FreeBSD man pages : disklabel (8)
DISKLABEL(8) FreeBSD System Manager's Manual DISKLABEL(8)
NAME
disklabel - read and write disk pack label
SYNOPSIS
disklabel [-r] disk
disklabel -w [-r] [-n] disk disktype/auto [packid]
disklabel -e [-r] [-n] disk
disklabel -R [-r] [-n] disk protofile
disklabel [-NW] disk
disklabel -B [-b boot1 -s boot2] disk [disktype/auto]
disklabel -w -B [-n] [-b boot1 -s boot2] disk disktype/auto [packid]
disklabel -R -B [-n] [-b boot1 -s boot2] disk protofile [disktype/auto]
DESCRIPTION
The disklabel 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 (dis-
play), install or edit the label on a disk. In addition, disklabel can
install bootstrap code.
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 disklabel access the in-core copy of the label. To access
the raw (on-disk) copy, use the -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 -r is described
under each command.
Disk device name
All disklabel forms require a disk device name, which should always be
the raw device name representing the disk or slice. For example da0 rep-
resents the entire disk regardless of any DOS partitioning, and da0s1
represents a slice. Some devices, most notably ccd, require that the
``whole-disk'' (or ``c'') partition be specified. For example ccd0c.
You do not have to include the /dev/ path prefix when specifying the
device. The disklabel utility will automatically prepend it.
Reading the disk label
To examine the label on a disk drive, use disklabel without options:
disklabel [-r] disk
disk represents the raw disk in question, and may be in the form da0 or
/dev/da0c. It will display all of the parameters associated with the
drive and its partition layout. Unless the -r flag is given, the ker-
nel'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 -r flag is given, disklabel
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 ini-
tialized or is corrupt.
Writing a standard label
To write a standard label, use the form
disklabel -w [-r] [-n] disk disktype/auto [packid]
disklabel -w [-r] [-n] disk auto
The required arguments to disklabel are the drive to be labeled and the
drive type as described in the 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 identi-
fication string, up to 16 characters long. The pack id must be quoted if
it contains blanks.
If the -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.
If the -r flag is given, the disk sectors containing the label and boot-
strap will be written directly. A side-effect of this is that any exist-
ing 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 -r is not specified, the existing label
will be updated via the in-core copy and any bootstrap code will be unaf-
fected. If the disk does not already have a label, the -r flag must be
used. In either case, the kernel's in-core label is replaced.
For a virgin disk that is not known to disktab(5), disktype can be speci-
fied as ``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 suc-
ceed for all SCSI disks, most IDE disks, and vnode devices. Writing a
label to the disk is the only supported operation, and the disk itself
must be provided as the canonical name, i.e. not as a full path name.
For most harddisks, a label based on percentages for most partitions (and
one partition with a size of `*') will produce a reasonable configura-
tion.
PC-based systems have special requirements in order for the BIOS to prop-
erly recognize a FreeBSD disklabel. Older systems may require what is
known as a ``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
partition using fdisk and then create a FreeBSD disklabel within that
slice. This is described later on in this page.
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.
Editing an existing disk label
To edit an existing disk label, use the form
disklabel -e [-r] [-n] disk
This command reads the label from the in-core kernel copy, or directly
from the disk if the -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 EDITOR environment variable, 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 -r was speci-
fied. If -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.
Restoring a disk label from a file
To restore a disk label from a file, use the form
disklabel -R [-r] [-n] disk protofile
disklabel 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. As when writing a new
label, any existing bootstrap code will be clobbered if -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 -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.
Enabling and disabling writing to the disk label area
By default, it is not possible to write to the disk label area at the
beginning of a disk. The disk driver arranges for write(2) and similar
system calls to return EROFS on any attempt to do so. If you need to
write to this area (for example, to obliterate the label), use the form
disklabel -W disk
To disallow writing to the label area after previously allowing it, use
the command
disklabel -N disk
Installing bootstraps
The final three forms of disklabel are used to install bootstrap code.
