1SFDISK(8) Linux Programmer's Manual 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 GUID Partition Table (GPT) and it is not
18 designed for large partitions. In particular case use more advanced GNU
19 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) or so. Here partition
28 is usually something like /dev/hda1 or /dev/sdb12, but may also be an
29 entire disk, like /dev/xda.
30 % sfdisk -s /dev/hda9
31 81599
32 %
33 If the partition argument is omitted, sfdisk will list the sizes of all
34 block devices, and the total:
35 % sfdisk -s
36 /dev/hda: 208896
37 /dev/hdb: 1025136
38 /dev/hdc: 1031063
39 /dev/sda: 8877895
40 /dev/sdb: 1758927
41 total: 12901917 blocks
42 %
43 List Partitions
46 The second type of invocation: sfdisk -l [options] device will list the
47 partitions on this device. If the device argument is omitted, the par‐
48 titions on all hard block devices are listed.
49 % sfdisk -l /dev/hdc
50 Disk /dev/hdc: 16 heads, 63 sectors, 2045 cylinders
52 Units = cylinders of 516096 bytes, blocks of 1024 bytes, counting from 0
53 Device Boot Start End #cyls #blocks Id System
55 /dev/hdc1 0+ 406 407- 205096+ 83 Linux native
56 /dev/hdc2 407 813 407 205128 83 Linux native
57 /dev/hdc3 814 2044 1231 620424 83 Linux native
58 /dev/hdc4 0 - 0 0 0 Empty
59 %
60 The trailing - and + signs indicate that rounding has taken place, and
61 that the actual value is slightly less (more). To see the exact val‐
62 ues, ask for a listing with sectors as unit.
63 Check partitions
66 The third type of invocation: sfdisk -V device will apply various con‐
67 sistency checks to the partition tables on device. It prints `OK' or
68 complains. The -V option can be used together with -l. In a shell
69 script one might use sfdisk -V -q device which only returns a status.
70 Create partitions
73 The fourth type of invocation: sfdisk device will cause sfdisk to read
74 the specification for the desired partitioning of device from its stan‐
75 dard input, and then to change the partition tables on that block
76 device. Thus, it is possible to use sfdisk from a shell script. When
77 sfdisk determines that its standard input is a terminal, it will be
78 conversational; otherwise it will abort on any error.
79 BE EXTREMELY CAREFUL - ONE TYPING MISTAKE AND ALL YOUR DATA IS LOST
81 As a precaution, one can save the sectors changed by sfdisk:
83 % sfdisk /dev/hdd -O hdd-partition-sectors.save
84 ...
85 %
86 Then, if you discover that you did something stupid before anything
88 else has been written to block device, it may be possible to recover
89 the old situation with
90 % sfdisk /dev/hdd -I hdd-partition-sectors.save
91 %
92 (This is not the same as saving the old partition table: a readable
94 version of the old partition table can be saved using the -d option.
95 However, if you create logical partitions, the sectors describing them
96 are located somewhere on block device possibly on sectors that were not
97 part of the partition table before. Thus, the information the -O option
98 saves is not a binary version of the output of -d.)
99 There are many options.
101
104 -v or --version
105 Print version number of sfdisk and exit immediately.
106 -? or --help
108 Print a usage message and exit immediately.
109 -T or --list-types
111 Print the recognized types (system Id's).
112 -s or --show-size
114 List the size of a partition.
115 -g or --show-geometry
117 List the kernel's idea of the geometry of the indicated block
118 device(s)
119 -G or --show-pt-geometry
121 List the geometry of the indicated block devices guessed by
122 looking at the partition table.
123 -l or --list
125 List the partitions of a device.
126 -d Dump the partitions of a device in a format useful as input to
128 sfdisk. For example,
129 % sfdisk -d /dev/hda > hda.out
130 % sfdisk /dev/hda < hda.out
131 will correct the bad last extended partition that the OS/2 fdisk
132 creates.
