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35 .\" @(#)disklabel.8 8.2 (Berkeley) 4/19/94
43 .Nd read and write disk pack label
52 .Ar disk Ar disktype/auto
75 .Oo Ar disktype/auto Oc
84 .Ar disk Ar disktype/auto
95 .Oo Ar disktype/auto Oc
100 installs, examines or modifies the label on a disk drive or pack. When writing
101 the label, it can be used to change the drive identification, the disk
102 partitions on the drive, or to replace a damaged label. There are several forms
103 of the command that read (display), install or edit the label on a disk. In
106 can install bootstrap code.
107 .Ss Raw or in-core label
109 The disk label resides close to or at the beginning of each disk slice.
110 For faster access, the kernel maintains a copy in core at all times. By
113 access the in-core copy of the label. To access the raw (on-disk) copy, use the
115 option. This option allows a label to be installed on a disk without kernel
116 support for a label, such as when labels are first installed on a system; it
117 must be used when first installing a label on a disk. The specific effect of
119 is described under each command.
125 forms require a disk device name, which should always be the raw
126 device name representing the disk or slice. For example
128 represents the entire disk regardless of any DOS partitioning,
131 represents a slice. Some devices, most notably
137 partition be specified. For example
139 You do not have to include the
141 path prefix when specifying the device.
144 utility will automatically prepend it.
145 .Ss Reading the disk label
147 To examine the label on a disk drive, use
156 represents the raw disk in question, and may be in the form
160 It will display all of the parameters associated with the drive and its
161 partition layout. Unless the
164 the kernel's in-core copy of the label is displayed;
165 if the disk has no label, or the partition types on the disk are incorrect,
166 the kernel may have constructed or modified the label.
171 reads the label from the raw disk and displays it. Both versions are usually
172 identical except in the case where a label has not yet been initialized or
174 .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
265 To edit an existing disk label, use the form
273 This command reads the label from the in-core kernel copy, or directly from the
276 flag is also specified. The label is written to a file in ASCII and then
277 supplied to an editor for changes. If no editor is specified in an
279 environment variable,
281 is used. When the editor terminates, the label file is used to rewrite the disk
282 label. Existing bootstrap code is unchanged regardless of whether
286 is specified, no data will be written to the device, and instead the
287 disklabel that would have been written will be printed to stdout. This is
288 useful to see how a partitioning scheme will work out for a specific disk.
289 .Ss Restoring a disk label from a file
291 To restore a disk label from a file, use the form
297 .Ar disk Ar protofile
300 is capable of restoring a disk label that was previously saved in a file in ASCII format.
301 The prototype file used to create the label should be in the same format as that
302 produced when reading or editing a label. Comments are delimited by
304 and newline. As when writing a new label, any existing bootstrap code will be
307 is specified and will be unaffected otherwise. See the boot options below for a
308 method of restoring the label and writing the bootstrap at the same time.
311 is used, no data will be written to the device, and instead the
312 disklabel that would have been written will be printed to stdout. This is
313 useful to see how a partitioning scheme will work out for a specific disk.
314 .Ss Enabling and disabling writing to the disk label area
316 By default, it is not possible to write to the disk label area at the beginning
317 of a disk. The disk driver arranges for
319 and similar system calls
322 on any attempt to do so. If you need
323 to write to this area (for example, to obliterate the label), use the form
329 To disallow writing to the label area after previously allowing it, use the
335 .Ss Installing bootstraps
337 The final three forms of
339 are used to install bootstrap code. If you are creating a
340 .Dq dangerously-dedicated
341 slice for compatibility with older PC systems,
342 you generally want to specify the raw disk name such as
344 If you are creating a label within an existing DOS slice,
346 the partition name such as
348 Making a slice bootable can be tricky. If you are using a normal DOS
349 slice you typically install (or leave) a standard MBR on the base disk and
352 bootblocks in the slice.
363 This form installs the bootstrap only. It does not change the disk label.
364 You should never use this command on a base disk unless you intend to create a
365 .Dq dangerously-dedicated
368 This command is typically run on a slice such as
382 This form corresponds to the
384 command described above.
385 In addition to writing a new volume label, it also installs the bootstrap.
386 If run on a base disk this command will create a
387 .Dq dangerously-dedicated
388 label. This command is normally run on a slice rather than a base disk.
391 is used, no data will be written to the device, and instead the
392 disklabel that would have been written will be printed to stdout.
402 .Ar disk Ar protofile
405 This form corresponds to the
407 command described above.
408 In addition to restoring the volume label, it also installs the bootstrap.
409 If run on a base disk this command will create a
410 .Dq dangerously-dedicated
411 label. This command is normally run on a slice rather than a base disk.
