Annotation of src/sbin/fdisk/fdisk.8, Revision 1.62
1.62 ! yamt 1: .\" $NetBSD: fdisk.8,v 1.61 2009/07/02 00:49:58 snj Exp $
1.8 cgd 2: .\"
1.62 ! yamt 3: .Dd August 10, 2009
1.1 cgd 4: .Dt FDISK 8
1.25 wiz 5: .Os
1.1 cgd 6: .Sh NAME
7: .Nm fdisk
1.43 lukem 8: .Nd MS-DOS partition maintenance program
1.1 cgd 9: .Sh SYNOPSIS
1.34 wiz 10: .Nm
1.44 dyoung 11: .Op Fl afiuvBFS
1.17 mycroft 12: .Bk -words
1.9 phil 13: .Op Fl 0 | 1 | 2 | 3
1.17 mycroft 14: .Ek
15: .Bk -words
1.44 dyoung 16: .Op Fl t Ar disktab
17: .Ek
18: .Bk -words
19: .Op Fl T Ar disktype
20: .Ek
21: .Bk -words
1.35 dsl 22: .Op Fl E Ar number
23: .Ek
24: .Bk -words
1.10 phil 25: .Op Fl b Ar cylinders/heads/sectors
1.17 mycroft 26: .Ek
27: .Bk -words
1.38 wiz 28: .Op Fl s Ar id/start/size Ns Bq Ar /bootmenu
1.17 mycroft 29: .Ek
30: .Bk -words
1.16 ws 31: .Op Fl c Ar bootcode
1.17 mycroft 32: .Ek
33: .Bk -words
1.35 dsl 34: .Op Fl r|w Ar file
35: .Ek
36: .Bk -words
1.6 mycroft 37: .Op Ar device
1.17 mycroft 38: .Ek
1.35 dsl 39: .Nm
40: .Fl l
1.24 lukem 41: .Sh DESCRIPTION
1.35 dsl 42: The
1.1 cgd 43: .Nm
1.54 apb 44: program is used to display or update the
45: .Em "master boot record"
46: or
47: .Em MBR
48: in the first sector (sector 0)
49: of a disk that uses the MBR style of partitioning.
50: The following
51: .Nx
52: ports use this style of disk partitioning:
53: amd64, arc, bebox, cobalt, hpcarm, hpcmips, hpcsh, i386, macppc,
54: mvmeppc, netwinder, ofppc, playstation2, and prep.
55: .Pp
56: The MBR contains bootable code, a partition table,
57: an indication of which partition is
58: .Sq active ,
59: and (optionally, depending on the boot code) a menu
60: for selecting a partition to be booted.
1.35 dsl 61: There can be at most 4 partitions defined in sector 0,
62: one of which can be an extended
63: partition which can be split into any number of sub-partitions.
1.6 mycroft 64: .Pp
1.54 apb 65: The boot code in the MBR is usually invoked by the BIOS or firmware,
66: and the MBR passes control to the next stage boot code
67: stored in the first sector of the partition to be booted
68: (the
69: .Em "partition boot record"
70: or
71: .Em PBR ) .
72: .Pp
73: After booting,
1.13 perry 74: .Nx
1.35 dsl 75: does not use the partitioning done by
76: .Nm ,
77: instead it uses a
78: .Nx
79: disklabel saved in sector 1 of the
80: .Nx
81: partition.
1.54 apb 82: See
83: .Xr mbrlabel 8
84: for a way of using information from the MBR
85: to construct a
86: .Nx
87: disklabel.
1.1 cgd 88: .Pp
1.45 snj 89: The standard MBR boot code will only boot the
90: .Sq active
91: partition.
1.35 dsl 92: However
93: .Nx
1.59 dsl 94: contains additional boot programs which allow the user to
1.35 dsl 95: interactively select which of the partitions to boot.
1.45 snj 96: The
97: .Sq mbr_ext
1.59 dsl 98: code will also boot
1.13 perry 99: .Nx
1.35 dsl 100: from an extended partition but will not work on old systems that do not
1.59 dsl 101: support LBA reads, the
102: .Sq mbr_com0
103: and
104: .Sq mbr_com0_9600
105: will read and write from a serial port.
1.24 lukem 106: At the start the
107: .Nm
108: program will determine whether the disk sector 0 is valid as a boot sector.
109: (This is determined by checking the magic number.)
110: If not,
111: .Nm
1.35 dsl 112: will initialise the boot code as well as the partition table.
1.24 lukem 113: During this, all four partitions will be marked empty.
