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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 silently ignores any attempt to do so. If you need
318 to write to this area (for example, to obliterate the label), use the form
324 To disallow writing to the label area after previously allowing it, use the
330 .Ss Installing bootstraps
332 The final three forms of
334 are used to install bootstrap code. If you are creating a
335 .Dq dangerously-dedicated
336 slice for compatibility with older PC systems,
337 you generally want to specify the raw disk name such as
339 If you are creating a label within an existing DOS slice,
341 the partition name such as
343 Making a slice bootable can be tricky. If you are using a normal DOS
344 slice you typically install (or leave) a standard MBR on the base disk and
347 bootblocks in the slice.
358 This form installs the bootstrap only. It does not change the disk label.
359 You should never use this command on a base disk unless you intend to create a
360 .Dq dangerously-dedicated
363 This command is typically run on a slice such as
377 This form corresponds to the
379 command described above.
380 In addition to writing a new volume label, it also installs the bootstrap.
381 If run on a base disk this command will create a
382 .Dq dangerously-dedicated
383 label. This command is normally run on a slice rather than a base disk.
386 is used, no data will be written to the device, and instead the
387 disklabel that would have been written will be printed to stdout.
397 .Ar disk Ar protofile
400 This form corresponds to the
402 command described above.
403 In addition to restoring the volume label, it also installs the bootstrap.
404 If run on a base disk this command will create a
405 .Dq dangerously-dedicated
406 label. This command is normally run on a slice rather than a base disk.
408 The bootstrap commands always access the disk directly, so it is not necessary
413 is used, no data will be written to the device, and instead the
414 disklabel that would have been written will be printed to stdout.
416 The bootstrap code is comprised of two boot programs. Specify the name of the
417 boot programs to be installed in one of these ways:
420 Specify the names explicitly with the
426 indicates the primary boot program and
428 the secondary boot program. The boot programs are located in
435 flags are not specified, but
437 was specified, the names of the programs are taken from the
443 entry for the disk if the disktab entry exists and includes those parameters.
445 Otherwise, the default boot image names are used:
449 for the standard stage1 and stage2 boot images (details may vary
450 on architectures like the Alpha, where only a single-stage boot is used).
452 .Ss Initializing/Formatting a bootable disk from scratch
454 To initialize a disk from scratch the following sequence is recommended.
455 Please note that this will wipe everything that was previously on the disk,
463 to initialize the hard disk, and create a slice table, referred to
464 as the partition table in DOS.
465 Here you will define disk slices for your system.
469 to define and write partitions and mount points.
470 You are not required to define the mount points here though,
471 they can be defined later using
476 to create a filesystem on the new partition.
477 A typical partitioning scheme would be to have an
480 of approximately 128MB to hold the root filesystem, a
485 partition for /var (usually 128MB), an
488 for /var/tmp (usually 128MB), an
490 partition for /usr (usually around 2G),
493 partition for /home (usually all remaining space).
494 Your mileage may vary.
497 .Nm fdisk Fl BI Ar da0
510 .Bl -tag -width Pa -compact
515 .Sh SAVED FILE FORMAT
519 uses an ASCII version of the label when examining, editing or restoring a disk
520 label. The format is:
521 .Bd -literal -offset 4n
530 sectors/cylinder: 969
532 sectors/unit: 1173930
537 headswitch: 0 # milliseconds
538 track-to-track seek: 0 # milliseconds
542 # size offset fstype [fsize bsize bps/cpg]
543 a: 81920 0 4.2BSD 1024 8192 16 # (Cyl. 0 - 84*)
544 b: 160000 81920 swap # (Cyl. 84* - 218*)
545 c: 1173930 0 unused 0 0 # (Cyl. 0 - 1211*)
546 h: 962010 211920 vinum # (Cyl. 218*- 1211*)
549 Lines starting with a # mark are comments. Most of the other specifications are
550 no longer used. The ones which must still be set correctly are:
554 is an optional label, set by the
556 option when writing a label.
564 is set for removable media drives, but no current
566 driver evaluates this
569 is no longer supported;
571 specifies that the drive can perform bad sector remapping.
573 describes the total size of the disk. This value must be correct.
574 .It Nm the partition table
577 partition table, not the Microsoft partition table described in
581 The partition table can have up to 8 entries. It contains the following
585 The partition identifier is a single letter in the range
589 By convention, partition
591 is reserved to describe the entire disk.
593 is the size of the partition in sectors,
597 (megabytes - 1024*1024),
599 (gigabytes - 1024*1024*1024),
601 (percentage of free space AFTER removing any fixed-size partitions other
606 (all remaining free space AFTER fixed-size and percentage
607 partitions). For partition
611 indicates the entire disk. Lowercase versions of
616 Size and type should be specifed without any spaces between them.
618 Example: 2097152, 1g, 1024m and 1048576k are all the same size
619 (assuming 512-byte sectors).
621 is the offset of the start of the partition from the beginning of the
626 calculate the correct offset to use (the end of the previous partition plus
627 one, ignoring partition
632 will be interpreted as an offset of 0.
634 describes the purpose of the partition. The example shows all currently used
636 For UFS filesystems and ccd partitions, use type
638 For Vinum drives, use type
640 Other common types are
644 By convention, partition
646 represents the entire slice and should be of type
650 does not enforce this convention.
