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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 1.14 2007/06/18 05:13:38 dillon Exp $
44 .Nd read and write 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. When writing
105 the label, it can be used to change the drive identification, the disk
106 partitions on the drive, or to replace a damaged label. There are several forms
107 of the command that read (display), install or edit the label on a disk. In
110 can install bootstrap code.
111 .Ss Raw or in-core label
112 The disk label resides close to or at the beginning of each disk slice.
113 For faster access, the kernel maintains a copy in core at all times. By
114 default, most forms of the
116 command access the in-core copy of the label. To access the raw (on-disk)
119 option. This option allows a label to be installed on a disk without kernel
120 support for a label, such as when labels are first installed on a system; it
121 must be used when first installing a label on a disk. The specific effect of
123 is described under each command.
127 forms require a disk device name, which should always be the raw
128 device name representing the disk or slice. For example
130 represents the entire disk regardless of any DOS partitioning,
133 represents a slice. Some devices, most notably
139 partition be specified. For example
141 You do not have to include the
143 path prefix when specifying the device.
146 utility will automatically prepend it.
147 .Ss Reading the disk label
148 To examine the label on a disk drive, use
157 represents the raw disk in question, and may be in the form
161 It will display all of the parameters associated with the drive and its
162 partition layout. Unless the
165 the kernel's in-core copy of the label is displayed;
166 if the disk has no label, or the partition types on the disk are incorrect,
167 the kernel may have constructed or modified the label.
172 reads the label from the raw disk and displays it. Both versions are usually
173 identical except in the case where a label has not yet been initialized or
175 .Ss Writing a standard label
176 To write a standard label, use the form
182 .Ar disk Ar disktype/auto
192 The required arguments to
194 are the drive to be labeled and the drive type as described in the
196 file. The drive parameters and partitions are taken from that file. If
197 different disks of the same physical type are to have different partitions, it
198 will be necessary to have separate disktab entries describing each, or to edit
199 the label after installation as described below. The optional argument is a
200 pack identification string, up to 16 characters long. The pack id must be
201 quoted if it contains blanks.
205 flag is given, no data will be written to the device, and instead the
206 disklabel that would have been written will be printed to stdout.
210 flag is given, the disk sectors containing the label and bootstrap
211 will be written directly.
212 A side-effect of this is that any existing bootstrap code will be overwritten
213 and the disk rendered unbootable. See the boot options below for a method of
214 writing the label and the bootstrap at the same time.
218 the existing label will be updated via the in-core copy and any bootstrap
219 code will be unaffected.
220 If the disk does not already have a label, the
223 In either case, the kernel's in-core label is replaced.
225 For a virgin disk that is not known to
230 In this case, the driver is requested to produce a virgin label for the
231 disk. This might or might not be successful, depending on whether the
232 driver for the disk is able to get the required data without reading
233 anything from the disk at all. It will likely succeed for all SCSI
234 disks, most IDE disks, and vnode devices. Writing a label to the
235 disk is the only supported operation, and the
237 itself must be provided as the canonical name, i.e. not as a full
240 For most harddisks, a label based on percentages for most partitions (and
241 one partition with a size of
243 will produce a reasonable configuration.
245 PC-based systems have special requirements in order for the BIOS to properly
248 disklabel. Older systems may require what is known as a
249 .Dq dangerously dedicated
250 disklabel, which creates a fake DOS partition to work around problems older
251 BIOSes have with modern disk geometries.
252 On newer systems you generally want
253 to create a normal DOS partition using
257 disklabel within that slice. This is described
258 later on in this page.
260 Installing a new disklabel does not in of itself allow your system to boot
261 a kernel using that label. You must also install boot blocks, which is
262 described later on in this manual page.
