sbin/disklabel/disklabel.8

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.\"	@(#)disklabel.8	8.2 (Berkeley) 4/19/94
.\"
.Dd $Mdocdate: November 10 2021 $
.Dt DISKLABEL 8
.Os
.Sh NAME
.Nm disklabel
.Nd read and write disk pack label
.Sh SYNOPSIS
.Nm disklabel
.Op Fl Acdtv
.Op Fl h | p Ar unit
.Op Fl T Ar file
.Ar disk
.Nm disklabel
.Fl w
.Op Fl Acdnv
.Op Fl T Ar file
.Ar disk disktype
.Op Ar packid
.Nm disklabel
.Fl e
.Op Fl Acdnv
.Op Fl T Ar file
.Ar disk
.Nm disklabel
.Fl E
.Op Fl Acdnv
.Op Fl F Ns | Ns Fl f Ar file
.Op Fl T Ar file
.Ar disk
.Nm disklabel
.Fl R
.Op Fl nv
.Op Fl F Ns | Ns Fl f Ar file
.Ar disk protofile
.Sh DESCRIPTION
The
.Nm
utility can be used to install, examine, or modify the label on a disk drive or
pack.
The disk label contains information about disk characteristics
.Pq size, type, etc.
and the partition layout, stored on the disk itself.
It is used by the operating system to optimize disk I/O and
locate the filesystems resident on the disk.
.Pp
.Nm
supports 15 configurable partitions,
.Sq a
through
.Sq p ,
excluding
.Sq c .
The
.Sq c
partition describes the entire physical disk, is automatically created
by the kernel, and cannot be modified or deleted by
.Nm .
By convention, the
.Sq a
partition of the boot disk is the root partition, and the
.Sq b
partition of the boot disk is the swap partition,
but all other letters can be used in any order for any other
partitions as desired.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl A
Automatically allocate all the disk space in the
.Ox
portion of the disk in the recommended manner.
See
.Sx AUTOMATIC DISK ALLOCATION ,
below.
.It Fl c
Clear the system's in-core copy of the label and update it based on
the on-disk label.
.It Fl d
Use the
.Em default
label.
This ignores any existing
.Ox
disk label on the disk.
.It Fl E
Use the built-in command-driven label editor described below.
.It Fl e
Edit an existing disk label using the editor specified in the
.Ev EDITOR
environment variable, or
.Xr vi 1
if none is specified.
.It Fl F Ar file
Write entries to
.Ar file
in
.Xr fstab 5
format for any partitions for which mount point information is known.
The entries will be written using disklabel UIDs.
The
.Fl F
flag is only valid when used in conjunction with the
.Fl E
or
.Fl R
flags.
If
.Ar file
already exists, it will be overwritten.
.It Fl f Ar file
The same as
.Fl F
except that entries will be written using disk device names.
.It Fl h
Print partition sizes in human readable format.
.It Fl n
Make no permanent changes to the disklabel
.Pq useful for debugging purposes .
.It Fl p Ar unit
Print partition sizes in
.Ar unit
instead of sectors.
Valid units are b(ytes), c(ylinders), k(ilobytes), m(egabytes), g(igabytes)
and t(erabytes).
.It Fl R
Restore a disk label that was formatted in a prior operation and
saved in an ASCII file.
.It Fl T Ar file
Read the template for automatic allocation from
.Ar file
instead of using the builtin one.
See
.Sx AUTOMATIC DISK ALLOCATION
below for the format.
.It Fl t
Format the label as a
.Xr disktab 5
entry.
.It Fl v
Print additional information during operation
.Pq verbose mode .
.It Fl w
Write a standard label on the designated drive.
.It Ar disk
Specify the
.Ar disk
to operate on.
It can be specified by its full pathname, by an abbreviated disk form,
or by its disklabel UID.
In its abbreviated form, the path to the device, the
.Sq r
denoting
.Qq raw device ,
and the partition letter, can all be omitted.
For example, the first IDE disk can be specified as either
.Pa /dev/rwd0c ,
.Pa /dev/wd0c ,
or
.Ar wd0 .
.It Ar disktype
Specify a
.Ar disktype
entry from the
.Xr disktab 5
database.
.It Ar packid
Specify a pack identification string for the device
.Pq see below .
.It Ar protofile
Used with the restore option
.Pq Fl R
to specify a file to read an ASCII label from.
.El
.Pp
The first form of the command
.Pq read
is used to examine the label on the named disk drive.
It will display all of the parameters associated with the drive
and its partition layout.
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.
.Pp
The second form of the command
.Pq write
is used to write a standard label on the designated drive.
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.
The existing label will be updated via the in-core
copy.
.Pp
In the third form of the command
.Pq edit ,
the label is read from the in-core kernel copy
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 formatted label is reread and
used to rewrite the disk label.
.Pp
The built-in label editor
.Pq fourth form
provides a simple interactive label editor.
The editor prompt contains information about the state of the edit
process.