133 -V or --verify
135 Test whether partitions seem correct. (See above.)
136 -i or --increment
138 Number cylinders etc. starting from 1 instead of 0.
139 -N number
141 Change only the single partition indicated. For example:
142 % sfdisk /dev/hdb -N5
143 ,,,*
144 %
145 will make the fifth partition on /dev/hdb bootable (`active')
146 and change nothing else. (Probably this fifth partition is
147 called /dev/hdb5, but you are free to call it something else,
148 like `/my_equipment/disks/2/5' or so).
149 -A number
151 Make the indicated partition(s) active, and all others inactive.
152 -c or --id number [Id]
154 If no Id argument given: print the partition Id of the indicated
155 partition. If an Id argument is present: change the type (Id) of
156 the indicated partition to the given value. This option has the
157 two very long forms --print-id and --change-id. For example:
158 % sfdisk --print-id /dev/hdb 5
159 6
160 % sfdisk --change-id /dev/hdb 5 83
161 OK
162 first reports that /dev/hdb5 has Id 6, and then changes that
163 into 83.
164 -uS or -uB or -uC or -uM
166 Accept or report in units of sectors (blocks, cylinders,
167 megabytes, respectively). The default is cylinders, at least
168 when the geometry is known.
169 -x or --show-extended
171 Also list non-primary extended partitions on output, and expect
172 descriptors for them on input.
173 -C cylinders
175 Specify the number of cylinders, possibly overriding what the
176 kernel thinks.
177 -H heads
179 Specify the number of heads, possibly overriding what the kernel
180 thinks.
181 -S sectors
183 Specify the number of sectors, possibly overriding what the ker‐
184 nel thinks.
185 -f or --force
187 Do what I say, even if it is stupid.
188 -q or --quiet
190 Suppress warning messages.
191 -L or --Linux
193 Do not complain about things irrelevant for Linux.
194 -D or --DOS
196 For DOS-compatibility: waste a little space. (More precisely:
197 if a partition cannot contain sector 0, e.g. because that is the
198 MBR of the device, or contains the partition table of an
199 extended partition, then sfdisk would make it start the next
200 sector. However, when this option is given it skips to the start
201 of the next track, wasting for example 33 sectors (in case of 34
202 sectors/track), just like certain versions of DOS do.) Certain
203 Disk Managers and boot loaders (such as OSBS, but not LILO or
204 the OS/2 Boot Manager) also live in this empty space, so maybe
205 you want this option if you use one.
206 -E or --DOS-extended
208 Take the starting sector numbers of "inner" extended partitions
209 to be relative to the starting cylinder boundary of the outer
210 one, (like some versions of DOS do) rather than to the starting
211 sector (like Linux does). (The fact that there is a difference
212 here means that one should always let extended partitions start
213 at cylinder boundaries if DOS and Linux should interpret the
214 partition table in the same way. Of course one can only know
215 where cylinder boundaries are when one knows what geometry DOS
216 will use for this block device.)
217 --IBM or --leave-last
219 Certain IBM diagnostic programs assume that they can use the
220 last cylinder on a block device for disk-testing purposes. If
221 you think you might ever run such programs, use this option to
222 tell sfdisk that it should not allocate the last cylinder.
223 Sometimes the last cylinder contains a bad sector table.
224 -n Go through all the motions, but do not actually write to block
226 device.
227 -R Only execute the BLKRRPART ioctl (to make the kernel re-read the
229 partition table). This can be useful for checking in advance
230 that the final BLKRRPART will be successful, and also when you
231 changed the partition table `by hand' (e.g., using dd from a
232 backup). If the kernel complains (`device busy for revalidation
233 (usage = 2)') then something still uses the device, and you
234 still have to unmount some file system, or say swapoff to some
235 swap partition.
236 --no-reread
238 When starting a repartitioning of a block device, sfdisk checks
239 that this device is not mounted, or in use as a swap device, and
240 refuses to continue if it is. This option suppresses the test.
241 (On the other hand, the -f option would force sfdisk to continue
242 even when this test fails.)
243 -O file
245 Just before writing the new partition, output the sectors that
246 are going to be overwritten to file (where hopefully file
247 resides on another block device, or on a floppy).
248 -I file
250 After destroying your filesystems with an unfortunate sfdisk
251 command, you would have been able to restore the old situation
252 if only you had preserved it using the -O flag.
