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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 64 bit disk pack label
52 .Ar disk Ar disktype Ns / Ns Cm auto
75 .Oo Ar disktype Ns / Ns Cm auto Oc
84 .Ar disk Ar disktype Ns / Ns Cm auto
95 .Oo Ar disktype Ns / Ns Cm auto Oc
100 installs, examines or modifies a 64 bit label on a disk drive or pack.
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.
104 There are several forms
105 of the command that read (display), install or edit the label on a disk.
109 can install bootstrap code.
110 .Ss Raw or in-core label
111 The disk label resides close to or at the beginning of each disk slice.
112 For faster access, the kernel maintains a copy in core at all times.
114 default, most forms of the
116 command access the in-core copy of the label.
117 To access the raw (on-disk)
121 This option allows a label to be installed on a disk without kernel
122 support for a label, such as when labels are first installed on a system; it
123 must be used when first installing a label on a disk.
124 The specific effect of
126 is described under each command.
130 forms require a disk device name, which should always be the raw
131 device name representing the disk or slice.
133 uses the following scheme for slice numbering:
134 If the disk doesn't use GPT (typically laid out by
136 but e.g.\& MBR (typically laid out by
140 represents the entire disk regardless of any DOS partitioning.
141 Slice 0 is called the compatibility slice,
142 and slice 1 and onward, e.g.\&
147 If the disk does use GPT, then all slices are
149 slices, slice 0 isn't special, it is just the first slice on the disk.
150 You do not have to include the
152 path prefix when specifying the device.
155 utility will automatically prepend it.
156 .Ss Reading the disk label
157 To examine the label on a disk drive, use
166 represents the raw disk in question, and may be in the form
170 It will display all of the parameters associated with the drive and its
175 the kernel's in-core copy of the label is displayed;
176 if the disk has no label, or the partition types on the disk are incorrect,
177 the kernel may have constructed or modified the label.
182 reads the label from the raw disk and displays it.
183 Both versions are usually
184 identical except in the case where a label has not yet been initialized or
186 .Ss Writing a standard label
187 To write a standard label, use the form
193 .Ar disk Ar disktype Ns / Ns Cm auto
196 The required arguments to
198 are the drive to be labeled and the drive type as described in the
201 The drive parameters and partitions are taken from that file.
203 different disks of the same physical type are to have different partitions, it
204 will be necessary to have separate disktab entries describing each, or to edit
205 the label after installation as described below.
206 The optional argument is a
207 pack identification string, up to 16 characters long.
209 quoted if it contains blanks.
213 flag is given, no data will be written to the device, and instead the
214 disklabel that would have been written will be printed to stdout.
218 flag is given, the disk sectors containing the label and bootstrap
219 will be written directly.
220 A side-effect of this is that any existing bootstrap code will be overwritten
221 and the disk rendered unbootable.
222 See the boot options below for a method of
223 writing the label and the bootstrap at the same time.
227 the existing label will be updated via the in-core copy and any bootstrap
228 code will be unaffected.
229 If the disk does not already have a label, the
232 In either case, the kernel's in-core label is replaced.
234 For a virgin disk that is not known to
239 In this case, the driver is requested to produce a virgin label for the
241 This might or might not be successful, depending on whether the
242 driver for the disk is able to get the required data without reading
243 anything from the disk at all.
244 It will likely succeed for all SCSI
245 disks, most IDE disks, and vnode devices.
246 Writing a label to the
247 disk is the only supported operation, and the
249 itself must be provided as the canonical name, i.e.\& not as a full
252 For most harddisks, a label based on percentages for most partitions (and
253 one partition with a size of
255 will produce a reasonable configuration.
257 PC-based systems have special requirements in order for the BIOS to properly
261 Older systems may require what is known as a
262 .Dq dangerously dedicated
263 disklabel, which creates a fake DOS partition to work around problems older
264 BIOSes have with modern disk geometries.
265 On newer systems you generally want
266 to create a normal DOS partition using
270 disklabel within that slice.
272 later on in this page.
274 Installing a new disklabel does not in of itself allow your system to boot
275 a kernel using that label.
276 You must also install boot blocks, which is
277 described later on in this manual page.
278 .Ss Editing an existing disk label
279 To edit an existing disk label, use the form
287 This command reads the label from the in-core kernel copy, or directly from the
290 flag is also specified.
291 The label is written to a file in ASCII and then
292 supplied to an editor for changes.