.Pp
.Dl Ar disk Ns *>
.Pp
Where
.Ar disk
is the name of the disk being edited,
.Sq *
means that the in-memory copy of the partition table has been modified but
not yet written to disk and the
.Sq >
is replaced by
.Sq #
when the editor is in expert mode.
.Pp
Some commands or prompts take an optional unit.
Available units are
.Sq b
for bytes,
.Sq c
for cylinders,
.Sq k
for kilobytes,
.Sq m
for megabytes,
.Sq g
for gigabytes,
and
.Sq t
for terabytes.
If no unit is given, the default is to use sectors
(usually 512 bytes).
.Pp
Quantities are rounded to the nearest
cylinder when units are specified for sizes
.Pq or offsets .
At prompts that request a size,
.Ql *
may be entered to indicate the rest of the available space,
.Sq %
for percentage of total, and
.Sq &
for percentage free.
Commands may be aborted by entering
.Ql ^D
.Pq Control-D .
Entering
.Ql ^D
at the main prompt will exit the editor.
.Pp
The editor commands are as follows:
.Bl -tag -width "p [unit] "
.It Cm \&? | h
Display help message with all available commands.
There is also
.Pq simple
context-sensitive help available at most prompts.
.It Cm A
Allocate all the disk space in the recommended manner.
See
.Sx AUTOMATIC DISK ALLOCATION ,
below.
.It Cm a Op Ar part
Add new partition.
This option adds a new partition to the disk label.
If no partition letter is specified
.Pq a\-p ,
the user will be prompted for one.
.It Cm b
Set
.Ox
disk boundaries.
This option tells
.Nm
which parts of the disk it is allowed to modify.
This option is probably only useful for ports with
.Xr fdisk 8
partition tables where the ending sector in the MBR is incorrect.
The user may enter
.Ql *
at the
.Dq Size
prompt to indicate the entire size of the disk
.Pq minus the starting sector .
This is useful for disks where the
fdisk partition table is incapable of storing the real size.
Note: data may become corrupted if boundaries are extended such
that they overlap with other resident operating systems.
.It Cm c Op Ar part
Change the size of an existing partition.
If no partition is specified, the user will be prompted for one.
The new size may be
in terms of the aforementioned units and may also be prefixed with
.Ql +
or
.Ql -
to change the size by a relative amount.
.It Cm D
Sets the disk label to the default values as reported by the kernel.
This simulates the case where there is no disk label.
.It Cm d Op Ar part
Delete an existing partition (or
.Ql *
to delete all partitions).
If no partition is specified, the user will be prompted for one.
.It Cm e
Edit drive parameters.
This option is used to set the following parameters:
disk type, a descriptive label string, sectors/track,
tracks/cylinder, sectors/cylinder, number of cylinders,
total sectors, rpm, and interleave.
.It Xo
.Cm g
.Op Ar d | u
.Xc
Set disk geometry based on what the
.Em disk
or
.Em user
thinks (the
.Em user
geometry is simply what the label said before
.Nm
made any changes).
.It Cm i
Change the disklabel UID, specified as a 16-character hexadecimal string.
If set to all zeros, a new UID will automatically be allocated when the
disklabel is written to disk.
.It Cm l Op Ar unit
Print the disk label header.
.It Cm M
Display this manual page.
The manual page is piped through the pager specified by the
.Ev PAGER
environment variable or 'less' if
.Ev PAGER
is not set.
.It Cm m Op Ar part
Modify parameters for an existing partition.
If no partition is specified, the user will be prompted for one.
This option allows
the user to change the filesystem type, starting offset, partition size,
and mount point for the specified partition.
If expert mode is enabled (see
.Cm X
below), then block fragment size, block size, and cylinders per group
can also be modified.
Note that not all parameters are configurable for
.Pf non- Bx
partitions.
.It Cm n Op Ar part
Name the mount point for an existing partition.
If no partition is specified, the user will be prompted for one.
This option is only valid if
.Nm
was invoked with the
.Fl f
flag.
.It Cm p Op Ar unit
Print the current partition list.
If a
.Em unit
is given, the size and offsets are displayed in terms of the
specified unit.
If the unit is
.Sq *
it is automatically determined by the size of the smallest
partition.
.It Cm q
Quit the editor.
If any changes have been made, the user will be
asked whether or not to save the changes to the on-disk label.
.It Cm R Op Ar part
Resize a partition in an automatically allocated label,
compacting unused space between partitions with a higher offset.
The last partition will be shrunk if necessary.
Works only for automatically allocated labels with no spoofed partitions.
.It Cm r
Recalculate free space.
This command displays all the free areas on the disk and the total
number of free sectors.
.It Cm s Op Ar path
Save the label to a file in ASCII format (suitable for loading via the
.Fl R
option).
If no path is specified, the user will be prompted for one.
.It Cm U
Undo all changes made since entering the editor.
.It Cm u
Undo
.Pq or redo
last change.
Entering
.Em u
once will undo the last change.
Entering it again will restore the change.
.It Cm w
Write the label to disk.
This option will commit any changes to the on-disk label.
