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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 1.4 2004/05/09 22:55:31 cpressey 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
110 The disk label resides close to or at the beginning of each disk slice.
111 For faster access, the kernel maintains a copy in core at all times. By
112 default, most forms of the
114 command access the in-core copy of the label. To access the raw (on-disk)
117 option. This option allows a label to be installed on a disk without kernel
118 support for a label, such as when labels are first installed on a system; it
119 must be used when first installing a label on a disk. The specific effect of
121 is described under each command.
127 forms require a disk device name, which should always be the raw
128 device name representing the disk or slice. For example
130 represents the entire disk regardless of any DOS partitioning,
133 represents a slice. Some devices, most notably
139 partition be specified. For example
141 You do not have to include the
143 path prefix when specifying the device.
146 utility will automatically prepend it.
147 .Ss Reading the disk label
149 To examine the label on a disk drive, use
158 represents the raw disk in question, and may be in the form
162 It will display all of the parameters associated with the drive and its
163 partition layout. Unless the
166 the kernel's in-core copy of the label is displayed;
167 if the disk has no label, or the partition types on the disk are incorrect,
168 the kernel may have constructed or modified the label.
173 reads the label from the raw disk and displays it. Both versions are usually
174 identical except in the case where a label has not yet been initialized or
176 .Ss Writing a standard label
178 To write a standard label, use the form
184 .Ar disk Ar disktype/auto
194 The required arguments to
196 are the drive to be labeled and the drive type as described in the
198 file. The drive parameters and partitions are taken from that file. If
199 different disks of the same physical type are to have different partitions, it
200 will be necessary to have separate disktab entries describing each, or to edit
201 the label after installation as described below. The optional argument is a
202 pack identification string, up to 16 characters long. The pack id must be
203 quoted if it contains blanks.
207 flag is given, no data will be written to the device, and instead the
208 disklabel that would have been written will be printed to stdout.
212 flag is given, the disk sectors containing the label and bootstrap
213 will be written directly.
214 A side-effect of this is that any existing bootstrap code will be overwritten
215 and the disk rendered unbootable. See the boot options below for a method of
216 writing the label and the bootstrap at the same time.
220 the existing label will be updated via the in-core copy and any bootstrap
221 code will be unaffected.
222 If the disk does not already have a label, the
225 In either case, the kernel's in-core label is replaced.
227 For a virgin disk that is not known to
232 In this case, the driver is requested to produce a virgin label for the
233 disk. This might or might not be successful, depending on whether the
234 driver for the disk is able to get the required data without reading
235 anything from the disk at all. It will likely succeed for all SCSI
236 disks, most IDE disks, and vnode devices. Writing a label to the
237 disk is the only supported operation, and the
239 itself must be provided as the canonical name, i.e. not as a full
242 For most harddisks, a label based on percentages for most partitions (and
243 one partition with a size of
245 will produce a reasonable configuration.
247 PC-based systems have special requirements in order for the BIOS to properly
250 disklabel. Older systems may require what is known as a
251 .Dq dangerously dedicated
252 disklabel, which creates a fake DOS partition to work around problems older
253 BIOSes have with modern disk geometries.
254 On newer systems you generally want
255 to create a normal DOS partition using
259 disklabel within that slice. This is described
260 later on in this page.
262 Installing a new disklabel does not in of itself allow your system to boot
263 a kernel using that label. You must also install boot blocks, which is
264 described later on in this manual page.
265 .Ss Editing an existing disk label
267 To edit an existing disk label, use the form
275 This command reads the label from the in-core kernel copy, or directly from the
278 flag is also specified. The label is written to a file in ASCII and then
279 supplied to an editor for changes. If no editor is specified in an
281 environment variable,
283 is used. When the editor terminates, the label file is used to rewrite the disk
284 label. Existing bootstrap code is unchanged regardless of whether
288 is specified, no data will be written to the device, and instead the
289 disklabel that would have been written will be printed to stdout. This is
290 useful to see how a partitioning scheme will work out for a specific disk.
291 .Ss Restoring a disk label from a file
293 To restore a disk label from a file, use the form
299 .Ar disk Ar protofile
302 is capable of restoring a disk label that was previously saved in a file in ASCII format.
303 The prototype file used to create the label should be in the same format as that
304 produced when reading or editing a label. Comments are delimited by
306 and newline. As when writing a new label, any existing bootstrap code will be
309 is specified and will be unaffected otherwise. See the boot options below for a
310 method of restoring the label and writing the bootstrap at the same time.
313 is used, no data will be written to the device, and instead the
314 disklabel that would have been written will be printed to stdout. This is
315 useful to see how a partitioning scheme will work out for a specific disk.
316 .Ss Enabling and disabling writing to the disk label area
318 By default, it is not possible to write to the disk label area at the beginning
319 of a disk. The disk driver arranges for
321 and similar system calls
324 on any attempt to do so. If you need
325 to write to this area (for example, to obliterate the label), use the form
331 To disallow writing to the label area after previously allowing it, use the
337 .Ss Installing bootstraps
339 The final three forms of
341 are used to install bootstrap code. If you are creating a
342 .Dq dangerously-dedicated
343 slice for compatibility with older PC systems,
344 you generally want to specify the raw disk name such as
346 If you are creating a label within an existing DOS slice,
348 the partition name such as
350 Making a slice bootable can be tricky. If you are using a normal DOS
351 slice you typically install (or leave) a standard MBR on the base disk and
354 bootblocks in the slice.
