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35 .\" @(#)disklabel.8 8.2 (Berkeley) 4/19/94
36 .\" $FreeBSD: src/sbin/disklabel/disklabel.8,v 1.15.2.22 2003/04/17 17:56:34 trhodes Exp $
37 .\" $DragonFly: src/sbin/disklabel/disklabel.8,v 1.28 2008/09/06 10:15:29 thomas Exp $
44 .Nd read and write 32 bit disk pack label
53 .Ar disk Ar disktype/auto
76 .Oo Ar disktype/auto Oc
85 .Ar disk Ar disktype/auto
96 .Oo Ar disktype/auto Oc
98 .Fl f Ar slice_start_lba
104 installs, examines or modifies the label on a disk drive or pack.
106 the label, it can be used to change the drive identification, the disk
107 partitions on the drive, or to replace a damaged label.
108 There are several forms
109 of the command that read (display), install or edit the label on a disk.
113 can install bootstrap code.
114 .Ss Raw or in-core label
115 The disk label resides close to or at the beginning of each disk slice.
116 For faster access, the kernel maintains a copy in core at all times.
118 default, most forms of the
120 command access the in-core copy of the label.
121 To access the raw (on-disk)
125 This option allows a label to be installed on a disk without kernel
126 support for a label, such as when labels are first installed on a system; it
127 must be used when first installing a label on a disk.
128 The specific effect of
130 is described under each command.
134 forms require a disk device name, which should always be the raw
135 device name representing the disk or slice.
137 uses the following scheme for slice numbering:
138 If the disk doesn't use GPT (typically laid out by
140 but e.g.\& MBR (typically laid out by
144 represents the entire disk regardless of any DOS partitioning.
145 Slice 0 is called the compatibility slice,
146 and slice 1 and onward, e.g.\&
151 If the disk does use GPT, then all slices are
153 slices, slice 0 isn't special, it is just the first slice on the disk.
154 You do not have to include the
156 path prefix when specifying the device.
159 utility will automatically prepend it.
160 .Ss Reading the disk label
161 To examine the label on a disk drive, use
170 represents the raw disk in question, and may be in the form
174 It will display all of the parameters associated with the drive and its
179 the kernel's in-core copy of the label is displayed;
180 if the disk has no label, or the partition types on the disk are incorrect,
181 the kernel may have constructed or modified the label.
186 reads the label from the raw disk and displays it.
187 Both versions are usually
188 identical except in the case where a label has not yet been initialized or
190 .Ss Writing a standard label
191 To write a standard label, use the form
197 .Ar disk Ar disktype/auto
207 The required arguments to
209 are the drive to be labeled and the drive type as described in the
212 The drive parameters and partitions are taken from that file.
214 different disks of the same physical type are to have different partitions, it
215 will be necessary to have separate disktab entries describing each, or to edit
216 the label after installation as described below.
217 The optional argument is a
218 pack identification string, up to 16 characters long.
220 quoted if it contains blanks.
224 flag is given, no data will be written to the device, and instead the
225 disklabel that would have been written will be printed to stdout.
229 flag is given, the disk sectors containing the label and bootstrap
230 will be written directly.
231 A side-effect of this is that any existing bootstrap code will be overwritten
232 and the disk rendered unbootable.
233 See the boot options below for a method of
234 writing the label and the bootstrap at the same time.
238 the existing label will be updated via the in-core copy and any bootstrap
239 code will be unaffected.
240 If the disk does not already have a label, the
243 In either case, the kernel's in-core label is replaced.
245 For a virgin disk that is not known to
250 In this case, the driver is requested to produce a virgin label for the
252 This might or might not be successful, depending on whether the
253 driver for the disk is able to get the required data without reading
254 anything from the disk at all.
255 It will likely succeed for all SCSI
256 disks, most IDE disks, and vnode devices.
257 Writing a label to the
258 disk is the only supported operation, and the
260 itself must be provided as the canonical name, i.e.\& not as a full
263 For most harddisks, a label based on percentages for most partitions (and
264 one partition with a size of
266 will produce a reasonable configuration.
