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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
98 installs, examines or modifies the label on a disk drive or pack. When writing
99 the label, it can be used to change the drive identification, the disk
100 partitions on the drive, or to replace a damaged label. There are several forms
101 of the command that read (display), install or edit the label on a disk. In
104 can install bootstrap code.
105 .Ss Raw or in-core label
107 The disk label resides close to or at the beginning of each disk slice.
108 For faster access, the kernel maintains a copy in core at all times. By
111 access the in-core copy of the label. To access the raw (on-disk) copy, use the
113 option. This option allows a label to be installed on a disk without kernel
114 support for a label, such as when labels are first installed on a system; it
115 must be used when first installing a label on a disk. The specific effect of
117 is described under each command.
123 forms require a disk device name, which should always be the raw
124 device name representing the disk or slice. For example
126 represents the entire disk regardless of any DOS partitioning,
129 represents a slice. Some devices, most notably
135 partition be specified. For example
137 You do not have to include the
139 path prefix when specifying the device.
141 will automatically prepend it.
142 .Ss Reading the disk label
144 To examine the label on a disk drive, use
153 represents the raw disk in question, and may be in the form
157 It will display all of the parameters associated with the drive and its
158 partition layout. Unless the
161 the kernel's in-core copy of the label is displayed;
162 if the disk has no label, or the partition types on the disk are incorrect,
163 the kernel may have constructed or modified the label.
168 reads the label from the raw disk and displays it. Both versions are usually
169 identical except in the case where a label has not yet been initialized or
171 .Ss Writing a standard label
173 To write a standard label, use the form
179 .Ar disk Ar disktype/auto
189 The required arguments to
191 are the drive to be labeled and the drive type as described in the
193 file. The drive parameters and partitions are taken from that file. If
194 different disks of the same physical type are to have different partitions, it
195 will be necessary to have separate disktab entries describing each, or to edit
196 the label after installation as described below. The optional argument is a
197 pack identification string, up to 16 characters long. The pack id must be
198 quoted if it contains blanks.
202 flag is given, no data will be written to the device, and instead the
203 disklabel that would have been written will be printed to stdout.
207 flag is given, the disk sectors containing the label and bootstrap
208 will be written directly.
209 A side-effect of this is that any existing bootstrap code will be overwritten
210 and the disk rendered unbootable. See the boot options below for a method of
211 writing the label and the bootstrap at the same time.
215 the existing label will be updated via the in-core copy and any bootstrap
216 code will be unaffected.
217 If the disk does not already have a label, the
220 In either case, the kernel's in-core label is replaced.
222 For a virgin disk that is not known to
227 In this case, the driver is requested to produce a virgin label for the
228 disk. This might or might not be successful, depending on whether the
229 driver for the disk is able to get the required data without reading
230 anything from the disk at all. It will likely succeed for all SCSI
231 disks, most IDE disks, and vnode devices. Writing a label to the
232 disk is the only supported operation, and the
234 itself must be provided as the canonical name, i.e. not as a full
237 For most harddisks, a label based on percentages for most partitions (and
238 one partition with a size of
240 will produce a reasonable configuration.
242 PC-based systems have special requirements in order for the BIOS to properly
245 disklabel. Older systems may require what is known as a
246 .Dq dangerously dedicated
247 disklabel, which creates a fake DOS partition to work around problems older
248 BIOSes have with modern disk geometries.
249 On newer systems you generally want
250 to create a normal DOS partition using
254 disklabel within that slice. This is described
255 later on in this page.
257 Installing a new disklabel does not in of itself allow your system to boot
258 a kernel using that label. You must also install boot blocks, which is
259 described later on in this manual page.
