6.Sh NAME
7.Nm fdisk
8.Nd PC partition table maintenance program
9.Sh SYNOPSIS
10.Nm
11.Op Fl BIaistu
12.Op Fl b Ar bootcode
13.Op Fl 1234
14.Op Ar disk
15.Bl -tag -width time
16.Nm
17.Fl f Ar configfile
18.Op Fl itv
19.Op Ar disk
20.Sh PROLOGUE
21In order for the BIOS to boot the kernel,
22certain conventions must be adhered to.
23Sector 0 of the disk must contain boot code,
24a partition table,
25and a magic number.
26BIOS partitions can be used to break the disk up into several pieces.
27The BIOS brings in sector 0 and verifies the magic number. The sector
280 boot code then searches the partition table to determine which
29partition is marked
30.Em active .
31This boot code then brings in the bootstrap from the
32.Em active
33partition and, if marked bootable, runs it.
34Under DOS,
35you can have one or more partitions with one
36.Em active .
37The DOS
38.Nm
39program can be used to divide space on the disk into partitions and set one
40.Em active .
41.Sh DESCRIPTION
42The
43.Fx
44program
45.Nm
46serves a similar purpose to the DOS program. The first form is used to
47display partition information or to interactively edit the partition
48table. The second is used to write a partition table using a
49.Ar configfile
50and is designed to be used by other scripts/programs.
51.Pp
52Options are:
53.It Fl a
54Change the active partition only. Ignored if
55.Fl f
56is given.
57.It Fl b Ar bootcode
58Get the boot code from the file
59.Ar bootcode .
60.It Fl B
61Reinitialize the boot code contained in sector 0 of the disk. Ignored
62if
63.Fl f
64is given.
65.It Fl f Ar configfile
66Set partition values using the file
67.Ar configfile .
68The
69.Ar configfile
70always modifies existing partitions, unless
71.Fl i
72is also given, in which case all existing partitions are deleted (marked
73as "unused") before the
74.Ar configfile
75is read. The
76.Ar configfile
77can be "-", in which case
78.Ar stdin
79is read. See
80.Sx CONFIGURATION FILE ,
81below, for file syntax.
82.Pp
83.Em WARNING Ns :
84when
85.Fl f
86is used, you are not asked if you really want to write the partition
87table (as you are in the interactive mode). Use with caution!
88.It Fl i
89Initialize sector 0 of the disk. This implies
90.Fl u ,
91unless
92.Fl f
93is given.
94.It Fl I
95Initialize the contents of sector 0
96with one
97.Fx
98slice covering the entire disk.
99.It Fl s
100Print summary information and exit.
101.It Fl t
102Test mode; do not write partition values. Generally used with the
103.Fl f
104option to see what would be written to the partition table. Implies
105.Fl v .
106.It Fl u
107Is used for updating (editing) sector 0 of the disk. Ignored if
108.Fl f
109is given.
110.It Fl v
111Be verbose. When
112.Fl f
113is used,
114.Nm
115prints out the partition table that is written to the disk.
116.It Fl 1234
117Operate on a single fdisk entry only. Ignored if
118.Fl f
119is given.
120.El
121.Pp
122The final disk name can be provided as a
123.Sq bare
124disk name only, e.g.
125.Ql da0 ,
126or as a fully qualified device node under
127.Pa /dev .
128If omitted, the disks
129.Ql wd0 ,
130.Ql da0 ,
131and
132.Ql od0
133are being searched in that order, until one is
134being found responding.
135.Pp
136When called with no arguments, it prints the sector 0 partition table.
