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 a slice table in
115 configuration file format and exit; see
116 .Sx CONFIGURATION FILE ,
120 Benign warnings (such as "GEOM not found") are suppressed.
122 Print summary information and exit.
124 Test mode; do not write slice values.
125 Generally used with the
127 option to see what would be written to the slice table.
131 Update (edit) the disk's sector 0 slice table.
141 prints out the slice table that is written to the disk.
143 Operate on a single slice table entry only.
149 The final disk name can be provided as a
151 disk name only, e.g.\&
153 or as a full pathname.
156 tries to figure out the default disk device name from the
159 When called with no arguments, it prints the sector 0 slice table.
162 ******* Working on device /dev/ada0 *******
163 parameters extracted from in-core disklabel are:
164 cylinders=769 heads=15 sectors/track=33 (495 blks/cyl)
166 parameters to be used for BIOS calculations are:
167 cylinders=769 heads=15 sectors/track=33 (495 blks/cyl)
169 Warning: BIOS sector numbering starts with sector 1
170 Information from DOS bootblock is:
171 The data for partition 1 is:
172 sysid 165,(FreeBSD/NetBSD/386BSD)
173 start 495, size 380160 (185 Meg), flag 0
174 beg: cyl 1/ sector 1/ head 0;
175 end: cyl 768/ sector 33/ head 14
176 The data for partition 2 is:
178 start 378180, size 2475 (1 Meg), flag 0
179 beg: cyl 764/ sector 1/ head 0;
180 end: cyl 768/ sector 33/ head 14
181 The data for partition 3 is:
183 The data for partition 4 is:
184 sysid 99,(ISC UNIX, other System V/386, GNU HURD or Mach)
185 start 380656, size 224234 (109 Meg), flag 80
186 beg: cyl 769/ sector 2/ head 0;
187 end: cyl 197/ sector 33/ head 14
190 The disk is divided into three slices that happen to fill the disk.
191 The second slice overlaps the end of the first.
192 (Used for debugging purposes.)
193 .Bl -tag -width ".Em cyl , sector No and Em head"
195 is used to label the slice.
198 magic number 165 decimal (A5 in hex).
204 fields provide the start address
205 and size of a slice in sectors.
207 specifies that this is the active slice.
213 fields are used to specify the beginning and end addresses of the slice.
217 these numbers are calculated using BIOS's understanding of the disk geometry
218 and saved in the bootblock.
224 flags are used to indicate that the slice data is to be updated.
227 option is also given,
229 will enter a conversational mode.
230 In this mode, no changes will be written to disk unless you explicitly tell
236 utility will display each slice and ask whether you want to edit it.
239 will step through each field, show you the old value,
240 and ask you for a new one.
241 When you are done with the slice,
243 will display it and ask you whether it is correct.
244 It will then proceed to the next entry.
250 fields correct is tricky, so by default,
251 they will be calculated for you;
252 you can specify them if you choose to though.
254 After all the slices are processed,
255 you are given the option to change the
258 Finally, when all the new data for sector 0 has been accumulated,
259 you are asked to confirm whether you really want to rewrite it.
261 The difference between the
268 flag edits (updates) the existing slice parameters
273 them (old values will be ignored);
274 if you edit the first slice,
276 will also set it up to use the whole disk for
280 The automatic calculation of starting cylinder etc.\& uses
281 a set of figures that represent what the BIOS thinks the
282 geometry of the drive is.
283 These figures are taken from the in-core disklabel by default,
286 initially gives you an opportunity to change them.
287 This allows you to create a bootblock that can work with drives
288 that use geometry translation under the BIOS.
290 If you hand craft your disk layout,
291 please make sure that the
293 slice starts on a cylinder boundary.
295 Editing an existing slice will most likely result in the loss of
296 all data in that slice.
300 interactively once or twice to see how it works.
301 This is completely safe as long as you answer the last question
303 There are subtleties that
305 detects that are not fully explained in this manual page.
306 .Sh CONFIGURATION FILE
309 option is given, a disk's slice table can be written using values
312 The syntax of this file is very simple;
313 each line is either a comment or a specification, as follows:
314 .Bl -tag -width indent
315 .It Ic # Ar comment ...
316 Lines beginning with a
318 are comments and are ignored.
319 .It Ic g Ar spec1 spec2 spec3
320 Set the BIOS geometry used in slice calculations.
322 three values specified, with a letter preceding each number:
323 .Bl -tag -width indent
325 Set the number of cylinders to
328 Set the number of heads to
331 Set the number of sectors/track to
335 These specs can occur in any order, as the leading letter determines
336 which value is which; however, all three must be specified.
338 This line must occur before any lines that specify slice
341 It is an error if the following is not true:
342 .Bd -literal -offset indent
343 1 <= number of cylinders
344 1 <= number of heads <= 256
345 1 <= number of sectors/track < 64
348 The number of cylinders should be less than or equal to 1024, but this
349 is not enforced, although a warning will be printed.
354 file system) must lie completely within the
355 first 1024 cylinders; if this is not true, booting may fail.
356 Non-bootable slices do not have this restriction.
358 Example (all of these are equivalent), for a disk with 1019 cylinders,
359 39 heads, and 63 sectors:
360 .Bd -literal -offset indent
365 .It Ic p Ar slice type start length
366 Set the slice given by
389 measurement respectively.
394 it is set to the value of the previous partition end.
399 the partition end is set to the end of the disk.
401 Only those slices explicitly mentioned by these lines are modified;
402 any slice not referenced by a
404 line will not be modified.
405 However, if an invalid slice table is present, or the
407 option is specified, all existing slice entries will be cleared
408 (marked as unused), and these
410 lines will have to be used to
411 explicitly set slice information.
412 If multiple slices need to be
415 lines must be specified; one for each slice.
417 These slice lines must occur after any geometry specification lines,
425 Specifying a slice type of zero is
426 the same as clearing the slice and marking it as unused; however,
427 dummy values (such as
429 must still be specified for
434 Note: the start offset will be rounded upwards to a head boundary if
435 necessary, and the end offset will be rounded downwards to a cylinder
436 boundary if necessary.
438 Example: to clear slice 4 and mark it as unused:
442 Example: to set slice 1 to a
444 slice, starting at sector 1
445 for 2503871 sectors (note: these numbers will be rounded upwards and
446 downwards to correspond to head and cylinder boundaries):
448 .Dl "p 1 165 1 2503871"
450 Example: to set slices 1, 2 and 4 to
452 slices, the first being 2 Gigabytes, the second being 10 Gigabytes and the
453 forth being the remainder of the disk (again, numbers will be rounded
464 Can occur anywhere in the config file, but only
467 Example: to make slice 1 the active slice:
472 .Bl -tag -width ".Pa /boot/mbr" -compact
474 The default boot code.
482 The default boot code will not necessarily handle all slice types
483 correctly, in particular those introduced since
487 The entire utility should be made more user-friendly.
491 do not understand the difference between
495 causing difficulty to adjust.
497 You cannot use this command to completely dedicate a disk to
501 command must be used for this.