freebsd/sbin/disklabel/disklabel.8

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.\"	@(#)disklabel.8	8.2 (Berkeley) 4/19/94
.\" $FreeBSD$
.\"
.Dd March 15, 2003
.Dt DISKLABEL 8
.Os
.Sh NAME
.Nm disklabel
.Nd read and write disk pack label
.Sh SYNOPSIS
.Nm
.Op Fl r
.Ar disk
.Nm
.Fl w
.Op Fl nr
.Op Fl m Ar machine
.Ar disk type
.Op Ar packid
.Nm
.Fl e
.Op Fl nr
.Op Fl m Ar machine
.Ar disk
.Nm
.Fl R
.Op Fl nr
.Op Fl m Ar machine
.Ar disk protofile
.Pp
.Nm
.Fl B
.Op Fl b Ar boot
.Op Fl m Ar machine
.Ar disk
.Nm
.Fl w B
.Op Fl n
.Op Fl b Ar boot
.Op Fl m Ar machine
.Ar disk type
.Op Ar packid
.Nm
.Fl R B
.Op Fl n
.Op Fl b Ar boot
.Op Fl m Ar machine
.Ar disk protofile
.Sh DESCRIPTION
The
.Nm
utility
installs, examines or modifies 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,
.Nm
can install bootstrap code.
.Ss Raw or In-Core Label
The disk label resides close to or at the beginning of each disk slice.
For faster access, the kernel maintains a copy in core at all times.
By default, most
.Nm
access the in-core copy of the label.
To access the raw (on-disk) copy, use the
.Fl 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
.Fl r
is described under each command.
.Ss Disk Device Name
All
.Nm
forms require a disk device name, which should always be the raw
device name representing the disk or slice.
For example,
.Pa da0
represents the entire disk regardless of any
.Tn DOS
partitioning,
and
.Pa da0s1
represents a slice.
Some devices, most notably
.Xr ccd 4 ,
require that the
.Dq whole-disk
(or
.Ql c )
partition be specified.
For example,
.Pa ccd0c .
When specifying the device,
the
.Pa /dev/
path prefix may be omitted;
the
.Nm
utility will automatically prepend it.
.Ss Reading the Disk Label
To examine the label on a disk drive, use
.Nm
without options:
.Pp
.Nm
.Op Fl r
.Ar disk
.Pp
.Ar disk
represents the raw disk in question, and may be in the form
.Pa da0
or
.Pa /dev/da0c .
It will display all of the parameters associated with the drive and its
partition layout.
Unless the
.Fl r
option 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
.Fl r
option is given,
.Nm
reads the label from the raw disk and displays it.
Both versions are usually
identical except in the case where a label has not yet been initialized or
is corrupt.
.Ss Writing a Standard Label
To write a standard label, use the form
.Pp
.Nm
.Fl w
.Op Fl nr
.Op Fl m Ar machine
.Ar disk type
.Op Ar packid
.Pp
The required arguments to
.Nm
are the drive to be labeled, and the drive type as described in the
.Xr 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
.Xr disktab 5
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
.Ar packid
must be quoted if it contains blanks.
.Pp
If the
.Fl m
option is given, then label will be written so that
it is understood by the target
.Ar machine ;
defaults to the current hardware architecture.
.Pp
If
.Fl n
is used, no data will be written to the device, and instead the
disk label that would have been written will be printed to standard output.
.Pp
If the
.Fl r
option 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 and the bootstrap at the same time.
If
.Fl 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
.Fl r
option must be used.
In either case, the kernel's in-core label is replaced.
.Pp
For a virgin disk that is not known to
.Xr disktab 5 ,
.Ar type
can be specified as
.Cm 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
.Tn SCSI
disks, most
.Tn IDE
disks, and
.Cm vnode
type memory disks
.Pq Xr md 4 .
Writing a label to the
disk is the only supported operation, and the
.Ar disk
itself must be provided as the canonical name, i.e., not as a full
path name.
.Pp
For most harddisks, a label based on percentages for most partitions (and
one partition with a size of
.Ql * )
will produce a reasonable configuration.