253
256 Block 0 of a block device (the Master Boot Record) contains among other
257 things four partition descriptors. The partitions described here are
258 called primary partitions.
259 A partition descriptor has 6 fields:
261 struct partition {
262 unsigned char bootable; /* 0 or 0x80 */
263 hsc begin_hsc;
264 unsigned char id;
265 hsc end_hsc;
266 unsigned int starting_sector;
267 unsigned int nr_of_sectors;
268 }
269 The two hsc fields indicate head, sector and cylinder of the begin and
271 the end of the partition. Since each hsc field only takes 3 bytes, only
272 24 bits are available, which does not suffice for big block devices
273 (say > 8GB). In fact, due to the wasteful representation (that uses a
274 byte for the number of heads, which is typically 16), problems already
275 start with 0.5GB. However Linux does not use these fields, and prob‐
276 lems can arise only at boot time, before Linux has been started. For
277 more details, see the lilo documentation.
278 Each partition has a type, its `Id', and if this type is 5 or f
280 (`extended partition') the starting sector of the partition again con‐
281 tains 4 partition descriptors. MSDOS only uses the first two of these:
282 the first one an actual data partition, and the second one again an
283 extended partition (or empty). In this way one gets a chain of
284 extended partitions. Other operating systems have slightly different
285 conventions. Linux also accepts type 85 as equivalent to 5 and f -
286 this can be useful if one wants to have extended partitions under Linux
287 past the 1024 cylinder boundary, without DOS FDISK hanging. (If there
288 is no good reason, you should just use 5, which is understood by other
289 systems.)
290 Partitions that are not primary or extended are called logical. Often,
292 one cannot boot from logical partitions (because the process of finding
293 them is more involved than just looking at the MBR). Note that of an
294 extended partition only the Id and the start are used. There are vari‐
295 ous conventions about what to write in the other fields. One should not
296 try to use extended partitions for data storage or swap.
297
300 sfdisk reads lines of the form
301 <start> <size> <id> <bootable> <c,h,s> <c,h,s>
302 where each line fills one partition descriptor.
303 Fields are separated by whitespace, or comma or semicolon possibly fol‐
305 lowed by whitespace; initial and trailing whitespace is ignored. Num‐
306 bers can be octal, decimal or hexadecimal, decimal is default. When a
307 field is absent or empty, a default value is used.
308 The <c,h,s> parts can (and probably should) be omitted - sfdisk com‐
310 putes them from <start> and <size> and the block device geometry as
311 given by the kernel or specified using the -H, -S, -C flags.
312 Bootable is specified as [*|-], with as default not-bootable. (The
314 value of this field is irrelevant for Linux - when Linux runs it has
315 been booted already - but might play a role for certain boot loaders
316 and for other operating systems. For example, when there are several
317 primary DOS partitions, DOS assigns C: to the first among these that is
318 bootable.)
319 Id is given in hex, without the 0x prefix, or is [E|S|L|X], where L
321 (LINUX_NATIVE (83)) is the default, S is LINUX_SWAP (82), E is
322 EXTENDED_PARTITION (5), and X is LINUX_EXTENDED (85).
323 The default value of start is the first nonassigned sector/cylinder/...
325 The default value of size is as much as possible (until next partition
327 or end-of-device).
328 However, for the four partitions inside an extended partition, the
330 defaults are: Linux partition, Extended partition, Empty, Empty.
331 But when the -N option (change a single partition only) is given, the
333 default for each field is its previous value.
334
337 The command
338 sfdisk /dev/hdc << EOF
339 0,407
340 ,407
341 ;
342 ;
343 EOF
344 will partition /dev/hdc just as indicated above.
345 The command
347 sfdisk /dev/hdb << EOF
348 ,3,L
349 ,60,L
350 ,19,S
351 ,,E
352 ,130,L
353 ,130,L
354 ,130,L
355 ,,L
356 EOF
357 will partition /dev/hdb into two Linux partitions of 3 and 60 cylin‐
358 ders, a swap space of 19 cylinders, and an extended partition covering
359 the rest. Inside the extended partition there are four Linux logical
360 partitions, three of 130 cylinders and one covering the rest.
