1SFDISK(8) Linux Programmer's Manual SFDISK(8)
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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 List Sizes
23 sfdisk -s partition gives the size of partition in blocks. This may be
24 useful in connection with programs like mkswap or so. Here partition is
25 usually something like /dev/hda1 or /dev/sdb12, but may also be an
26 entire disk, like /dev/xda.
27 % sfdisk -s /dev/hda9
28 81599
29 %
30 If the partition argument is omitted, sfdisk will list the sizes of all
31 disks, and the total:
32 % sfdisk -s
33 /dev/hda: 208896
34 /dev/hdb: 1025136
35 /dev/hdc: 1031063
36 /dev/sda: 8877895
37 /dev/sdb: 1758927
38 total: 12901917 blocks
39 %
40 List Partitions
43 The second type of invocation: sfdisk -l [options] device will list the
44 partitions on this device. If the device argument is omitted, the par‐
45 titions on all hard disks are listed.
46 % sfdisk -l /dev/hdc
47 Disk /dev/hdc: 16 heads, 63 sectors, 2045 cylinders
49 Units = cylinders of 516096 bytes, blocks of 1024 bytes, counting from 0
50 Device Boot Start End #cyls #blocks Id System
52 /dev/hdc1 0+ 406 407- 205096+ 83 Linux native
53 /dev/hdc2 407 813 407 205128 83 Linux native
54 /dev/hdc3 814 2044 1231 620424 83 Linux native
55 /dev/hdc4 0 - 0 0 0 Empty
56 %
57 The trailing - and + signs indicate that rounding has taken place, and
58 that the actual value is slightly less (more). To see the exact val‐
59 ues, ask for a listing with sectors as unit.
60 Check partitions
63 The third type of invocation: sfdisk -V device will apply various con‐
64 sistency checks to the partition tables on device. It prints `OK' or
65 complains. The -V option can be used together with -l. In a shell
66 script one might use sfdisk -V -q device which only returns a status.
67 Create partitions
70 The fourth type of invocation: sfdisk device will cause sfdisk to read
71 the specification for the desired partitioning of device from its stan‐
72 dard input, and then to change the partition tables on that disk. Thus,
73 it is possible to use sfdisk from a shell script. When sfdisk deter‐
74 mines that its standard input is a terminal, it will be conversational;
75 otherwise it will abort on any error.
76 BE EXTREMELY CAREFUL - ONE TYPING MISTAKE AND ALL YOUR DATA IS LOST
78 As a precaution, one can save the sectors changed by sfdisk:
80 % sfdisk /dev/hdd -O hdd-partition-sectors.save
81 ...
82 %
83 Then, if you discover that you did something stupid before anything
85 else has been written to disk, it may be possible to recover the old
86 situation with
87 % sfdisk /dev/hdd -I hdd-partition-sectors.save
88 %
89 (This is not the same as saving the old partition table: a readable
91 version of the old partition table can be saved using the -d option.
92 However, if you create logical partitions, the sectors describing them
93 are located somewhere on disk, possibly on sectors that were not part
94 of the partition table before. Thus, the information the -O option
95 saves is not a binary version of the output of -d.)
96 There are many options.
98
101 -v or --version
102 Print version number of sfdisk and exit immediately.
103 -? or --help
105 Print a usage message and exit immediately.
106 -T or --list-types
108 Print the recognized types (system Id's).
109 -s or --show-size
111 List the size of a partition.
112 -g or --show-geometry
114 List the kernel's idea of the geometry of the indicated disk(s).
115 -G or --show-pt-geometry
117 List the geometry of the indicated disks guessed by looking at
118 the partition table.
119 -l or --list
121 List the partitions of a device.
122 -d Dump the partitions of a device in a format useful as input to
124 sfdisk. For example,
125 % sfdisk -d /dev/hda > hda.out
126 % sfdisk /dev/hda < hda.out
127 will correct the bad last extended partition that the OS/2 fdisk
128 creates.
129 -V or --verify
131 Test whether partitions seem correct. (See above.)
132 -i or --increment
134 Number cylinders etc. starting from 1 instead of 0.
135 -N number
137 Change only the single partition indicated. For example:
138 % sfdisk /dev/hdb -N5
139 ,,,*
140 %
141 will make the fifth partition on /dev/hdb bootable (`active')
142 and change nothing else. (Probably this fifth partition is
143 called /dev/hdb5, but you are free to call it something else,
144 like `/my_equipment/disks/2/5' or so).
