1SFDISK(8) System Administration SFDISK(8)
2
6 sfdisk - partition table manipulator for Linux
7
9 sfdisk [options] device
10 sfdisk -s [partition]
11
13 sfdisk has four (main) uses: list the size of a partition, list the
14 partitions on a device, check the partitions on a device, and - very
15 dangerous - repartition a device.
16 sfdisk doesn't understand the GUID Partition Table (GPT) format and it
18 is not designed for large partitions. In these cases use the more
19 advanced GNU parted(8).
20 Note that sfdisk does not align partitions to block device I/O limits.
22 This functionality is provided by fdisk(8).
23 List sizes
26 sfdisk -s partition gives the size of partition in blocks. This may be
27 useful in connection with programs like mkswap(8). Here partition is
28 usually something like /dev/hda1 or /dev/sdb12, but may also be an
29 entire disk, like /dev/xda.
30 % sfdisk -s /dev/hda9
32 81599
33 If the partition argument is omitted, sfdisk will list the sizes of all
35 block devices, and the total:
36 % sfdisk -s
38 /dev/hda: 208896
39 /dev/hdb: 1025136
40 /dev/hdc: 1031063
41 /dev/sda: 8877895
42 /dev/sdb: 1758927
43 total: 12901917 blocks
44 List partitions
47 The second type of invocation: sfdisk -l device will list the parti‐
48 tions on the specified device. If the device argument is omitted, the
49 partitions on all block devices are listed.
50 % sfdisk -l /dev/hdc
52 Disk /dev/hdc: 16 heads, 63 sectors, 2045 cylinders
54 Units = cylinders of 516096 bytes, blocks of 1024 bytes, counting from 0
55 Device Boot Start End #cyls #blocks Id System
57 /dev/hdc1 0+ 406 407- 205096+ 83 Linux native
58 /dev/hdc2 407 813 407 205128 83 Linux native
59 /dev/hdc3 814 2044 1231 620424 83 Linux native
60 /dev/hdc4 0 - 0 0 0 Empty
61 The trailing - and + signs indicate that rounding has taken place, and
63 that the actual value is slightly less or more. To see the exact val‐
64 ues, ask for a listing with sectors as unit (-u S).
65 Check partitions
68 The third type of invocation: sfdisk -V device will apply various con‐
69 sistency checks to the partition tables on device. It prints `OK' or
70 complains. The -V option can be used together with -l. In a shell
71 script one might use sfdisk -V -q device which only returns a status.
72 Create partitions
75 The fourth type of invocation: sfdisk device will cause sfdisk to read
76 the specification for the desired partitioning of device from standard
77 input, and then to change the partition tables on that block device.
78 Thus it is possible to use sfdisk from a shell script. When sfdisk
79 determines that its standard input is a terminal, it will be conversa‐
80 tional; otherwise it will abort on any error.
81 BE EXTREMELY CAREFUL - ONE TYPING MISTAKE AND ALL YOUR DATA IS LOST
83 As a precaution, one can save the sectors changed by sfdisk:
85 % sfdisk /dev/hdd -O hdd-partition-sectors.save
87 ...
88 Then, if you discover that you did something stupid before anything
91 else has been written to the block device, it may be possible to
92 recover the old situation with:
93 % sfdisk /dev/hdd -I hdd-partition-sectors.save
95 (This is not the same as saving the old partition table: a readable
98 version of the old partition table can be saved using the -d option.
99 However, if you create logical partitions, the sectors describing them
100 are located somewhere on block device, possibly on sectors that were
101 not part of the partition table before. Thus, the information the -O
102 option saves is not a binary version of the output of -d.)
103 There are many options.
105
108 -v, --version
109 Print version number of sfdisk and exit immediately.
110 -h, --help
112 Print a usage message and exit immediately.
113 -T, --list-types
115 Print the recognized types (system Id's).
116 -s, --show-size
118 List the size of a partition.
119 -g, --show-geometry
121 List the kernel's idea of the geometry of the indicated block
122 device(s).
123 -G, --show-pt-geometry
125 List the geometry of the indicated block devices guessed by
126 looking at the partition table.
127 -l, --list
129 List the partitions of a device.
130 -d, --dump
132 Dump the partitions of a device in a format that is usable as
133 input to sfdisk. For example,
134 % sfdisk -d /dev/hda > hda.out
135 % sfdisk /dev/hda < hda.out
136 will correct the bad last extended partition that the OS/2 fdisk
137 creates.
138 -V, --verify
140 Test whether partitions seem correct. (See the third invocation
141 type above.)
