DISKLABEL ( 8 ) FreeBSD System Manager's Manual DISKLABEL ( 8 )
disklabel - read and write disk pack label
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disklabel [ -r ] disk disklabel -w [ -r ] [ -n ] disk disktype/auto [packid] disklabel -B [ -b boot1 -s boot2] disk [disktype/auto] disklabel -w -B [ -n ] |
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 la-
bel. There are several forms of the command that read (display), install or edit the label on a disk. In addi-
tion, disklabel can install bootstrap code.
Raw or in-core label
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 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 repre-
senting the disk or slice. For example da0 represents the entire disk irregardless 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. disklabel will automatically prepend it.
Reading the disk label
To examine or save 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 in-
correct, 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 initialized 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 de-
scribing each, or to edit the label after installation as described below. The optional argument is a pack FreeBSD July 30, 1999 1
DISKLABEL ( 8 ) FreeBSD System Manager's Manual DISKLABEL ( 8 )
identification 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 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 -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 -r flag must be used. In either case, the kernel's in-core la-
bel is replaced.
For a virgin disk that is not known to disktab(5), disktype can be specified as ``auto''. In this case,
the driver is requested to produce a virgin label for the disk. This might or might not be successful, de-
pending 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 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 configuration.
PC-based systems have special requirements in order for the BIOS to properly recognize a FreeBSD diskla-
bel. 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 slice using fdisk and then create a FreeBSD diskla-
bel 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 edit-
ing a label. Comments are delimited by # and newline. As when writing a new label, any existing boot-
strap code will be clobbered if -r is specified and will be unaffected otherwise. See the boot options be-
low 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 std-
out. This is useful to see how a partitioning scheme will work out for a specific disk.
FreeBSD July 30, 1999 2
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DISKLABEL ( 8 ) FreeBSD System Manager's Manual Enabling and disabling writing to the disk label area |
DISKLABEL ( 8 ) |
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
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'' partition 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 speci-
fy the slice name such as 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 FreeBSD boot-
blocks 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 com-
mand on a base disk unless you intend to create a ``dangerously-dedicated'' disk, such as da0. This com-
mand 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 vol-
ume 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 std-
out.
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 vol-
ume 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.
The bootstrap commands always access the disk directly, so it is not necessary 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 in-
stalled in one of these ways:
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1. |
Specify the names explicitly with the -b and -s flags. -b indicates the primary boot program and |
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2. |
If the -b and -s flags are not specified, but disktype was specified, the names of the programs are taken from the ``b0'' and ``b1'' parameters of the disktab(5) entry for the disk if the disktab en- try exists and includes those parameters. |
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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
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DISKLABEL ( 8 ) FreeBSD System Manager's Manual DISKLABEL ( 8 )
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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-Fx slices. 1. Use fdisk to initialize the DOS partition table, creating a real whole-disk slice to hold the |
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FreeBSD 2. Use disklabel to initialize a virgin |
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FreeBSD disklabel and install FreeBSD boot blocks. |
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3. Use disklabel to edit your newly created label, adding appropriate partitions. 4. Finally newfs the filesystem partitions you created in the label. A typical disklabel partitioning scheme fdisk -BI da0 disklabel -w -r -B da0s1 auto disklabel -e da0s1 |
FILES
/etc/disktab
/boot/
/boot/boot<n>
disklabel uses an ASCII version of the label when examining, editing or restoring a disk label. The
format is:
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# /dev/da1c: 8 partitions: |
bsize bps/cpg] |
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FreeBSD |
a: 81920 0 4.2BSD 1024 July 30, 1999 |
8192 16 # (Cyl. 0 - 84*) 4 |
DISKLABEL ( 8 ) FreeBSD System Manager's Manual DISKLABEL ( 8 )
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:
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label flags |
is an optional label, set by the packid option when writing a label. Flags may be removable, ecc or badsect. removable is set for removable media drives, but no current |
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FreeBSD driver evaluates this flag. ecc is no longer |
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supported; badsect specifies that the drive can perform bad sector remapping. |
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sectors/unit |
describes the total size of the disk. This value must be correct. |
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the partition table This is the UNIX partition table, not the Microsoft partition table described 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 re- size is the size of the partition in sectors, K (kilobytes - 1024), M (megabytes - 1024*1024), G (giga- Example: 2097152, 1g, 1024m and 1048576k are all the same size (assuming 512-byte sec- offset is the offset of the start of the partition from the beginning of the drive in sectors, or * to have fstype describes the purpose of the partition. The example shows most normal usages. For UFS file fsize For 4.2BSD and LFS file systems only, the fragment size. Defaults to 8192 for partitions bsize For 4.2BSD and LFS file systems only, the block size. Defaults to 1024 for partitions smaller bps/cpg For 4.2BSD file systems, the number of cylinders in a cylinder group. For LFS file systems, The remainder of the line is a comment and shows the cylinder allocations based on the obsolete (but pos- sibly correct) geometry information about the drive. The asterisk (*) indicates that the partition does not begin or end exactly on a cylinder boundary. |
disklabel da0
Display the in-core label for da0s1 as obtained via /dev/da0s1. When reading a label, FreeBSD will al-
low 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 re-
store the label at a later date.
FreeBSD July 30, 1999 5
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DISKLABEL ( 8 ) FreeBSD System Manager's Manual disklabel -w -r /dev/da0s1 da2212 foo |
DISKLABEL ( 8 ) |
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 partitioning 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 newboot 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 -r -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
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FreeBSD |
disklabel -R ad0s1c new_label_file # /dev/ad0s1c: July 30, 1999 |
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DISKLABEL ( 8 ) FreeBSD System Manager's Manual DISKLABEL ( 8 )
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sectors/track: 63 8 partitions: |
bsize bps/cpg] |
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a: 400M 0 4.2BSD 4096 |
16384 75 # (Cyl. 0 - 812*) |
disklabel(5), disktab(5), boot0cfg(8), fdisk(8)
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The kernel device drivers will not allow the size of a disk partition to be decreased or the offset of a parti- tion 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 filesystems. As a result, it may not be possible to have filesystems on some partitions of a ``bootable'' disk. When in- stalling 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 filesystems on FS_BOOT partitions. Conversely, if a partition has a type other than FS_UNUSED or FS_BOOT, disklabel will not install bootstrap code that overlaps it. |
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When For disklabel FreeBSD |
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. Disklabel takes care to not clobber it when installing a bootstrap only ( -B ) , or when editing an existing label disklabel does not perform all possible error checking. Warning *is* given if partitions overlap; if an absolute offset doesn't match the expected offset; if the c partition doesn't start at 0 or doesn't 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. July 30, 1999 7 |