114: .Pp
1.1 cgd 115: The flags
1.9 phil 116: .Fl a ,
1.26 wiz 117: .Fl i
1.1 cgd 118: or
119: .Fl u
1.4 jtc 120: are used to indicate that the partition data is to be updated.
1.1 cgd 121: The
122: .Nm
1.24 lukem 123: program will enter an interactive conversational mode.
1.6 mycroft 124: This mode is designed not to change any data unless you explicitly tell it to;
1.1 cgd 125: .Nm
1.35 dsl 126: selects defaults for its questions to guarantee that behaviour.
1.1 cgd 127: .Pp
1.61 snj 128: If partition data is going to be updated and the disk carries GUID Partition
129: Tables,
1.60 christos 130: .Nm
131: will remove both primary and backup GPT headers from the disk.
132: See
133: .Xr gpt 8
134: for information on how to manipulate GUID Partition Tables.
135: .Pp
1.35 dsl 136: .Nm
137: will calculate the correct
1.11 lukem 138: .Em cylinder ,
139: .Em head ,
1.1 cgd 140: and
1.11 lukem 141: .Em sector
1.38 wiz 142: values for any partition you edit.
143: If you specify
1.35 dsl 144: .Fl v
145: you will be asked whether you want to specify them yourself.
1.1 cgd 146: .Pp
1.35 dsl 147: Finally, when all the data for the first sector has been accumulated,
1.6 mycroft 148: .Nm
1.35 dsl 149: will ask if you really want to write the new partition table.
1.6 mycroft 150: Only if you reply affirmatively to this question will
151: .Nm
152: write anything to the disk.
1.1 cgd 153: .Pp
1.24 lukem 154: Available options:
1.18 fvdl 155: .Pp
1.24 lukem 156: .Bl -tag -width Ds
157: .It Fl 0
158: Update partition slot 0.
159: .It Fl 1
160: Update partition slot 1.
161: .It Fl 2
162: Update partition slot 2.
163: .It Fl 3
164: Update partition slot 3.
165: .It Fl a
166: Change the active partition.
167: In interactive mode this question will be asked after the partitions
168: have been processed.
169: .It Fl b Ar cylinders/heads/sectors
170: Specify the BIOS parameters for
171: .Ar cylinders ,
1.38 wiz 172: .Ar heads ,
1.10 phil 173: and
1.24 lukem 174: .Ar sectors .
175: It is used only in conjunction with the
1.10 phil 176: .Fl u
1.15 ws 177: flag.
1.24 lukem 178: .It Fl B
1.35 dsl 179: On an i386 or amd64 system, interactively update the boot selector settings.
1.32 perry 180: (The boot selector permits the user to interactively select the boot
181: partition, and thus which operating system is run, at system boot time.
1.33 wiz 182: See
1.32 perry 183: .Xr mbr 8
184: for more information.)
1.24 lukem 185: .It Fl c Ar bootcode
186: Specify the filename that
187: .Nm
188: should read the bootcode from.
1.35 dsl 189: If the name of a directory is specified, then
190: .Nm
191: will look for files with the default names in that directory.
1.24 lukem 192: The default is to read from
1.35 dsl 193: .Pa /usr/mdec/mbr ,
194: .Pa /usr/mdec/mbr_bootsel
195: or
196: .Pa /usr/mdec/mbr_ext
197: depending on whether
1.40 dsl 198: .Ar bootmenu
1.35 dsl 199: was specified for any partitions
200: on an i386 machine, and leave the bootcode empty for other
1.24 lukem 201: machines.
1.35 dsl 202: .It Fl E Ar number
203: Update extended partition
1.40 dsl 204: .Ar number .
1.35 dsl 205: If the specified extended partition doesn't exist an additional extended
206: partition will be created.
1.24 lukem 207: .It Fl f
208: Run
1.9 phil 209: .Nm
1.24 lukem 210: in a non-interactive mode.
1.26 wiz 211: In this mode, you can only change the disk parameters by using the
1.10 phil 212: .Fl b
1.24 lukem 213: flag.
214: This is provided only so scripts or other programs may use
215: .Nm
216: as part of an automatic installation process.
1.47 lukem 217: .Pp
1.24 lukem 218: Using the
1.9 phil 219: .Fl f
1.12 ross 220: flag with
1.9 phil 221: .Fl u
1.10 phil 222: makes it impossible to specify the starting and ending
1.24 lukem 223: .Ar cylinder ,
1.38 wiz 224: .Ar head ,
1.26 wiz 225: and
1.24 lukem 226: .Ar sector
227: fields.
228: They will be automatically computed using the BIOS geometry.