142 -i, --increment
144 Number cylinders etc. starting from 1 instead of 0.
145 -N number
147 Change only the single partition indicated. For example:
148 % sfdisk /dev/hdb -N5
149 ,,,*
150 will make the fifth partition on /dev/hdb bootable (`active')
151 and change nothing else. (Probably this fifth partition is
152 called /dev/hdb5, but you are free to call it something else,
153 like `/my_equipment/disks/2/5' or so).
154 -A, --activate number
156 Make the indicated partition(s) active, and all others inactive.
157 -c, --id number [Id]
159 If no Id argument given: print the partition Id of the indicated
160 partition. If an Id argument is present: change the type (Id)
161 of the indicated partition to the given value. This option has
162 two longer forms, --print-id and --change-id. For example:
163 % sfdisk --print-id /dev/hdb 5
164 6
165 % sfdisk --change-id /dev/hdb 5 83
166 OK
167 first reports that /dev/hdb5 has Id 6, and then changes that
168 into 83.
169 -u, --unit letter
171 Interpret the input and show the output in the units specified
172 by letter. This letter can be one of S, C, B or M, meaning Sec‐
173 tors, Cylinders, Blocks and Megabytes, respectively. The
174 default is cylinders, at least when the geometry is known.
175 -x, --show-extended
177 Also list non-primary extended partitions on output, and expect
178 descriptors for them on input.
179 -C, --cylinders cylinders
181 Specify the number of cylinders, possibly overriding what the
182 kernel thinks.
183 -H, --heads heads
185 Specify the number of heads, possibly overriding what the kernel
186 thinks.
187 -S, --sectors sectors
189 Specify the number of sectors, possibly overriding what the ker‐
190 nel thinks.
191 -f, --force
193 Do what I say, even if it is stupid.
194 -q, --quiet
196 Suppress warning messages.
197 -L, --Linux
199 Do not complain about things irrelevant for Linux.
200 -D, --DOS
202 For DOS-compatibility: waste a little space. (More precisely:
203 if a partition cannot contain sector 0, e.g. because that is the
204 MBR of the device, or contains the partition table of an
205 extended partition, then sfdisk would make it start the next
206 sector. However, when this option is given it skips to the
207 start of the next track, wasting for example 33 sectors (in case
208 of 34 sectors/track), just like certain versions of DOS do.)
209 Certain Disk Managers and boot loaders (such as OSBS, but not
210 LILO or the OS/2 Boot Manager) also live in this empty space, so
211 maybe you want this option if you use one.
212 -E, --DOS-extended
214 Take the starting sector numbers of "inner" extended partitions
215 to be relative to the starting cylinder boundary of the outer
216 one (like some versions of DOS do), rather than relative to the
217 actual starting sector (like Linux does). (The fact that there
218 is a difference here means that one should always let extended
219 partitions start at cylinder boundaries if DOS and Linux should
220 interpret the partition table in the same way. Of course one
221 can only know where cylinder boundaries are when one knows what
222 geometry DOS will use for this block device.)
223 --IBM, --leave-last
225 Certain IBM diagnostic programs assume that they can use the
226 last cylinder on a device for disk-testing purposes. If you
227 think you might ever run such programs, use this option to tell
228 sfdisk that it should not allocate the last cylinder. Sometimes
229 the last cylinder contains a bad sector table.
230 -n Go through all the motions, but do not actually write to block
232 device.
233 -R, --re-read
235 Only execute the BLKRRPART ioctl (to make the kernel re-read the
236 partition table). This can be useful for checking in advance
237 that the final BLKRRPART will be successful, and also when you
238 changed the partition table `by hand' (e.g., using dd from a
239 backup). If the kernel complains (`device busy for revalidation
240 (usage = 2)') then something still uses the device, and you
241 still have to unmount some file system, or say swapoff to some
242 swap partition.
243 --no-reread
245 When starting a repartitioning of a block device, sfdisk checks
246 that this device is not mounted, or in use as a swap device, and
247 refuses to continue if it is. This option suppresses the test.
248 (On the other hand, the -f option would force sfdisk to continue
249 even when this test fails.)
250 --in-order
252 Caution, see warning section. To be documented.
253 --not-in-order
255 Caution, see warning section. To be documented.
256 --inside-outer
258 Caution, see warning section. Chaining order.
259 --not-inside-outer
261 Caution, see warning section. Chaining order.
262 --nested
264 Caution, see warning section. Every partition is contained in
265 the surrounding partitions and is disjoint from all others.
