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DISKLABEL32(8) System Manager's Manual DISKLABEL32(8)

disklabel32 — read and write 32 bit disk pack label

disklabel32 [-r] disk

disklabel32 -w [-r] [-n] disk disktype/auto [packid]

disklabel32 -e [-r] [-n] disk

disklabel32 -R [-r] [-n] disk protofile

disklabel32 [-NW] disk


disklabel32 -B [-b boot1 -s boot2] disk [disktype/auto]

disklabel32 -w -B [-n] [-b boot1 -s boot2] disk disktype/auto [packid]

disklabel32 -R -B [-n] [-b boot1 -s boot2] disk protofile [disktype/auto]

disklabel32 -f slice_start_lba [options]

The disklabel32 utility installs, examines or modifies a 32 bit 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, disklabel32 can install bootstrap code.

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 forms of the disklabel32 command 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.

All disklabel32 forms require a disk device name, which should always be the raw device name representing the disk or slice. DragonFly uses the following scheme for slice numbering: If the disk doesn't use GPT (typically laid out by gpt(8)), but e.g. MBR (typically laid out by fdisk(8)), then slice 0, e.g. da0s0, represents the entire disk regardless of any DOS partitioning. Slice 0 is called the compatibility slice, and slice 1 and onward, e.g. da0s1, represents a BSD slice. If the disk does use GPT, then all slices are BSD slices, slice 0 isn't special, it is just the first slice on the disk. You do not have to include the /dev/ path prefix when specifying the device. The disklabel32 utility will automatically prepend it.

To examine the label on a disk drive, use disklabel32 without options:

disklabel32 [-r] disk

disk represents the raw disk in question, and may be in the form da0s1 or /dev/da0s1. It will display all of the parameters associated with the drive and its partition layout. Unless the -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 -r flag is given, disklabel32 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.

To write a standard label, use the form

disklabel32 -w [-r] [-n] disk disktype/auto [packid]

The required arguments to disklabel32 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 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 label 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, 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 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 DragonFly 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 DragonFly 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.

To edit an existing disk label, use the form

disklabel32 -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 specified. 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.

To restore a disk label from a file, use the form

disklabel32 -R [-r] [-n] disk protofile

disklabel32 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.

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

disklabel32 -W disk

To disallow writing to the label area after previously allowing it, use the command

disklabel32 -N disk

The final three forms of disklabel32 are used to install bootstrap code, which allows boot from a UFS(5) file system. If you are creating a “dangerously-dedicated” slice for compatibility with older PC systems, you generally want to specify the compatibility slice, such as da0s0. If you are creating a label within an existing DOS slice, you should specify the slice name such as da0s1. Making a slice 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 DragonFly bootblocks in the slice.

disklabel32 -B [-b boot1 -s boot2] disk [disktype/auto]

This form installs the bootstrap only. It does not change the disk label. You should never use this command on the compatibility slice unless you intend to create a “dangerously-dedicated” disk, such as da0s0. This command is typically run on a BSD slice such as da0s1.

disklabel32 -w -B [-n] [-b boot1 -s boot2] disk disktype/auto [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 the compatibility slice this command will create a “dangerously-dedicated” label. This command is normally run on a BSD slice rather than the compatibility slice. 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.

disklabel32 -R -B [-n] [-b boot1 -s boot2] disk protofile [disktype/auto]

This form corresponds to the “restore label” command described above. In addition to restoring the volume label, it also installs the bootstrap. If run on the compatibility slice this command will create a “dangerously-dedicated” label. This command is normally run on a BSD slice rather than the compatibility slice.

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 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 normally located in /boot.
  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 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.

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-DragonFly slices.

  1. Use gpt(8) or fdisk(8) to initialize the hard disk, and create a GPT or MBR slice table, referred to as the “partition table” in DOS.
  2. Use disklabel32 or disklabel64(8) to define partitions on DragonFly slices created in the previous step.
  3. Finally use newfs_hammer(8) or newfs(8) to create file systems on new partitions.

A typical partitioning scheme would be to have an ‘a’ partition of approximately 512MB to hold the root file system, a ‘b’ partition for swap (usually 4GB), a ‘d’ partition for /var (usually 2GB), an ‘e’ partition for /var/tmp (usually 2GB), an ‘f’ partition for /usr (usually around 4GB), and finally a ‘g’ partition for /home (usually all remaining space). If you are tight on space all sizes can be halved. Your mileage may vary.

fdisk -BI da0
disklabel32 -w -B da0s1 auto
disklabel32 -e da0s1

DragonFly no longer snoop-adjusts the on-disk label when reading or writing raw labels. disklabel32 is now responsible for adjusting the label when operating in raw mode. Traditional (32 bit, BSD) disklabels store offsets as absolute block numbers rather than slice-relative block numbers. If disklabel32 is unable to issue the DIOCGPART ioctl to get slice information it will refuse to read or write the label in raw mode. The -f option may be used to force the operation by supplying a manual offset.

/boot/boot1
Default stage1 boot image.
/boot/boot2
Default stage2 boot image.
/etc/disktab
Disk description file.

