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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 1.19 2008/04/23 21:59:22 thomas Exp $
38 .\"
39 .Dd August 10, 2007
40 .Dt DISKLABEL 8
41 .Os
42 .Sh NAME
43 .Nm disklabel
44 .Nd read and write disk pack label
45 .Sh SYNOPSIS
46 .Nm
47 .Op Fl r
48 .Ar disk
49 .Nm
50 .Fl w
51 .Op Fl r
52 .Op Fl n
53 .Ar disk Ar disktype/auto
54 .Oo Ar packid Oc
55 .Nm
56 .Fl e
57 .Op Fl r
58 .Op Fl n
59 .Ar disk
60 .Nm
61 .Fl R
62 .Op Fl r
63 .Op Fl n
64 .Ar disk Ar protofile
65 .Nm
66 .Op Fl NW
67 .Ar disk
68 .Pp
69 .Nm
70 .Fl B
71 .Oo
72 .Fl b Ar boot1
73 .Fl s Ar boot2
74 .Oc
75 .Ar disk
76 .Oo Ar disktype/auto Oc
77 .Nm
78 .Fl w
79 .Fl B
80 .Op Fl n
81 .Oo
82 .Fl b Ar boot1
83 .Fl s Ar boot2
84 .Oc
85 .Ar disk Ar disktype/auto
86 .Oo Ar packid Oc
87 .Nm
88 .Fl R
89 .Fl B
90 .Op Fl n
91 .Oo
92 .Fl b Ar boot1
93 .Fl s Ar boot2
94 .Oc
95 .Ar disk Ar protofile
96 .Oo Ar disktype/auto Oc
97 .Nm
98 .Fl f Ar slice_start_lba
99 .Oo Ar options Oc
100 .Sh DESCRIPTION
101 The
102 .Nm
103 utility
104 installs, examines or modifies the label on a disk drive or pack.
105 When writing
106 the label, it can be used to change the drive identification, the disk
107 partitions on the drive, or to replace a damaged label.
108 There are several forms
109 of the command that read (display), install or edit the label on a disk.
110 In
111 addition,
112 .Nm
113 can install bootstrap code.
114 .Ss Raw or in-core label
115 The disk label resides close to or at the beginning of each disk slice.
116 For faster access, the kernel maintains a copy in core at all times.
117 By
118 default, most forms of the
119 .Nm
120 command access the in-core copy of the label.
121 To access the raw (on-disk)
122 copy, use the
123 .Fl r
124 option.
125 This option allows a label to be installed on a disk without kernel
126 support for a label, such as when labels are first installed on a system; it
127 must be used when first installing a label on a disk.
128 The specific effect of
129 .Fl r
130 is described under each command.
131 .Ss Disk device name
132 All
133 .Nm
134 forms require a disk device name, which should always be the raw
135 device name representing the disk or slice.
136 For example
137 .Pa da0s0
138 represents the entire disk regardless of any DOS partitioning,
139 this is called the compatibility slice,
140 and
141 .Pa da0s1
142 represents a BSD slice.
143 You do not have to include the
144 .Pa /dev/
145 path prefix when specifying the device.
146 The
147 .Nm
148 utility will automatically prepend it.
149 .Ss Reading the disk label
150 To examine the label on a disk drive, use
151 .Nm
152 without options:
153 .Pp
154 .Nm
155 .Op Fl r
156 .Ar disk
157 .Pp
158 .Ar disk
159 represents the raw disk in question, and may be in the form
160 .Pa da0s1
161 or
162 .Pa /dev/da0s1 .
163 It will display all of the parameters associated with the drive and its
164 partition layout.
165 Unless the
166 .Fl r
167 flag is given,
168 the kernel's in-core copy of the label is displayed;
169 if the disk has no label, or the partition types on the disk are incorrect,
170 the kernel may have constructed or modified the label.
171 If the
172 .Fl r
173 flag is given,
174 .Nm
175 reads the label from the raw disk and displays it.
176 Both versions are usually
177 identical except in the case where a label has not yet been initialized or
178 is corrupt.
179 .Ss Writing a standard label
180 To write a standard label, use the form
181 .Pp
182 .Nm
183 .Fl w
184 .Op Fl r
185 .Op Fl n
186 .Ar disk Ar disktype/auto
187 .Oo Ar packid Oc
188 .Pp
189 .Nm
190 .Fl w
191 .Op Fl r
192 .Op Fl n
193 .Ar disk
194 auto
195 .Pp
196 The required arguments to
197 .Nm
198 are the drive to be labeled and the drive type as described in the
199 .Xr disktab 5
200 file.