266 --chained
268 Caution, see warning section. Every data partition is contained
269 in the surrounding partitions and disjoint from all others, but
270 extended partitions may lie outside (insofar as allowed by
271 all_logicals_inside_outermost_extended).
272 --onesector
274 Caution, see warning section. All data partitions are mutually
275 disjoint; extended partitions each use one sector only (except
276 perhaps for the outermost one).
277 -O file
279 Just before writing the new partition, output the sectors that
280 are going to be overwritten to file (where hopefully file
281 resides on another block device, or on a floppy).
282 -I file
284 After destroying your filesystems with an unfortunate sfdisk
285 command, you would have been able to restore the old situation
286 if only you had preserved it using the -O flag.
287
290 Block 0 of a block device (the Master Boot Record) contains among other
291 things four partition descriptors. The partitions described here are
292 called primary partitions.
293 A partition descriptor has 6 fields:
295 struct partition {
296 unsigned char bootable; /* 0 or 0x80 */
297 hsc begin_hsc;
298 unsigned char id;
299 hsc end_hsc;
300 unsigned int starting_sector;
301 unsigned int nr_of_sectors;
302 }
303 The two hsc fields indicate head, sector and cylinder of the begin and
305 the end of the partition. Since each hsc field only takes 3 bytes, only
306 24 bits are available, which does not suffice for big block devices
307 (say > 8GB). In fact, due to the wasteful representation (that uses a
308 byte for the number of heads, which is typically 16), problems already
309 start with 0.5GB. However Linux does not use these fields, and prob‐
310 lems can arise only at boot time, before Linux has been started. For
311 more details, see the lilo documentation.
312 Each partition has a type, its `Id', and if this type is 5 or f
314 (`extended partition') the starting sector of the partition again con‐
315 tains 4 partition descriptors. MSDOS only uses the first two of these:
316 the first one an actual data partition, and the second one again an
317 extended partition (or empty). In this way one gets a chain of
318 extended partitions. Other operating systems have slightly different
319 conventions. Linux also accepts type 85 as equivalent to 5 and f -
320 this can be useful if one wants to have extended partitions under Linux
321 past the 1024 cylinder boundary, without DOS FDISK hanging. (If there
322 is no good reason, you should just use 5, which is understood by other
323 systems.)
324 Partitions that are not primary or extended are called logical. Often,
326 one cannot boot from logical partitions (because the process of finding
327 them is more involved than just looking at the MBR). Note that of an
328 extended partition only the Id and the start are used. There are vari‐
329 ous conventions about what to write in the other fields. One should not
330 try to use extended partitions for data storage or swap.
331
334 sfdisk reads lines of the form
335 <start> <size> <id> <bootable> <c,h,s> <c,h,s>
336 where each line fills one partition descriptor.
337 Fields are separated by whitespace, or comma or semicolon possibly fol‐
339 lowed by whitespace; initial and trailing whitespace is ignored. Num‐
340 bers can be octal, decimal or hexadecimal, decimal is default. When a
341 field is absent or empty, a default value is used.
342 The <c,h,s> parts can (and probably should) be omitted - sfdisk com‐
344 putes them from <start> and <size> and the block device geometry as
345 given by the kernel or specified using the -H, -S, -C flags.
346 Bootable is specified as [*|-], with as default not-bootable. (The
348 value of this field is irrelevant for Linux - when Linux runs it has
349 been booted already - but might play a role for certain boot loaders
350 and for other operating systems. For example, when there are several
351 primary DOS partitions, DOS assigns C: to the first among these that is
352 bootable.)
353 Id is given in hex, without the 0x prefix, or is [E|S|L|X], where L
355 (LINUX_NATIVE (83)) is the default, S is LINUX_SWAP (82), E is
356 EXTENDED_PARTITION (5), and X is LINUX_EXTENDED (85).
357 The default value of start is the first nonassigned sector/cylinder/...
359 The default value of size is as much as possible (until next partition
361 or end-of-device).
362 However, for the four partitions inside an extended partition, the
364 defaults are: Linux partition, Extended partition, Empty, Empty.
365 But when the -N option (change a single partition only) is given, the
367 default for each field is its previous value.
368 A '+' can be specified instead of a number for size, which means as
370 much as possible. This is useful with the -N option.
371
373 The command
374 sfdisk /dev/hdc << EOF
375 0,407
376 ,407
377 ;
378 ;
379 EOF
380 will partition /dev/hdc just as indicated above.
