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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 1.11 2007/01/21 10:06:10 swildner 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
101 installs, examines or modifies the label on a disk drive or pack. When writing
102 the label, it can be used to change the drive identification, the disk
103 partitions on the drive, or to replace a damaged label. There are several forms
104 of the command that read (display), install or edit the label on a disk. In
107 can install bootstrap code.
108 .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
111 default, most forms of the
113 command access the in-core copy of the label. To access the raw (on-disk)
116 option. This option allows a label to be installed on a disk without kernel
117 support for a label, such as when labels are first installed on a system; it
118 must be used when first installing a label on a disk. The specific effect of
120 is described under each command.
124 forms require a disk device name, which should always be the raw
125 device name representing the disk or slice. For example
127 represents the entire disk regardless of any DOS partitioning,
130 represents a slice. Some devices, most notably
136 partition be specified. For example
138 You do not have to include the
140 path prefix when specifying the device.
143 utility will automatically prepend it.
144 .Ss Reading the disk label
145 To examine the label on a disk drive, use
154 represents the raw disk in question, and may be in the form
158 It will display all of the parameters associated with the drive and its
159 partition layout. Unless the
162 the kernel's in-core copy of the label is displayed;
163 if the disk has no label, or the partition types on the disk are incorrect,
164 the kernel may have constructed or modified the label.
169 reads the label from the raw disk and displays it. Both versions are usually
170 identical except in the case where a label has not yet been initialized or
172 .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
261 To edit an existing disk label, use the form
269 This command reads the label from the in-core kernel copy, or directly from the
272 flag is also specified. The label is written to a file in ASCII and then
273 supplied to an editor for changes. If no editor is specified in an
275 environment variable,
277 is used. When the editor terminates, the label file is used to rewrite the disk
278 label. Existing bootstrap code is unchanged regardless of whether
282 is specified, no data will be written to the device, and instead the
283 disklabel that would have been written will be printed to stdout. This is
284 useful to see how a partitioning scheme will work out for a specific disk.
285 .Ss Restoring a disk label from a file
286 To restore a disk label from a file, use the form
292 .Ar disk Ar protofile
295 is capable of restoring a disk label that was previously saved in a file in ASCII format.
296 The prototype file used to create the label should be in the same format as that
297 produced when reading or editing a label. Comments are delimited by
299 and newline. As when writing a new label, any existing bootstrap code will be
302 is specified and will be unaffected otherwise. See the boot options below for a
303 method of restoring the label and writing the bootstrap at the same time.
306 is used, no data will be written to the device, and instead the
307 disklabel that would have been written will be printed to stdout. This is
308 useful to see how a partitioning scheme will work out for a specific disk.
309 .Ss Enabling and disabling writing to the disk label area
310 By default, it is not possible to write to the disk label area at the beginning
311 of a disk. The disk driver arranges for
313 and similar system calls
316 on any attempt to do so. If you need
317 to write to this area (for example, to obliterate the label), use the form
323 To disallow writing to the label area after previously allowing it, use the
329 .Ss Installing bootstraps
330 The final three forms of
332 are used to install bootstrap code. If you are creating a
333 .Dq dangerously-dedicated
334 slice for compatibility with older PC systems,
335 you generally want to specify the raw disk name such as
337 If you are creating a label within an existing DOS slice,
339 the partition name such as
341 Making a slice bootable can be tricky. If you are using a normal DOS
342 slice you typically install (or leave) a standard MBR on the base disk and
345 bootblocks in the slice.
356 This form installs the bootstrap only. It does not change the disk label.
357 You should never use this command on a base disk unless you intend to create a
358 .Dq dangerously-dedicated
361 This command is typically run on a slice such as
375 This form corresponds to the
377 command described above.
378 In addition to writing a new volume label, it also installs the bootstrap.
379 If run on a base disk this command will create a
380 .Dq dangerously-dedicated
381 label. This command is normally run on a slice rather than a base disk.
384 is used, no data will be written to the device, and instead the
385 disklabel that would have been written will be printed to stdout.
395 .Ar disk Ar protofile
398 This form corresponds to the
400 command described above.
401 In addition to restoring the volume label, it also installs the bootstrap.
402 If run on a base disk this command will create a
403 .Dq dangerously-dedicated
404 label. This command is normally run on a slice rather than a base disk.