.Pp
PC-based systems have special requirements in order for the
.Tn BIOS
to properly recognize a
.Fx
disk label.
Older systems may require what is known as a
.Dq dangerously-dedicated
disk label, which creates a fake
.Tn DOS
partition to work around problems older
.Tn BIOS Ns es
have with modern disk geometries.
On newer systems, a normal
.Tn DOS
partition should generally be created using
.Xr fdisk 8 ,
and then a
.Fx
disk label within that slice.
This is described later on in this page.
.Pp
Installing a new disk label does not in of itself allow the system to boot
a kernel using that label.
Boot blocks must also be installed, which is
described later on in this manual page.
.Ss Editing an Existing Disk Label
To edit an existing disk label, use the form
.Pp
.Nm
.Fl e
.Op Fl nr
.Op Fl m Ar machine
.Ar disk
.Pp
This command reads the label from the in-core kernel copy, or directly from the
disk if the
.Fl r
option is also specified.
The label is written to a file in
.Tn ASCII
format, and then supplied to an editor for changes.
If no editor is specified in the
.Ev EDITOR
environment variable,
.Xr 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
.Fl r
was specified.
.Pp
If the
.Fl m
option is given, then the label will be written so that
it is understood by the target
.Ar machine ;
defaults to the current hardware architecture.
.Pp
If
.Fl n
is used, no data will be written to the device, and instead the
disk label that would have been written will be printed to standard output.
This is
useful to see how a partitioning scheme will work out for a specific 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 nr
.Op Fl m Ar machine
.Ar disk protofile
.Pp
.Nm
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.
As when writing a new label, any existing bootstrap code will be
clobbered if
.Fl 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.
.Pp
If the
.Fl m
option is given, then the label will be written so that
it is understood by the target
.Ar machine ;
defaults to the current hardware architecture.
.Pp
If
.Fl n
is used, no data will be written to the device, and instead the
disk label that would have been written will be printed to standard output.
This is
useful to see how a partitioning scheme will work out for a specific disk.
.Ss Installing Bootstraps
The final three forms of
.Nm
are used to install bootstrap code.
If a
.Dq dangerously-dedicated
disk is created for compatibility with older PC systems,
the raw disk name such as
.Pa da0
should be specified.
If an existing slice should be labeled,
the slice name such as
.Pa da0s1
should be specified,
and to make it bootable,
.Tn MBR
on the base disk should probably be updated; see
.Xr fdisk 8 .
.Pp
.Nm
.Fl B
.Op Fl b Ar boot
.Op Fl m Ar machine
.Ar disk
.Pp
This form installs the bootstrap only.
It does not change the disk label.
Never use this command on a base disk, such as
.Pa da0 ,
unless the intent is to create a
.Dq dangerously-dedicated
disk.
This command is typically run on a slice such as
.Pa da0s1 .
.Pp
The
.Fl m
option should be specified if the label was
created for a different hardware architecture,
.Ar machine .
.Pp
.Nm
.Fl w B
.Op Fl n
.Op Fl b Ar boot
.Op Fl m Ar machine
.Ar disk type
.Op Ar packid
.Pp
This form corresponds to the
.Dq "write label"
command described above.
In addition to writing a new volume label, it also installs the bootstrap.
If run on a base disk, this command will create a
.Dq dangerously-dedicated
label.
This command is normally run on a slice rather than a base disk.
.Pp
If the
.Fl m
option is given, then the label and bootstrap will be written so that
they are understood by the target
.Ar machine ;
defaults to the current hardware architecture.
.Pp
If
.Fl n
is used, no data will be written to the device, and instead the
disk label that would have been written will be printed to standard output.
.Pp
.Nm
.Fl R B
.Op Fl n
.Op Fl b Ar boot
.Op Fl m Ar machine
.Ar disk protofile
.Pp
This form corresponds to the
.Dq "restore label"
command described above.
In addition to restoring the volume label, it also installs the bootstrap.
If run on a base disk, this command will create a
.Dq dangerously-dedicated
label.
This command is normally run on a slice rather than a base disk.
.Pp
The bootstrap commands always access the disk directly, so it is not necessary
to specify the
.Fl r
option.