If you are creating a ``dangerously-dedicated'' slice for compatibility
with older PC systems, you generally want to specify the raw disk name
such as da0. If you are creating a label within an existing DOS slice,
you should specify the partition name such as da0s1a. Making a slice
bootable can be tricky. If you are using a normal DOS slice you typi-
cally install (or leave) a standard MBR on the base disk and then install
the FreeBSD bootblocks in the slice.
disklabel -B [-b boot1 -s boot2] disk [disktype]
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 ``dangerously-dedicated'' disk, such as da0. This
command is typically run on a slice such as da0s1.
disklabel -w -B [-n] [-b boot1 -s boot2] disk disktype [packid]
This form corresponds to the ``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
``dangerously-dedicated'' label. This command is normally run on a slice
rather than a base disk. If -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.
disklabel -R -B [-n] [-b boot1 -s boot2] disk protofile [disktype]
This form corresponds to the ``restore label'' command described above.
In addition to restoring the volume label, it also installs the boot-
strap. If run on a base disk this command will create a
``dangerously-dedicated'' label. This command is normally run on a slice
rather than a base disk.
The bootstrap commands always access the disk directly, so it is not nec-
essary to specify the -r flag. If -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.
The bootstrap code is comprised of two boot programs. Specify the name
of the boot programs to be installed in one of these ways:
1. Specify the names explicitly with the -b and -s flags. -b indicates
the primary boot program and -s the secondary boot program. The
boot programs are located in /boot.
2. If the -b and -s flags are not specified, but disktype was speci-
fied, the names of the programs are taken from the ``b0'' and ``b1''
parameters of the disktab(5) entry for the disk if the disktab entry
exists and includes those parameters.
3. Otherwise, the default boot image names are used: /boot/boot1 and
/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).
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 non-FreeBSD slices.
1. Use fdisk(8) to initialize the hard disk, and create a slice table,
referred to as the partition table in DOS. Here you will define
disk slices for your system.
2. Use disklabel to define and write partitions and mount points. You
are not required to define the mount points here though, they can be
defined later using mount(8).
3. Finally use newfs(8) to create a file system on the new partition.
A typical partitioning scheme would be to have an ``a'' partition of
approximately 128MB to hold the root file system, a ``b'' partition
for swap, a ``d'' partition for /var (usually 128MB), an ``e'' par-
tition for /var/tmp (usually 128MB), an ``f'' partition for /usr
(usually around 2G), and finally a ``g'' partition for /home (usu-
ally all remaining space). Your mileage may vary.
fdisk -BI da0
disklabel -w -B da0s1 auto
disklabel -e da0s1
FILES
/etc/disktab
/boot/
/boot/boot<n>
SAVED FILE FORMAT
The disklabel utility uses an ASCII version of the label when examining,
editing or restoring a disk label. 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 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*)
Lines starting with a # mark are comments. Most of the other specifica-
tions are no longer used. The ones which must still be set correctly
are:
label is an optional label, set by the packid option when
writing a label.
flags Flags may be removable, ecc or badsect. removable
is set for removable media drives, but no current
FreeBSD driver evaluates this flag. ecc is no
longer supported; badsect specifies that the drive
can perform bad sector remapping.
sectors/unit describes the total size of the disk. This value
must be correct.
the partition table This is the UNIX partition table, not the Microsoft
partition table described in fdisk(8).
The partition table can have up to 8 entries. It contains the following
information:
identifier The partition identifier is a single letter in the range
``a'' to ``h''. By convention, partition ``c'' is reserved
to describe the entire disk.
size is the size of the partition in sectors, K (kilobytes -
1024), M (megabytes - 1024*1024), G (gigabytes -
1024*1024*1024), % (percentage of free space AFTER removing
any fixed-size 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 K, M, and G are allowed.
Size and type should be specifed without any spaces between
them.
Example: 2097152, 1g, 1024m and 1048576k are all the same
size (assuming 512-byte sectors).
offset is the offset of the start of the partition from the begin-
ning of the drive in sectors, or * to have disklabel calcu-
late the correct offset to use (the end of the previous par-
tition plus one, ignoring partition ``c''. For partition
``c'', * will be interpreted as an offset of 0.
fstype describes the purpose of the partition. The example shows
all currently used partition types. For UFS file systems and
ccd partitions, use type 4.2BSD. For Vinum drives, use type
vinum. Other common types are unused and swap. By conven-
tion, partition ``c'' represents the entire slice and should
be of type unused, though disklabel does not enforce this
convention. The disklabel 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
/usr/include/sys/disklabel.h for more details.
fsize For 4.2BSD and LFS file systems only, the fragment size.