260 .Ss Editing an existing disk label
262 To edit an existing disk label, use the form
270 This command reads the label from the in-core kernel copy, or directly from the
273 flag is also specified. The label is written to a file in ASCII and then
274 supplied to an editor for changes. If no editor is specified in an
276 environment variable,
278 is used. When the editor terminates, the label file is used to rewrite the disk
279 label. Existing bootstrap code is unchanged regardless of whether
283 is specified, no data will be written to the device, and instead the
284 disklabel that would have been written will be printed to stdout. This is
285 useful to see how a partitioning scheme will work out for a specific disk.
286 .Ss Restoring a disk label from a file
288 To restore a disk label from a file, use the form
294 .Ar disk Ar protofile
297 is capable of restoring a disk label that was previously saved in a file in ASCII format.
298 The prototype file used to create the label should be in the same format as that
299 produced when reading or editing a label. Comments are delimited by
301 and newline. As when writing a new label, any existing bootstrap code will be
304 is specified and will be unaffected otherwise. See the boot options below for a
305 method of restoring the label and writing the bootstrap at the same time.
308 is used, no data will be written to the device, and instead the
309 disklabel that would have been written will be printed to stdout. This is
310 useful to see how a partitioning scheme will work out for a specific disk.
311 .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 silently ignores any attempt to do so. If you need
315 to write to this area (for example, to obliterate the label), use the form
321 To disallow writing to the label area after previously allowing it, use the
327 .Ss Installing bootstraps
329 The final three forms of
331 are used to install bootstrap code. If you are creating a
332 .Dq dangerously-dedicated
333 slice for compatibility with older PC systems,
334 you generally want to specify the raw disk name such as
336 If you are creating a label within an existing DOS slice,
338 the partition name such as
340 Making a slice bootable can be tricky. If you are using a normal DOS
341 slice you typically install (or leave) a standard MBR on the base disk and
344 bootblocks in the slice.
355 This form installs the bootstrap only. It does not change the disk label.
356 You should never use this command on a base disk unless you intend to create a
357 .Dq dangerously-dedicated
360 This command is typically run on a slice such as
374 This form corresponds to the
376 command described above.
377 In addition to writing a new volume label, it also installs the bootstrap.
378 If run on a base disk this command will create a
379 .Dq dangerously-dedicated
380 label. This command is normally run on a slice rather than a base disk.
383 is used, no data will be written to the device, and instead the
384 disklabel that would have been written will be printed to stdout.
394 .Ar disk Ar protofile
397 This form corresponds to the
399 command described above.
400 In addition to restoring the volume label, it also installs the bootstrap.
401 If run on a base disk this command will create a
402 .Dq dangerously-dedicated
403 label. This command is normally run on a slice rather than a base disk.
405 The bootstrap commands always access the disk directly, so it is not necessary
410 is used, no data will be written to the device, and instead the
411 disklabel that would have been written will be printed to stdout.
413 The bootstrap code is comprised of two boot programs. Specify the name of the
414 boot programs to be installed in one of these ways:
417 Specify the names explicitly with the
423 indicates the primary boot program and
425 the secondary boot program. The boot programs are located in
432 flags are not specified, but
434 was specified, the names of the programs are taken from the
440 entry for the disk if the disktab entry exists and includes those parameters.
442 Otherwise, the default boot image names are used:
446 for the standard stage1 and stage2 boot images (details may vary
447 on architectures like the Alpha, where only a single-stage boot is used).
449 .Ss Initializing/Formatting a bootable disk from scratch
451 To initialize a disk from scratch the following sequence is recommended.
452 Please note that this will wipe everything that was previously on the disk,
460 to initialize the hard disk, and create a slice table, referred to
461 as the partition table in DOS.
462 Here you will define disk slices for your system.
466 to define and write partitions and mount points.
467 You are not required to define the mount points here though,
468 they can be defined later using
473 to create a filesystem on the new partition.
474 A typical partitioning scheme would be to have an
477 of approximately 128MB to hold the root filesystem, a
482 partition for /var (usually 128MB), an
485 for /var/tmp (usually 128MB), an
487 partition for /usr (usually around 2G),
490 partition for /home (usually all remaining space).
