freebsd-src/sbin/disklabel/disklabel.8

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.\"	@(#)disklabel.8	8.2 (Berkeley) 4/19/94
.\" $FreeBSD$
.\"
.Dd July 30, 1999
.Dt DISKLABEL 8
.Os FreeBSD
.Sh NAME
.Nm disklabel
.Nd read and write disk pack label
.Sh SYNOPSIS
.Nm
.Op Fl r
.Ar disk
.Nm
.Fl w
.Op Fl r
.Op Fl n
.Ar disk Ar disktype/auto
.Oo Ar packid Oc
.Nm
.Fl e
.Op Fl r
.Op Fl n
.Ar disk
.Nm
.Fl R
.Op Fl r
.Op Fl n
.Ar disk Ar protofile
.Nm
.Op Fl NW
.Ar disk
.Pp
.Nm
.Fl B
.Oo
.Fl b Ar boot1
.Fl s Ar boot2
.Oc
.Ar disk
.Oo Ar disktype/auto Oc
.Nm
.Fl w
.Fl B
.Op Fl n
.Oo
.Fl b Ar boot1
.Fl s Ar boot2
.Oc
.Ar disk Ar disktype/auto
.Oo Ar packid Oc
.Nm
.Fl R
.Fl B
.Op Fl n
.Oo
.Fl b Ar boot1
.Fl s Ar boot2
.Oc
.Ar disk Ar protofile
.Oo Ar disktype/auto Oc
.Sh DESCRIPTION
.Nm Disklabel
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
.Pp
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
.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.
.Pp
.Ss Disk device name
.Pp
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 irregardless of any DOS partitioning,
and
.Pa da0s1
represents a slice.  Some devices, most notably
.Ar ccd ,
require that the
.Dq whole-disk
(or
.Dq c )
partition be specified.  For example
.Pa ccd0c .
You do not have to include the
.Pa /dev/
path prefix when specifying the device.
.Nm
will automatically prepend it.
.Ss Reading the disk label
.Pp
To examine or save 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
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
.Fl r
flag 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
.Pp
To write a standard label, use the form
.Pp
.Nm
.Fl w
.Op Fl r
.Op Fl n
.Ar disk Ar disktype/auto
.Oo Ar packid Oc
.Pp
.Nm
.Fl w
.Op Fl r
.Op Fl n
.Ar disk
auto
.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 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.
.Pp
If the
.Fl n
flag is given, no data will be written to the device, and instead the
disklabel that would have been written will be printed to stdout.
.Pp
If the
.Fl 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
.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
flag 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 disktype
can be specified as
.Dq 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
.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 BIOS to properly
recognize a
.Fx
disklabel.  Older systems may require what is known as a
.Dq dangerously dedicated
disklabel, which creates a fake DOS partition to work around problems older
BIOSes have with modern disk geometries.  On newer systems you generally want
to create a normal DOS slice using
.Ar fdisk
and then create a
.Fx
disklabel within that slice.  This is described
later on in this page.
.Pp
Installing a new disklabel does not in of itself allow your system to boot
a kernel using that label.  You must also install boot blocks, which is
described later on in this manual page.
.Ss Editing an existing disk label
.Pp
To edit an existing disk label, use the form
.Pp
.Nm
.Fl e
.Op Fl r
.Op Fl n
.Ar disk
.Pp
This command reads the label from the in-core kernel copy, or directly from the
disk if the
.Fl 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
.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.  If
.Fl n
is specified, no data will be written to the device, and instead the
disklabel that would have been written will be printed to stdout.  This is
useful to see how a partitioning scheme will work out for a specific disk.
.Ss Restoring a disk label from a file
.Pp
To restore a disk label from a file, use the form
.Pp
.Nm
.Fl R
.Op Fl r
.Op Fl n
.Ar disk Ar protofile
.Pp
.Nm
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
.Ar \&#
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.
If
.Fl n
is used, no data will be written to the device, and instead the
disklabel that would have been written will be printed to stdout.  This is
useful to see how a partitioning scheme will work out for a specific disk.