137An example follows:
138
139.Bd -literal
140 ******* Working on device /dev/rwd0 *******
141 parameters extracted from in-core disklabel are:
142 cylinders=769 heads=15 sectors/track=33 (495 blks/cyl)
143
144 parameters to be used for BIOS calculations are:
145 cylinders=769 heads=15 sectors/track=33 (495 blks/cyl)
146
147 Warning: BIOS sector numbering starts with sector 1
148 Information from DOS bootblock is:
149 The data for partition 1 is:
150 sysid 165,(FreeBSD/NetBSD/386BSD)
151 start 495, size 380160 (185 Meg), flag 0
152 beg: cyl 1/ sector 1/ head 0;
153 end: cyl 768/ sector 33/ head 14
154 The data for partition 2 is:
155 sysid 164,(unknown)
156 start 378180, size 2475 (1 Meg), flag 0
157 beg: cyl 764/ sector 1/ head 0;
158 end: cyl 768/ sector 33/ head 14
159 The data for partition 3 is:
160 <UNUSED>
161 The data for partition 4 is:
162 sysid 99,(ISC UNIX, other System V/386, GNU HURD or Mach)
163 start 380656, size 224234 (109 Meg), flag 80
164 beg: cyl 769/ sector 2/ head 0;
165 end: cyl 197/ sector 33/ head 14
166.Ed
167.Pp
168The disk is divided into three partitions that happen to fill the disk.
169The second partition overlaps the end of the first.
170(Used for debugging purposes)
171.Bl -tag -width "cyl, sector and head"
172.It Em "sysid"
173is used to label the partition.
174.Fx
175reserves the
176magic number 165 decimal (A5 in hex).
177.It Em "start and size"
178fields provide the start address
179and size of a partition in sectors.
180.It Em "flag 80"
181specifies that this is the active partition.
182.It Em "cyl, sector and head"
183fields are used to specify the beginning address
184and end address for the partition.
185.It Em "Note:"
186these numbers are calculated using BIOS's understanding of the disk geometry
187and saved in the bootblock.
188.El
189.Pp
190The flags
191.Fl i
192or
193.Fl u
194are used to indicate that the partition data is to be updated, unless the
195.Fl f
196option is used. If the
197.Fl f
198option is not used, the
199.Nm
200program will enter a conversational mode.
201This mode is designed not to change any data unless you explicitly tell it to.
202.Nm Fdisk
203selects defaults for its questions to guarantee the above behavior.
204.Pp
205It displays each partition
206and ask if you want to edit it.
207If you say yes,
208it will step through each field showing the old value
209and asking for a new one.
210When you are done with a partition,
211.Nm
212will display it and ask if it is correct.
213.Nm Fdisk
214will then proceed to the next entry.
215.Pp
216Getting the
217.Em cyl, sector,
218and
219.Em head
220fields correct is tricky.
221So by default,
222they will be calculated for you;
223you can specify them if you choose.
224.Pp
225After all the partitions are processed,
226you are given the option to change the
227.Em active
228partition.
229Finally,
230when the all the data for the first sector has been accumulated,
231you are asked if you really want to rewrite sector 0.
232Only if you answer yes,
233will the data be written to disk.
234.Pp
235The difference between the
236.Fl u
237flag and
238.Fl i
239flag is that
240the
241.Fl u
242flag just edits the fields as they appear on the disk.
243While the
244.Fl i
245flag is used to "initialize" sector 0;
246it will setup the last BIOS partition to use the whole disk for
247.Fx ;
248and make it active.
249.Sh NOTES
250The automatic calculation of starting cylinder etc. uses
251a set of figures that represent what the BIOS thinks is the
252geometry of the drive.
253These figures are by default taken from the incore disklabel,
254but the program initially gives you an opportunity to change them.
255This allows the user to create a bootblock that can work with drives
256that use geometry translation under the BIOS.
257.Pp
258If you hand craft your disk layout,
259please make sure that the
260.Fx
261partition starts on a cylinder boundary.
262A number of decisions made later may assume this.
263(This might not be necessary later.)
264.Pp
265Editing an existing partition will most likely cause you to
266lose all the data in that partition.
267.Pp
268You should run this program interactively once or twice to see how it
269works. This is completely safe as long as you answer the last question
270in the negative. There are subtleties that the program detects that are
271not fully explained in this manual page.
272.Sh CONFIGURATION FILE
273When the
274.Fl f
275option is given, a disk's partition table can be written using values
276from a
277.Ar configfile .
278The syntax of this file is very simple. Each line is either a comment or
279a specification, and whitespace (except for newlines) are ignored:
280.Bl -tag -width Ds
281.It Xo
282.Ic #
283.No Ar comment ...
284.Xc
285Lines beginning with a "#" are comments and are ignored.