.Pp
If the
.Fl m
option is given, then the label and bootstrap will be written so that
they are understood by the target
.Ar machine ;
defaults to the current hardware architecture.
.Pp
If
.Fl n
is used, no data will be written to the device, and instead the
disk label that would have been written will be printed to standard output.
.Pp
The bootstrap code is comprised of two boot programs compiled into a single
.Pa /boot/boot
image.
An alternative boot image may be specified with the
.Fl b
option.
.Ss Initializing/Formatting a Bootable Disk From Scratch
To initialize a disk from scratch, the following sequence is recommended.
Please note that this will wipe everything that was previously on the disk,
including any
.No non- Ns Fx
slices.
.Bl -enum
.It
Use
.Xr fdisk 8
to initialize the hard disk, and create a slice table, referred to
as the
.Dq "partition table"
in
.Tn DOS .
.It
Use
.Nm
to define partitions on
.Fx
slices created in the previous step.
.It
Finally use
.Xr newfs 8
to create file systems on new partitions.
.El
.Pp
A typical partitioning scheme would be to have an
.Ql a
partition
of approximately 128MB to hold the root file system, a
.Ql b
partition for
swap, a
.Ql d
partition for
.Pa /var
(usually 128MB), an
.Ql e
partition
for
.Pa /var/tmp
(usually 128MB), an
.Ql f
partition for
.Pa /usr
(usually around 2GB),
and finally a
.Ql g
partition for
.Pa /home
(usually all remaining space).
Your mileage may vary.
.Pp
.Nm fdisk Fl BI Pa da0
.Pp
.Nm
.Fl w B
.Pa da0s1
.Cm auto
.Pp
.Nm
.Fl e
.Pa da0s1
.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
# /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*)
.Ed
.Pp
Lines starting with a
.Ql #
mark are comments.
Most of the other specifications are no longer used.
The ones which must still be set correctly are:
.Pp
.Bl -inset
.It Ar label
is an optional label, set by the
.Ar packid
option when writing a label.
.It Ar flags
may be
.Cm removable , ecc
or
.Cm badsect .
.Cm removable
is set for removable media drives, but no current
.Fx
driver evaluates this
flag.
.Cm ecc
is no longer supported;
.Cm badsect
specifies that the drive can perform bad sector remapping.
.It Ar sectors/unit
describes the total size of the disk.
This value must be correct.
.It Ar "the partition table"
is the
.Ux
partition table, not the
.Tn DOS
partition table described in
.Xr fdisk 8 .
.El
.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
.Cm K , M ,
and
.Cm G
are allowed.
Size and type should be specifed 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.
.It Ar fstype
Describes the purpose of the partition.
The 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
.Aq Pa sys/disklabel.h
for more details.)
.It Ar fsize
For
.Cm 4.2BSD
and
.Tn LFS
file systems only, the fragment size.
Defaults to 1024 for partitions smaller than 1GB,
4096 for partitions 1GB or larger.
.It Ar bsize
For
.Cm 4.2BSD
and
.Tn LFS
file systems only, the block size.
Defaults to 8192 for partitions smaller than 1GB,
16384 for partitions 1GB or larger.
.It Ar bps/cpg
For
.Cm 4.2BSD
file systems, the number of cylinders in a cylinder group.
For
.Tn LFS
file systems, the segment shift value.
Defaults to 16 for partitions smaller than 1GB,
64 for partitions 1GB or larger.
.El
.Pp
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
.Pq Ql *
indicates that the partition does not begin or end exactly on a
cylinder boundary.
.Sh EXAMPLES
.Dl "disklabel da0s1"
.Pp
Display the in-core label for the first slice of the
.Pa da0
disk, as obtained via
.Pa /dev/da0s1 .
(If the disk is
.Dq dangerously-dedicated ,
the base disk name should be specified, such as
.Pa da0 . )
.Pp
.Dl "disklabel da0s1 > savedlabel"
.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 "disklabel -w -r /dev/da0s1 da2212 foo"
.Pp
Create a label for
.Pa da0s1
based on information for
.Dq da2212
found in
.Pa /etc/disktab .