263 .Ss Editing an existing disk label
264 To edit an existing disk label, use the form
272 This command reads the label from the in-core kernel copy, or directly from the
275 flag is also specified. The label is written to a file in ASCII and then
276 supplied to an editor for changes. If no editor is specified in an
278 environment variable,
280 is used. When the editor terminates, the label file is used to rewrite the disk
281 label. Existing bootstrap code is unchanged regardless of whether
285 is specified, no data will be written to the device, and instead the
286 disklabel that would have been written will be printed to stdout. This is
287 useful to see how a partitioning scheme will work out for a specific disk.
288 .Ss Restoring a disk label from a file
289 To restore a disk label from a file, use the form
295 .Ar disk Ar protofile
298 is capable of restoring a disk label that was previously saved in a file in ASCII format.
299 The prototype file used to create the label should be in the same format as that
300 produced when reading or editing a label. Comments are delimited by
302 and newline. As when writing a new label, any existing bootstrap code will be
305 is specified and will be unaffected otherwise. See the boot options below for a
306 method of restoring the label and writing the bootstrap at the same time.
309 is used, no data will be written to the device, and instead the
310 disklabel that would have been written will be printed to stdout. This is
311 useful to see how a partitioning scheme will work out for a specific disk.
312 .Ss Enabling and disabling writing to the disk label area
313 By default, it is not possible to write to the disk label area at the beginning
314 of a disk. The disk driver arranges for
316 and similar system calls
319 on any attempt to do so. If you need
320 to write to this area (for example, to obliterate the label), use the form
326 To disallow writing to the label area after previously allowing it, use the
332 .Ss Installing bootstraps
333 The final three forms of
335 are used to install bootstrap code. If you are creating a
336 .Dq dangerously-dedicated
337 slice for compatibility with older PC systems,
338 you generally want to specify the raw disk name such as
340 If you are creating a label within an existing DOS slice,
342 the partition name such as
344 Making a slice bootable can be tricky. If you are using a normal DOS
345 slice you typically install (or leave) a standard MBR on the base disk and
348 bootblocks in the slice.
359 This form installs the bootstrap only. It does not change the disk label.
360 You should never use this command on a base disk unless you intend to create a
361 .Dq dangerously-dedicated
364 This command is typically run on a slice such as
378 This form corresponds to the
380 command described above.
381 In addition to writing a new volume label, it also installs the bootstrap.
382 If run on a base disk this command will create a
383 .Dq dangerously-dedicated
384 label. This command is normally run on a slice rather than a base disk.
387 is used, no data will be written to the device, and instead the
388 disklabel that would have been written will be printed to stdout.
398 .Ar disk Ar protofile
401 This form corresponds to the
403 command described above.
404 In addition to restoring the volume label, it also installs the bootstrap.
405 If run on a base disk this command will create a
406 .Dq dangerously-dedicated
407 label. This command is normally run on a slice rather than a base disk.
409 The bootstrap commands always access the disk directly, so it is not necessary
414 is used, no data will be written to the device, and instead the
415 disklabel that would have been written will be printed to stdout.
417 The bootstrap code is comprised of two boot programs. Specify the name of the
418 boot programs to be installed in one of these ways:
421 Specify the names explicitly with the
427 indicates the primary boot program and
429 the secondary boot program. The boot programs are located in
436 flags are not specified, but
438 was specified, the names of the programs are taken from the
444 entry for the disk if the disktab entry exists and includes those parameters.
446 Otherwise, the default boot image names are used:
450 for the standard stage1 and stage2 boot images.
452 .Ss Initializing/Formatting a bootable disk from scratch
453 To initialize a disk from scratch the following sequence is recommended.
454 Please note that this will wipe everything that was previously on the disk,
462 to initialize the hard disk, and create a slice table, referred to
464 .Dq "partition table"
470 to define partitions on
472 slices created in the previous step.
476 to create file systems on new partitions.
479 A typical partitioning scheme would be to have an
482 of approximately 128MB to hold the root file system, a
498 (usually around 2GB),
503 (usually all remaining space).