201 The drive parameters and partitions are taken from that file.
202 If
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.
208 The pack id must be
209 quoted if it contains blanks.
210 .Pp
211 If the
212 .Fl n
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.
215 .Pp
216 If the
217 .Fl r
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.
224 If
225 .Fl r
226 is not specified,
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
230 .Fl r
231 flag must be used.
232 In either case, the kernel's in-core label is replaced.
233 .Pp
234 For a virgin disk that is not known to
235 .Xr disktab 5 ,
236 .Ar disktype
237 can be specified as
238 .Dq auto .
239 In this case, the driver is requested to produce a virgin label for the
240 disk.
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
248 .Ar disk
249 itself must be provided as the canonical name, i.e.\& not as a full
250 path name.
251 .Pp
252 For most harddisks, a label based on percentages for most partitions (and
253 one partition with a size of
254 .Ql * )
255 will produce a reasonable configuration.
256 .Pp
257 PC-based systems have special requirements in order for the BIOS to properly
258 recognize a
259 .Dx
260 disklabel.
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
267 .Ar fdisk
268 and then create a
269 .Dx
270 disklabel within that slice.
271 This is described
272 later on in this page.
273 .Pp
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
280 .Pp
281 .Nm
282 .Fl e
283 .Op Fl r
284 .Op Fl n
285 .Ar disk
286 .Pp
287 This command reads the label from the in-core kernel copy, or directly from the
288 disk if the
289 .Fl r
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
294 .Ev EDITOR
295 environment variable,
296 .Xr vi 1
297 is used.
298 When the editor terminates, the label file is used to rewrite the disk
299 label.
300 Existing bootstrap code is unchanged regardless of whether
301 .Fl r
302 was specified.
303 If
304 .Fl n
305 is specified, no data will be written to the device, and instead the
306 disklabel that would have been written will be printed to stdout.
307 This is
308 useful to see how a partitioning scheme will work out for a specific disk.
309 .Ss Restoring a disk label from a file
310 To restore a disk label from a file, use the form
311 .Pp
312 .Nm
313 .Fl R
314 .Op Fl r
315 .Op Fl n
316 .Ar disk Ar protofile
317 .Pp
318 .Nm
319 is capable of restoring a disk label that was previously saved in a file
320 in ASCII format.
321 The prototype file used to create the label should be in the same format
322 as that produced when reading or editing a label.
323 Comments are delimited by
324 .Ar \&#
325 and newline.
326 As when writing a new label, any existing bootstrap code will be
327 clobbered if
328 .Fl r
329 is specified and will be unaffected otherwise.
330 See the boot options below for a
331 method of restoring the label and writing the bootstrap at the same time.
332 If
333 .Fl n
334 is used, no data will be written to the device, and instead the
335 disklabel that would have been written will be printed to stdout.
336 This is
337 useful to see how a partitioning scheme will work out for a specific disk.
338 .Ss Enabling and disabling writing to the disk label area
339 By default, it is not possible to write to the disk label area at the beginning
340 of a disk.
341 The disk driver arranges for
342 .Xr write 2
343 and similar system calls
344 to return
345 .Er EROFS
346 on any attempt to do so.
347 If you need
348 to write to this area (for example, to obliterate the label), use the form
349 .Pp
350 .Nm
351 .Fl W
352 .Ar disk
353 .Pp
354 To disallow writing to the label area after previously allowing it, use the
355 command
356 .Pp
357 .Nm
358 .Fl N
359 .Ar disk
360 .Ss Installing bootstraps
361 The final three forms of
362 .Nm
363 are used to install bootstrap code.
364 If you are creating a
365 .Dq dangerously-dedicated
366 slice for compatibility with older PC systems,
367 you generally want to specify the compatibility slice, such as
368 .Pa da0s0 .
369 If you are creating a label within an existing DOS slice,
370 you should specify
371 the slice name such as
372 .Pa da0s1 .
373 Making a slice bootable can be tricky.
374 If you are using a normal DOS
375 slice you typically install (or leave) a standard MBR on the base disk and
376 then install the
377 .Dx
378 bootblocks in the slice.
