8 .Nd PC slice table maintenance program
21 In order for the BIOS to boot the kernel,
22 certain conventions must be adhered to.
23 Sector 0 of the disk must contain boot code,
26 BIOS slices can be used to break the disk up into several pieces.
27 The BIOS brings in sector 0 and verifies the magic number. The sector
28 0 boot code then searches the slice table to determine which
31 This boot code then brings in the bootstrap from the
33 slice and, if marked bootable, runs it.
35 you can have one or more slices with one
39 program can be used to divide space on the disk into slices and set one
46 serves a similar purpose to the DOS program. The first form is used to
47 display slice information or to interactively edit the slice
48 table. The second is used to write a slice table using a
50 and is designed to be used by other scripts/programs.
54 Change the active slice only. Ignored if
58 Get the boot code from the file
63 Reinitialize the boot code contained in sector 0 of the disk. Ignored
67 .It Fl f Ar configfile
68 Set slice values using the file
72 always modifies existing slices, unless
74 is also given, in which case all existing slices are deleted (marked
75 as "unused") before the
79 can be "-", in which case
82 .Sx CONFIGURATION FILE ,
83 below, for file syntax.
88 is used, you are not asked if you really want to write the slices
89 table (as you are in the interactive mode). Use with caution!
91 Initialize sector 0 of the disk. This implies
97 Initialize the contents of sector 0
100 slice covering the entire disk.
102 Print summary information and exit.
104 Test mode; do not write slice values. Generally used with the
106 option to see what would be written to the slice table. Implies
109 Is used for updating (editing) sector 0 of the disk. Ignored if
117 prints out the slice table that is written to the disk.
119 Operate on a single fdisk entry only. Ignored if
124 The final disk name can be provided as a
126 disk name only, e.g.\&
128 or as a full pathname.
131 tries to figure out the default disk device name from the
134 When called with no arguments, it prints the sector 0 partition table.
137 ******* Working on device /dev/ad0 *******
138 parameters extracted from in-core disklabel are:
139 cylinders=769 heads=15 sectors/track=33 (495 blks/cyl)
141 parameters to be used for BIOS calculations are:
142 cylinders=769 heads=15 sectors/track=33 (495 blks/cyl)
144 Warning: BIOS sector numbering starts with sector 1
145 Information from DOS bootblock is:
146 The data for partition 1 is:
147 sysid 165,(FreeBSD/NetBSD/386BSD)
148 start 495, size 380160 (185 Meg), flag 0
149 beg: cyl 1/ sector 1/ head 0;
150 end: cyl 768/ sector 33/ head 14
151 The data for partition 2 is:
153 start 378180, size 2475 (1 Meg), flag 0
154 beg: cyl 764/ sector 1/ head 0;
155 end: cyl 768/ sector 33/ head 14
156 The data for partition 3 is:
158 The data for partition 4 is:
159 sysid 99,(ISC UNIX, other System V/386, GNU HURD or Mach)
160 start 380656, size 224234 (109 Meg), flag 80
161 beg: cyl 769/ sector 2/ head 0;
162 end: cyl 197/ sector 33/ head 14
165 The disk is divided into three slices that happen to fill the disk.
166 The second slice overlaps the end of the first.
167 (Used for debugging purposes.)
168 .Bl -tag -width "cyl, sector and head"
170 is used to label the slice.
173 magic number 165 decimal (A5 in hex).
174 .It Em start No and Em size
175 fields provide the start address
176 and size of a slice in sectors.
178 specifies that this is the active slice.
179 .It Em cyl , sector No and Em head
180 fields are used to specify the beginning and end addresses of the slice.
182 these numbers are calculated using BIOS's understanding of the disk geometry
183 and saved in the bootblock.
190 flags are used to indicate that the slice data is to be updated.
193 option is also given,
195 will enter a conversational mode.
196 In this mode, no changes will be written to disk unless you explicitly tell
201 will display each slice and ask whether you want to edit it.
204 will step through each field, show you the old value,
205 and ask you for a new one.
206 When you are done with the slice,
208 will display it and ask you whether it is correct.