504 Your mileage may vary.
506 .Nm fdisk Fl BI Pa da0
517 .Bl -tag -width ".Pa /etc/disktab" -compact
521 Disk description file.
523 .Sh SAVED FILE FORMAT
529 version of the label when examining, editing, or restoring a disk
532 .Bd -literal -offset 4n
541 sectors/cylinder: 969
543 sectors/unit: 1173930
548 headswitch: 0 # milliseconds
549 track-to-track seek: 0 # milliseconds
553 # size offset fstype [fsize bsize bps/cpg]
554 a: 81920 0 4.2BSD 1024 8192 16 # (Cyl. 0 - 84*)
555 b: 160000 81920 swap # (Cyl. 84* - 218*)
556 c: 1173930 0 unused 0 0 # (Cyl. 0 - 1211*)
557 h: 962010 211920 vinum # (Cyl. 218*- 1211*)
560 Lines starting with a
563 Most of the other specifications are no longer used.
564 The ones which must still be set correctly are:
568 is an optional label, set by the
570 option when writing a label.
577 is set for removable media drives, but no current
579 driver evaluates this
582 is no longer supported;
584 specifies that the drive can perform bad sector remapping.
586 describes the total size of the disk.
587 This value must be correct.
588 .It Ar "the partition table"
591 partition table, not the
593 partition table described in
597 The partition table can have up to 16 entries.
598 It contains the following information:
599 .Bl -tag -width indent
601 The partition identifier is a single letter in the range
605 By convention, partition
607 is reserved to describe the entire disk.
609 The size of the partition in sectors,
613 (megabytes - 1024*1024),
615 (gigabytes - 1024*1024*1024),
617 (percentage of free space
619 removing any fixed-size partitions other than partition
623 (all remaining free space
625 fixed-size and percentage partitions).
630 indicates the entire disk.
631 Lowercase versions of
636 Size and type should be specified without any spaces between them.
638 Example: 2097152, 1G, 1024M and 1048576K are all the same size
639 (assuming 512-byte sectors).
641 The offset of the start of the partition from the beginning of the
646 calculate the correct offset to use (the end of the previous partition plus
647 one, ignoring partition
652 will be interpreted as an offset of 0.
654 Describes the purpose of the partition.
655 The example shows all currently used partition types.
662 For Vinum drives, use type
664 Other common types are
668 By convention, partition
670 represents the entire slice and should be of type
674 does not enforce this convention.
678 also knows about a number of other partition types,
679 none of which are in current use.
680 (See the definitions starting with
690 file systems only, the fragment size.
691 Defaults to 1024 for partitions smaller than 1GB,
692 2048 for partitions 1GB or larger.
698 file systems only, the block size.
699 Defaults to 8192 for partitions smaller than 1GB,
700 16384 for partitions 1GB or larger.
704 file systems, the number of cylinders in a cylinder group.
707 file systems, the segment shift value.
708 Defaults to 16 for partitions smaller than 1GB,
709 64 for partitions 1GB or larger.
712 The remainder of the line is a comment and shows the cylinder allocations based
713 on the obsolete (but possibly correct) geometry information about the drive.
716 indicates that the partition does not begin or end exactly on a
720 no longer snoop-adjusts the on-disklabel when reading or writing
723 is now responsible for adjusting the label when operating in raw mode.
724 Traditional (32 bit BSD) disklabels store offsets as absolute block numbers
725 rather than slice-relative block numbers.
728 is unable to issue the DIOCGPART ioctl to get slice information it will
729 refuse to read or write the label in raw mode.
732 option may be used to force the operation by supplying a manual offset.
734 .Dl "disklabel da0s1"
736 Display the in-core label for the first slice of the
738 disk, as obtained via
741 .Dq dangerously-dedicated ,
742 the base disk name should be specified, such as
745 .Dl "disklabel da0s1 > savedlabel"
747 Save the in-core label for
751 This file can be used with the
753 option to restore the label at a later date.
755 .Dl "disklabel -w -r /dev/da0s1 da2212 foo"
759 based on information for
763 Any existing bootstrap code will be clobbered
764 and the disk rendered unbootable.