379 .Pp
380 .Nm
381 .Fl B
382 .Oo
383 .Fl b Ar boot1
384 .Fl s Ar boot2
385 .Oc
386 .Ar disk
387 .Oo Ar disktype Oc
388 .Pp
389 This form installs the bootstrap only.
390 It does not change the disk label.
391 You should never use this command on the compatibility slice unless you
392 intend to create a
393 .Dq dangerously-dedicated
394 disk, such as
395 .Ar da0s0 .
396 This command is typically run on a BSD slice such as
397 .Ar da0s1 .
398 .Pp
399 .Nm
400 .Fl w
401 .Fl B
402 .Op Fl n
403 .Oo
404 .Fl b Ar boot1
405 .Fl s Ar boot2
406 .Oc
407 .Ar disk Ar disktype
408 .Oo Ar packid Oc
409 .Pp
410 This form corresponds to the
411 .Dq write label
412 command described above.
413 In addition to writing a new volume label, it also installs the bootstrap.
414 If run on the compatibility slice this command will create a
415 .Dq dangerously-dedicated
416 label.
417 This command is normally run on a BSD slice rather than the compatibility
418 slice.
419 If
420 .Fl n
421 is used, no data will be written to the device, and instead the
422 disklabel that would have been written will be printed to stdout.
423 .Pp
424 .Nm
425 .Fl R
426 .Fl B
427 .Op Fl n
428 .Oo
429 .Fl b Ar boot1
430 .Fl s Ar boot2
431 .Oc
432 .Ar disk Ar protofile
433 .Oo Ar disktype Oc
434 .Pp
435 This form corresponds to the
436 .Dq restore label
437 command described above.
438 In addition to restoring the volume label, it also installs the bootstrap.
439 If run on the compatibility slice this command will create a
440 .Dq dangerously-dedicated
441 label.
442 This command is normally run on a BSD slice rather than the compatibility
443 slice.
444 .Pp
445 The bootstrap commands always access the disk directly, so it is not necessary
446 to specify the
447 .Fl r
448 flag.
449 If
450 .Fl n
451 is used, no data will be written to the device, and instead the
452 disklabel that would have been written will be printed to stdout.
453 .Pp
454 The bootstrap code is comprised of two boot programs.
455 Specify the name of the
456 boot programs to be installed in one of these ways:
457 .Bl -enum
458 .It
459 Specify the names explicitly with the
460 .Fl b
461 and
462 .Fl s
463 flags.
464 .Fl b
465 indicates the primary boot program and
466 .Fl s
467 the secondary boot program.
468 The boot programs are located in
469 .Pa /boot .
470 .It
471 If the
472 .Fl b
473 and
474 .Fl s
475 flags are not specified, but
476 .Ar disktype
477 was specified, the names of the programs are taken from the
478 .Dq b0
479 and
480 .Dq b1
481 parameters of the
482 .Xr disktab 5
483 entry for the disk if the disktab entry exists and includes those parameters.
484 .It
485 Otherwise, the default boot image names are used:
486 .Pa /boot/boot1
487 and
488 .Pa /boot/boot2
489 for the standard stage1 and stage2 boot images.
490 .El
491 .Ss Initializing/Formatting a bootable disk from scratch
492 To initialize a disk from scratch the following sequence is recommended.
493 Please note that this will wipe everything that was previously on the disk,
494 including any
495 .No non- Ns Dx
496 slices.
497 .Bl -enum
498 .It
499 Use
500 .Xr fdisk 8
501 to initialize the hard disk, and create a slice table, referred to
502 as the
503 .Dq "partition table"
504 in
505 .Tn DOS .
506 .It
507 Use
508 .Nm
509 to define partitions on
510 .Dx
511 slices created in the previous step.
512 .It
513 Finally use
514 .Xr newfs 8
515 to create file systems on new partitions.
516 .El
517 .Pp
518 A typical partitioning scheme would be to have an
519 .Ql a
520 partition
521 of approximately 128MB to hold the root file system, a
522 .Ql b
523 partition for
524 swap, a
525 .Ql d
526 partition for
527 .Pa /var
528 (usually 128MB), an
529 .Ql e
530 partition
531 for
532 .Pa /var/tmp
533 (usually 128MB), an
534 .Ql f
535 partition for
536 .Pa /usr
537 (usually around 2GB),
538 and finally a
539 .Ql g
540 partition for
541 .Pa /home
542 (usually all remaining space).