406 The bootstrap commands always access the disk directly, so it is not necessary
411 is used, no data will be written to the device, and instead the
412 disklabel that would have been written will be printed to stdout.
414 The bootstrap code is comprised of two boot programs. Specify the name of the
415 boot programs to be installed in one of these ways:
418 Specify the names explicitly with the
424 indicates the primary boot program and
426 the secondary boot program. The boot programs are located in
433 flags are not specified, but
435 was specified, the names of the programs are taken from the
441 entry for the disk if the disktab entry exists and includes those parameters.
443 Otherwise, the default boot image names are used:
447 for the standard stage1 and stage2 boot images.
449 .Ss Initializing/Formatting a bootable disk from scratch
450 To initialize a disk from scratch the following sequence is recommended.
451 Please note that this will wipe everything that was previously on the disk,
459 to initialize the hard disk, and create a slice table, referred to
461 .Dq "partition table"
467 to define partitions on
469 slices created in the previous step.
473 to create file systems on new partitions.
476 A typical partitioning scheme would be to have an
479 of approximately 128MB to hold the root file system, a
495 (usually around 2GB),
500 (usually all remaining space).
501 Your mileage may vary.
503 .Nm fdisk Fl BI Pa da0
514 .Bl -tag -width ".Pa /etc/disktab" -compact
518 Disk description file.
520 .Sh SAVED FILE FORMAT
526 version of the label when examining, editing, or restoring a disk
529 .Bd -literal -offset 4n
538 sectors/cylinder: 969
540 sectors/unit: 1173930
545 headswitch: 0 # milliseconds
546 track-to-track seek: 0 # milliseconds
550 # size offset fstype [fsize bsize bps/cpg]
551 a: 81920 0 4.2BSD 1024 8192 16 # (Cyl. 0 - 84*)
552 b: 160000 81920 swap # (Cyl. 84* - 218*)
553 c: 1173930 0 unused 0 0 # (Cyl. 0 - 1211*)
554 h: 962010 211920 vinum # (Cyl. 218*- 1211*)
557 Lines starting with a
560 Most of the other specifications are no longer used.
561 The ones which must still be set correctly are:
565 is an optional label, set by the
567 option when writing a label.
574 is set for removable media drives, but no current
576 driver evaluates this
579 is no longer supported;
581 specifies that the drive can perform bad sector remapping.
583 describes the total size of the disk.
584 This value must be correct.
585 .It Ar "the partition table"
588 partition table, not the
590 partition table described in
594 The partition table can have up to 16 entries.
595 It contains the following information:
596 .Bl -tag -width indent
598 The partition identifier is a single letter in the range
602 By convention, partition
604 is reserved to describe the entire disk.
606 The size of the partition in sectors,
610 (megabytes - 1024*1024),
612 (gigabytes - 1024*1024*1024),
614 (percentage of free space
616 removing any fixed-size partitions other than partition
620 (all remaining free space
622 fixed-size and percentage partitions).
627 indicates the entire disk.
628 Lowercase versions of
633 Size and type should be specifed without any spaces between them.
635 Example: 2097152, 1G, 1024M and 1048576K are all the same size
636 (assuming 512-byte sectors).
638 The offset of the start of the partition from the beginning of the
643 calculate the correct offset to use (the end of the previous partition plus
644 one, ignoring partition
649 will be interpreted as an offset of 0.
651 Describes the purpose of the partition.
652 The example shows all currently used partition types.
659 For Vinum drives, use type
661 Other common types are
665 By convention, partition
667 represents the entire slice and should be of type
671 does not enforce this convention.
675 also knows about a number of other partition types,
676 none of which are in current use.
677 (See the definitions starting with
687 file systems only, the fragment size.
688 Defaults to 1024 for partitions smaller than 1GB,
689 2048 for partitions 1GB or larger.
695 file systems only, the block size.
696 Defaults to 8192 for partitions smaller than 1GB,
697 16384 for partitions 1GB or larger.
701 file systems, the number of cylinders in a cylinder group.
704 file systems, the segment shift value.
705 Defaults to 16 for partitions smaller than 1GB,
706 64 for partitions 1GB or larger.
709 The remainder of the line is a comment and shows the cylinder allocations based
710 on the obsolete (but possibly correct) geometry information about the drive.