361 With the -x option, the number of input lines must be a multiple of 4:
363 you have to list the two empty partitions that you never want using two
364 blank lines. Without the -x option, you give one line for the parti‐
365 tions inside a extended partition, instead of four, and terminate with
366 end-of-file (^D). (And sfdisk will assume that your input line repre‐
367 sents the first of four, that the second one is extended, and the 3rd
368 and 4th are empty.)
369
372 The DOS 6.x FORMAT command looks for some information in the first sec‐
373 tor of the data area of the partition, and treats this information as
374 more reliable than the information in the partition table. DOS FORMAT
375 expects DOS FDISK to clear the first 512 bytes of the data area of a
376 partition whenever a size change occurs. DOS FORMAT will look at this
377 extra information even if the /U flag is given -- we consider this a
378 bug in DOS FORMAT and DOS FDISK.
379 The bottom line is that if you use sfdisk to change the size of a DOS
381 partition table entry, then you must also use dd to zero the first 512
382 bytes of that partition before using DOS FORMAT to format the parti‐
383 tion. For example, if you were using sfdisk to make a DOS partition
384 table entry for /dev/hda1, then (after exiting sfdisk and rebooting
385 Linux so that the partition table information is valid) you would use
386 the command "dd if=/dev/zero of=/dev/hda1 bs=512 count=1" to zero the
387 first 512 bytes of the partition. BE EXTREMELY CAREFUL if you use the
388 dd command, since a small typo can make all of the data on your block
389 device useless.
390 For best results, you should always use an OS-specific partition table
392 program. For example, you should make DOS partitions with the DOS
393 FDISK program and Linux partitions with the Linux sfdisk program.
394
397 Stephen Tweedie reported (930515): `Most reports of superblock corrup‐
398 tion turn out to be due to bad partitioning, with one filesystem over‐
399 running the start of the next and corrupting its superblock. I have
400 even had this problem with the supposedly-reliable DRDOS. This was
401 quite possibly due to DRDOS-6.0's FDISK command. Unless I created a
402 blank track or cylinder between the DRDOS partition and the immediately
403 following one, DRDOS would happily stamp all over the start of the next
404 partition. Mind you, as long as I keep a little free device space
405 after any DRDOS partition, I don't have any other problems with the two
406 coexisting on the one drive.'
407 A. V. Le Blanc writes in README.efdisk: `Dr. DOS 5.0 and 6.0 has been
409 reported to have problems cooperating with Linux, and with this version
410 of efdisk in particular. This efdisk sets the system type to hexadeci‐
411 mal 81. Dr. DOS seems to confuse this with hexadecimal 1, a DOS code.
412 If you use Dr. DOS, use the efdisk command 't' to change the system
413 code of any Linux partitions to some number less than hexadecimal 80; I
414 suggest 41 and 42 for the moment.'
415 A. V. Le Blanc writes in his README.fdisk: `DR-DOS 5.0 and 6.0 are
417 reported to have difficulties with partition ID codes of 80 or more.
418 The Linux `fdisk' used to set the system type of new partitions to
419 hexadecimal 81. DR-DOS seems to confuse this with hexadecimal 1, a DOS
420 code. The values 82 for swap and 83 for file systems should not cause
421 problems with DR-DOS. If they do, you may use the `fdisk' command `t'
422 to change the system code of any Linux partitions to some number less
423 than hexadecimal 80; I suggest 42 and 43 for the moment.'
424 In fact, it seems that only 4 bits are significant for the DRDOS FDISK,
426 so that for example 11 and 21 are listed as DOS 2.0. However, DRDOS
427 itself seems to use the full byte. I have not been able to reproduce
428 any corruption with DRDOS or its fdisk.
429
432 There are too many options.
433 There is no support for non-DOS partition types.
435
438 cfdisk(8), fdisk(8), mkfs(8), parted(8), partprobe(8), kpartx(8)
439
441 The sfdisk command is part of the util-linux-ng package and is avail‐
442 able from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.
443Linux 1 September 1995 SFDISK(8)