543 Your mileage may vary.
544 .Pp
545 .Nm fdisk Fl BI Pa da0
546 .Pp
547 .Nm
548 .Fl w B
549 .Pa da0s1
550 .Cm auto
551 .Pp
552 .Nm
553 .Fl e
554 .Pa da0s1
555 .Sh FILES
556 .Bl -tag -width ".Pa /etc/disktab" -compact
557 .It Pa /boot/boot1
558 Default stage1 boot image.
559 .It Pa /boot/boot2
560 Default stage2 boot image.
561 .It Pa /etc/disktab
562 Disk description file.
563 .El
564 .Sh SAVED FILE FORMAT
565 The
566 .Nm
567 utility
568 uses an
569 .Tn ASCII
570 version of the label when examining, editing, or restoring a disk
571 label.
572 The format is:
573 .Bd -literal -offset 4n
574 # /dev/da0s1:
575 type: SCSI
576 disk: da0s1
577 label:
578 flags:
579 bytes/sector: 512
580 sectors/track: 51
581 tracks/cylinder: 19
582 sectors/cylinder: 969
583 cylinders: 1211
584 sectors/unit: 1173930
585 rpm: 3600
586 interleave: 1
587 trackskew: 0
588 cylinderskew: 0
589 headswitch: 0 # milliseconds
590 track-to-track seek: 0 # milliseconds
591 drivedata: 0
593 16 partitions:
594 # size offset fstype
595 a: 81920 0 4.2BSD # 40.000MB
596 b: 160000 81920 swap # 78.125MB
597 c: 1173930 0 unused # 573.208MB
598 f: 320000 241920 HAMMER # 156.250MB
599 g: 300000 561920 ccd # 146.484MB
600 h: 312010 861920 vinum # 152.349MB
601 .Ed
602 .Pp
603 Lines starting with a
604 .Ql #
605 mark are comments.
606 Most of the other specifications are no longer used.
607 The ones which must still be set correctly are:
608 .Pp
609 .Bl -inset
610 .It Ar label
611 is an optional label, set by the
612 .Ar packid
613 option when writing a label.
614 .It Ar flags
615 may be
616 .Cm removable , ecc
617 or
618 .Cm badsect .
619 .Cm removable
620 is set for removable media drives, but no current
621 .Dx
622 driver evaluates this
623 flag.
624 .Cm ecc
625 is no longer supported;
626 .Cm badsect
627 specifies that the drive can perform bad sector remapping.
628 .It Ar sectors/unit
629 describes the total size of the disk.
630 This value must be correct.
631 .It Ar "the partition table"
632 is the
633 .Ux
634 partition table, not the
635 .Tn DOS
636 partition table described in
637 .Xr fdisk 8 .
638 .El
639 .Pp
640 The partition table can have up to 16 entries.
641 It contains the following information:
642 .Bl -tag -width indent
643 .It Ar #
644 The partition identifier is a single letter in the range
645 .Ql a
646 to
647 .Ql p .
648 By convention, partition
649 .Ql c
650 is reserved to describe the entire disk.
651 .It Ar size
652 The size of the partition in sectors,
653 .Cm K
654 (kilobytes - 1024),
655 .Cm M
656 (megabytes - 1024*1024),
657 .Cm G
658 (gigabytes - 1024*1024*1024),
659 .Cm %
660 (percentage of free space
661 .Em after
662 removing any fixed-size partitions other than partition
663 .Ql c ) ,
664 or
665 .Cm *
666 (all remaining free space
667 .Em after
668 fixed-size and percentage partitions).
669 For partition
670 .Ql c ,
671 a size of
672 .Cm *
673 indicates the entire disk.
674 Lowercase versions of
675 .Cm K , M ,
676 and
677 .Cm G
678 are allowed.
679 Size and type should be specified without any spaces between them.
680 .Pp
681 Example: 2097152, 1G, 1024M and 1048576K are all the same size
682 (assuming 512-byte sectors).
683 .It Ar offset
684 The offset of the start of the partition from the beginning of the
685 drive in sectors, or
686 .Cm *
687 to have
688 .Nm
689 calculate the correct offset to use (the end of the previous partition plus
690 one, ignoring partition
691 .Ql c .
692 For partition
693 .Ql c ,
694 .Cm *
695 will be interpreted as an offset of 0.
696 .It Ar fstype
697 Describes the purpose of the partition.
698 The example shows all currently used partition types.
699 For
700 .Tn UFS
701 file systems, use type
702 .Cm 4.2BSD .
