8 .Nd PC slice table maintenance utility
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,
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.
28 0 boot code then searches the slice table to determine which
31 This boot code then brings in the bootstrap from the
32 active slice and, if marked bootable, runs it.
35 you can have one or more slices with one active.
39 utility can be used to divide space on the disk into slices and set one
46 serves a similar purpose to the
49 The first form is used to
50 display slice information or to interactively edit the slice
52 The second is used to write a slice table using a
54 and is designed to be used by other scripts/programs.
57 .Bl -tag -width indent
59 Change the active slice only.
64 Get the boot code from the file
69 Reinitialize the boot code contained in sector 0 of the disk.
73 .It Fl f Ar configfile
74 Set slice values using the file
78 only modifies explicitly specified slices, unless
80 is also given, in which case all existing slices are deleted (marked
90 in which case standard input is read.
92 .Sx CONFIGURATION FILE ,
93 below, for file syntax.
98 is used, you are not asked if you really want to write the slices
99 table (as you are in the interactive mode).
102 Initialize sector 0 of the disk.
103 Existing slice entries will be cleared
104 (marked as unused) before editing.
108 Initialize sector 0 slice table
111 slice covering the entire disk.
113 Print summary information and exit.
115 Test mode; do not write slice values.
116 Generally used with the
118 option to see what would be written to the slice table.
122 Update (edit) the disk's sector 0 slice table.
132 prints out the slice table that is written to the disk.
134 Operate on a single slice table entry only.
140 The final disk name can be provided as a
142 disk name only, e.g.\&
144 or as a full pathname.
147 tries to figure out the default disk device name from the
150 When called with no arguments, it prints the sector 0 slice table.
153 ******* Working on device /dev/ad0 *******
154 parameters extracted from in-core disklabel are:
155 cylinders=769 heads=15 sectors/track=33 (495 blks/cyl)
157 parameters to be used for BIOS calculations are:
158 cylinders=769 heads=15 sectors/track=33 (495 blks/cyl)
160 Warning: BIOS sector numbering starts with sector 1
161 Information from DOS bootblock is:
162 The data for partition 1 is:
163 sysid 165,(FreeBSD/NetBSD/386BSD)
164 start 495, size 380160 (185 Meg), flag 0
165 beg: cyl 1/ sector 1/ head 0;
166 end: cyl 768/ sector 33/ head 14
167 The data for partition 2 is:
169 start 378180, size 2475 (1 Meg), flag 0
170 beg: cyl 764/ sector 1/ head 0;
171 end: cyl 768/ sector 33/ head 14
172 The data for partition 3 is:
174 The data for partition 4 is:
175 sysid 99,(ISC UNIX, other System V/386, GNU HURD or Mach)
176 start 380656, size 224234 (109 Meg), flag 80
177 beg: cyl 769/ sector 2/ head 0;
178 end: cyl 197/ sector 33/ head 14
181 The disk is divided into three slices that happen to fill the disk.
182 The second slice overlaps the end of the first.
183 (Used for debugging purposes.)
184 .Bl -tag -width ".Em cyl , sector No and Em head"
186 is used to label the slice.
189 magic number 165 decimal (A5 in hex).
195 fields provide the start address
196 and size of a slice in sectors.
198 specifies that this is the active slice.
204 fields are used to specify the beginning and end addresses of the slice.
208 these numbers are calculated using BIOS's understanding of the disk geometry
209 and saved in the bootblock.
215 flags are used to indicate that the slice data is to be updated.
218 option is also given,
220 will enter a conversational mode.
221 In this mode, no changes will be written to disk unless you explicitly tell
227 utility will display each slice and ask whether you want to edit it.
230 will step through each field, show you the old value,
231 and ask you for a new one.
232 When you are done with the slice,
234 will display it and ask you whether it is correct.
235 It will then proceed to the next entry.
241 fields correct is tricky, so by default,
242 they will be calculated for you;
243 you can specify them if you choose to though.