The disklabel32 utility uses an ASCII version of the label when examining, editing, or restoring a disk label. The format is:

# /dev/ad4s4:
type: unknown
disk: amnesiac
label: fictitious
flags:
bytes/sector: 512
sectors/track: 63
tracks/cylinder: 24
sectors/cylinder: 1512
cylinders: 161098
sectors/unit: 243581184
rpm: 3600
interleave: 1
trackskew: 0
cylinderskew: 0
headswitch: 0		# milliseconds
track-to-track seek: 0	# milliseconds
drivedata: 0

16 partitions:
#          size     offset    fstype
  a:    1048560         16    4.2BSD	#     511.992MB
  b:    8388608    1048576      swap	#    4096.000MB
  c:  243581184          0    unused	#  118936.125MB
  d:    4194304    9437184    4.2BSD	#    2048.000MB
  e:    4194304   13631488    4.2BSD	#    2048.000MB
  f:    8388608   17825792    4.2BSD	#    4096.000MB
  h:  196395264   26214400    HAMMER	#   95896.125MB
  i:   10485760  222609664       ccd	#    5120.000MB
  j:   10485760  233095424     vinum	#    5120.000MB

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:

label
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 DragonFly 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
is the UNIX partition table, not the DOS partition table described in fdisk(8).

The partition table can have up to 16 entries. It contains the following information:

#
The partition identifier is a single letter in the range ‘a’ to ‘p’. By convention, partition ‘c’ is reserved to describe the entire disk.
size
The size of the partition in sectors, K (kilobytes - 1024), M (megabytes - 1024*1024), G (gigabytes - 1024*1024*1024), T (gigabytes - 1024*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, G, and T are allowed. Size and type should be specified without any spaces between them.

Example: 2097152, 1G, 1024M and 1048576K are all the same size (assuming 512-byte sectors).

offset
The offset of the start of the partition from the beginning of the drive in sectors, or * to have disklabel32 calculate the correct offset to use (the end of the previous partition 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(5) file systems, use type 4.2BSD. For HAMMER(5) file systems, use type HAMMER. For ccd(4) partitions, use type ccd. For Vinum drives, use type vinum. Other common types are swap and unused. By convention, partition ‘c’ represents the entire slice and should be of type unused, though disklabel32 does not enforce this convention. The disklabel32 utility also knows about a number of other partition types, none of which are in current use. (See fstypenames in <sys/dtype.h> for more details).

The remainder of the line is a comment and shows the size of the partition in MB.

disklabel32 da0s1

Display the in-core label for the first slice of the da0 disk, as obtained via /dev/da0s1. (If the disk is “dangerously-dedicated”, the compatibility slice name should be specified, such as da0s0.)

disklabel32 da0s1 > savedlabel

Save the in-core label for da0s1 into the file savedlabel. This file can be used with the -R option to restore the label at a later date.

disklabel32 -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 and the disk rendered unbootable.

disklabel32 -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.

disklabel32 -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 install the new label either in-core or on-disk.

disklabel32 -r -w da0s1 auto

Try to auto-detect the required information from da0s1, and write a new label to the disk. Use another disklabel32 -e command to edit the partitioning and file system information.

disklabel32 -R da0s1 savedlabel

Restore the on-disk and in-core label for da0s1 from information in savedlabel. Existing bootstrap code is unaffected.

disklabel32 -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 allotted for various partitions with a labelling scheme using %-based or * partition sizes.

disklabel32 -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.

disklabel32 -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 newboot1 and 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
disklabel32 -w -B da0s1 auto
disklabel32 -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.

disklabel32 -W da0s1
dd if=/dev/zero of=/dev/da0s1 bs=512 count=32
disklabel64 -r -w da0s1 auto
disklabel64 -N da0s1

Completely wipe any prior information on the slice, changing label format to 64 bit. The wiping is needed as disklabel64 and disklabel32, as a safety measure, won't do any operations if label with other format is already installed.

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

disklabel32 -R ad0s1 new_label_file
# /dev/ad0s1:
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

16 partitions:
#          size     offset    fstype
  a:       400M          0    4.2BSD
  b:         1G          *      swap
  c:          *          *    unused
  e:     204800          *    4.2BSD
  f:         5g          *    4.2BSD
  g:          *          *    4.2BSD

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 ‘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 possible to have file systems on some partitions of a “bootable” disk. When installing bootstrap code, disklabel32 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, disklabel32 will not install bootstrap code that overlaps it.

Due to disklabel32(5) storing sector numbers in 32 bit format disklabel32 is restricted to 2TB, using the prevalent sector size of 512B. disklabel64(5) labels should be used to partition larger disks.

The various BSDs use slightly different versions of BSD disklabels and are not generally compatible. The DragonFly kernel can often use labels from other BSDs for read-only operation.

dd(1), ccd(4), disklabel32(5), disktab(5), boot0cfg(8), diskinfo(8), disklabel64(8), fdisk(8), gpt(8), newfs(8), newfs_hammer(8), vinum(8)

The disklabel32 utility does not perform all possible error checking. Warning 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.

August 3, 2012 DragonFly-5.6.1