Defaults to 1024 for partitions smaller than 1 GB, 4096 for
partitions 1GB or larger.
bsize For 4.2BSD and LFS file systems only, the block size.
Defaults to 8192 for partitions smaller than 1 GB, 16384 for
partitions 1GB or larger.
bps/cpg For 4.2BSD file systems, the number of cylinders in a cylin-
der group. For LFS file systems, the segment shift value.
Defaults to 16 for partitions smaller than 1 GB, 64 for par-
titions 1GB or larger.
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.
EXAMPLES
disklabel da0
Display the in-core label for da0s1 as obtained via /dev/da0s1. When
reading a label, FreeBSD 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
``dangerously-dedicated'' label. Normally you specify the slice.
disklabel da0s1 > savedlabel
Save the in-core label for da0s1 into the file savedlabel. This file can
be used with the -R flag to restore the label at a later date.
disklabel -w -r /dev/da0s1 da2212 foo
Create a label for da0s1 based on information for ``da2212'' found in
/etc/disktab. Any existing bootstrap code will be clobbered.
disklabel -e -r da0s1
Read the on-disk label for da0s1, edit it and reinstall in-core as well
as on-disk. Existing bootstrap code is unaffected.
disklabel -e -r -n 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.
disklabel -r -w da0s1 auto
Try to auto-detect the required information from da0s1, and write a new
label to the disk. Use another disklabel -e command to edit the parti-
tioning and file system information.
disklabel -R da0s1 savedlabel
Restore the on-disk and in-core label for da0s1 from information in
savedlabel. Existing bootstrap code is unaffected.
disklabel -R -n da0s1 label_layout
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
alloted for various partitions with a labelling scheme using %-based or *
partition sizes.
disklabel -B da0s1
Install a new bootstrap on da0s1. The boot code comes from /boot/boot1
and possibly /boot/boot2. On-disk and in-core labels are unchanged.
disklabel -w -B /dev/da0s1 -b newboot1 -s newboot2 da2212
Install a new label and bootstrap. The label is derived from disktab
information for ``da2212'' and installed both in-core and on-disk. The
bootstrap code comes from the files /boot/newboot1 and /boot/newboot2.
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
Completely wipe any prior information on the disk, creating a new
bootable disk with a DOS partition table containing one ``whole-disk''
slice. Then initialize the slice, then edit it to your needs. The dd
commands are optional, but may be necessary for some BIOSes to properly
recognize the disk.
This is an example disklabel that uses some of the new partition size
types such as %, M, G, and *, which could be used as a source file for
disklabel -R ad0s1c new_label_file
# /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
SEE ALSO
ccd(4), disklabel(5), disktab(5), boot0cfg(8), fdisk(8), vinum(8)
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 parti-
tion if a disk is unlabeled; thus, the label must be written to the ``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 ``a'' partition.
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 possi-
ble to have file systems on some partitions of a ``bootable'' disk. When
installing bootstrap code, disklabel 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 newfs(8) utility will disallow creation of
file systems on FS_BOOT partitions. Conversely, if a partition has a
type other than FS_UNUSED or FS_BOOT, disklabel will not install boot-
strap code that overlaps it.
BUGS
When a disk name is given without a full pathname, the constructed device
name uses the ``c'' partition.
For the i386 architecture, the primary bootstrap sector contains an
embedded fdisk table. The disklabel utility takes care to not clobber it
when installing a bootstrap only (-B), or when editing an existing label
(-e), but it unconditionally writes the primary bootstrap program onto
the disk for -w or -R, thus replacing the fdisk table by the dummy one in
the bootstrap program. This is only of concern if the disk is fully ded-
icated, so that the BSD disklabel starts at absolute block 0 on the disk.
The disklabel utility 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 ``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.
FreeBSD 4.8 July 30, 1999 FreeBSD 4.8
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