413 The bootstrap commands always access the disk directly, so it is not necessary
418 is used, no data will be written to the device, and instead the
419 disklabel that would have been written will be printed to stdout.
421 The bootstrap code is comprised of two boot programs. Specify the name of the
422 boot programs to be installed in one of these ways:
425 Specify the names explicitly with the
431 indicates the primary boot program and
433 the secondary boot program. The boot programs are located in
440 flags are not specified, but
442 was specified, the names of the programs are taken from the
448 entry for the disk if the disktab entry exists and includes those parameters.
450 Otherwise, the default boot image names are used:
454 for the standard stage1 and stage2 boot images (details may vary
455 on architectures like the Alpha, where only a single-stage boot is used).
457 .Ss Initializing/Formatting a bootable disk from scratch
459 To initialize a disk from scratch the following sequence is recommended.
460 Please note that this will wipe everything that was previously on the disk,
468 to initialize the hard disk, and create a slice table, referred to
469 as the partition table in DOS.
470 Here you will define disk slices for your system.
474 to define and write partitions and mount points.
475 You are not required to define the mount points here though,
476 they can be defined later using
481 to create a file system on the new partition.
482 A typical partitioning scheme would be to have an
485 of approximately 128MB to hold the root file system, a
490 partition for /var (usually 128MB), an
493 for /var/tmp (usually 128MB), an
495 partition for /usr (usually around 2G),
498 partition for /home (usually all remaining space).
499 Your mileage may vary.
502 .Nm fdisk Fl BI Ar da0
515 .Bl -tag -width Pa -compact
520 .Sh SAVED FILE FORMAT
524 uses an ASCII version of the label when examining, editing or restoring a disk
525 label. The format is:
526 .Bd -literal -offset 4n
535 sectors/cylinder: 969
537 sectors/unit: 1173930
542 headswitch: 0 # milliseconds
543 track-to-track seek: 0 # milliseconds
547 # size offset fstype [fsize bsize bps/cpg]
548 a: 81920 0 4.2BSD 1024 8192 16 # (Cyl. 0 - 84*)
549 b: 160000 81920 swap # (Cyl. 84* - 218*)
550 c: 1173930 0 unused 0 0 # (Cyl. 0 - 1211*)
551 h: 962010 211920 vinum # (Cyl. 218*- 1211*)
554 Lines starting with a # mark are comments. Most of the other specifications are
555 no longer used. The ones which must still be set correctly are:
559 is an optional label, set by the
561 option when writing a label.
569 is set for removable media drives, but no current
571 driver evaluates this
574 is no longer supported;
576 specifies that the drive can perform bad sector remapping.
578 describes the total size of the disk. This value must be correct.
579 .It Nm the partition table
582 partition table, not the Microsoft partition table described in
586 The partition table can have up to 8 entries. It contains the following
590 The partition identifier is a single letter in the range
594 By convention, partition
596 is reserved to describe the entire disk.
598 is the size of the partition in sectors,
602 (megabytes - 1024*1024),
604 (gigabytes - 1024*1024*1024),
606 (percentage of free space AFTER removing any fixed-size partitions other
611 (all remaining free space AFTER fixed-size and percentage
612 partitions). For partition
616 indicates the entire disk. Lowercase versions of
621 Size and type should be specifed without any spaces between them.
623 Example: 2097152, 1g, 1024m and 1048576k are all the same size
624 (assuming 512-byte sectors).
626 is the offset of the start of the partition from the beginning of the
631 calculate the correct offset to use (the end of the previous partition plus
632 one, ignoring partition
637 will be interpreted as an offset of 0.
639 describes the purpose of the partition. The example shows all currently used
641 For UFS file systems and ccd partitions, use type
643 For Vinum drives, use type
645 Other common types are
649 By convention, partition
651 represents the entire slice and should be of type
655 does not enforce this convention.
659 also knows about a number of other partition types, none of which are in current
661 See the definitions starting with
664 .Pa /usr/include/sys/disklabel.h
669 and LFS file systems only, the fragment size. Defaults to 1024 for
670 partitions smaller than 1 GB, 4096 for partitions 1GB or larger.
674 and LFS file systems only, the block size. Defaults to 8192 for
675 partitions smaller than 1 GB, 16384 for partitions 1GB or larger.
679 file systems, the number of cylinders in a cylinder group. For LFS file
680 systems, the segment shift value. Defaults to 16 for
681 partitions smaller than 1 GB, 64 for partitions 1GB or larger.
684 The remainder of the line is a comment and shows the cylinder allocations based
685 on the obsolete (but possibly correct) geometry information about the drive.