293 If no editor is specified in an
295 environment variable,
298 When the editor terminates, the label file is used to rewrite the disk label.
299 Existing bootstrap code is unchanged regardless of whether
304 is specified, no data will be written to the device, and instead the
305 disklabel that would have been written will be printed to stdout.
307 useful to see how a partitioning scheme will work out for a specific disk.
308 .Ss Restoring a disk label from a file
309 To restore a disk label from a file, use the form
315 .Ar disk Ar protofile
318 is capable of restoring a disk label that was previously saved in a file
320 The prototype file used to create the label should be in the same format
321 as that produced when reading or editing a label.
322 Comments are delimited by
325 As when writing a new label, any existing bootstrap code will be
328 is specified and will be unaffected otherwise.
329 See the boot options below for a
330 method of restoring the label and writing the bootstrap at the same time.
333 is used, no data will be written to the device, and instead the
334 disklabel that would have been written will be printed to stdout.
336 useful to see how a partitioning scheme will work out for a specific disk.
337 .Ss Enabling and disabling writing to the disk label area
338 By default, it is not possible to write to the disk label area at the beginning
340 The disk driver arranges for
342 and similar system calls
345 on any attempt to do so.
347 to write to this area (for example, to obliterate the label), use the form
353 To disallow writing to the label area after previously allowing it,
359 .Ss Installing bootstraps
360 The final three forms of
362 are used to install bootstrap code, which allows boot from a
367 If you are creating a
368 .Dq dangerously-dedicated
369 slice for compatibility with older PC systems,
370 you generally want to specify the compatibility slice, such as
372 If you are creating a label within an existing DOS slice,
374 the slice name such as
376 Making a slice bootable can be tricky.
377 If you are using a normal DOS
378 slice you typically install (or leave) a standard MBR on the base disk and
381 bootblocks in the slice.
390 .Oo Ar disktype Ns / Ns Cm auto Oc
392 This form installs the bootstrap only.
393 It does not change the disk label.
394 You should never use this command on the compatibility slice unless you
396 .Dq dangerously-dedicated
399 This command is typically run on a
412 .Ar disk Ar disktype Ns / Ns Cm auto
415 This form corresponds to the
417 command described above.
418 In addition to writing a new volume label, it also installs the bootstrap.
419 If run on the compatibility slice this command will create a
420 .Dq dangerously-dedicated
422 This command is normally run on a
424 slice rather than the compatibility slice.
427 is used, no data will be written to the device, and instead the
428 disklabel that would have been written will be printed to stdout.
438 .Ar disk Ar protofile
439 .Oo Ar disktype Ns / Ns Cm auto Oc
441 This form corresponds to the
443 command described above.
444 In addition to restoring the volume label, it also installs the bootstrap.
445 If run on the compatibility slice this command will create a
446 .Dq dangerously-dedicated
448 This command is normally run on a
450 slice rather than the compatibility
453 The bootstrap commands always access the disk directly,
454 so it is not necessary to specify the
459 is used, no data will be written to the device, and instead the
460 disklabel that would have been written will be printed to stdout.
462 The bootstrap code is comprised of two boot programs.
463 Specify the name of the
464 boot programs to be installed in one of these ways:
467 Specify the names explicitly with the
473 indicates the primary boot program and
475 the secondary boot program.
476 The boot programs are normally located in
483 flags are not specified, but
485 was specified, the names of the programs are taken from the
491 entry for the disk if the disktab entry exists and includes those parameters.
493 Otherwise, the default boot image names are used:
497 for the standard stage1 and stage2 boot images.
499 .Ss Initializing/Formatting a bootable disk from scratch
500 To initialize a disk from scratch the following sequence is recommended.
501 Please note that this will wipe everything that was previously on the disk,
511 to initialize the hard disk, and create a GPT or MBR slice table,
513 .Dq "partition table"
521 to define partitions on
523 slices created in the previous step.
529 to create file systems on new partitions.
532 A typical partitioning scheme would be to have an
535 of approximately 512MB to hold the root file system, a
538 swap (usually 4GB), a
550 (usually around 4GB),
555 (usually all remaining space).
556 If you are tight on space all sizes can be halved.
557 Your mileage may vary.
561 .Dl "disklabel64 -B -r -w da0s0 auto"
562 .Dl "disklabel64 -e da0s0"
564 When a virgin disklabel64 is laid down a
566 or later kernel will align the partition start offset relative to the
567 physical drive instead of relative to the slice start.