703 For
704 .Tn HAMMER
705 file systems, use type
706 .Cm HAMMER .
707 For
708 .Xr ccd 4
709 partitions, use type
710 .Cm ccd .
711 For Vinum drives, use type
712 .Cm vinum .
713 Other common types are
714 .Cm swap
715 and
716 .Cm unused .
717 By convention, partition
718 .Ql c
719 represents the entire slice and should be of type
720 .Cm unused ,
721 though
722 .Nm
723 does not enforce this convention.
724 The
725 .Nm
726 utility
727 also knows about a number of other partition types,
728 none of which are in current use.
729 (See
730 .Dv fstypenames
731 in
732 .In sys/dtype.h
733 for more details).
734 .El
735 .Pp
736 The remainder of the line is a comment and shows the size of the partition
737 in MB.
738 .Pp
739 .Dx
740 no longer snoop-adjusts the on-disklabel when reading or writing
741 raw labels.
742 .Nm
743 is now responsible for adjusting the label when operating in raw mode.
744 Traditional (32 bit BSD) disklabels store offsets as absolute block numbers
745 rather than slice-relative block numbers.
746 If
747 .Nm
748 is unable to issue the
749 .Dv DIOCGPART
750 ioctl to get slice information it will
751 refuse to read or write the label in raw mode.
752 The
753 .Fl f
754 option may be used to force the operation by supplying a manual offset.
755 .Sh EXAMPLES
756 .Dl "disklabel da0s1"
757 .Pp
758 Display the in-core label for the first slice of the
759 .Pa da0
760 disk, as obtained via
761 .Pa /dev/da0s1 .
762 (If the disk is
763 .Dq dangerously-dedicated ,
764 the compatibility slice name should be specified, such as
765 .Pa da0s0 . )
766 .Pp
767 .Dl "disklabel da0s1 > savedlabel"
768 .Pp
769 Save the in-core label for
770 .Pa da0s1
771 into the file
772 .Pa savedlabel .
773 This file can be used with the
774 .Fl R
775 option to restore the label at a later date.
776 .Pp
777 .Dl "disklabel -w -r /dev/da0s1 da2212 foo"
778 .Pp
779 Create a label for
780 .Pa da0s1
781 based on information for
782 .Dq da2212
783 found in
784 .Pa /etc/disktab .
785 Any existing bootstrap code will be clobbered
786 and the disk rendered unbootable.
787 .Pp
788 .Dl "disklabel -e -r da0s1"
789 .Pp
790 Read the on-disk label for
791 .Pa da0s1 ,
792 edit it, and reinstall in-core as well as on-disk.
793 Existing bootstrap code is unaffected.
794 .Pp
795 .Dl "disklabel -e -r -n da0s1"
796 .Pp
797 Read the on-disk label for
798 .Pa da0s1 ,
799 edit it, and display what the new label would be (in sectors).
800 It does
801 .Em not
802 install the new label either in-core or on-disk.
803 .Pp
804 .Dl "disklabel -r -w da0s1 auto"
805 .Pp
806 Try to auto-detect the required information from
807 .Pa da0s1 ,
808 and write a new label to the disk.
809 Use another
810 .Nm Fl e
811 command to edit the
812 partitioning and file system information.
813 .Pp
814 .Dl "disklabel -R da0s1 savedlabel"
815 .Pp
816 Restore the on-disk and in-core label for
817 .Pa da0s1
818 from information in
819 .Pa savedlabel .
820 Existing bootstrap code is unaffected.
821 .Pp
822 .Dl "disklabel -R -n da0s1 label_layout"
823 .Pp
824 Display what the label would be for
825 .Pa da0s1
826 using the partition layout in
827 .Pa label_layout .
828 This is useful for determining how much space would be allotted for various
829 partitions with a labelling scheme using
830 .Cm % Ns -based
831 or
832 .Cm *
833 partition sizes.
834 .Pp
835 .Dl disklabel -B da0s1
836 .Pp
837 Install a new bootstrap on
838 .Pa da0s1 .
839 The boot code comes from
840 .Pa /boot/boot1
841 and possibly
842 .Pa /boot/boot2 .
843 On-disk and in-core labels are unchanged.
844 .Pp
845 .Dl disklabel -w -B /dev/da0s1 -b newboot1 -s newboot2 da2212
846 .Pp
847 Install a new label and bootstrap.
848 The label is derived from disktab information for
849 .Dq da2212
850 and installed both in-core and on-disk.