245 After all the slices are processed,
246 you are given the option to change the
249 Finally, when all the new data for sector 0 has been accumulated,
250 you are asked to confirm whether you really want to rewrite it.
252 The difference between the
259 flag edits (updates) the existing slice parameters
264 them (old values will be ignored);
265 if you edit the first slice,
267 will also set it up to use the whole disk for
271 The automatic calculation of starting cylinder etc.\& uses
272 a set of figures that represent what the BIOS thinks the
273 geometry of the drive is.
274 These figures are taken from the in-core disklabel by default,
277 initially gives you an opportunity to change them.
278 This allows you to create a bootblock that can work with drives
279 that use geometry translation under the BIOS.
281 If you hand craft your disk layout,
282 please make sure that the
284 slice starts on a cylinder boundary.
286 Editing an existing slice will most likely result in the loss of
287 all data in that slice.
291 interactively once or twice to see how it works.
292 This is completely safe as long as you answer the last question
294 There are subtleties that
296 detects that are not fully explained in this manual page.
297 .Sh CONFIGURATION FILE
300 option is given, a disk's slice table can be written using values
303 The syntax of this file is very simple;
304 each line is either a comment or a specification, as follows:
305 .Bl -tag -width indent
306 .It Ic # Ar comment ...
307 Lines beginning with a
309 are comments and are ignored.
310 .It Ic g Ar spec1 spec2 spec3
311 Set the BIOS geometry used in slice calculations.
313 three values specified, with a letter preceding each number:
314 .Bl -tag -width indent
316 Set the number of cylinders to
319 Set the number of heads to
322 Set the number of sectors/track to
326 These specs can occur in any order, as the leading letter determines
327 which value is which; however, all three must be specified.
329 This line must occur before any lines that specify slice
332 It is an error if the following is not true:
333 .Bd -literal -offset indent
334 1 <= number of cylinders
335 1 <= number of heads <= 256
336 1 <= number of sectors/track < 64
339 The number of cylinders should be less than or equal to 1024, but this
340 is not enforced, although a warning will be printed.
345 file system) must lie completely within the
346 first 1024 cylinders; if this is not true, booting may fail.
347 Non-bootable slices do not have this restriction.
349 Example (all of these are equivalent), for a disk with 1019 cylinders,
350 39 heads, and 63 sectors:
351 .Bd -literal -offset indent
356 .It Ic p Ar slice type start length
357 Set the slice given by
367 Only those slices explicitly mentioned by these lines are modified;
368 any slice not referenced by a
370 line will not be modified.
371 However, if an invalid slice table is present, or the
373 option is specified, all existing slice entries will be cleared
374 (marked as unused), and these
376 lines will have to be used to
377 explicitly set slice information.
378 If multiple slices need to be
381 lines must be specified; one for each slice.
383 These slice lines must occur after any geometry specification lines,
391 Specifying a slice type of zero is
392 the same as clearing the slice and marking it as unused; however,
393 dummy values (such as
395 must still be specified for
400 Note: the start offset will be rounded upwards to a head boundary if
401 necessary, and the end offset will be rounded downwards to a cylinder
402 boundary if necessary.
404 Example: to clear slice 4 and mark it as unused:
408 Example: to set slice 1 to a
410 slice, starting at sector 1
411 for 2503871 sectors (note: these numbers will be rounded upwards and
412 downwards to correspond to head and cylinder boundaries):
414 .Dl "p 1 165 1 2503871"
419 Can occur anywhere in the config file, but only
422 Example: to make slice 1 the active slice:
427 .Bl -tag -width ".Pa /boot/mbr" -compact
429 The default boot code.
436 The default boot code will not necessarily handle all slice types
437 correctly, in particular those introduced since
441 The entire utility should be made more user-friendly.
445 do not understand the difference between
449 causing difficulty to adjust.
451 You cannot use this command to completely dedicate a disk to
455 command must be used for this.