145 -Anumber
147 Make the indicated partition(s) active, and all others inactive.
148 -c or --id number [Id]
150 If no Id argument given: print the partition Id of the indicated
151 partition. If an Id argument is present: change the type (Id) of
152 the indicated partition to the given value. This option has the
153 two very long forms --print-id and --change-id. For example:
154 % sfdisk --print-id /dev/hdb 5
155 6
156 % sfdisk --change-id /dev/hdb 5 83
157 OK
158 first reports that /dev/hdb5 has Id 6, and then changes that
159 into 83.
160 -uS or -uB or -uC or -uM
162 Accept or report in units of sectors (blocks, cylinders,
163 megabytes, respectively). The default is cylinders, at least
164 when the geometry is known.
165 -x or --show-extended
167 Also list non-primary extended partitions on output, and expect
168 descriptors for them on input.
169 -C cylinders
171 Specify the number of cylinders, possibly overriding what the
172 kernel thinks.
173 -H heads
175 Specify the number of heads, possibly overriding what the kernel
176 thinks.
177 -S sectors
179 Specify the number of sectors, possibly overriding what the ker‐
180 nel thinks.
181 -f or --force
183 Do what I say, even if it is stupid.
184 -q or --quiet
186 Suppress warning messages.
187 -L or --Linux
189 Do not complain about things irrelevant for Linux.
190 -D or --DOS
192 For DOS-compatibility: waste a little space. (More precisely:
193 if a partition cannot contain sector 0, e.g. because that is the
194 MBR of the device, or contains the partition table of an
195 extended partition, then sfdisk would make it start the next
196 sector. However, when this option is given it skips to the start
197 of the next track, wasting for example 33 sectors (in case of 34
198 sectors/track), just like certain versions of DOS do.) Certain
199 Disk Managers and boot loaders (such as OSBS, but not LILO or
200 the OS/2 Boot Manager) also live in this empty space, so maybe
201 you want this option if you use one.
202 -E or --DOS-extended
204 Take the starting sector numbers of "inner" extended partitions
205 to be relative to the starting cylinder boundary of the outer
206 one, (like some versions of DOS do) rather than to the starting
207 sector (like Linux does). (The fact that there is a difference
208 here means that one should always let extended partitions start
209 at cylinder boundaries if DOS and Linux should interpret the
210 partition table in the same way. Of course one can only know
211 where cylinder boundaries are when one knows what geometry DOS
212 will use for this disk.)
213 --IBM or --leave-last
215 Certain IBM diagnostic programs assume that they can use the
216 last cylinder on a disk for disk-testing purposes. If you think
217 you might ever run such programs, use this option to tell sfdisk
218 that it should not allocate the last cylinder. Sometimes the
219 last cylinder contains a bad sector table.
220 -n Go through all the motions, but do not actually write to disk.
222 -R Only execute the BLKRRPART ioctl (to make the kernel re-read the
224 partition table). This can be useful for checking in advance
225 that the final BLKRRPART will be successful, and also when you
226 changed the partition table `by hand' (e.g., using dd from a
227 backup). If the kernel complains (`device busy for revalidation
228 (usage = 2)') then something still uses the device, and you
229 still have to unmount some file system, or say swapoff to some
230 swap partition.
231 --no-reread
233 When starting a repartitioning of a disk, sfdisk checks that
234 this disk is not mounted, or in use as a swap device, and
235 refuses to continue if it is. This option suppresses the test.
236 (On the other hand, the -f option would force sfdisk to continue
237 even when this test fails.)
238 -O file
240 Just before writing the new partition, output the sectors that
241 are going to be overwritten to file (where hopefully file
242 resides on another disk, or on a floppy).
243 -I file
245 After destroying your filesystems with an unfortunate sfdisk
246 command, you would have been able to restore the old situation
247 if only you had preserved it using the -O flag.
248
251 Block 0 of a disk (the Master Boot Record) contains among other things
252 four partition descriptors. The partitions described here are called
253 primary partitions.