851 The bootstrap code comes from the files
852 .Pa /boot/newboot1
853 and
854 .Pa /boot/newboot2 .
855 .Pp
856 .Dl dd if=/dev/zero of=/dev/da0 bs=512 count=32
857 .Dl fdisk -BI da0
858 .Dl dd if=/dev/zero of=/dev/da0s1 bs=512 count=32
859 .Dl disklabel -w -B da0s1 auto
860 .Dl disklabel -e da0s1
861 .Pp
862 Completely wipe any prior information on the disk, creating a new bootable
863 disk with a DOS partition table containing one
864 .Dq whole-disk
865 slice.
866 Then
867 initialize the slice, then edit it to your needs.
868 The
869 .Pa dd
870 commands are optional, but may be necessary for some BIOSes to properly
871 recognize the disk.
872 .Pp
873 This is an example disklabel that uses some of the new partition size types
874 such as
875 .Cm % , M , G ,
876 and
877 .Cm * ,
878 which could be used as a source file for
879 .Pp
880 .Dl disklabel -R ad0s1 new_label_file
881 .Bd -literal -offset 4n
882 # /dev/ad0s1:
883 type: ESDI
884 disk: ad0s1
885 label:
886 flags:
887 bytes/sector: 512
888 sectors/track: 63
889 tracks/cylinder: 16
890 sectors/cylinder: 1008
891 cylinders: 40633
892 sectors/unit: 40959009
893 rpm: 3600
894 interleave: 1
895 trackskew: 0
896 cylinderskew: 0
897 headswitch: 0 # milliseconds
898 track-to-track seek: 0 # milliseconds
899 drivedata: 0
901 16 partitions:
902 # size offset fstype
903 a: 400M 0 4.2BSD
904 b: 1G * swap
905 c: * * unused
906 e: 204800 * 4.2BSD
907 f: 5g * 4.2BSD
908 g: * * 4.2BSD
909 .Ed
910 .Sh DIAGNOSTICS
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
915 .Dq a
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
920 shrinking the
921 .Dq a
922 partition.
923 .Pp
924 On some machines the bootstrap code may not fit entirely in the area
925 allocated for it by some file systems.
926 As a result, it may not be possible to have file systems on some partitions
927 of a
928 .Dq bootable
929 disk.
930 When installing bootstrap code,
931 .Nm
932 checks for these cases.
933 If the installed boot code would overlap a partition of type
934 .Dv FS_UNUSED
935 it is marked as type
936 .Dv FS_BOOT .
937 The
938 .Xr newfs 8
939 utility will disallow creation of file systems on
940 .Dv FS_BOOT
941 partitions.
942 Conversely, if a partition has a type other than
943 .Dv FS_UNUSED
944 or
945 .Dv FS_BOOT ,
946 .Nm
947 will not install bootstrap code that overlaps it.
948 .Sh SEE ALSO
949 .Xr ccd 4 ,
950 .Xr disklabel 5 ,
951 .Xr disktab 5 ,
952 .Xr boot0cfg 8 ,
953 .Xr diskinfo 8 ,
954 .Xr disklabel64 8 ,
955 .Xr fdisk 8 ,
956 .Xr vinum 8
957 .Sh BUGS
958 When a disk name is given without a full pathname,
959 the constructed device name uses the
960 .Dq c
961 partition.
962 .Pp
963 For the i386 architecture, the primary bootstrap sector contains
964 an embedded
965 .Em fdisk
966 table.
967 The
968 .Nm
969 utility takes care to not clobber it when installing a bootstrap only
970 .Pq Fl B ,
971 or when editing an existing label
972 .Pq Fl e ,
973 but it unconditionally writes the primary bootstrap program onto
974 the disk for
975 .Fl w
976 or
977 .Fl R ,
978 thus replacing the
979 .Em fdisk
980 table by the dummy one in the bootstrap program.
981 This is only of
982 concern if the disk is fully dedicated, so that the
983 .Bx
984 disklabel
985 starts at absolute block 0 on the disk.
986 .Pp
987 The
988 .Nm
989 utility
990 does not perform all possible error checking.
991 Warning *is* given if partitions
992 overlap; if an absolute offset does not match the expected offset; if the
993 .Dq c
994 partition does not start at 0 or does not cover the entire slice; if a
995 partition runs past the end of the device; and a number of other errors; but
996 no warning is given if space remains unused.