268 PC-based systems have special requirements in order for the BIOS to properly
272 Older systems may require what is known as a
273 .Dq dangerously dedicated
274 disklabel, which creates a fake DOS partition to work around problems older
275 BIOSes have with modern disk geometries.
276 On newer systems you generally want
277 to create a normal DOS partition using
281 disklabel within that slice.
283 later on in this page.
285 Installing a new disklabel does not in of itself allow your system to boot
286 a kernel using that label.
287 You must also install boot blocks, which is
288 described later on in this manual page.
289 .Ss Editing an existing disk label
290 To edit an existing disk label, use the form
298 This command reads the label from the in-core kernel copy, or directly from the
301 flag is also specified.
302 The label is written to a file in ASCII and then
303 supplied to an editor for changes.
304 If no editor is specified in an
306 environment variable,
309 When the editor terminates, the label file is used to rewrite the disk
311 Existing bootstrap code is unchanged regardless of whether
316 is specified, no data will be written to the device, and instead the
317 disklabel that would have been written will be printed to stdout.
319 useful to see how a partitioning scheme will work out for a specific disk.
320 .Ss Restoring a disk label from a file
321 To restore a disk label from a file, use the form
327 .Ar disk Ar protofile
330 is capable of restoring a disk label that was previously saved in a file
332 The prototype file used to create the label should be in the same format
333 as that produced when reading or editing a label.
334 Comments are delimited by
337 As when writing a new label, any existing bootstrap code will be
340 is specified and will be unaffected otherwise.
341 See the boot options below for a
342 method of restoring the label and writing the bootstrap at the same time.
345 is used, no data will be written to the device, and instead the
346 disklabel that would have been written will be printed to stdout.
348 useful to see how a partitioning scheme will work out for a specific disk.
349 .Ss Enabling and disabling writing to the disk label area
350 By default, it is not possible to write to the disk label area at the beginning
352 The disk driver arranges for
354 and similar system calls
357 on any attempt to do so.
359 to write to this area (for example, to obliterate the label), use the form
365 To disallow writing to the label area after previously allowing it, use the
371 .Ss Installing bootstraps
372 The final three forms of
374 are used to install bootstrap code.
375 If you are creating a
376 .Dq dangerously-dedicated
377 slice for compatibility with older PC systems,
378 you generally want to specify the compatibility slice, such as
380 If you are creating a label within an existing DOS slice,
382 the slice name such as
384 Making a slice bootable can be tricky.
385 If you are using a normal DOS
386 slice you typically install (or leave) a standard MBR on the base disk and
389 bootblocks in the slice.
400 This form installs the bootstrap only.
401 It does not change the disk label.
402 You should never use this command on the compatibility slice unless you
404 .Dq dangerously-dedicated
407 This command is typically run on a
423 This form corresponds to the
425 command described above.
426 In addition to writing a new volume label, it also installs the bootstrap.
427 If run on the compatibility slice this command will create a
428 .Dq dangerously-dedicated
430 This command is normally run on a
432 slice rather than the compatibility
436 is used, no data will be written to the device, and instead the
437 disklabel that would have been written will be printed to stdout.
447 .Ar disk Ar protofile
450 This form corresponds to the
452 command described above.
453 In addition to restoring the volume label, it also installs the bootstrap.
454 If run on the compatibility slice this command will create a
455 .Dq dangerously-dedicated
457 This command is normally run on a
459 slice rather than the compatibility
462 The bootstrap commands always access the disk directly, so it is not necessary
468 is used, no data will be written to the device, and instead the
469 disklabel that would have been written will be printed to stdout.
471 The bootstrap code is comprised of two boot programs.
472 Specify the name of the
473 boot programs to be installed in one of these ways:
476 Specify the names explicitly with the
482 indicates the primary boot program and
484 the secondary boot program.
485 The boot programs are located in
492 flags are not specified, but
494 was specified, the names of the programs are taken from the
500 entry for the disk if the disktab entry exists and includes those parameters.
502 Otherwise, the default boot image names are used:
506 for the standard stage1 and stage2 boot images.
508 .Ss Initializing/Formatting a bootable disk from scratch
509 To initialize a disk from scratch the following sequence is recommended.
510 Please note that this will wipe everything that was previously on the disk,
518 to initialize the hard disk, and create a slice table, referred to
520 .Dq "partition table"
526 to define partitions on
528 slices created in the previous step.
