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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
320 to return EROFS on any attempt to do so. If you need
321 to write to this area (for example, to obliterate the label), use the form
327 To disallow writing to the label area after previously allowing it, use the
333 .Ss Installing bootstraps
335 The final three forms of
337 are used to install bootstrap code. If you are creating a
338 .Dq dangerously-dedicated
339 slice for compatibility with older PC systems,
340 you generally want to specify the raw disk name such as
342 If you are creating a label within an existing DOS slice,
344 the partition name such as
346 Making a slice bootable can be tricky. If you are using a normal DOS
347 slice you typically install (or leave) a standard MBR on the base disk and
350 bootblocks in the slice.
361 This form installs the bootstrap only. It does not change the disk label.
362 You should never use this command on a base disk unless you intend to create a
363 .Dq dangerously-dedicated
366 This command is typically run on a slice such as
380 This form corresponds to the
382 command described above.
383 In addition to writing a new volume label, it also installs the bootstrap.
384 If run on a base disk this command will create a
385 .Dq dangerously-dedicated
386 label. This command is normally run on a slice rather than a base disk.
389 is used, no data will be written to the device, and instead the
390 disklabel that would have been written will be printed to stdout.
400 .Ar disk Ar protofile
403 This form corresponds to the
405 command described above.
406 In addition to restoring the volume label, it also installs the bootstrap.
407 If run on a base disk this command will create a
408 .Dq dangerously-dedicated
409 label. This command is normally run on a slice rather than a base disk.
411 The bootstrap commands always access the disk directly, so it is not necessary
416 is used, no data will be written to the device, and instead the
417 disklabel that would have been written will be printed to stdout.
419 The bootstrap code is comprised of two boot programs. Specify the name of the
420 boot programs to be installed in one of these ways:
423 Specify the names explicitly with the
429 indicates the primary boot program and
431 the secondary boot program. The boot programs are located in
438 flags are not specified, but
440 was specified, the names of the programs are taken from the
446 entry for the disk if the disktab entry exists and includes those parameters.
448 Otherwise, the default boot image names are used:
452 for the standard stage1 and stage2 boot images (details may vary
453 on architectures like the Alpha, where only a single-stage boot is used).
455 .Ss Initializing/Formatting a bootable disk from scratch
457 To initialize a disk from scratch the following sequence is recommended.
458 Please note that this will wipe everything that was previously on the disk,
466 to initialize the hard disk, and create a slice table, referred to
467 as the partition table in DOS.
468 Here you will define disk slices for your system.
472 to define and write partitions and mount points.
473 You are not required to define the mount points here though,
474 they can be defined later using
479 to create a file system on the new partition.
480 A typical partitioning scheme would be to have an
483 of approximately 128MB to hold the root file system, a
488 partition for /var (usually 128MB), an
491 for /var/tmp (usually 128MB), an
493 partition for /usr (usually around 2G),
496 partition for /home (usually all remaining space).
497 Your mileage may vary.
500 .Nm fdisk Fl BI Ar da0
513 .Bl -tag -width Pa -compact
518 .Sh SAVED FILE FORMAT
522 uses an ASCII version of the label when examining, editing or restoring a disk
523 label. The format is:
524 .Bd -literal -offset 4n
533 sectors/cylinder: 969
535 sectors/unit: 1173930
540 headswitch: 0 # milliseconds
541 track-to-track seek: 0 # milliseconds
545 # size offset fstype [fsize bsize bps/cpg]
546 a: 81920 0 4.2BSD 1024 8192 16 # (Cyl. 0 - 84*)
547 b: 160000 81920 swap # (Cyl. 84* - 218*)
548 c: 1173930 0 unused 0 0 # (Cyl. 0 - 1211*)
549 h: 962010 211920 vinum # (Cyl. 218*- 1211*)
552 Lines starting with a # mark are comments. Most of the other specifications are
553 no longer used. The ones which must still be set correctly are:
557 is an optional label, set by the
559 option when writing a label.
567 is set for removable media drives, but no current
569 driver evaluates this
572 is no longer supported;
574 specifies that the drive can perform bad sector remapping.
576 describes the total size of the disk. This value must be correct.
577 .It Nm the partition table
580 partition table, not the Microsoft partition table described in
584 The partition table can have up to 8 entries. It contains the following
588 The partition identifier is a single letter in the range
592 By convention, partition
594 is reserved to describe the entire disk.
596 is the size of the partition in sectors,
600 (megabytes - 1024*1024),
602 (gigabytes - 1024*1024*1024),
604 (percentage of free space AFTER removing any fixed-size partitions other
609 (all remaining free space AFTER fixed-size and percentage
610 partitions). For partition
614 indicates the entire disk. Lowercase versions of
619 Size and type should be specifed without any spaces between them.
621 Example: 2097152, 1g, 1024m and 1048576k are all the same size
622 (assuming 512-byte sectors).
624 is the offset of the start of the partition from the beginning of the
629 calculate the correct offset to use (the end of the previous partition plus
630 one, ignoring partition
635 will be interpreted as an offset of 0.
637 describes the purpose of the partition. The example shows all currently used
639 For UFS file systems and ccd partitions, use type
641 For Vinum drives, use type
643 Other common types are
647 By convention, partition
649 represents the entire slice and should be of type
653 does not enforce this convention.