654 also knows about a number of other partition types, none of which are in current
656 See the definitions starting with
659 .Pa /usr/include/sys/disklabel.h
664 and LFS filesystems only, the fragment size. Defaults to 1024 for
665 partitions smaller than 1 GB, 4096 for partitions 1GB or larger.
669 and LFS filesystems only, the block size. Defaults to 8192 for
670 partitions smaller than 1 GB, 16384 for partitions 1GB or larger.
674 filesystems, the number of cylinders in a cylinder group. For LFS file
675 systems, the segment shift value. Defaults to 16 for
676 partitions smaller than 1 GB, 64 for partitions 1GB or larger.
679 The remainder of the line is a comment and shows the cylinder allocations based
680 on the obsolete (but possibly correct) geometry information about the drive.
681 The asterisk (*) indicates that the partition does not begin or end exactly on a
686 Display the in-core label for
690 When reading a label,
692 will allow you to specify the base disk name
693 even if the label resides on a slice. However, to be proper you should
694 specify the base disk name only if you are using a
695 .Dq dangerously-dedicated
696 label. Normally you specify the slice.
698 .Dl disklabel da0s1 > savedlabel
700 Save the in-core label for
704 This file can be used with the
706 flag to restore the label at a later date.
708 .Dl disklabel -w -r /dev/da0s1 da2212 foo
712 based on information for
716 Any existing bootstrap code will be clobbered.
718 .Dl disklabel -e -r da0s1
720 Read the on-disk label for
722 edit it and reinstall in-core as well as on-disk. Existing bootstrap code is
725 .Dl disklabel -e -r -n da0s1
727 Read the on-disk label for
729 edit it, and display what the new label would be (in sectors). It does
730 NOT install the new label either in-core or on-disk.
732 .Dl disklabel -r -w da0s1 auto
734 Try to auto-detect the required information from
736 and write a new label to the disk. Use another disklabel -e command to edit the
737 partitioning and filesystem information.
739 .Dl disklabel -R da0s1 savedlabel
741 Restore the on-disk and in-core label for
745 Existing bootstrap code is unaffected.
747 .Dl disklabel -R -n da0s1 label_layout
749 Display what the label would be for
751 using the partition layout in
753 This is useful for determining how much space would be alloted for various
754 partitions with a labelling scheme using
760 .Dl disklabel -B da0s1
762 Install a new bootstrap on
764 The boot code comes from
768 On-disk and in-core labels are unchanged.
770 .Dl disklabel -w -B /dev/da0s1 -b newboot1 -s newboot2 da2212
772 Install a new label and bootstrap.
773 The label is derived from disktab information for
775 and installed both in-core and on-disk.
776 The bootstrap code comes from the files
781 .Dl dd if=/dev/zero of=/dev/da0 bs=512 count=32
783 .Dl dd if=/dev/zero of=/dev/da0s1 bs=512 count=32
784 .Dl disklabel -w -B da0s1 auto
785 .Dl disklabel -e da0s1
787 Completely wipe any prior information on the disk, creating a new bootable
788 disk with a DOS partition table containing one
791 initialize the slice, then edit it to your needs. The
793 commands are optional, but may be necessary for some BIOSes to properly
796 This is an example disklabel that uses some of the new partition size types
801 which could be used as a source file for
803 .Dl disklabel -R ad0s1c new_label_file
804 .Bd -literal -offset 4n
813 sectors/cylinder: 1008
815 sectors/unit: 40959009
820 headswitch: 0 # milliseconds
821 track-to-track seek: 0 # milliseconds
825 # size offset fstype [fsize bsize bps/cpg]
826 a: 400M 0 4.2BSD 4096 16384 75 # (Cyl. 0 - 812*)
841 The kernel device drivers will not allow the size of a disk partition
842 to be decreased or the offset of a partition to be changed while it is open.
843 Some device drivers create a label containing only a single large partition
844 if a disk is unlabeled; thus, the label must be written to the
846 partition of the disk while it is open. This sometimes requires the desired
847 label to be set in two steps, the first one creating at least one other
848 partition, and the second setting the label on the new partition while shrinking
853 On some machines the bootstrap code may not fit entirely in the area
854 allocated for it by some filesystems.
855 As a result, it may not be possible to have filesystems on some partitions
859 When installing bootstrap code,
861 checks for these cases.
862 If the installed boot code would overlap a partition of type FS_UNUSED
863 it is marked as type FS_BOOT.
866 utility will disallow creation of filesystems on FS_BOOT partitions.
867 Conversely, if a partition has a type other than FS_UNUSED or FS_BOOT,
869 will not install bootstrap code that overlaps it.
871 When a disk name is given without a full pathname,
872 the constructed device name uses the
876 For the i386 architecture, the primary bootstrap sector contains
882 utility takes care to not clobber it when installing a bootstrap only
884 or when editing an existing label
886 but it unconditionally writes the primary bootstrap program onto
893 table by the dummy one in the bootstrap program. This is only of
894 concern if the disk is fully dedicated, so that the
897 starts at absolute block 0 on the disk.
902 does not perform all possible error checking. Warning *is* given if partitions
903 overlap; if an absolute offset does not match the expected offset; if the
905 partition does not start at 0 or does not cover the entire slice; if a
906 partition runs past the end of the device; and a number of other errors; but
907 no warning is given if space remains unused.
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