1 .\" $FreeBSD: src/sbin/i386/fdisk/fdisk.8,v 1.17.2.11 2002/04/25 16:25:12 trhodes Exp $
2 .\" $DragonFly: src/sbin/i386/fdisk/fdisk.8,v 1.9 2006/02/28 02:25:10 swildner Exp $
9 .Nd PC slice table maintenance program
22 In order for the BIOS to boot the kernel,
23 certain conventions must be adhered to.
24 Sector 0 of the disk must contain boot code,
27 BIOS slices can be used to break the disk up into several pieces.
28 The BIOS brings in sector 0 and verifies the magic number. The sector
29 0 boot code then searches the slice table to determine which
32 This boot code then brings in the bootstrap from the
34 slice and, if marked bootable, runs it.
36 you can have one or more slices with one
40 program can be used to divide space on the disk into slices and set one
47 serves a similar purpose to the DOS program. The first form is used to
48 display slice information or to interactively edit the slice
49 table. The second is used to write a slice table using a
51 and is designed to be used by other scripts/programs.
54 .Bl -tag -width indent
56 Change the active slice only. Ignored if
60 Get the boot code from the file
65 The disk image is specified as a normal file instead of as a device,
66 which is useful when building emulated disks for vmware, bochs, etc.
68 Reinitialize the boot code contained in sector 0 of the disk. Ignored
72 .It Fl f Ar configfile
73 Set slice values using the file
77 always modifies existing slices, unless
79 is also given, in which case all existing slices are deleted (marked
80 as "unused") before the
84 can be "-", in which case
87 .Sx CONFIGURATION FILE ,
88 below, for file syntax.
93 is used, you are not asked if you really want to write the slices
94 table (as you are in the interactive mode). Use with caution!
96 Initialize sector 0 of the disk. This implies
102 Initialize the contents of sector 0
105 slice covering the entire disk.
107 Print a summary of all slices on the disk and exit.
108 All other options will be ignored.
110 Test mode; do not write slice values. Generally used with the
112 option to see what would be written to the slice table. Implies
115 Is used for updating (editing) sector 0 of the disk. Ignored if
123 prints out the slice table that is written to the disk.
125 Operate on a single fdisk entry only. Ignored if
130 The final disk name can be provided as a
132 disk name only, e.g.\&
134 or as a fully qualified device node under
136 If omitted, the disks
140 are searched in that order, until one is found to respond.
142 When called without options,
144 prints the sector 0 slice table.
147 ******* Working on device /dev/ad0 *******
148 parameters extracted from in-core disklabel are:
149 cylinders=769 heads=15 sectors/track=33 (495 blks/cyl)
151 parameters to be used for BIOS calculations are:
152 cylinders=769 heads=15 sectors/track=33 (495 blks/cyl)
154 Warning: BIOS sector numbering starts with sector 1
155 Information from DOS bootblock is:
156 The data for partition 1 is:
157 sysid 165,(DragonFly/FreeBSD/NetBSD/386BSD)
158 start 495, size 380160 (185 Meg), flag 0
159 beg: cyl 1/ sector 1/ head 0;
160 end: cyl 768/ sector 33/ head 14
161 The data for partition 2 is:
163 start 378180, size 2475 (1 Meg), flag 0
164 beg: cyl 764/ sector 1/ head 0;
165 end: cyl 768/ sector 33/ head 14
166 The data for partition 3 is:
168 The data for partition 4 is:
169 sysid 99,(ISC UNIX, other System V/386, GNU HURD or Mach)
170 start 380656, size 224234 (109 Meg), flag 80
171 beg: cyl 769/ sector 2/ head 0;
172 end: cyl 197/ sector 33/ head 14
175 The disk is divided into three slices that happen to fill the disk.
176 The second slice overlaps the end of the first.
177 (Used for debugging purposes.)
178 .Bl -tag -width "cyl, sector and head"
180 is used to label the slice.
183 magic number 165 decimal (A5 in hex).
184 .It Em start No and Em size
185 fields provide the start address
186 and size of a slice in sectors.
188 specifies that this is the active slice.
189 .It Em cyl , sector No and Em head
190 fields are used to specify the beginning and end addresses of the slice.
192 these numbers are calculated using BIOS's understanding of the disk geometry
193 and saved in the bootblock.
200 flags are used to indicate that the slice data is to be updated.
203 option is also given,
205 will enter a conversational mode.