657 also knows about a number of other partition types, none of which are in current
659 See the definitions starting with
662 .Pa /usr/include/sys/disklabel.h
667 and LFS file systems only, the fragment size. Defaults to 1024 for
668 partitions smaller than 1 GB, 4096 for partitions 1GB or larger.
672 and LFS file systems only, the block size. Defaults to 8192 for
673 partitions smaller than 1 GB, 16384 for partitions 1GB or larger.
677 file systems, the number of cylinders in a cylinder group. For LFS file
678 systems, the segment shift value. Defaults to 16 for
679 partitions smaller than 1 GB, 64 for partitions 1GB or larger.
682 The remainder of the line is a comment and shows the cylinder allocations based
683 on the obsolete (but possibly correct) geometry information about the drive.
684 The asterisk (*) indicates that the partition does not begin or end exactly on a
689 Display the in-core label for
693 When reading a label,
695 will allow you to specify the base disk name
696 even if the label resides on a slice. However, to be proper you should
697 specify the base disk name only if you are using a
698 .Dq dangerously-dedicated
699 label. Normally you specify the slice.
701 .Dl disklabel da0s1 > savedlabel
703 Save the in-core label for
707 This file can be used with the
709 flag to restore the label at a later date.
711 .Dl disklabel -w -r /dev/da0s1 da2212 foo
715 based on information for
719 Any existing bootstrap code will be clobbered.
721 .Dl disklabel -e -r da0s1
723 Read the on-disk label for
725 edit it and reinstall in-core as well as on-disk. Existing bootstrap code is
728 .Dl disklabel -e -r -n da0s1
730 Read the on-disk label for
732 edit it, and display what the new label would be (in sectors). It does
733 NOT install the new label either in-core or on-disk.
735 .Dl disklabel -r -w da0s1 auto
737 Try to auto-detect the required information from
739 and write a new label to the disk. Use another disklabel -e command to edit the
740 partitioning and file system information.
742 .Dl disklabel -R da0s1 savedlabel
744 Restore the on-disk and in-core label for
748 Existing bootstrap code is unaffected.
750 .Dl disklabel -R -n da0s1 label_layout
752 Display what the label would be for
754 using the partition layout in
756 This is useful for determining how much space would be alloted for various
757 partitions with a labelling scheme using
763 .Dl disklabel -B da0s1
765 Install a new bootstrap on
767 The boot code comes from
771 On-disk and in-core labels are unchanged.
773 .Dl disklabel -w -B /dev/da0s1 -b newboot1 -s newboot2 da2212
775 Install a new label and bootstrap.
776 The label is derived from disktab information for
778 and installed both in-core and on-disk.
779 The bootstrap code comes from the files
784 .Dl dd if=/dev/zero of=/dev/da0 bs=512 count=32
786 .Dl dd if=/dev/zero of=/dev/da0s1 bs=512 count=32
787 .Dl disklabel -w -B da0s1 auto
788 .Dl disklabel -e da0s1
790 Completely wipe any prior information on the disk, creating a new bootable
791 disk with a DOS partition table containing one
794 initialize the slice, then edit it to your needs. The
796 commands are optional, but may be necessary for some BIOSes to properly
799 This is an example disklabel that uses some of the new partition size types
804 which could be used as a source file for
806 .Dl disklabel -R ad0s1c new_label_file
807 .Bd -literal -offset 4n
816 sectors/cylinder: 1008
818 sectors/unit: 40959009
823 headswitch: 0 # milliseconds
824 track-to-track seek: 0 # milliseconds
828 # size offset fstype [fsize bsize bps/cpg]
829 a: 400M 0 4.2BSD 4096 16384 75 # (Cyl. 0 - 812*)
844 The kernel device drivers will not allow the size of a disk partition
845 to be decreased or the offset of a partition to be changed while it is open.
846 Some device drivers create a label containing only a single large partition
847 if a disk is unlabeled; thus, the label must be written to the
849 partition of the disk while it is open. This sometimes requires the desired
850 label to be set in two steps, the first one creating at least one other
851 partition, and the second setting the label on the new partition while shrinking
856 On some machines the bootstrap code may not fit entirely in the area
857 allocated for it by some file systems.
858 As a result, it may not be possible to have file systems on some partitions
862 When installing bootstrap code,
864 checks for these cases.
865 If the installed boot code would overlap a partition of type FS_UNUSED
866 it is marked as type FS_BOOT.
869 utility will disallow creation of file systems on FS_BOOT partitions.
870 Conversely, if a partition has a type other than FS_UNUSED or FS_BOOT,
872 will not install bootstrap code that overlaps it.
874 When a disk name is given without a full pathname,
875 the constructed device name uses the
879 For the i386 architecture, the primary bootstrap sector contains
885 utility takes care to not clobber it when installing a bootstrap only
887 or when editing an existing label
889 but it unconditionally writes the primary bootstrap program onto
896 table by the dummy one in the bootstrap program. This is only of
897 concern if the disk is fully dedicated, so that the
900 starts at absolute block 0 on the disk.
905 does not perform all possible error checking. Warning *is* given if partitions
906 overlap; if an absolute offset does not match the expected offset; if the
908 partition does not start at 0 or does not cover the entire slice; if a
909 partition runs past the end of the device; and a number of other errors; but
910 no warning is given if space remains unused.
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