532 to create file systems on new partitions.
535 A typical partitioning scheme would be to have an
538 of approximately 512MB to hold the root file system, a
541 swap (usually 4GB), a
554 (usually around 4GB),
559 (usually all remaining space).
560 Your mileage may vary.
562 .Nm fdisk Fl BI Pa da0
574 no longer snoop-adjusts the on-disk label when reading or writing
577 is now responsible for adjusting the label when operating in raw mode.
580 disklabels store offsets as absolute block numbers
581 rather than slice-relative block numbers.
584 is unable to issue the
586 ioctl to get slice information it will
587 refuse to read or write the label in raw mode.
590 option may be used to force the operation by supplying a manual offset.
592 .Bl -tag -width ".Pa /etc/disktab" -compact
594 Default stage1 boot image.
596 Default stage2 boot image.
598 Disk description file.
600 .Sh SAVED FILE FORMAT
606 version of the label when examining, editing, or restoring a disk
609 .Bd -literal -offset 4n
618 sectors/cylinder: 1512
620 sectors/unit: 243581184
625 headswitch: 0 # milliseconds
626 track-to-track seek: 0 # milliseconds
631 a: 1048560 16 4.2BSD # 511.992MB
632 b: 8388608 1048576 swap # 4096.000MB
633 c: 243581184 0 unused # 118936.125MB
634 d: 4194304 9437184 4.2BSD # 2048.000MB
635 e: 4194304 13631488 4.2BSD # 2048.000MB
636 f: 8388608 17825792 4.2BSD # 4096.000MB
637 h: 196395264 26214400 HAMMER # 95896.125MB
638 i: 10485760 222609664 ccd # 5120.000MB
639 j: 10485760 233095424 vinum # 5120.000MB
642 Lines starting with a
645 Most of the other specifications are no longer used.
646 The ones which must still be set correctly are:
649 is an optional label, set by the
651 option when writing a label.
658 is set for removable media drives, but no current
660 driver evaluates this
663 is no longer supported;
665 specifies that the drive can perform bad sector remapping.
667 describes the total size of the disk.
668 This value must be correct.
669 .It Ar "the partition table"
672 partition table, not the
674 partition table described in
678 The partition table can have up to 16 entries.
679 It contains the following information:
680 .Bl -tag -width indent
682 The partition identifier is a single letter in the range
686 By convention, partition
688 is reserved to describe the entire disk.
690 The size of the partition in sectors,
694 (megabytes - 1024*1024),
696 (gigabytes - 1024*1024*1024),
698 (percentage of free space
700 removing any fixed-size partitions other than partition
704 (all remaining free space
706 fixed-size and percentage partitions).
711 indicates the entire disk.
712 Lowercase versions of
717 Size and type should be specified without any spaces between them.
719 Example: 2097152, 1G, 1024M and 1048576K are all the same size
720 (assuming 512-byte sectors).
722 The offset of the start of the partition from the beginning of the
727 calculate the correct offset to use (the end of the previous partition plus
728 one, ignoring partition
733 will be interpreted as an offset of 0.
735 Describes the purpose of the partition.
736 The example shows all currently used partition types.
739 file systems, use type
743 file systems, use type
749 For Vinum drives, use type
751 Other common types are
755 By convention, partition
757 represents the entire slice and should be of type
761 does not enforce this convention.
765 also knows about a number of other partition types,
766 none of which are in current use.
774 The remainder of the line is a comment and shows the size of the partition
777 .Dl "disklabel da0s1"
779 Display the in-core label for the first slice of the
781 disk, as obtained via
784 .Dq dangerously-dedicated ,
785 the compatibility slice name should be specified, such as
788 .Dl "disklabel da0s1 > savedlabel"
790 Save the in-core label for
794 This file can be used with the
796 option to restore the label at a later date.
798 .Dl "disklabel -w -r /dev/da0s1 da2212 foo"
802 based on information for
806 Any existing bootstrap code will be clobbered
807 and the disk rendered unbootable.