210 will then proceed to the next entry.
216 fields correct is tricky, so by default,
217 they will be calculated for you;
218 you can specify them if you choose to though.
220 After all the slices are processed,
221 you are given the option to change the
224 Finally, when all the new data for sector 0 has been accumulated,
225 you are asked to confirm whether you really want to rewrite it.
227 The difference between the
234 flag just edits (updates) the fields as they appear on the disk,
237 flag is used to "initialize" sector 0;
238 it will set up the last BIOS slice to use the whole disk for
242 The automatic calculation of starting cylinder etc. uses
243 a set of figures that represent what the BIOS thinks the
244 geometry of the drive is.
245 These figures are taken from the in-core disklabel by default,
248 initially gives you an opportunity to change them.
249 This allows you to create a bootblock that can work with drives
250 that use geometry translation under the BIOS.
252 If you hand craft your disk layout,
253 please make sure that the
255 slice starts on a cylinder boundary.
256 A number of decisions made later may assume this.
257 (This might not be necessary later.)
259 Editing an existing slice will most likely result in the loss of
260 all data in that slice.
264 interactively once or twice to see how it works.
265 This is completely safe as long as you answer the last question
266 in the negative. There are subtleties that
268 detects that are not fully explained in this manual page.
269 .Sh CONFIGURATION FILE
272 option is given, a disk's slice table can be written using values
275 The syntax of this file is very simple;
276 each line is either a comment or a specification, as follows:
282 Lines beginning with a "#" are comments and are ignored.
289 Set the BIOS geometry used in slice calculations. There must be
290 three values specified, with a letter preceding each number:
295 Set the number of cylinders to
300 Set the number of heads to
305 Set the number of sectors/track to
309 These specs can occur in any order, as the leading letter determines
310 which value is which; however, all three must be specified.
312 This line must occur before any lines that specify slice
315 It is an error if the following is not true:
316 .Bd -literal -offset indent
317 1 <= number of cylinders
318 1 <= number of heads <= 256
319 1 <= number of sectors/track < 64
322 The number of cylinders should be less than or equal to 1024, but this
323 is not enforced, although a warning will be printed. Note that bootable
325 slices (the "/" filesystem) must lie completely within the
326 first 1024 cylinders; if this is not true, booting may fail.
327 Non-bootable slices do not have this restriction.
329 Example (all of these are equivalent), for a disk with 1019 cylinders,
330 39 heads, and 63 sectors:
331 .Bd -literal -offset indent
343 Set the slice given by
353 Only those slices explicitly mentioned by these lines are modified;
354 any slice not referenced by a "p" line will not be modified.
355 However, if an invalid slice table is present, or the
357 option is specified, all existing slice entries will be cleared
358 (marked as unused), and these "p" lines will have to be used to
359 explicitly set slice information. If multiple slices need to be
360 set, multiple "p" lines must be specified; one for each slice.
362 These slice lines must occur after any geometry specification lines,
369 slices. Specifying a slice type of zero is
370 the same as clearing the slice and marking it as unused; however,
371 dummy values (such as "0") must still be specified for
376 Note: the start offset will be rounded upwards to a head boundary if
377 necessary, and the end offset will be rounded downwards to a cylinder
378 boundary if necessary.
380 Example: to clear slice 4 and mark it as unused:
381 .Bd -literal -offset indent
385 Example: to set slice 1 to a
387 slice, starting at sector 1
388 for 2503871 sectors (note: these numbers will be rounded upwards and
389 downwards to correspond to head and cylinder boundaries):
391 .Bd -literal -offset indent
401 the active slice. Can occur anywhere in the config file, but only
404 Example: to make slice 1 the active slice:
405 .Bd -literal -offset indent
410 .Bl -tag -width /boot/mbr -compact
412 The default boot code
419 The default boot code will not necessarily handle all slice types
420 correctly, in particular those introduced since MS-DOS 6.x.
422 The entire program should be made more user-friendly.
426 do not understand the difference between
430 causing difficulty to adjust.
432 You cannot use this command to completely dedicate a disk to
436 command must be used for this.
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