1.47 lukem 229: .Pp
1.35 dsl 230: If
231: .Fl u
232: and
1.42 joda 233: .Fl s
1.35 dsl 234: are specified then the details of the specified partition will be changed.
235: Any other partitions which overlap the requested part of the disk will be
236: silently deleted.
1.45 snj 237: .It Fl F
1.44 dyoung 238: Indicate that
239: .Ar device
1.45 snj 240: is a regular file.
241: Unless the geometry of
1.44 dyoung 242: .Ar device
243: is told to
1.46 wiz 244: .Nm
1.44 dyoung 245: by
246: .Fl T Ar disktype ,
1.46 wiz 247: .Nm
1.44 dyoung 248: will count the 512-byte sectors in
249: .Ar device
250: and produce a fake geometry.
1.24 lukem 251: .It Fl i
1.35 dsl 252: Explicitly request initialisation of the master boot code
1.24 lukem 253: (similar to what
1.46 wiz 254: .Ic fdisk /mbr
1.24 lukem 255: does under
1.43 lukem 256: .Tn MS-DOS ) ,
1.26 wiz 257: even if the magic number in the first sector is ok.
1.24 lukem 258: The partition table is left alone by this (but see above).
1.30 christos 259: .It Fl l
260: Lists known
261: .Em sysid
262: values and exit.
1.35 dsl 263: .It Fl r Ar file
264: Read the boot record from file
265: .Ar file
266: instead of the specified disk.
267: The geometry information used is still that of the disk volume.
268: Any changes are written back to the file.
1.38 wiz 269: .It Fl s Ar id/start/size Ns Bq Ar /bootmenu
1.24 lukem 270: Specify the partition
271: .Ar id ,
1.35 dsl 272: .Ar start ,
1.38 wiz 273: .Ar size ,
1.35 dsl 274: and optionally
275: .Ar bootmenu .
1.24 lukem 276: This flag requires the use of a partition selection flag
277: .Po
278: .Fl 0 ,
279: .Fl 1 ,
280: .Fl 2 ,
1.35 dsl 281: .Fl 3 ,
1.24 lukem 282: or
1.35 dsl 283: .Fl E Ar number
1.24 lukem 284: .Pc
285: .It Fl S
1.26 wiz 286: When used with no other flags print a series of
1.24 lukem 287: .Pa /bin/sh
288: commands for setting variables to the partition information.
1.35 dsl 289: This could be used by installation scripts.
1.44 dyoung 290: .It Fl t Ar disktab
1.45 snj 291: Read
1.44 dyoung 292: .Ar disktype
1.45 snj 293: from the named
294: .Xr disktab 5
1.44 dyoung 295: file instead of from
1.45 snj 296: .Pa /etc/disktab .
1.44 dyoung 297: .It Fl T Ar disktype
1.45 snj 298: Use the disklabel
1.44 dyoung 299: .Ar disktype
300: instead of the disklabel on
301: .Ar device .
1.24 lukem 302: .It Fl u
1.35 dsl 303: Display the partitions and interactively ask which one you want to edit.
1.24 lukem 304: .Nm
1.35 dsl 305: will step through each field showing the old value and asking for a new one.
306: The
307: .Em start
1.36 wiz 308: and
1.35 dsl 309: .Em size
1.51 dsl 310: can be specified in blocks (nn), cylinders (nnc), megabytes (nnm),
311: or gigabytes (nng), values in megabytes and gigabytes
312: will be rounded to the nearest cylinder boundary.
1.35 dsl 313: The
314: .Em size
315: may be specified as
316: .Em $
317: in which case the partition will extend to the end of the available free space.
1.47 lukem 318: .Pp
1.35 dsl 319: .Nm
320: will not allow you to create partitions which overlap.
321: .Pp
322: If
323: .Em bootmenu
324: is specified for any partition
325: .Nm
326: will determine whether the installed boot code supports the bootselect code,
327: if it doesn't you will be asked whether you want to install the required
1.53 wiz 328: boot code.
329: To remove a
1.52 jmcneill 330: .Em bootmenu
1.53 wiz 331: label, simply press
332: .Aq space
333: followed by
334: .Aq return .
1.35 dsl 335: .It Fl v
336: Be more verbose, specifying
337: .Fl v
338: more than once may increase the amount of output.
1.47 lukem 339: .Pp
340: Using
1.35 dsl 341: .Fl v
342: with
343: .Fl u
1.47 lukem 344: allows the user to change more parameters than normally permitted.
1.35 dsl 345: .It Fl w Ar file
346: Write the modified partition table to file
347: .Ar file
348: instead of the disk.
349: .El
350: .Pp
351: When called with no arguments, it prints the partition table.