206 In this mode, no changes will be written to disk unless you explicitly tell
211 will display each slice and ask whether you want to edit it.
214 will step through each field, show you the old value,
215 and ask you for a new one.
216 When you are done with the slice,
218 will display it and ask you whether it is correct.
220 will then proceed to the next entry.
226 fields correct is tricky, so by default,
227 they will be calculated for you;
228 you can specify them if you choose to though.
230 After all the slices are processed,
231 you are given the option to change the
234 Finally, when all the new data for sector 0 has been accumulated,
235 you are asked to confirm whether you really want to rewrite it.
237 The difference between the
244 flag just edits (updates) the fields as they appear on the disk,
247 flag is used to "initialize" sector 0;
248 it will set up the last BIOS slice to use the whole disk for
252 The automatic calculation of starting cylinder etc. uses
253 a set of figures that represent what the BIOS thinks the
254 geometry of the drive is.
255 These figures are taken from the in-core disklabel by default,
258 initially gives you an opportunity to change them.
259 This allows you to create a bootblock that can work with drives
260 that use geometry translation under the BIOS.
262 If you hand craft your disk layout,
263 please make sure that the
265 slice starts on a cylinder boundary.
266 A number of decisions made later may assume this.
267 (This might not be necessary later.)
269 Editing an existing slice will most likely result in the loss of
270 all data in that slice.
274 interactively once or twice to see how it works.
275 This is completely safe as long as you answer the last question
276 in the negative. There are subtleties that
278 detects that are not fully explained in this manual page.
279 .Sh CONFIGURATION FILE
282 option is given, a disk's slice table can be written using values
285 The syntax of this file is very simple;
286 each line is either a comment or a specification, as follows:
292 Lines beginning with a "#" are comments and are ignored.
299 Set the BIOS geometry used in slice calculations. There must be
300 three values specified, with a letter preceding each number:
305 Set the number of cylinders to
310 Set the number of heads to
315 Set the number of sectors/track to
319 These specs can occur in any order, as the leading letter determines
320 which value is which; however, all three must be specified.
322 This line must occur before any lines that specify slice
325 It is an error if the following is not true:
326 .Bd -literal -offset indent
327 1 \(<= number of cylinders
328 1 \(<= number of heads \(<= 256
329 1 \(<= number of sectors/track < 64
332 The number of cylinders should be less than or equal to 1024, but this
333 is not enforced, although a warning will be printed. Note that bootable
335 slices (the "/" filesystem) must lie completely within the
336 first 1024 cylinders; if this is not true, booting may fail.
337 Non-bootable slices do not have this restriction.
339 Example (all of these are equivalent), for a disk with 1019 cylinders,
340 39 heads, and 63 sectors:
341 .Bd -literal -offset indent
353 Set the slice given by
363 Only those slices explicitly mentioned by these lines are modified;
364 any slice not referenced by a "p" line will not be modified.
365 However, if an invalid slice table is present, or the
367 option is specified, all existing slice entries will be cleared
368 (marked as unused), and these "p" lines will have to be used to
369 explicitly set slice information. If multiple slices need to be
370 set, multiple "p" lines must be specified; one for each slice.
372 These slice lines must occur after any geometry specification lines,
379 slices. Specifying a slice type of zero is
380 the same as clearing the slice and marking it as unused; however,
381 dummy values (such as "0") must still be specified for
386 Note: the start offset will be rounded upwards to a head boundary if
387 necessary, and the end offset will be rounded downwards to a cylinder
388 boundary if necessary.
390 Example: to clear slice 4 and mark it as unused:
391 .Bd -literal -offset indent
395 Example: to set slice 1 to a
397 slice, starting at sector 1
398 for 2503871 sectors (note: these numbers will be rounded upwards and
399 downwards to correspond to head and cylinder boundaries):
401 .Bd -literal -offset indent
411 the active slice. Can occur anywhere in the config file, but only
415 line is present, all slices of the disk are made inactive.
417 Example: to make slice 1 the active slice:
418 .Bd -literal -offset indent
423 .Bl -tag -width /boot/mbr -compact
425 The default boot code
432 The default boot code will not necessarily handle all slice types
433 correctly, in particular those introduced since MS-DOS 6.x.
435 The entire program should be made more user-friendly.
439 do not understand the difference between
443 causing difficulty to adjust.
445 You cannot use this command to completely dedicate a disk to
449 command must be used for this.