Any existing bootstrap code will be clobbered
and the disk rendered unbootable.
.Pp
.Dl "disklabel -e -r da0s1"
.Pp
Read the on-disk label for
.Pa da0s1 ,
edit it, and reinstall in-core as well as on-disk.
Existing bootstrap code is unaffected.
.Pp
.Dl "disklabel -e -r -n 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 "disklabel -r -w da0s1 auto"
.Pp
Try to auto-detect the required information from
.Pa da0s1 ,
and write a new label to the disk.
Use another
.Nm Fl e
command to edit the
partitioning and file system information.
.Pp
.Dl "disklabel -R da0s1 savedlabel"
.Pp
Restore the on-disk and in-core label for
.Pa da0s1
from information in
.Pa savedlabel .
Existing bootstrap code is unaffected.
.Pp
.Dl "disklabel -R -n da0s1 label_layout"
.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 alloted for various
partitions with a labelling scheme using
.Cm % Ns -based
or
.Cm *
partition sizes.
.Pp
.Dl "disklabel -B da0s1"
.Pp
Install a new bootstrap on
.Pa da0s1 .
The boot code comes from
.Pa /boot/boot .
On-disk and in-core labels are unchanged.
.Pp
.Dl "disklabel -w -B /dev/da0s1 -b newboot da2212"
.Pp
Install a new label and bootstrap.
The label is derived from
.Xr disktab 5
information for
.Dq da2212 ,
and installed both in-core and on-disk.
The bootstrap code comes from the file
.Pa newboot
in the current working directory.
.Bd -literal -offset indent
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
disklabel -w -B da0s1 auto
disklabel -e da0s1
.Ed
.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.
.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 "disklabel -R ad0s1c new_label_file" :
.Bd -literal -offset 4n
# /dev/ad0s1c:
type: ESDI
disk: ad0s1
label:
flags:
bytes/sector: 512
sectors/track: 63
tracks/cylinder: 16
sectors/cylinder: 1008
cylinders: 40633
sectors/unit: 40959009
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:   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
.Ed
.Sh SEE ALSO
.Xr ccd 4 ,
.Xr md 4 ,
.Xr disklabel 5 ,
.Xr disktab 5 ,
.Xr boot0cfg 8 ,
.Xr fdisk 8 ,
.Xr vinum 8
.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.
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
.Ql 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 one setting the label on the new partition
while shrinking the
.Ql a
partition.
.Pp
On some machines, the bootstrap code may not fit entirely in the area
allocated for it by some file systems.
As a result,
it may not be possible to have file systems on some partitions of a
.Dq bootable
disk.
When installing bootstrap code,
.Nm
checks for these cases.
If the installed boot code would overlap a partition of type
.Dv FS_UNUSED ,
it is marked as type
.Dv FS_BOOT .
The
.Xr newfs 8
utility will disallow creation of file systems on
.Dv FS_BOOT
partitions.
Conversely, if a partition has a type other than
.Dv FS_UNUSED
or
.Dv FS_BOOT ,
.Nm
will not install bootstrap code that overlaps it.
.Sh BUGS
When a disk name is given without a full pathname,
the constructed device name uses the
.Ql c
partition.
.Pp
For the i386 architecture, the primary bootstrap sector contains
an embedded
.Em fdisk
table.
The
.Nm
utility takes care to not clobber it when installing a bootstrap only
.Pq Fl B ,
or when editing an existing label
.Pq Fl e ,
but it unconditionally writes the primary bootstrap program onto
the disk for
.Fl w
or
.Fl R ,
thus replacing the
.Em fdisk
table by the dummy one in the bootstrap program.
This is only of
concern if the disk is fully dedicated, so that the
.Fx
disk label
starts at absolute block 0 on the disk.
.Pp
The
.Nm
utility
does not perform all possible error checking.
Warnings are given if partitions overlap,
if an absolute offset does not match the expected offset,
if the
.Ql c
partition does not start at 0 or does not cover the entire slice,
if a partition runs past the end of the device,
and a number of other errors,
but no warning is given if space remains unused.