766 .Dl "disklabel -e -r da0s1"
768 Read the on-disk label for
770 edit it, and reinstall in-core as well as on-disk.
771 Existing bootstrap code is unaffected.
773 .Dl "disklabel -e -r -n da0s1"
775 Read the on-disk label for
777 edit it, and display what the new label would be (in sectors).
780 install the new label either in-core or on-disk.
782 .Dl "disklabel -r -w da0s1 auto"
784 Try to auto-detect the required information from
786 and write a new label to the disk.
790 partitioning and file system information.
792 .Dl "disklabel -R da0s1 savedlabel"
794 Restore the on-disk and in-core label for
798 Existing bootstrap code is unaffected.
800 .Dl "disklabel -R -n da0s1 label_layout"
802 Display what the label would be for
804 using the partition layout in
806 This is useful for determining how much space would be allotted for various
807 partitions with a labelling scheme using
813 .Dl disklabel -B da0s1
815 Install a new bootstrap on
817 The boot code comes from
821 On-disk and in-core labels are unchanged.
823 .Dl disklabel -w -B /dev/da0s1 -b newboot1 -s newboot2 da2212
825 Install a new label and bootstrap.
826 The label is derived from disktab information for
828 and installed both in-core and on-disk.
829 The bootstrap code comes from the files
834 .Dl dd if=/dev/zero of=/dev/da0 bs=512 count=32
836 .Dl dd if=/dev/zero of=/dev/da0s1 bs=512 count=32
837 .Dl disklabel -w -B da0s1 auto
838 .Dl disklabel -e da0s1
840 Completely wipe any prior information on the disk, creating a new bootable
841 disk with a DOS partition table containing one
844 initialize the slice, then edit it to your needs. The
846 commands are optional, but may be necessary for some BIOSes to properly
849 This is an example disklabel that uses some of the new partition size types
854 which could be used as a source file for
856 .Dl disklabel -R ad0s1c new_label_file
857 .Bd -literal -offset 4n
866 sectors/cylinder: 1008
868 sectors/unit: 40959009
873 headswitch: 0 # milliseconds
874 track-to-track seek: 0 # milliseconds
878 # size offset fstype [fsize bsize bps/cpg]
879 a: 400M 0 4.2BSD 4096 16384 75 # (Cyl. 0 - 812*)
887 The kernel device drivers will not allow the size of a disk partition
888 to be decreased or the offset of a partition to be changed while it is open.
889 Some device drivers create a label containing only a single large partition
890 if a disk is unlabeled; thus, the label must be written to the
892 partition of the disk while it is open. This sometimes requires the desired
893 label to be set in two steps, the first one creating at least one other
894 partition, and the second setting the label on the new partition while shrinking
899 On some machines the bootstrap code may not fit entirely in the area
900 allocated for it by some file systems.
901 As a result, it may not be possible to have file systems on some partitions
905 When installing bootstrap code,
907 checks for these cases.
908 If the installed boot code would overlap a partition of type FS_UNUSED
909 it is marked as type FS_BOOT.
912 utility will disallow creation of file systems on FS_BOOT partitions.
913 Conversely, if a partition has a type other than FS_UNUSED or FS_BOOT,
915 will not install bootstrap code that overlaps it.
925 When a disk name is given without a full pathname,
926 the constructed device name uses the
930 For the i386 architecture, the primary bootstrap sector contains
936 utility takes care to not clobber it when installing a bootstrap only
938 or when editing an existing label
940 but it unconditionally writes the primary bootstrap program onto
947 table by the dummy one in the bootstrap program. This is only of
948 concern if the disk is fully dedicated, so that the
951 starts at absolute block 0 on the disk.
956 does not perform all possible error checking. Warning *is* given if partitions
957 overlap; if an absolute offset does not match the expected offset; if the
959 partition does not start at 0 or does not cover the entire slice; if a
960 partition runs past the end of the device; and a number of other errors; but
961 no warning is given if space remains unused.
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