491 Your mileage may vary.
494 .Nm fdisk Fl BI Ar da0
507 .Bl -tag -width Pa -compact
512 .Sh SAVED FILE FORMAT
514 uses an ASCII version of the label when examining, editing or restoring a disk
515 label. The format is:
516 .Bd -literal -offset 4n
525 sectors/cylinder: 969
527 sectors/unit: 1173930
532 headswitch: 0 # milliseconds
533 track-to-track seek: 0 # milliseconds
537 # size offset fstype [fsize bsize bps/cpg]
538 a: 81920 0 4.2BSD 1024 8192 16 # (Cyl. 0 - 84*)
539 b: 160000 81920 swap # (Cyl. 84* - 218*)
540 c: 1173930 0 unused 0 0 # (Cyl. 0 - 1211*)
541 h: 962010 211920 vinum # (Cyl. 218*- 1211*)
544 Lines starting with a # mark are comments. Most of the other specifications are
545 no longer used. The ones which must still be set correctly are:
549 is an optional label, set by the
551 option when writing a label.
559 is set for removable media drives, but no current
561 driver evaluates this
564 is no longer supported;
566 specifies that the drive can perform bad sector remapping.
568 describes the total size of the disk. This value must be correct.
569 .It Nm the partition table
572 partition table, not the Microsoft partition table described in
576 The partition table can have up to 8 entries. It contains the following
580 The partition identifier is a single letter in the range
584 By convention, partition
586 is reserved to describe the entire disk.
588 is the size of the partition in sectors,
592 (megabytes - 1024*1024),
594 (gigabytes - 1024*1024*1024),
596 (percentage of free space AFTER removing any fixed-size partitions other
601 (all remaining free space AFTER fixed-size and percentage
602 partitions). For partition
606 indicates the entire disk. Lowercase versions of
611 Size and type should be specifed without any spaces between them.
613 Example: 2097152, 1g, 1024m and 1048576k are all the same size
614 (assuming 512-byte sectors).
616 is the offset of the start of the partition from the beginning of the
621 calculate the correct offset to use (the end of the previous partition plus
622 one, ignoring partition
627 will be interpreted as an offset of 0.
629 describes the purpose of the partition. The example shows all currently used
631 For UFS filesystems and ccd partitions, use type
633 For Vinum drives, use type
635 Other common types are
639 By convention, partition
641 represents the entire slice and should be of type
645 does not enforce this convention.
647 also knows about a number of other partition types, none of which are in current
649 See the definitions starting with
652 .Pa /usr/include/sys/disklabel.h
657 and LFS filesystems only, the fragment size. Defaults to 1024 for
658 partitions smaller than 1 GB, 4096 for partitions 1GB or larger.
662 and LFS filesystems only, the block size. Defaults to 8192 for
663 partitions smaller than 1 GB, 16384 for partitions 1GB or larger.
667 filesystems, the number of cylinders in a cylinder group. For LFS file
668 systems, the segment shift value. Defaults to 16 for
669 partitions smaller than 1 GB, 64 for partitions 1GB or larger.
672 The remainder of the line is a comment and shows the cylinder allocations based
673 on the obsolete (but possibly correct) geometry information about the drive.
674 The asterisk (*) indicates that the partition does not begin or end exactly on a
679 Display the in-core label for
683 When reading a label,
685 will allow you to specify the base disk name
686 even if the label resides on a slice. However, to be proper you should
687 specify the base disk name only if you are using a
688 .Dq dangerously-dedicated
689 label. Normally you specify the slice.
691 .Dl disklabel da0s1 > savedlabel
693 Save the in-core label for
697 This file can be used with the
699 flag to restore the label at a later date.