713 indicates that the partition does not begin or end exactly on a
716 .Dl "disklabel da0s1"
718 Display the in-core label for the first slice of the
720 disk, as obtained via
723 .Dq dangerously-dedicated ,
724 the base disk name should be specified, such as
727 .Dl "disklabel da0s1 > savedlabel"
729 Save the in-core label for
733 This file can be used with the
735 option to restore the label at a later date.
737 .Dl "disklabel -w -r /dev/da0s1 da2212 foo"
741 based on information for
745 Any existing bootstrap code will be clobbered
746 and the disk rendered unbootable.
748 .Dl "disklabel -e -r da0s1"
750 Read the on-disk label for
752 edit it, and reinstall in-core as well as on-disk.
753 Existing bootstrap code is unaffected.
755 .Dl "disklabel -e -r -n da0s1"
757 Read the on-disk label for
759 edit it, and display what the new label would be (in sectors).
762 install the new label either in-core or on-disk.
764 .Dl "disklabel -r -w da0s1 auto"
766 Try to auto-detect the required information from
768 and write a new label to the disk.
772 partitioning and file system information.
774 .Dl "disklabel -R da0s1 savedlabel"
776 Restore the on-disk and in-core label for
780 Existing bootstrap code is unaffected.
782 .Dl "disklabel -R -n da0s1 label_layout"
784 Display what the label would be for
786 using the partition layout in
788 This is useful for determining how much space would be alloted for various
789 partitions with a labelling scheme using
795 .Dl disklabel -B da0s1
797 Install a new bootstrap on
799 The boot code comes from
803 On-disk and in-core labels are unchanged.
805 .Dl disklabel -w -B /dev/da0s1 -b newboot1 -s newboot2 da2212
807 Install a new label and bootstrap.
808 The label is derived from disktab information for
810 and installed both in-core and on-disk.
811 The bootstrap code comes from the files
816 .Dl dd if=/dev/zero of=/dev/da0 bs=512 count=32
818 .Dl dd if=/dev/zero of=/dev/da0s1 bs=512 count=32
819 .Dl disklabel -w -B da0s1 auto
820 .Dl disklabel -e da0s1
822 Completely wipe any prior information on the disk, creating a new bootable
823 disk with a DOS partition table containing one
826 initialize the slice, then edit it to your needs. The
828 commands are optional, but may be necessary for some BIOSes to properly
831 This is an example disklabel that uses some of the new partition size types
836 which could be used as a source file for
838 .Dl disklabel -R ad0s1c new_label_file
839 .Bd -literal -offset 4n
848 sectors/cylinder: 1008
850 sectors/unit: 40959009
855 headswitch: 0 # milliseconds
856 track-to-track seek: 0 # milliseconds
860 # size offset fstype [fsize bsize bps/cpg]
861 a: 400M 0 4.2BSD 4096 16384 75 # (Cyl. 0 - 812*)
869 The kernel device drivers will not allow the size of a disk partition
870 to be decreased or the offset of a partition to be changed while it is open.
871 Some device drivers create a label containing only a single large partition
872 if a disk is unlabeled; thus, the label must be written to the
874 partition of the disk while it is open. This sometimes requires the desired
875 label to be set in two steps, the first one creating at least one other
876 partition, and the second setting the label on the new partition while shrinking
881 On some machines the bootstrap code may not fit entirely in the area
882 allocated for it by some file systems.
883 As a result, it may not be possible to have file systems on some partitions
887 When installing bootstrap code,
889 checks for these cases.
890 If the installed boot code would overlap a partition of type FS_UNUSED
891 it is marked as type FS_BOOT.
894 utility will disallow creation of file systems on FS_BOOT partitions.
895 Conversely, if a partition has a type other than FS_UNUSED or FS_BOOT,
897 will not install bootstrap code that overlaps it.
906 When a disk name is given without a full pathname,
907 the constructed device name uses the
911 For the i386 architecture, the primary bootstrap sector contains
917 utility takes care to not clobber it when installing a bootstrap only
919 or when editing an existing label
921 but it unconditionally writes the primary bootstrap program onto
928 table by the dummy one in the bootstrap program. This is only of
929 concern if the disk is fully dedicated, so that the
932 starts at absolute block 0 on the disk.
937 does not perform all possible error checking. Warning *is* given if partitions
938 overlap; if an absolute offset does not match the expected offset; if the
940 partition does not start at 0 or does not cover the entire slice; if a
941 partition runs past the end of the device; and a number of other errors; but
942 no warning is given if space remains unused.
projects / dragonfly.git / blob