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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 $
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
470 .Dq "partition table"
476 to define partitions on
478 slices created in the previous step.
482 to create file systems on new partitions.
485 A typical partitioning scheme would be to have an
488 of approximately 128MB to hold the root file system, a
504 (usually around 2GB),
509 (usually all remaining space).
510 Your mileage may vary.
512 .Nm fdisk Fl BI Pa da0
523 .Bl -tag -width ".Pa /etc/disktab" -compact
527 Disk description file.
529 .Sh SAVED FILE FORMAT
535 version of the label when examining, editing, or restoring a disk
538 .Bd -literal -offset 4n
547 sectors/cylinder: 969
549 sectors/unit: 1173930
554 headswitch: 0 # milliseconds
555 track-to-track seek: 0 # milliseconds
559 # size offset fstype [fsize bsize bps/cpg]
560 a: 81920 0 4.2BSD 1024 8192 16 # (Cyl. 0 - 84*)
561 b: 160000 81920 swap # (Cyl. 84* - 218*)
562 c: 1173930 0 unused 0 0 # (Cyl. 0 - 1211*)
563 h: 962010 211920 vinum # (Cyl. 218*- 1211*)
566 Lines starting with a
569 Most of the other specifications are no longer used.
570 The ones which must still be set correctly are:
574 is an optional label, set by the
576 option when writing a label.
583 is set for removable media drives, but no current
585 driver evaluates this
588 is no longer supported;
590 specifies that the drive can perform bad sector remapping.
592 describes the total size of the disk.
593 This value must be correct.
594 .It Ar "the partition table"
597 partition table, not the
599 partition table described in
603 The partition table can have up to 8 entries.
604 It contains the following information:
605 .Bl -tag -width indent
607 The partition identifier is a single letter in the range
611 By convention, partition
613 is reserved to describe the entire disk.
615 The size of the partition in sectors,
619 (megabytes - 1024*1024),
621 (gigabytes - 1024*1024*1024),
623 (percentage of free space
625 removing any fixed-size partitions other than partition
629 (all remaining free space
631 fixed-size and percentage partitions).
636 indicates the entire disk.
637 Lowercase versions of
642 Size and type should be specifed without any spaces between them.
644 Example: 2097152, 1G, 1024M and 1048576K are all the same size
645 (assuming 512-byte sectors).
647 The offset of the start of the partition from the beginning of the
652 calculate the correct offset to use (the end of the previous partition plus
653 one, ignoring partition
658 will be interpreted as an offset of 0.
660 Describes the purpose of the partition.
661 The example shows all currently used partition types.
668 For Vinum drives, use type
670 Other common types are
674 By convention, partition
676 represents the entire slice and should be of type
680 does not enforce this convention.
684 also knows about a number of other partition types,
685 none of which are in current use.
686 (See the definitions starting with
689 .Aq Pa sys/disklabel.h
696 file systems only, the fragment size.
697 Defaults to 1024 for partitions smaller than 1GB,
698 4096 for partitions 1GB or larger.
704 file systems only, the block size.
705 Defaults to 8192 for partitions smaller than 1GB,
706 16384 for partitions 1GB or larger.
710 file systems, the number of cylinders in a cylinder group.
713 file systems, the segment shift value.
714 Defaults to 16 for partitions smaller than 1GB,
715 64 for partitions 1GB or larger.
718 The remainder of the line is a comment and shows the cylinder allocations based
719 on the obsolete (but possibly correct) geometry information about the drive.
722 indicates that the partition does not begin or end exactly on a
725 .Dl "disklabel da0s1"
727 Display the in-core label for the first slice of the
729 disk, as obtained via
732 .Dq dangerously-dedicated ,
733 the base disk name should be specified, such as
736 .Dl "disklabel da0s1 > savedlabel"
738 Save the in-core label for
742 This file can be used with the
744 option to restore the label at a later date.
746 .Dl "disklabel -w -r /dev/da0s1 da2212 foo"
750 based on information for
754 Any existing bootstrap code will be clobbered
755 and the disk rendered unbootable.