686 The asterisk (*) indicates that the partition does not begin or end exactly on a
691 Display the in-core label for
695 When reading a label,
697 will allow you to specify the base disk name
698 even if the label resides on a slice. However, to be proper you should
699 specify the base disk name only if you are using a
700 .Dq dangerously-dedicated
701 label. Normally you specify the slice.
703 .Dl disklabel da0s1 > savedlabel
705 Save the in-core label for
709 This file can be used with the
711 flag to restore the label at a later date.
713 .Dl disklabel -w -r /dev/da0s1 da2212 foo
717 based on information for
721 Any existing bootstrap code will be clobbered.
723 .Dl disklabel -e -r da0s1
725 Read the on-disk label for
727 edit it and reinstall in-core as well as on-disk. Existing bootstrap code is
730 .Dl disklabel -e -r -n da0s1
732 Read the on-disk label for
734 edit it, and display what the new label would be (in sectors). It does
735 NOT install the new label either in-core or on-disk.
737 .Dl disklabel -r -w da0s1 auto
739 Try to auto-detect the required information from
741 and write a new label to the disk. Use another disklabel -e command to edit the
742 partitioning and file system information.
744 .Dl disklabel -R da0s1 savedlabel
746 Restore the on-disk and in-core label for
750 Existing bootstrap code is unaffected.
752 .Dl disklabel -R -n da0s1 label_layout
754 Display what the label would be for
756 using the partition layout in
758 This is useful for determining how much space would be alloted for various
759 partitions with a labelling scheme using
765 .Dl disklabel -B da0s1
767 Install a new bootstrap on
769 The boot code comes from
773 On-disk and in-core labels are unchanged.
775 .Dl disklabel -w -B /dev/da0s1 -b newboot1 -s newboot2 da2212
777 Install a new label and bootstrap.
778 The label is derived from disktab information for
780 and installed both in-core and on-disk.
781 The bootstrap code comes from the files
786 .Dl dd if=/dev/zero of=/dev/da0 bs=512 count=32
788 .Dl dd if=/dev/zero of=/dev/da0s1 bs=512 count=32
789 .Dl disklabel -w -B da0s1 auto
790 .Dl disklabel -e da0s1
792 Completely wipe any prior information on the disk, creating a new bootable
793 disk with a DOS partition table containing one
796 initialize the slice, then edit it to your needs. The
798 commands are optional, but may be necessary for some BIOSes to properly
801 This is an example disklabel that uses some of the new partition size types
806 which could be used as a source file for
808 .Dl disklabel -R ad0s1c new_label_file
809 .Bd -literal -offset 4n
818 sectors/cylinder: 1008
820 sectors/unit: 40959009
825 headswitch: 0 # milliseconds
826 track-to-track seek: 0 # milliseconds
830 # size offset fstype [fsize bsize bps/cpg]
831 a: 400M 0 4.2BSD 4096 16384 75 # (Cyl. 0 - 812*)
846 The kernel device drivers will not allow the size of a disk partition
847 to be decreased or the offset of a partition to be changed while it is open.
848 Some device drivers create a label containing only a single large partition
849 if a disk is unlabeled; thus, the label must be written to the
851 partition of the disk while it is open. This sometimes requires the desired
852 label to be set in two steps, the first one creating at least one other
853 partition, and the second setting the label on the new partition while shrinking
858 On some machines the bootstrap code may not fit entirely in the area
859 allocated for it by some file systems.
860 As a result, it may not be possible to have file systems on some partitions
864 When installing bootstrap code,
866 checks for these cases.
867 If the installed boot code would overlap a partition of type FS_UNUSED
868 it is marked as type FS_BOOT.
871 utility will disallow creation of file systems on FS_BOOT partitions.
872 Conversely, if a partition has a type other than FS_UNUSED or FS_BOOT,
874 will not install bootstrap code that overlaps it.
876 When a disk name is given without a full pathname,
877 the constructed device name uses the
881 For the i386 architecture, the primary bootstrap sector contains
887 utility takes care to not clobber it when installing a bootstrap only
889 or when editing an existing label
891 but it unconditionally writes the primary bootstrap program onto
898 table by the dummy one in the bootstrap program. This is only of
899 concern if the disk is fully dedicated, so that the
902 starts at absolute block 0 on the disk.
907 does not perform all possible error checking. Warning *is* given if partitions
908 overlap; if an absolute offset does not match the expected offset; if the
910 partition does not start at 0 or does not cover the entire slice; if a
911 partition runs past the end of the device; and a number of other errors; but
912 no warning is given if space remains unused.
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