701 .Dl disklabel -w -r /dev/da0s1 da2212 foo
705 based on information for
709 Any existing bootstrap code will be clobbered.
711 .Dl disklabel -e -r da0s1
713 Read the on-disk label for
715 edit it and reinstall in-core as well as on-disk. Existing bootstrap code is
718 .Dl disklabel -e -r -n da0s1
720 Read the on-disk label for
722 edit it, and display what the new label would be (in sectors). It does
723 NOT install the new label either in-core or on-disk.
725 .Dl disklabel -r -w da0s1 auto
727 Try to auto-detect the required information from
729 and write a new label to the disk. Use another disklabel -e command to edit the
730 partitioning and filesystem information.
732 .Dl disklabel -R da0s1 savedlabel
734 Restore the on-disk and in-core label for
738 Existing bootstrap code is unaffected.
740 .Dl disklabel -R -n da0s1 label_layout
742 Display what the label would be for
744 using the partition layout in
746 This is useful for determining how much space would be alloted for various
747 partitions with a labelling scheme using
753 .Dl disklabel -B da0s1
755 Install a new bootstrap on
757 The boot code comes from
761 On-disk and in-core labels are unchanged.
763 .Dl disklabel -w -B /dev/da0s1 -b newboot1 -s newboot2 da2212
765 Install a new label and bootstrap.
766 The label is derived from disktab information for
768 and installed both in-core and on-disk.
769 The bootstrap code comes from the files
774 .Dl dd if=/dev/zero of=/dev/da0 bs=512 count=32
776 .Dl dd if=/dev/zero of=/dev/da0s1 bs=512 count=32
777 .Dl disklabel -w -B da0s1 auto
778 .Dl disklabel -e da0s1
780 Completely wipe any prior information on the disk, creating a new bootable
781 disk with a DOS partition table containing one
784 initialize the slice, then edit it to your needs. The
786 commands are optional, but may be necessary for some BIOSes to properly
789 This is an example disklabel that uses some of the new partition size types
794 which could be used as a source file for
796 .Dl disklabel -R ad0s1c new_label_file
797 .Bd -literal -offset 4n
806 sectors/cylinder: 1008
808 sectors/unit: 40959009
813 headswitch: 0 # milliseconds
814 track-to-track seek: 0 # milliseconds
818 # size offset fstype [fsize bsize bps/cpg]
819 a: 400M 0 4.2BSD 4096 16384 75 # (Cyl. 0 - 812*)
834 The kernel device drivers will not allow the size of a disk partition
835 to be decreased or the offset of a partition to be changed while it is open.
836 Some device drivers create a label containing only a single large partition
837 if a disk is unlabeled; thus, the label must be written to the
839 partition of the disk while it is open. This sometimes requires the desired
840 label to be set in two steps, the first one creating at least one other
841 partition, and the second setting the label on the new partition while shrinking
846 On some machines the bootstrap code may not fit entirely in the area
847 allocated for it by some filesystems.
848 As a result, it may not be possible to have filesystems on some partitions
852 When installing bootstrap code,
854 checks for these cases.
855 If the installed boot code would overlap a partition of type FS_UNUSED
856 it is marked as type FS_BOOT.
859 utility will disallow creation of filesystems on FS_BOOT partitions.
860 Conversely, if a partition has a type other than FS_UNUSED or FS_BOOT,
862 will not install bootstrap code that overlaps it.
864 When a disk name is given without a full pathname,
865 the constructed device name uses the
869 For the i386 architecture, the primary bootstrap sector contains
874 takes care to not clobber it when installing a bootstrap only
876 or when editing an existing label
878 but it unconditionally writes the primary bootstrap program onto
885 table by the dummy one in the bootstrap program. This is only of
886 concern if the disk is fully dedicated, so that the
889 starts at absolute block 0 on the disk.
892 does not perform all possible error checking. Warning *is* given if partitions
893 overlap; if an absolute offset does not match the expected offset; if the
895 partition does not start at 0 or does not cover the entire slice; if a
896 partition runs past the end of the device; and a number of other errors; but
897 no warning is given if space remains unused.
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