.Ss Enabling and disabling writing to the disk label area
.Pp
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
.Pp
.Nm
.Op Fl W
.Ar disk
.Pp
To disallow writing to the label area after previously allowing it, use the
command
.Pp
.Nm
.Op Fl N
.Ar disk
.Ss Installing bootstraps
.Pp
The final three forms of
.Nm
are used to install bootstrap code.  If you are creating a
.Dq dangerously-dedicated
partition for compatibility with older PC systems,
you generally want to specify the raw disk name such as
.Pa da0 .
If you are creating a label within an existing DOS slice, you should specify
the slice name such as
.Pa da0s1 .
Making a partition bootable can be tricky.  If you are using a normal DOS
slice you typically install (or leave) a standard MBR on the base disk and
then install the
.Fx
bootblocks in the slice.
.Pp
.Nm
.Fl B
.Oo
.Fl b Ar boot1
.Fl s Ar boot2
.Oc
.Ar disk
.Oo Ar disktype Oc
.Pp
This form installs the bootstrap only.  It does not change the disk label.
You should never use this command on a base disk unless you intend to create a
.Dq dangerously-dedicated
disk, such as
.Ar da0 .
This command is typically run on a slice such as 
.Ar da0s1 .
.Pp
.Nm
.Fl w
.Fl B
.Op Fl n
.Oo
.Fl b Ar boot1
.Fl s Ar boot2
.Oc
.Ar disk Ar disktype
.Oo Ar packid Oc
.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.
If
.Fl n
is used, no data will be written to the device, and instead the
disklabel that would have been written will be printed to stdout.
.Pp
.Nm
.Fl R
.Fl B
.Op Fl n
.Oo
.Fl b Ar boot1
.Fl s Ar boot2
.Oc
.Ar disk Ar protofile
.Oo Ar disktype Oc
.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
flag.  If
.Fl n
is used, no data will be written to the device, and instead the
disklabel that would have been written will be printed to stdout.
.Pp
The bootstrap code is comprised of two boot programs.  Specify the name of the
boot programs to be installed in one of these ways:
.Bl -enum
.It
Specify the names explicitly with the
.Fl b
and
.Fl s
flags. 
.Fl b
indicates the primary boot program and
.Fl s
the secondary boot program.  The boot programs are located in
.Pa /boot .
.It
If the
.Fl b
and
.Fl s
flags are not specified, but 
.Ar disktype
was specified, the names of the programs are taken from the 
.Dq b0
and 
.Dq b1
parameters of the
.Xr disktab 5
entry for the disk if the disktab entry exists and includes those parameters.
.It
Otherwise, the default boot image names are used:
.Pa /boot/boot1
and
.Pa /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).
.El
.Ss Initializing/Formatting a bootable disk from scratch
.Pp
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
.Ar fdisk
to initialize the DOS partition table, creating a real whole-disk slice to
hold the
.Fx
disklabel, and installing a master boot record.
.It
Use
.Ar disklabel
to initialize a virgin
.Fx
disklabel and install
.Fx
boot blocks.
.It
Use
.Ar disklabel
to edit your newly created label, adding appropriate partitions.
.It
Finally newfs the filesystem partitions you created in the label.  A typical
disklabel partitioning scheme would be to have an
.Dq a
partition 
of approximately 128MB to hold the root filesystem, a
.Dq b
partition for
swap, a
.Dq d
partition for /var (usually 128MB), an
.Dq e
partition
for /var/tmp (usually 128MB), an
.Dq f
partition for /usr (usually around 2G),
and finally a
.Dq g
partition for /home (usually all remaining space).
Your mileage may vary.
.El
.Pp
.Nm fdisk Fl BI Ar da0
.Pp
.Nm
.Fl w
.Fl r
.Fl B
.Ar da0s1
auto
.Pp
.Pp
.Nm
.Fl e
.Ar da0s1
.Pp
.Sh FILES
.Bl -tag -width Pa -compact
.It Pa /etc/disktab
.It Pa /boot/
.It Pa /boot/boot<n>
.El
.Sh SAVED FILE FORMAT
.Nm
uses an 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 # mark are comments.  Most of the other specifications are
no longer used.  The ones which must still be set correctly are:
.Pp
.Bl -hang -width 20n
.It Nm label
is an optional label, set by the
.Ar packid
option when writing a label.