757 .Dl "disklabel -e -r da0s1"
759 Read the on-disk label for
761 edit it, and reinstall in-core as well as on-disk.
762 Existing bootstrap code is unaffected.
764 .Dl "disklabel -e -r -n da0s1"
766 Read the on-disk label for
768 edit it, and display what the new label would be (in sectors).
771 install the new label either in-core or on-disk.
773 .Dl "disklabel -r -w da0s1 auto"
775 Try to auto-detect the required information from
777 and write a new label to the disk.
781 partitioning and file system information.
783 .Dl "disklabel -R da0s1 savedlabel"
785 Restore the on-disk and in-core label for
789 Existing bootstrap code is unaffected.
791 .Dl "disklabel -R -n da0s1 label_layout"
793 Display what the label would be for
795 using the partition layout in
797 This is useful for determining how much space would be alloted for various
798 partitions with a labelling scheme using
804 .Dl disklabel -B da0s1
806 Install a new bootstrap on
808 The boot code comes from
812 On-disk and in-core labels are unchanged.
814 .Dl disklabel -w -B /dev/da0s1 -b newboot1 -s newboot2 da2212
816 Install a new label and bootstrap.
817 The label is derived from disktab information for
819 and installed both in-core and on-disk.
820 The bootstrap code comes from the files
825 .Dl dd if=/dev/zero of=/dev/da0 bs=512 count=32
827 .Dl dd if=/dev/zero of=/dev/da0s1 bs=512 count=32
828 .Dl disklabel -w -B da0s1 auto
829 .Dl disklabel -e da0s1
831 Completely wipe any prior information on the disk, creating a new bootable
832 disk with a DOS partition table containing one
835 initialize the slice, then edit it to your needs. The
837 commands are optional, but may be necessary for some BIOSes to properly
840 This is an example disklabel that uses some of the new partition size types
845 which could be used as a source file for
847 .Dl disklabel -R ad0s1c new_label_file
848 .Bd -literal -offset 4n
857 sectors/cylinder: 1008
859 sectors/unit: 40959009
864 headswitch: 0 # milliseconds
865 track-to-track seek: 0 # milliseconds
869 # size offset fstype [fsize bsize bps/cpg]
870 a: 400M 0 4.2BSD 4096 16384 75 # (Cyl. 0 - 812*)
885 The kernel device drivers will not allow the size of a disk partition
886 to be decreased or the offset of a partition to be changed while it is open.
887 Some device drivers create a label containing only a single large partition
888 if a disk is unlabeled; thus, the label must be written to the
890 partition of the disk while it is open. This sometimes requires the desired
891 label to be set in two steps, the first one creating at least one other
892 partition, and the second setting the label on the new partition while shrinking
897 On some machines the bootstrap code may not fit entirely in the area
898 allocated for it by some file systems.
899 As a result, it may not be possible to have file systems on some partitions
903 When installing bootstrap code,
905 checks for these cases.
906 If the installed boot code would overlap a partition of type FS_UNUSED
907 it is marked as type FS_BOOT.
910 utility will disallow creation of file systems on FS_BOOT partitions.
911 Conversely, if a partition has a type other than FS_UNUSED or FS_BOOT,
913 will not install bootstrap code that overlaps it.
915 When a disk name is given without a full pathname,
916 the constructed device name uses the
920 For the i386 architecture, the primary bootstrap sector contains
926 utility takes care to not clobber it when installing a bootstrap only
928 or when editing an existing label
930 but it unconditionally writes the primary bootstrap program onto
937 table by the dummy one in the bootstrap program. This is only of
938 concern if the disk is fully dedicated, so that the
941 starts at absolute block 0 on the disk.
946 does not perform all possible error checking. Warning *is* given if partitions
947 overlap; if an absolute offset does not match the expected offset; if the
949 partition does not start at 0 or does not cover the entire slice; if a
950 partition runs past the end of the device; and a number of other errors; but
951 no warning is given if space remains unused.
projects / dragonfly.git / blob