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1 .\" $FreeBSD$
2 .\"
3 .Dd October 1, 2013
4 .Dt FDISK 8
5 .Os
6 .Sh NAME
7 .Nm fdisk
8 .Nd PC slice table maintenance utility
9 .Sh SYNOPSIS
10 .Nm
11 .Op Fl BIaipqstu
12 .Op Fl b Ar bootcode
13 .Op Fl 1234
14 .Op Ar disk
15 .Nm
16 .Fl f Ar configfile
17 .Op Fl itv
18 .Op Ar disk
19 .Sh PROLOGUE
20 In order for the BIOS to boot the kernel,
21 certain conventions must be adhered to.
22 Sector 0 of the disk must contain boot code,
23 a slice table,
24 and a magic number.
25 BIOS slices can be used to break the disk up into several pieces.
26 The BIOS brings in sector 0 and verifies the magic number.
27 The sector
28 0 boot code then searches the slice table to determine which
29 slice is marked
30 .Dq active .
31 This boot code then brings in the bootstrap from the
32 active slice and, if marked bootable, runs it.
33 Under
34 .Tn DOS ,
35 you can have one or more slices with one active.
36 The
37 .Tn DOS
38 .Nm
39 utility can be used to divide space on the disk into slices and set one
40 active.
41 .Sh DESCRIPTION
42 .Bf -symbolic
43 This command is obsolete.
44 Users are advised to use
45 .Xr gpart 8
46 instead.
47 .Ef
48 .Pp
49 The
50 .Fx
51 utility,
52 .Nm ,
53 serves a similar purpose to the
54 .Tn DOS
55 utility.
56 The first form is used to
57 display slice information or to interactively edit the slice
58 table.
59 The second is used to write a slice table using a
60 .Ar configfile ,
61 and is designed to be used by other scripts/programs.
62 .Pp
63 Options are:
64 .Bl -tag -width indent
65 .It Fl a
66 Change the active slice only.
67 Ignored if
68 .Fl f
69 is given.
70 .It Fl b Ar bootcode
71 Get the boot code from the file
72 .Ar bootcode .
73 Default is
74 .Pa /boot/mbr .
75 .It Fl B
76 Reinitialize the boot code contained in sector 0 of the disk.
77 Ignored if
78 .Fl f
79 is given.
80 .It Fl f Ar configfile
81 Set slice values using the file
82 .Ar configfile .
83 The
84 .Ar configfile
85 only modifies explicitly specified slices, unless
86 .Fl i
87 is also given, in which case all existing slices are deleted (marked
88 as
89 .Dq unused )
90 before the
91 .Ar configfile
92 is read.
93 The
94 .Ar configfile
95 can be
96 .Sq Fl ,
97 in which case standard input is read.
98 See
99 .Sx CONFIGURATION FILE ,
100 below, for file syntax.
101 .Pp
102 .Em WARNING :
103 when
104 .Fl f
105 is used, you are not asked if you really want to write the slices
106 table (as you are in the interactive mode).
107 Use with caution!
108 .It Fl i
109 Initialize sector 0 of the disk.
110 Existing slice entries will be cleared
111 (marked as unused) before editing.
112 (Compare with
113 .Fl u . )
114 .It Fl I
115 Initialize sector 0 slice table
116 for one
117 .Fx
118 slice covering the entire disk.
119 .It Fl p
120 Print a slice table in
121 .Nm
122 configuration file format and exit; see
123 .Sx CONFIGURATION FILE ,
124 below.
125 .It Fl q
126 Be quiet.
127 Benign warnings (such as "GEOM not found") are suppressed.
128 .It Fl s
129 Print summary information and exit.
130 .It Fl t
131 Test mode; do not write slice values.
132 Generally used with the
133 .Fl f
134 option to see what would be written to the slice table.
135 Implies
136 .Fl v .
137 .It Fl u
138 Update (edit) the disk's sector 0 slice table.
139 Ignored if
140 .Fl f
141 is given.
142 .It Fl v
143 Be verbose.
144 When
145 .Fl f
146 is used,
147 .Nm
148 prints out the slice table that is written to the disk.
149 .It Fl 1234
150 Operate on a single slice table entry only.
151 Ignored if
152 .Fl f
153 is given.
154 .El
155 .Pp
156 The final disk name can be provided as a
157 .Dq bare
158 disk name only, e.g.\&
159 .Pa da0 ,
160 or as a full pathname.
161 If omitted,
162 .Nm
163 tries to figure out the default disk device name from the
164 mounted root device.