352: An example follows:
353: .Bd -literal
354: Disk: /dev/rwd0d
355: NetBSD disklabel disk geometry:
356: cylinders: 16383, heads: 16, sectors/track: 63 (1008 sectors/cylinder)
357: total sectors: 40032696
358:
359: BIOS disk geometry:
360: cylinders: 1023, heads: 255, sectors/track: 63 (16065 sectors/cylinder)
361: total sectors: 40032696
362:
363: Partition table:
364: 0: NetBSD (sysid 169)
365: bootmenu: net 1.5.
366: start 4209030, size 8289540 (4048 MB, Cyls 262-778), Active
367: 1: Primary DOS with 32 bit FAT (sysid 11)
368: bootmenu: win98
369: start 63, size 4208967 (2055 MB, Cyls 0-262)
370: 2: NetBSD (sysid 169)
371: bootmenu: current
372: start 32515560, size 7517136 (3670 MB, Cyls 2024-2491/234/40)
373: 3: Ext. partition - LBA (sysid 15)
374: start 12498570, size 20016990 (9774 MB, Cyls 778-2024)
375: Extended partition table:
376: E0: NetBSD (sysid 169)
377: bootmenu: test
378: start 12498633, size 12305727 (6009 MB, Cyls 778-1544)
379: E1: Primary DOS with 32 bit FAT (sysid 11)
380: start 24804423, size 4096512 (2000 MB, Cyls 1544-1799)
381: E2: Primary DOS with 32 bit FAT (sysid 11)
382: start 28900998, size 3614562 (1765 MB, Cyls 1799-2024)
383: Bootselector enabled, infinite timeout.
1.57 apb 384: First active partition: 0
1.35 dsl 385: .Ed
386: .Pp
387: This example disk is divided into four partitions the last of which is
388: an extended partition.
389: The sub-partitions of the extended partition are also shown.
390: In this case there is no free space in either the disk or in the extended
391: partition.
392: .Pp
393: The various fields in each partition entry are:
394: .br
395: .in +4
396: .Em ptn_number : id_name
397: (sysid
398: .Em id_number )
399: .br
400: .in +4
401: bootmenu:
402: .Em bootmenu
403: .br
404: start
405: .Em start ,
406: size
1.39 wiz 407: .Em size ( MB
1.35 dsl 408: MB, Cyls
1.39 wiz 409: .Em first Ns No - Ns Em next )
1.35 dsl 410: .Op , Active
411: .in -4
412: .in -4
413: .Bl -tag -width "bootmenu"
414: .It Em ptn_number
415: is the number of the partition.
416: .It Em id_name
417: is the name of the filesystem type or operating system that uses this partition.
418: .It Em id_number
419: is the number that identifies the partition type.
420: 169 decimal is used for
421: .Nx
422: partitions,
423: 15 decimal to create an extended partition
424: and 0 to mark a partition as unused.
425: Use
1.24 lukem 426: .Nm
1.35 dsl 427: .Fl l
428: to list the known partition types.
429: .It Em bootmenu
430: is the menu prompt output by the interactive boot code for this partition.
431: This line is omitted if the prompt is not defined.
432: .It Xo
433: .Em start ,
434: .Em size
435: .Xc
436: are the start address and size of the partition in sectors.
437: .It Em MB
438: is the size of the partition in megabytes.
439: .It Xo
440: .Em first ,
441: .Em next
442: .Xc
443: are the bounds of this partition displayed as cylinder/head/sector.
444: If the partition starts (or ends) on a cylinder boundary the head and
445: sector values are omitted.
1.36 wiz 446: If
1.35 dsl 447: .Fl v
448: is not specified the start of extended partitions and the first partition
449: on the disk are rounded down to include the mandatory red tape in the
1.45 snj 450: preceding track.
1.35 dsl 451: .It Active
452: is output if this is the active partition.
453: .El
454: .Pp
455: If the
456: .Fl v
1.56 wiz 457: flag is specified, the beginning and end of each partition are also
1.54 apb 458: displayed as follows:
1.35 dsl 459: .in +4
460: beg: cylinder
461: .Em cylinder ,
462: head
463: .Em head ,
464: sector
465: .Em sector
466: .br
467: end: cylinder
468: .Em cylinder ,
469: head
470: .Em head ,
471: sector
472: .Em sector
473: .in -4
474: .Bl -tag -width "bootmenu"
475: .It Xo
476: .Em "cylinder" ,
477: .Em "head" ,
478: .Em "sector"
479: .Xc
480: are the beginning or ending address of a partition.
1.47 lukem 481: .Pp
1.35 dsl 482: .Em "Note:"
483: these numbers are read from the bootblock, so are the values calculated
484: by a previous run of
485: .Nm .