365 This form installs the bootstrap only. It does not change the disk label.
366 You should never use this command on a base disk unless you intend to create a
367 .Dq dangerously-dedicated
370 This command is typically run on a slice such as
384 This form corresponds to the
386 command described above.
387 In addition to writing a new volume label, it also installs the bootstrap.
388 If run on a base disk this command will create a
389 .Dq dangerously-dedicated
390 label. This command is normally run on a slice rather than a base disk.
393 is used, no data will be written to the device, and instead the
394 disklabel that would have been written will be printed to stdout.
404 .Ar disk Ar protofile
407 This form corresponds to the
409 command described above.
410 In addition to restoring the volume label, it also installs the bootstrap.
411 If run on a base disk this command will create a
412 .Dq dangerously-dedicated
413 label. This command is normally run on a slice rather than a base disk.
415 The bootstrap commands always access the disk directly, so it is not necessary
420 is used, no data will be written to the device, and instead the
421 disklabel that would have been written will be printed to stdout.
423 The bootstrap code is comprised of two boot programs. Specify the name of the
424 boot programs to be installed in one of these ways:
427 Specify the names explicitly with the
433 indicates the primary boot program and
435 the secondary boot program. The boot programs are located in
442 flags are not specified, but
444 was specified, the names of the programs are taken from the
450 entry for the disk if the disktab entry exists and includes those parameters.
452 Otherwise, the default boot image names are used:
456 for the standard stage1 and stage2 boot images (details may vary
457 on architectures like the Alpha, where only a single-stage boot is used).
459 .Ss Initializing/Formatting a bootable disk from scratch
461 To initialize a disk from scratch the following sequence is recommended.
462 Please note that this will wipe everything that was previously on the disk,
470 to initialize the hard disk, and create a slice table, referred to
472 .Dq "partition table"
478 to define partitions on
480 slices created in the previous step.
484 to create file systems on new partitions.
487 A typical partitioning scheme would be to have an
490 of approximately 128MB to hold the root file system, a
506 (usually around 2GB),
511 (usually all remaining space).
512 Your mileage may vary.
514 .Nm fdisk Fl BI Pa da0
525 .Bl -tag -width ".Pa /etc/disktab" -compact
529 Disk description file.
531 .Sh SAVED FILE FORMAT
537 version of the label when examining, editing, or restoring a disk
540 .Bd -literal -offset 4n
549 sectors/cylinder: 969
551 sectors/unit: 1173930
556 headswitch: 0 # milliseconds
557 track-to-track seek: 0 # milliseconds
561 # size offset fstype [fsize bsize bps/cpg]
562 a: 81920 0 4.2BSD 1024 8192 16 # (Cyl. 0 - 84*)
563 b: 160000 81920 swap # (Cyl. 84* - 218*)
564 c: 1173930 0 unused 0 0 # (Cyl. 0 - 1211*)
565 h: 962010 211920 vinum # (Cyl. 218*- 1211*)
568 Lines starting with a
571 Most of the other specifications are no longer used.
572 The ones which must still be set correctly are:
576 is an optional label, set by the
578 option when writing a label.
585 is set for removable media drives, but no current
587 driver evaluates this
590 is no longer supported;
592 specifies that the drive can perform bad sector remapping.
594 describes the total size of the disk.
595 This value must be correct.
596 .It Ar "the partition table"
599 partition table, not the
601 partition table described in
605 The partition table can have up to 8 entries.
606 It contains the following information:
607 .Bl -tag -width indent
609 The partition identifier is a single letter in the range
613 By convention, partition
615 is reserved to describe the entire disk.
617 The size of the partition in sectors,
621 (megabytes - 1024*1024),
623 (gigabytes - 1024*1024*1024),
625 (percentage of free space
627 removing any fixed-size partitions other than partition
631 (all remaining free space
633 fixed-size and percentage partitions).
638 indicates the entire disk.
639 Lowercase versions of
644 Size and type should be specifed without any spaces between them.
646 Example: 2097152, 1G, 1024M and 1048576K are all the same size
647 (assuming 512-byte sectors).
649 The offset of the start of the partition from the beginning of the
654 calculate the correct offset to use (the end of the previous partition plus
655 one, ignoring partition
660 will be interpreted as an offset of 0.
662 Describes the purpose of the partition.
663 The example shows all currently used partition types.
670 For Vinum drives, use type
672 Other common types are
676 By convention, partition
678 represents the entire slice and should be of type
682 does not enforce this convention.
686 also knows about a number of other partition types,
687 none of which are in current use.
688 (See the definitions starting with
691 .Aq Pa sys/disklabel.h
698 file systems only, the fragment size.