165 .Pp
166 When called with no arguments, it prints the sector 0 slice table.
167 An example follows:
168 .Bd -literal
169 ******* Working on device /dev/ada0 *******
170 parameters extracted from in-core disklabel are:
171 cylinders=769 heads=15 sectors/track=33 (495 blks/cyl)
173 parameters to be used for BIOS calculations are:
174 cylinders=769 heads=15 sectors/track=33 (495 blks/cyl)
176 Warning: BIOS sector numbering starts with sector 1
177 Information from DOS bootblock is:
178 The data for partition 1 is:
179 sysid 165,(FreeBSD/NetBSD/386BSD)
180 start 495, size 380160 (185 Meg), flag 0
181 beg: cyl 1/ sector 1/ head 0;
182 end: cyl 768/ sector 33/ head 14
183 The data for partition 2 is:
184 sysid 164,(unknown)
185 start 378180, size 2475 (1 Meg), flag 0
186 beg: cyl 764/ sector 1/ head 0;
187 end: cyl 768/ sector 33/ head 14
188 The data for partition 3 is:
189 <UNUSED>
190 The data for partition 4 is:
191 sysid 99,(ISC UNIX, other System V/386, GNU HURD or Mach)
192 start 380656, size 224234 (109 Meg), flag 80
193 beg: cyl 769/ sector 2/ head 0;
194 end: cyl 197/ sector 33/ head 14
195 .Ed
196 .Pp
197 The disk is divided into three slices that happen to fill the disk.
198 The second slice overlaps the end of the first.
199 (Used for debugging purposes.)
200 .Bl -tag -width ".Em cyl , sector No and Em head"
201 .It Em sysid
202 is used to label the slice.
203 .Fx
204 reserves the
205 magic number 165 decimal (A5 in hex).
206 .It Xo
207 .Em start
208 and
209 .Em size
210 .Xc
211 fields provide the start address
212 and size of a slice in sectors.
213 .It Em "flag 80"
214 specifies that this is the active slice.
215 .It Xo
216 .Em cyl , sector
217 and
218 .Em head
219 .Xc
220 fields are used to specify the beginning and end addresses of the slice.
221 .El
222 .Pp
223 .Em Note :
224 these numbers are calculated using BIOS's understanding of the disk geometry
225 and saved in the bootblock.
226 .Pp
227 The
228 .Fl i
229 and
230 .Fl u
231 flags are used to indicate that the slice data is to be updated.
232 Unless the
233 .Fl f
234 option is also given,
235 .Nm
236 will enter a conversational mode.
237 In this mode, no changes will be written to disk unless you explicitly tell
238 .Nm
239 to.
240 .Pp
241 The
242 .Nm
243 utility will display each slice and ask whether you want to edit it.
244 If you say yes,
245 .Nm
246 will step through each field, show you the old value,
247 and ask you for a new one.
248 When you are done with the slice,
249 .Nm
250 will display it and ask you whether it is correct.
251 It will then proceed to the next entry.
252 .Pp
253 Getting the
254 .Em cyl , sector ,
255 and
256 .Em head
257 fields correct is tricky, so by default,
258 they will be calculated for you;
259 you can specify them if you choose to though.
260 .Pp
261 After all the slices are processed,
262 you are given the option to change the
263 .Dq active
264 slice.
265 Finally, when all the new data for sector 0 has been accumulated,
266 you are asked to confirm whether you really want to rewrite it.
267 .Pp
268 The difference between the
269 .Fl u
270 and
271 .Fl i
272 flags is that
273 the
274 .Fl u
275 flag edits (updates) the existing slice parameters
276 while the
277 .Fl i
278 flag is used to
279 .Dq initialize
280 them (old values will be ignored);
281 if you edit the first slice,
282 .Fl i
283 will also set it up to use the whole disk for
284 .Fx
285 and make it active.
286 .Sh NOTES
287 The automatic calculation of starting cylinder etc.\& uses
288 a set of figures that represent what the BIOS thinks the
289 geometry of the drive is.
290 These figures are taken from the in-core disklabel by default,
291 but
292 .Nm
293 initially gives you an opportunity to change them.
294 This allows you to create a bootblock that can work with drives
295 that use geometry translation under the BIOS.
296 .Pp
297 If you hand craft your disk layout,
298 please make sure that the
299 .Fx
300 slice starts on a cylinder boundary.
301 .Pp
302 Editing an existing slice will most likely result in the loss of
303 all data in that slice.
304 .Pp
305 You should run
306 .Nm
307 interactively once or twice to see how it works.
308 This is completely safe as long as you answer the last question
309 in the negative.
310 There are subtleties that
311 .Nm
312 detects that are not fully explained in this manual page.
313 .Sh CONFIGURATION FILE
314 When the
315 .Fl f
316 option is given, a disk's slice table can be written using values
317 from a
318 .Ar configfile .
319 The syntax of this file is very simple;
320 each line is either a comment or a specification, as follows:
321 .Bl -tag -width indent
322 .It Ic # Ar comment ...
323 Lines beginning with a
324 .Ic #
325 are comments and are ignored.
326 .It Ic g Ar spec1 spec2 spec3
327 Set the BIOS geometry used in slice calculations.
328 There must be
329 three values specified, with a letter preceding each number:
330 .Bl -tag -width indent
331 .It Cm c Ns Ar num
332 Set the number of cylinders to
333 .Ar num .
334 .It Cm h Ns Ar num
335 Set the number of heads to
336 .Ar num .
337 .It Cm s Ns Ar num
338 Set the number of sectors/track to
339 .Ar num .