809 .Dl "disklabel -e -r da0s1"
811 Read the on-disk label for
813 edit it, and reinstall in-core as well as on-disk.
814 Existing bootstrap code is unaffected.
816 .Dl "disklabel -e -r -n da0s1"
818 Read the on-disk label for
820 edit it, and display what the new label would be (in sectors).
823 install the new label either in-core or on-disk.
825 .Dl "disklabel -r -w da0s1 auto"
827 Try to auto-detect the required information from
829 and write a new label to the disk.
833 partitioning and file system information.
835 .Dl "disklabel -R da0s1 savedlabel"
837 Restore the on-disk and in-core label for
841 Existing bootstrap code is unaffected.
843 .Dl "disklabel -R -n da0s1 label_layout"
845 Display what the label would be for
847 using the partition layout in
849 This is useful for determining how much space would be allotted for various
850 partitions with a labelling scheme using
856 .Dl disklabel -B da0s1
858 Install a new bootstrap on
860 The boot code comes from
864 On-disk and in-core labels are unchanged.
866 .Dl disklabel -w -B /dev/da0s1 -b newboot1 -s newboot2 da2212
868 Install a new label and bootstrap.
869 The label is derived from disktab information for
871 and installed both in-core and on-disk.
872 The bootstrap code comes from the files
877 .Dl dd if=/dev/zero of=/dev/da0 bs=512 count=32
879 .Dl dd if=/dev/zero of=/dev/da0s1 bs=512 count=32
880 .Dl disklabel -w -B da0s1 auto
881 .Dl disklabel -e da0s1
883 Completely wipe any prior information on the disk, creating a new bootable
884 disk with a DOS partition table containing one
888 initialize the slice, then edit it to your needs.
891 commands are optional, but may be necessary for some BIOSes to properly
894 .Dl disklabel -W da0s1
895 .Dl dd if=/dev/zero of=/dev/da0s1 bs=512 count=32
896 .Dl disklabel64 -r -w da0s1 auto
897 .Dl disklabel64 -N da0s1
899 Completely wipe any prior information on the slice,
900 changing label format to 64 bit.
901 The wiping is needed as
906 won't do any operations if label with other format is already installed.
908 This is an example disklabel that uses some of the new partition size types
913 which could be used as a source file for
915 .Dl disklabel -R ad0s1 new_label_file
916 .Bd -literal -offset 4n
925 sectors/cylinder: 1008
927 sectors/unit: 40959009
932 headswitch: 0 # milliseconds
933 track-to-track seek: 0 # milliseconds
946 The kernel device drivers will not allow the size of a disk partition
947 to be decreased or the offset of a partition to be changed while it is open.
948 Some device drivers create a label containing only a single large partition
949 if a disk is unlabeled; thus, the label must be written to the
951 partition of the disk while it is open.
952 This sometimes requires the desired
953 label to be set in two steps, the first one creating at least one other
954 partition, and the second setting the label on the new partition while
959 On some machines the bootstrap code may not fit entirely in the area
960 allocated for it by some file systems.
961 As a result, it may not be possible to have file systems on some partitions
965 When installing bootstrap code,
967 checks for these cases.
968 If the installed boot code would overlap a partition of type
974 utility will disallow creation of file systems on
977 Conversely, if a partition has a type other than
982 will not install bootstrap code that overlaps it.
986 storing sector numbers in 32 bit format
988 is restricted to 2TB, using the prevalent sector size of 512B.
990 labels should be used to partition larger disks.
994 use slightly different versions of
997 and are not generally compatible.
1000 kernel can often use labels from other
1002 for read-only operation.
1014 For the i386 architecture, the primary bootstrap sector contains
1020 utility takes care to not clobber it when installing a bootstrap only
1022 or when editing an existing label
1024 but it unconditionally writes the primary bootstrap program onto
1031 table by the dummy one in the bootstrap program.
1033 concern if the disk is fully dedicated, so that the
1036 starts at absolute block 0 on the disk.
1041 does not perform all possible error checking.
1045 overlap; if an absolute offset does not match the expected offset; if the
1047 partition does not start at 0 or does not cover the entire slice; if a
1048 partition runs past the end of the device; and a number of other errors; but
1049 no warning is given if space remains unused.
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