286.It Xo
287.Ic g
288.No Ar spec1
289.No Ar spec2
290.No Ar spec3
291.Xc
292Set the BIOS geometry used in partition calculations. There must be
293three values specified, with a letter preceding each number:
294.Bl -tag -width Ds
295.Sm off
296.It Cm c No Ar num
297.Sm on
298Set the number of cylinders to
299.Ar num .
300.Sm off
301.It Cm h No Ar num
302.Sm on
303Set the number of heads to
304.Ar num .
305.Sm off
306.It Cm s No Ar num
307.Sm on
308Set the number of sectors/track to
309.Ar num .
310.El
311.Pp
312These specs can occur in any order, as the leading letter determines
313which value is which; however, all three must be specified.
314.Pp
315This line must occur before any lines that specify partition
316information.
317.Pp
318It is an error if the following is not true:
319.Bd -literal -offset indent
3201 <= number of cylinders
3211 <= number of heads <= 256
3221 <= number of sectors/track < 64
323.Ed
324.Pp
325The number of cylinders should be less than or equal to 1024, but this
326is not enforced, although a warning will be output. Note that bootable
327.Fx
328partitions (the "/" filesystem) must lie completely within the
329first 1024 cylinders; if this is not true, booting may fail.
330Non-bootable partitions do not have this restriction.
331.Pp
332Example (all of these are equivalent), for a disk with 1019 cylinders,
33339 heads, and 63 sectors:
334.Bd -literal -offset indent
335g c1019 h39 s63
336g h39 c1019 s63
337g s63 h39 c1019
338.Ed
339.It Xo
340.Ic p
341.No Ar partition
342.No Ar type
343.No Ar start
344.No Ar length
345.Xc
346Set the partition given by
347.Ar partition
348(1-4) to type
349.Ar type ,
350starting at sector
351.Ar start
352for
353.Ar length
354sectors.
355.Pp
356Only those partitions explicitly mentioned by these lines are modified;
357any partition not referenced by a "p" line will not be modified.
358However, if an invalid partition table is present, or the
359.Fl i
360option is specified, all existing partition entries will be cleared
361(marked as unused), and these "p" lines will have to be used to
362explicitly set partition information. If multiple partitions need to be
363set, multiple "p" lines must be specified; one for each partition.
364.Pp
365These partition lines must occur after any geometry specification lines,
366if one is present.
367.Pp
368The
369.Ar type
370is 165 for
371.Fx
372partitions. Specifying a partition type of zero is
373the same as clearing the partition and marking it as unused; however,
374dummy values (such as "0") must still be specified for
375.Ar start
376and
377.Ar length .
378.Pp
379Note: the start offset will be rounded upwards to a head boundary if
380necessary, and the end offset will be rounded downwards to a cylinder
381boundary if necessary.
382.Pp
383Example: to clear partition 4 and mark it as unused:
384.Bd -literal -offset indent
385p 4 0 0 0
386.Ed
387.Pp
388Example: to set partition 1 to a
389.Fx
390partition, starting at sector 1
391for 2503871 sectors (note: these numbers will be rounded upwards and
392downwards to correspond to head and cylinder boundaries):
393.Pp
394.Bd -literal -offset indent
395p 1 165 1 2503871
396.Ed
397.Pp
398.It Xo
399.Ic a
400.No Ar partition
401.Xc
402Make
403.Ar partition
404the active partition. Can occur anywhere in the config file, but only
405one must be present.
406.Pp
407Example: to make partition 1 the active partition:
408.Bd -literal -offset indent
409a 1
410.Ed
411.El
412.Sh FILES
413.Bl -tag -width /boot/mbr -compact
414.It Pa /boot/mbr
415The default boot code
416.El
417.Sh SEE ALSO
418.Xr disklabel 8
419.Sh BUGS
420The default boot code will not necessarily handle all partition types
421correctly, in particular those introduced since MS-DOS 6.x.
422.Pp
423The entire program should be made more user-friendly.
424.Pp
425Throughout this man page, the term
426.Sq partition
427is used where it should actually be
428.Sq slice ,
429in order to conform with the terms used elsewhere.
430.Pp
431You cannot use this command to completely dedicate a disk to
432.Fx .
433The
434.Xr disklabel 8
435command must be used for this.
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