlabel -w -B -b newboot /dev/da0s1"
.Pp
Completely wipe any prior information on the disk, creating a new bootable
disk with a
.Tn DOS
partition table containing one slice, covering the whole disk.
Initialize the label on this slice,
then edit it.
The
.Xr dd 1
commands are optional, but may be necessary for some
.Tn BIOS Ns es
to properly
recognize the disk:
.Bd -literal -offset indent
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
.Ed
.Pp
This is an example disk label that uses some of the new partition size types
such as
.Cm % , M , G ,
and
.Cm * ,
which could be used as a source file for
.Dq Li "bsdlabel -R ada0s1 new_label_file" :
.Bd -literal -offset 4n
# /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
.Ed
.Sh 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.
.Sh COMPATIBILITY
Due to the use of an
.Vt uint32_t
to store the number of sectors,
.Bx
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
.Xr gpart 8 .
.Pp
The various
.Bx Ns s
all use slightly different versions of
.Bx
labels and
are not generally compatible.
.Sh SEE ALSO
.Xr ccd 4 ,
.Xr geom 4 ,
.Xr md 4 ,
.Xr disktab 5 ,
.Xr boot0cfg 8 ,
.Xr gpart 8 ,
.Xr newfs 8
.Sh HISTORY
The
.Nm disklabel
utility appeared in
.Bx 4.3 Tahoe .