.It Cm X
Toggle
.Dq expert mode .
By default, some settings are reserved for experts only
(such as the block and fragment size on ffs partitions).
While in expert mode the command line prompt will end
with
.Ql #
instead of
.Ql > .
.It Cm x
Exit the editor without saving any changes to the on-disk label.
.It Cm z
Zero out the existing partition table and mount point information,
leaving only the 'c' partition.
The drive parameters are not changed.
.El
.Pp
In the restore form of the command
.Pq fifth form ,
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.
.Pp
Note that when a disk has no real
.Bx
disklabel, the kernel creates a
default label so that the disk can be used.
This default label will include other partitions found on the disk if
they are supported on your architecture.
For example, on systems that support
.Xr fdisk 8
partitions the default label will also include DOS and Linux partitions.
However, these entries are not dynamic, they are fixed at the time
.Nm
is run.
That means that subsequent changes that affect
.Pf non- Ox
partitions will not be present in the default label,
though they may be updated by hand.
To see the default label, run
.Nm
with the
.Fl d
flag.
.Nm
can then be run with the
.Fl e
flag and any entries pasted as desired from the default label into the real one.
.Sh AUTOMATIC DISK ALLOCATION
The
.Fl A
option and the editor command
.Cm A
automatically create a disklabel with a set of partitions
suitable for a majority of
.Ox
installations.
Any existing
.Ox
disklabel on the disk is ignored, but native partitions
that would normally be spoofed are preserved in the disklabel,
and are not modified during the allocation process.
.Pp
Disk size determines the set of partitions which are created.
Each partition is allocated space between a specified minimum
and maximum.
Initially, each partition is allocated its minimum space;
remaining space is split between the partitions according to the
given percentages,
up to their maximum allowed space.
Space left after all partitions have reached their maximum size
is left unallocated.
The sizes below are approximations,
and may vary from architecture to architecture.
.Pp
.Sy Disks >= 10 Gigabytes
.Bd -literal -offset indent -compact
/		 5% of disk.  150M \(en 1G
swap		10% of disk.   80M \(en 2x max physical memory
/tmp		 8% of disk.  120M \(en 4G
/var		13% of disk.   80M \(en 4G + 2x size of crash dump
/usr		10% of disk. 1500M \(en 6G
/usr/X11R6	 3% of disk.  384M \(en 1G
/usr/local	15% of disk.    1G \(en 20G
/usr/src	 2% of disk. 1500M \(en 3G
/usr/obj	 4% of disk.    5G \(en 6G
/home		30% of disk.    1G \(en 300G
.Ed
.Pp
.Sy Disks > 2.5 Gigabytes
.Bd -literal -offset indent -compact
/		 5% of disk.  800M \(en 2G
swap		10% of disk.   80M \(en 2x max physical memory
/usr		78% of disk. 1300M \(en 3G
/home		 7% of disk.  256M \(en 2G
.Ed
.Pp
.Sy Disks > 700 Megabytes
.Bd -literal -offset indent -compact
/		95% of disk. 700M \(en 4G
swap		 5% of disk.   1M \(en 2x max physical memory
.Ed
.Pp
A template for the automatic allocation can be passed to disklabel using
the
.Fl T
option.
The template consists of one line per partition, with each line giving
mount point, min-max size range, and percentage of disk, space-separated.
Max can be unlimited by specifying '*'.
If only mount point and min size are given, the partition is created with that
exact size.
.Bd -literal -offset indent
/		250M
swap		80M-256M 10%
/tmp		120M-4G	8%
/var		80M-4G	13%
/usr		1.5G-3G	5%
/usr/X11R6	512M-1G	3%
/usr/local	2G-10G	10%
/usr/src	1.5G-3G	2%
/usr/obj	1.3G-2G	4%
/home		1G-*	45%
.Ed
.Sh FILES
.Bl -tag -width Pa -compact
.It Pa /etc/disktab
Disk description file.
.El
.Sh EXAMPLES
Display the in-core label for sd0 as obtained via
.Pa /dev/rsd0c :
.Pp
.Dl # disklabel sd0
.Pp
Create a label for sd0 based on information for
.Dq sd2212
found in
.Pa /etc/disktab :
.Pp
.Dl # disklabel -w /dev/rsd0c sd2212 foo
.Pp
Read the on-disk label from a disk with DUID 3eb7f9da875cb9ee,
edit it and reinstall in-core as well as on-disk:
.Pp
.Dl # disklabel -E 3eb7f9da875cb9ee
.Pp
Restore the on-disk and in-core label for sd0 from information in
.Pa mylabel :
.Pp
.Dl # disklabel -R sd0 mylabel
.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
.Sq 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
.Sq a
partition.
.Sh SEE ALSO
.Xr disklabel 5 ,
.Xr disktab 5 ,
.Xr installboot 8 ,
.Xr scan_ffs 8
.Sh CAVEATS
The maximum disk and partition size is 64PB.
.Pp
On some machines, such as Sparc64, partition tables
may not exhibit the full functionality described above.