568 This overcomes the issue of fdisk creating a badly aligned slice by default.
569 The kernel will use a 1MiB (1024 * 1024 byte) alignment.
570 The purpose of this alignment is to match swap and cluster operations
571 against the physical block size of the underlying device.
573 Even though nearly all devices still report a logical sector size of 512,
574 newer hard drives are starting to use larger physical sector sizes
575 and, in particular, solid state drives (SSDs) use a physical block size
576 of 64K (SLC) or 128K (MLC). We choose a 1 megabyte alignment to cover our
577 bases down the road. 64-bit disklabels are not designed to be put on
578 ultra-tiny storage devices.
580 It is worth noting that aligning cluster operations is particularly
581 important for SSDs and doubly so when
584 Swapcache is able to use large bulk writes which greatly reduces the degree
585 of write magnification on SSD media and it is possible to get upwards of
586 5x more endurance out of the device than the vendor spec sheet indicates.
588 .Bl -tag -width ".Pa /boot/boot2_64" -compact
589 .It Pa /boot/boot1_64
590 Default stage1 boot image.
591 .It Pa /boot/boot2_64
592 Default stage2 boot image.
594 Disk description file.
596 .Sh SAVED FILE FORMAT
601 version of the label when examining, editing, or restoring a disk label.
603 .Bd -literal -offset 4n
606 # Informational fields calculated from the above
607 # All byte equivalent offsets must be aligned
609 # boot space: 32768 bytes
610 # data space: 121790552 blocks # 118936.09 MB (124713525248 bytes)
612 diskid: 5e3ef4db-4e24-11dd-8318-010e0cd0bad1
614 boot2 data base: 0x000000001000
615 partitions data base: 0x000000009000
616 partitions data stop: 0x001d0981f000
617 backup label: 0x001d0981f000
618 total size: 0x001d09820000 # 118936.12 MB
620 display block size: 1024 # for partition display only
623 # size offset fstype fsuuid
624 a: 524288 0 4.2BSD # 512.000MB
625 b: 4194304 524288 swap # 4096.000MB
626 d: 2097152 4718592 4.2BSD # 2048.000MB
627 e: 2097152 6815744 4.2BSD # 2048.000MB
628 f: 4194304 8912896 4.2BSD # 4096.000MB
629 g: 4194304 13107200 4.2BSD # 4096.000MB
630 h: 94003288 17301504 HAMMER # 91800.086MB
631 i: 5242880 111304792 ccd # 5120.000MB
632 j: 5242880 116547672 vinum # 5120.000MB
633 a-stor_uuid: 4370efdb-4e25-11dd-8318-010e0cd0bad1
634 b-stor_uuid: 4370eff4-4e25-11dd-8318-010e0cd0bad1
635 d-stor_uuid: 4370f00b-4e25-11dd-8318-010e0cd0bad1
636 e-stor_uuid: 4370f024-4e25-11dd-8318-010e0cd0bad1
637 f-stor_uuid: 4370f03a-4e25-11dd-8318-010e0cd0bad1
638 g-stor_uuid: 4370f053-4e25-11dd-8318-010e0cd0bad1
639 h-stor_uuid: 4370f06a-4e25-11dd-8318-010e0cd0bad1
640 i-stor_uuid: 4370f083-4e25-11dd-8318-010e0cd0bad1
641 j-stor_uuid: 4370f099-4e25-11dd-8318-010e0cd0bad1
644 Lines starting with a
647 The specifications which can be changed are:
650 is an optional label, set by the
652 option when writing a label.
653 .It Ar "the partition table"
656 partition table, not the
658 partition table described in
662 The partition table can have up to 16 entries.
663 It contains the following information:
664 .Bl -tag -width indent
666 The partition identifier is a single letter in the range
671 The size of the partition in sectors,
675 (megabytes - 1024*1024),
677 (gigabytes - 1024*1024*1024),
679 (terabytes - 1024*1024*1024*1024),
681 (percentage of free space
683 removing any fixed-size partitions),
685 (all remaining free space
687 fixed-size and percentage partitions).
688 Lowercase versions of
693 Size and type should be specified without any spaces between them.
695 Example: 2097152, 1G, 1024M and 1048576K are all the same size
696 (assuming 512-byte sectors).
698 The offset of the start of the partition from the beginning of the
703 calculate the correct offset to use (the end of the previous partition plus
706 Describes the purpose of the partition.
707 The example shows all currently used partition types.
710 file systems, use type
714 file systems, use type
720 For Vinum drives, use type
722 Other common types are
729 also knows about a number of other partition types,
730 none of which are in current use.