699 Defaults to 1024 for partitions smaller than 1GB,
700 4096 for partitions 1GB or larger.
706 file systems only, the block size.
707 Defaults to 8192 for partitions smaller than 1GB,
708 16384 for partitions 1GB or larger.
712 file systems, the number of cylinders in a cylinder group.
715 file systems, the segment shift value.
716 Defaults to 16 for partitions smaller than 1GB,
717 64 for partitions 1GB or larger.
720 The remainder of the line is a comment and shows the cylinder allocations based
721 on the obsolete (but possibly correct) geometry information about the drive.
724 indicates that the partition does not begin or end exactly on a
727 .Dl "disklabel da0s1"
729 Display the in-core label for the first slice of the
731 disk, as obtained via
734 .Dq dangerously-dedicated ,
735 the base disk name should be specified, such as
738 .Dl "disklabel da0s1 > savedlabel"
740 Save the in-core label for
744 This file can be used with the
746 option to restore the label at a later date.
748 .Dl "disklabel -w -r /dev/da0s1 da2212 foo"
752 based on information for
756 Any existing bootstrap code will be clobbered
757 and the disk rendered unbootable.
759 .Dl "disklabel -e -r da0s1"
761 Read the on-disk label for
763 edit it, and reinstall in-core as well as on-disk.
764 Existing bootstrap code is unaffected.
766 .Dl "disklabel -e -r -n da0s1"
768 Read the on-disk label for
770 edit it, and display what the new label would be (in sectors).
773 install the new label either in-core or on-disk.
775 .Dl "disklabel -r -w da0s1 auto"
777 Try to auto-detect the required information from
779 and write a new label to the disk.
783 partitioning and file system information.
785 .Dl "disklabel -R da0s1 savedlabel"
787 Restore the on-disk and in-core label for
791 Existing bootstrap code is unaffected.
793 .Dl "disklabel -R -n da0s1 label_layout"
795 Display what the label would be for
797 using the partition layout in
799 This is useful for determining how much space would be alloted for various
800 partitions with a labelling scheme using
806 .Dl disklabel -B da0s1
808 Install a new bootstrap on
810 The boot code comes from
814 On-disk and in-core labels are unchanged.
816 .Dl disklabel -w -B /dev/da0s1 -b newboot1 -s newboot2 da2212
818 Install a new label and bootstrap.
819 The label is derived from disktab information for
821 and installed both in-core and on-disk.
822 The bootstrap code comes from the files
827 .Dl dd if=/dev/zero of=/dev/da0 bs=512 count=32
829 .Dl dd if=/dev/zero of=/dev/da0s1 bs=512 count=32
830 .Dl disklabel -w -B da0s1 auto
831 .Dl disklabel -e da0s1
833 Completely wipe any prior information on the disk, creating a new bootable
834 disk with a DOS partition table containing one
837 initialize the slice, then edit it to your needs. The
839 commands are optional, but may be necessary for some BIOSes to properly
842 This is an example disklabel that uses some of the new partition size types
847 which could be used as a source file for
849 .Dl disklabel -R ad0s1c new_label_file
850 .Bd -literal -offset 4n
859 sectors/cylinder: 1008
861 sectors/unit: 40959009
866 headswitch: 0 # milliseconds
867 track-to-track seek: 0 # milliseconds
871 # size offset fstype [fsize bsize bps/cpg]
872 a: 400M 0 4.2BSD 4096 16384 75 # (Cyl. 0 - 812*)
887 The kernel device drivers will not allow the size of a disk partition
888 to be decreased or the offset of a partition to be changed while it is open.
889 Some device drivers create a label containing only a single large partition
890 if a disk is unlabeled; thus, the label must be written to the
892 partition of the disk while it is open. This sometimes requires the desired
893 label to be set in two steps, the first one creating at least one other
894 partition, and the second setting the label on the new partition while shrinking
899 On some machines the bootstrap code may not fit entirely in the area
900 allocated for it by some file systems.
901 As a result, it may not be possible to have file systems on some partitions
905 When installing bootstrap code,
907 checks for these cases.
908 If the installed boot code would overlap a partition of type FS_UNUSED
909 it is marked as type FS_BOOT.
912 utility will disallow creation of file systems on FS_BOOT partitions.
913 Conversely, if a partition has a type other than FS_UNUSED or FS_BOOT,
915 will not install bootstrap code that overlaps it.
917 When a disk name is given without a full pathname,
918 the constructed device name uses the
922 For the i386 architecture, the primary bootstrap sector contains
928 utility takes care to not clobber it when installing a bootstrap only
930 or when editing an existing label
932 but it unconditionally writes the primary bootstrap program onto
939 table by the dummy one in the bootstrap program. This is only of
940 concern if the disk is fully dedicated, so that the
943 starts at absolute block 0 on the disk.
948 does not perform all possible error checking. Warning *is* given if partitions
949 overlap; if an absolute offset does not match the expected offset; if the
951 partition does not start at 0 or does not cover the entire slice; if a
952 partition runs past the end of the device; and a number of other errors; but
953 no warning is given if space remains unused.
projects / dragonfly.git / blob