.It Nm flags
Flags may be
.Ar removable ,
.Ar ecc 
or
.Ar badsect .
.Ar removable
is set for removable media drives, but no current
.Fx
driver evaluates this
flag.
.Ar ecc
is no longer supported; 
.Ar badsect
specifies that the drive can perform bad sector remapping.
.It Nm sectors/unit
describes the total size of the disk.  This value must be correct.
.It Nm the partition table
This is the
.Ux
partition table, not the Microsoft partition table described in
.Xr fdisk 8 .
.El
.Pp
The partition table can have up to 8 entries.  It contains the following
information:
.Bl -hang -width 10n
.It identifier
The partition identifier is a single letter in the range
.Dq a
to
.Dq h .
By convention, partition
.Dq c
is reserved to describe the entire disk.
.It size
is 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 AFTER removing any fixed-size partitions other
than partition
.Dq c) ,
or
.Cm *
(all remaining free space AFTER fixed-size and percentage
partitions).  For partition
.Dq 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 offset
is 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
.Dq c .
For partition
.Dq c ,
.Cm *
will be interpreted as an offset of 0.
.It fstype
describes the purpose of the partition.  The example shows most normal usages.
For UFS file systems, use type
.Cm 4.2BSD .
Other common types are
.Cm unused
and
.Cm swap .
See
.Pa /usr/include/sys/disklabel.h 
for a complete list.
.It fsize
For
.Cm 4.2BSD
and LFS file systems only, the fragment size.  Defaults to 8192 for
partitions smaller than 1 GB, 16384 for partitions 1GB or larger.
.It bsize
For
.Cm 4.2BSD
and LFS file systems only, the block size.  Defaults to 1024 for
partitions smaller than 1 GB, 4096 for partitions 1GB or larger.
.It bps/cpg
For
.Cm 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 1 GB, 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 (*) indicates that the partition does not begin or end exactly on a
cylinder boundary.
.Sh EXAMPLES
.Dl disklabel da0
.Pp
Display the in-core label for 
.Pa da0s1
as obtained via
.Pa /dev/da0s1 .
When reading a label,
.Fx
will allow you to specify the base disk name
even if the label resides on a slice.  However, to be proper you should
specify the base disk name only if you are using a
.Dq dangerously-dedicated
label.  Normally you specify the slice.
.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
flag 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.
.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
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 disklabel -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/boot1
and possibly
.Pa /boot/boot2 .
On-disk and in-core labels are unchanged.
.Pp
.Dl disklabel -w -B /dev/da0s1 -b newboot1 -s newboot da2212
.Pp
Install a new label and bootstrap.
The label is derived from disktab information for
.Dq da2212
and installed both in-core and on-disk.
The bootstrap code comes from the files
.Pa /boot/newboot1
and
.Pa /boot/newboot2 .
.Pp
.Dl dd if=/dev/zero of=/dev/da0 bs=512 count=32
.Dl fdisk -BI da0
.Dl dd if=/dev/zero of=/dev/da0s1 bs=512 count=32
.Dl disklabel -w -r -B da0s1 auto
.Dl disklabel -e da0s1
.Pp
Completely wipe any prior information on the disk, creating a new bootable
disk with a DOS partition table containing one
.Dq whole-disk
slice.  Then
initialize the slice, then edit it to your needs.  The
.Pa dd
commands are optional, but may be necessary for some BIOSes to properly
recognize the disk.
.Pp
This is an example disklabel 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
.Pp
.Dl 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 disklabel 5 ,
.Xr disktab 5 ,
.Xr boot0cfg 8 ,
.Xr fdisk 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 
.Dq 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
.Dq a
partition.
.Pp
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
.Dq bootable
disk.
When installing bootstrap code,
.Nm
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
.Xr 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,
.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
.Dq c
partition.
.Pp
For the i386 architecture, the primary bootstrap sector contains
an embedded
.Em fdisk
table.
.Nm Disklabel
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 BSD disklabel
starts at absolute block 0 on the disk.
.Pp
.Nm
does not perform all possible error checking.  Warning *is* given if partitions
overlap; if an absolute offset does not match the expected offset; if the
.Dq 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.