1.24 lukem 486: .El
1.54 apb 487: .Pp
488: .Nm
489: attempts to check whether each partition is bootable,
490: by checking the magic number and some other characteristics
491: of the first sector of each partition (the PBR).
492: If the partition does not apear to be bootable,
493: .Nm
494: will print a line containing
495: .Dq "PBR is not bootable"
496: followed by an error message.
497: If the partition is bootable, and if the
498: .Fl v
499: flag is specified,
500: .Nm
501: will print
502: .Dq "PBR appears to be bootable" .
503: If the
504: .Fl v
505: flag is specified more than once,
506: .Nm
507: will print the heading
508: .Dq "Information from PBR:"
509: followed by one or more lines of information gleaned from the PBR;
510: this additional information may be incorrect or misleading,
511: because different operating systems use different PBR formats.
512: Note that, even if no errors are reported, an attempt to boot
513: from the partition might fail.
514: .Nx
515: partitions may be made bootable using
516: .Xr installboot 8 .
1.1 cgd 517: .Sh NOTES
1.48 darcy 518: This program is only available (and useful) on systems with PC-platform-style
1.49 wiz 519: MBR partitioning.
1.48 darcy 520: .Pp
1.35 dsl 521: Traditionally the partition boundaries should be on cylinder boundaries
1.58 apb 522: using the BIOS geometry, with the exception of the first partition,
523: which traditionally begins in the second track of the first cylinder
524: (cylinder 0, head 1, sector 1).
1.35 dsl 525: Although the BIOS geometry is typically different from the geometry
526: reported by the drive, neither will match the actual physical geometry
527: for modern disks (the actual geometry will vary across the disk).
528: Keeping the partition boundaries on cylinder boundaries makes partitioning
529: a driver easier as only relatively small numbers need be entered.
530: .Pp
1.12 ross 531: The automatic calculation of the starting cylinder and
532: other parameters uses
1.1 cgd 533: a set of figures that represent what the BIOS thinks is the
534: geometry of the drive.
1.35 dsl 535: The default values should be correct for the system on which
536: .Nm
537: is run, however if you move the disk to a different system the
538: BIOS of that system might use a different geometry translation.
539: .Pp
540: If you run the equivalent of
1.6 mycroft 541: .Nm
1.35 dsl 542: on a different operating system then the
1.40 dsl 543: .Ar bootmenu
1.35 dsl 544: strings associated with extended partitions may be lost.
1.1 cgd 545: .Pp
1.6 mycroft 546: Editing an existing partition is risky, and may cause you to
1.1 cgd 547: lose all the data in that partition.
548: .Pp
549: You should run this program interactively once or twice to see how it works.
550: This is completely safe as long as you answer the last question in the negative.
1.35 dsl 551: You can also specify
552: .Fl w Ar file
553: to write the output to a file and later specify
554: .Fl r Ar file
555: to read back the updated information.
556: This can be done without having write access to the disk volume.
1.16 ws 557: .Sh FILES
1.18 fvdl 558: .Bl -tag -width /usr/mdec/mbrxxxxxxxx -compact
1.16 ws 559: .It Pa /usr/mdec/mbr
560: Default location of i386 bootcode
1.18 fvdl 561: .It Pa /usr/mdec/mbr_bootsel
562: Default location of i386 bootselect code
1.35 dsl 563: .It Pa /usr/mdec/mbr_ext
564: Default location of i386 bootselect for extended partitions
1.16 ws 565: .El
1.62 ! yamt 566: .Sh EXAMPLES
! 567: Install MBR bootcode /usr/mdec/mbr_bootsel into /dev/rwd0d:
! 568: .Bd -literal -offset indent
! 569: fdisk -c /usr/mdec/mbr_bootsel /dev/rwd0d
! 570: .Ed
1.1 cgd 571: .Sh SEE ALSO
1.45 snj 572: .Xr disktab 5 ,
1.54 apb 573: .Xr boot 8 ,
1.23 abs 574: .Xr disklabel 8 ,
1.60 christos 575: .Xr gpt 8 ,
1.54 apb 576: .Xr installboot 8 ,
1.27 fair 577: .Xr mbr 8 ,
1.23 abs 578: .Xr mbrlabel 8
1.1 cgd 579: .Sh BUGS
1.45 snj 580: The word
581: .Sq partition
582: is used to mean both an MBR partition and a
1.35 dsl 583: .Nx
584: partition, sometimes in the same sentence.
585: .Pp
1.6 mycroft 586: There are subtleties that the program detects that are not explained in
587: this manual page.
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