738 The remainder of the line is a comment and shows the size of
741 .Dl "disklabel64 da0s1"
743 Display the in-core label for the first slice of the
745 disk, as obtained via
748 .Dq dangerously-dedicated ,
749 the compatibility slice name should be specified, such as
752 .Dl "disklabel64 da0s1 > savedlabel"
754 Save the in-core label for
758 This file can be used with the
760 option to restore the label at a later date.
762 .Dl "disklabel64 -w -r /dev/da0s1 da2212 foo"
766 based on information for
770 Any existing bootstrap code will be clobbered
771 and the disk rendered unbootable.
773 .Dl "disklabel64 -e -r da0s1"
775 Read the on-disk label for
777 edit it, and reinstall in-core as well as on-disk.
778 Existing bootstrap code is unaffected.
780 .Dl "disklabel64 -e -r -n da0s1"
782 Read the on-disk label for
784 edit it, and display what the new label would be (in sectors).
787 install the new label either in-core or on-disk.
789 .Dl "disklabel64 -r -w da0s1 auto"
791 Try to auto-detect the required information from
793 and write a new label to the disk.
796 command to edit the partitioning information.
798 .Dl "disklabel64 -R da0s1 savedlabel"
800 Restore the on-disk and in-core label for
804 Existing bootstrap code is unaffected.
806 .Dl "disklabel64 -R -n da0s1 label_layout"
808 Display what the label would be for
810 using the partition layout in
812 This is useful for determining how much space would be allotted for various
813 partitions with a labelling scheme using
819 .Dl "disklabel64 -B da0s1"
821 Install a new bootstrap on
823 The boot code comes from
827 On-disk and in-core labels are unchanged.
829 .Dl "disklabel64 -w -B /dev/da0s1 -b newboot1 -s newboot2 da2212"
831 Install a new label and bootstrap.
832 The label is derived from disktab information for
834 and installed both in-core and on-disk.
835 The bootstrap code comes from the files
840 .Dl "dd if=/dev/zero of=/dev/da0 bs=512 count=32"
842 .Dl "dd if=/dev/zero of=/dev/da0s1 bs=512 count=32"
843 .Dl "disklabel64 -w -B da0s1 auto"
844 .Dl "disklabel64 -e da0s1"
846 Completely wipe any prior information on the disk, creating a new bootable
847 disk with a DOS partition table containing one
851 initialize the slice, then edit it to your needs.
854 commands are optional, but may be necessary for some BIOSes to properly
857 .Dl "disklabel64 -W da0s1"
858 .Dl "dd if=/dev/zero of=/dev/da0s1 bs=512 count=32"
859 .Dl "disklabel -r -w da0s1 auto"
860 .Dl "disklabel -N da0s1"
862 Completely wipe any prior information on the slice,
863 changing label format to 32 bit.
864 The wiping is needed as
869 won't do any operations if label with other format is already installed.
871 This is an example disklabel that uses some of the new partition size types
876 which could be used as a source file for
878 .Dl "disklabel64 -R ad0s1 new_label_file"
879 .Bd -literal -offset 4n
882 # Informational fields calculated from the above
883 # All byte equivalent offsets must be aligned
885 # boot space: 32768 bytes
886 # data space: 121790552 blocks # 118936.09 MB (124713525248 bytes)
888 diskid: b1db58a3-4e26-11dd-8318-010e0cd0bad1
890 boot2 data base: 0x000000001000
891 partitions data base: 0x000000009000
892 partitions data stop: 0x001d0981f000
893 backup label: 0x001d0981f000
894 total size: 0x001d09820000 # 118936.12 MB
896 display block size: 1024 # for partition display only
899 # size offset fstype fsuuid
911 The kernel device drivers will not allow the size of a disk partition
912 to be decreased or the offset of a partition to be changed while it is open.
913 Some device drivers create a label containing only a single large partition
914 if a disk is unlabeled; thus, the label must be written to the
916 partition of the disk while it is open.
917 This sometimes requires the desired
918 label to be set in two steps, the first one creating at least one other
919 partition, and the second setting the label on the new partition while
941 does not perform all possible error checking.
945 overlap; if an absolute offset does not match the expected offset; if a
946 partition runs past the end of the device; and a number of other errors; but
947 no warning is given if space remains unused.
projects / dragonfly.git / blob