340 .El
341 .Pp
342 These specs can occur in any order, as the leading letter determines
343 which value is which; however, all three must be specified.
344 .Pp
345 This line must occur before any lines that specify slice
346 information.
347 .Pp
348 It is an error if the following is not true:
349 .Bd -literal -offset indent
350 1 <= number of cylinders
351 1 <= number of heads <= 256
352 1 <= number of sectors/track < 64
353 .Ed
354 .Pp
355 The number of cylinders should be less than or equal to 1024, but this
356 is not enforced, although a warning will be printed.
357 Note that bootable
358 .Fx
359 slices (the
360 .Dq Pa /
361 file system) must lie completely within the
362 first 1024 cylinders; if this is not true, booting may fail.
363 Non-bootable slices do not have this restriction.
364 .Pp
365 Example (all of these are equivalent), for a disk with 1019 cylinders,
366 39 heads, and 63 sectors:
367 .Bd -literal -offset indent
368 g c1019 h39 s63
369 g h39 c1019 s63
370 g s63 h39 c1019
371 .Ed
372 .It Ic p Ar slice type start length
373 Set the slice given by
374 .Ar slice
375 (1-4) to type
376 .Ar type ,
377 starting at sector
378 .Ar start
379 for
380 .Ar length
381 sectors.
382 If the
383 .Ar start
384 or
385 .Ar length
386 is suffixed with a
387 .Em K ,
388 .Em M
389 or
390 .Em G ,
391 it is taken as a
392 .Em Kilobyte ,
393 .Em Megabyte
394 or
395 .Em Gigabyte
396 measurement respectively.
397 If the
398 .Ar start
399 is given as
400 .Qq *
401 it is set to the value of the previous partition end.
402 If the
403 .Ar length
404 is given as
405 .Qq *
406 the partition end is set to the end of the disk.
407 .Pp
408 Only those slices explicitly mentioned by these lines are modified;
409 any slice not referenced by a
410 .Ic p
411 line will not be modified.
412 However, if an invalid slice table is present, or the
413 .Fl i
414 option is specified, all existing slice entries will be cleared
415 (marked as unused), and these
416 .Ic p
417 lines will have to be used to
418 explicitly set slice information.
419 If multiple slices need to be
420 set, multiple
421 .Ic p
422 lines must be specified; one for each slice.
423 .Pp
424 These slice lines must occur after any geometry specification lines,
425 if one is present.
426 .Pp
427 The
428 .Ar type
429 is 165 for
430 .Fx
431 slices.
432 Specifying a slice type of zero is
433 the same as clearing the slice and marking it as unused; however,
434 dummy values (such as
435 .Dq 0 )
436 must still be specified for
437 .Ar start
438 and
439 .Ar length .
440 .Pp
441 Note: the start offset will be rounded upwards to a head boundary if
442 necessary, and the end offset will be rounded downwards to a cylinder
443 boundary if necessary.
444 .Pp
445 Example: to clear slice 4 and mark it as unused:
446 .Pp
447 .Dl "p 4 0 0 0"
448 .Pp
449 Example: to set slice 1 to a
450 .Fx
451 slice, starting at sector 1
452 for 2503871 sectors (note: these numbers will be rounded upwards and
453 downwards to correspond to head and cylinder boundaries):
454 .Pp
455 .Dl "p 1 165 1 2503871"
456 .Pp
457 Example: to set slices 1, 2 and 4 to
458 .Fx
459 slices, the first being 2 Gigabytes, the second being 10 Gigabytes and the
460 forth being the remainder of the disk (again, numbers will be rounded
461 appropriately):
462 .Pp
463 .Dl "p 1 165 63 2G"
464 .Dl "p 2 165 * 10G"
465 .Dl "p 3 0 0 0"
466 .Dl "p 4 165 * *"
467 .It Ic a Ar slice
468 Make
469 .Ar slice
470 the active slice.
471 Can occur anywhere in the config file, but only
472 one must be present.
473 .Pp
474 Example: to make slice 1 the active slice:
475 .Pp
476 .Dl "a 1"
477 .El
478 .Sh FILES
479 .Bl -tag -width ".Pa /boot/mbr" -compact
480 .It Pa /boot/mbr
481 The default boot code.
482 .El
483 .Sh SEE ALSO
484 .Xr boot0cfg 8 ,
485 .Xr bsdlabel 8 ,
486 .Xr gpart 8 ,
487 .Xr newfs 8
488 .Sh BUGS
489 The default boot code will not necessarily handle all slice types
490 correctly, in particular those introduced since
491 .Tn MS-DOS
492 6.x.
493 .Pp
494 The entire utility should be made more user-friendly.
495 .Pp
496 Most users new to
497 .Fx
498 do not understand the difference between
499 .Dq slice
500 and
501 .Dq partition ,
502 causing difficulty to adjust.
503 .Pp
504 You cannot use this command to completely dedicate a disk to
505 .Fx .
506 The
507 .Xr bsdlabel 8
508 command must be used for this.