381 The command
383 sfdisk /dev/hdb << EOF
384 ,3,L
385 ,60,L
386 ,19,S
387 ,,E
388 ,130,L
389 ,130,L
390 ,130,L
391 ,,L
392 EOF
393 will partition /dev/hdb into two Linux partitions of 3 and 60 cylin‐
394 ders, a swap space of 19 cylinders, and an extended partition covering
395 the rest. Inside the extended partition there are four Linux logical
396 partitions, three of 130 cylinders and one covering the rest.
397 With the -x option, the number of input lines must be a multiple of 4:
399 you have to list the two empty partitions that you never want using two
400 blank lines. Without the -x option, you give one line for the parti‐
401 tions inside a extended partition, instead of four, and terminate with
402 end-of-file (^D). (And sfdisk will assume that your input line repre‐
403 sents the first of four, that the second one is extended, and the 3rd
404 and 4th are empty.)
405
407 The options marked with caution in the manual page are dangerous. For
408 example not all functionality is completely implemented, which can be a
409 reason for unexpected results.
410
412 The DOS 6.x FORMAT command looks for some information in the first sec‐
413 tor of the data area of the partition, and treats this information as
414 more reliable than the information in the partition table. DOS FORMAT
415 expects DOS FDISK to clear the first 512 bytes of the data area of a
416 partition whenever a size change occurs. DOS FORMAT will look at this
417 extra information even if the /U flag is given -- we consider this a
418 bug in DOS FORMAT and DOS FDISK.
419 The bottom line is that if you use sfdisk to change the size of a DOS
421 partition table entry, then you must also use dd to zero the first 512
422 bytes of that partition before using DOS FORMAT to format the parti‐
423 tion. For example, if you were using sfdisk to make a DOS partition
424 table entry for /dev/hda1, then (after exiting sfdisk and rebooting
425 Linux so that the partition table information is valid) you would use
426 the command "dd if=/dev/zero of=/dev/hda1 bs=512 count=1" to zero the
427 first 512 bytes of the partition. BE EXTREMELY CAREFUL if you use the
428 dd command, since a small typo can make all of the data on your block
429 device useless.
430 For best results, you should always use an OS-specific partition table
432 program. For example, you should make DOS partitions with the DOS
433 FDISK program and Linux partitions with the Linux sfdisk program.
434
437 Stephen Tweedie reported (930515): `Most reports of superblock corrup‐
438 tion turn out to be due to bad partitioning, with one filesystem over‐
439 running the start of the next and corrupting its superblock. I have
440 even had this problem with the supposedly-reliable DRDOS. This was
441 quite possibly due to DRDOS-6.0's FDISK command. Unless I created a
442 blank track or cylinder between the DRDOS partition and the immediately
443 following one, DRDOS would happily stamp all over the start of the next
444 partition. Mind you, as long as I keep a little free device space
445 after any DRDOS partition, I don't have any other problems with the two
446 coexisting on the one drive.'
447 A. V. Le Blanc writes in README.efdisk: `Dr. DOS 5.0 and 6.0 has been
449 reported to have problems cooperating with Linux, and with this version
450 of efdisk in particular. This efdisk sets the system type to hexadeci‐
451 mal 81. Dr. DOS seems to confuse this with hexadecimal 1, a DOS code.
452 If you use Dr. DOS, use the efdisk command 't' to change the system
453 code of any Linux partitions to some number less than hexadecimal 80; I
454 suggest 41 and 42 for the moment.'
455 A. V. Le Blanc writes in his README.fdisk: `DR-DOS 5.0 and 6.0 are
457 reported to have difficulties with partition ID codes of 80 or more.
458 The Linux `fdisk' used to set the system type of new partitions to
459 hexadecimal 81. DR-DOS seems to confuse this with hexadecimal 1, a DOS
460 code. The values 82 for swap and 83 for file systems should not cause
461 problems with DR-DOS. If they do, you may use the `fdisk' command `t'
462 to change the system code of any Linux partitions to some number less
463 than hexadecimal 80; I suggest 42 and 43 for the moment.'
464 In fact, it seems that only 4 bits are significant for the DRDOS FDISK,
466 so that for example 11 and 21 are listed as DOS 2.0. However, DRDOS
467 itself seems to use the full byte. I have not been able to reproduce
468 any corruption with DRDOS or its fdisk.
469
472 There are too many options.
473 There is no support for non-DOS partition types.
475
478 cfdisk(8), fdisk(8), mkfs(8), parted(8), partprobe(8), kpartx(8)
479
481 The sfdisk command is part of the util-linux package and is available
482 from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
483util-linux August 2011 SFDISK(8)