254 A partition descriptor has 6 fields:
256 struct partition {
257 unsigned char bootable; /* 0 or 0x80 */
258 hsc begin_hsc;
259 unsigned char id;
260 hsc end_hsc;
261 unsigned int starting_sector;
262 unsigned int nr_of_sectors;
263 }
264 The two hsc fields indicate head, sector and cylinder of the begin and
266 the end of the partition. Since each hsc field only takes 3 bytes, only
267 24 bits are available, which does not suffice for big disks (say >
268 8GB). In fact, due to the wasteful representation (that uses a byte for
269 the number of heads, which is typically 16), problems already start
270 with 0.5GB. However Linux does not use these fields, and problems can
271 arise only at boot time, before Linux has been started. For more
272 details, see the lilo documentation.
273 Each partition has a type, its `Id', and if this type is 5 or f
275 (`extended partition') the starting sector of the partition again con‐
276 tains 4 partition descriptors. MSDOS only uses the first two of these:
277 the first one an actual data partition, and the second one again an
278 extended partition (or empty). In this way one gets a chain of
279 extended partitions. Other operating systems have slightly different
280 conventions. Linux also accepts type 85 as equivalent to 5 and f -
281 this can be useful if one wants to have extended partitions under Linux
282 past the 1024 cylinder boundary, without DOS FDISK hanging. (If there
283 is no good reason, you should just use 5, which is understood by other
284 systems.)
285 Partitions that are not primary or extended are called logical. Often,
287 one cannot boot from logical partitions (because the process of finding
288 them is more involved than just looking at the MBR). Note that of an
289 extended partition only the Id and the start are used. There are vari‐
290 ous conventions about what to write in the other fields. One should not
291 try to use extended partitions for data storage or swap.
292
295 sfdisk reads lines of the form
296 <start> <size> <id> <bootable> <c,h,s> <c,h,s>
297 where each line fills one partition descriptor.
298 Fields are separated by whitespace, or comma or semicolon possibly fol‐
300 lowed by whitespace; initial and trailing whitespace is ignored. Num‐
301 bers can be octal, decimal or hexadecimal, decimal is default. When a
302 field is absent or empty, a default value is used.
303 The <c,h,s> parts can (and probably should) be omitted - sfdisk com‐
305 putes them from <start> and <size> and the disk geometry as given by
306 the kernel or specified using the -H, -S, -C flags.
307 Bootable is specified as [*|-], with as default not-bootable. (The
309 value of this field is irrelevant for Linux - when Linux runs it has
310 been booted already - but might play a role for certain boot loaders
311 and for other operating systems. For example, when there are several
312 primary DOS partitions, DOS assigns C: to the first among these that is
313 bootable.)
314 Id is given in hex, without the 0x prefix, or is [E|S|L|X], where L
316 (LINUX_NATIVE (83)) is the default, S is LINUX_SWAP (82), E is
317 EXTENDED_PARTITION (5), and X is LINUX_EXTENDED (85).
318 The default value of start is the first nonassigned sector/cylinder/...
320 The default value of size is as much as possible (until next partition
322 or end-of-disk).
323 However, for the four partitions inside an extended partition, the
325 defaults are: Linux partition, Extended partition, Empty, Empty.
326 But when the -N option (change a single partition only) is given, the
328 default for each field is its previous value.
329
332 The command
333 sfdisk /dev/hdc << EOF
334 0,407
335 ,407
336 ;
337 ;
338 EOF
339 will partition /dev/hdc just as indicated above.
340 The command
342 sfdisk /dev/hdb << EOF
343 ,3,L
344 ,60,L
345 ,19,S
346 ,,E
347 ,130,L
348 ,130,L
349 ,130,L
350 ,,L
351 EOF
352 will partition /dev/hdb into two Linux partitions of 3 and 60 cylin‐
353 ders, a swap space of 19 cylinders, and an extended partition covering
354 the rest. Inside the extended partition there are four Linux logical
355 partitions, three of 130 cylinders and one covering the rest.
356 With the -x option, the number of input lines must be a multiple of 4:
358 you have to list the two empty partitions that you never want using two
359 blank lines. Without the -x option, you give one line for the parti‐
360 tions inside a extended partition, instead of four, and terminate with
361 end-of-file (^D). (And sfdisk will assume that your input line repre‐
362 sents the first of four, that the second one is extended, and the 3rd
363 and 4th are empty.)
364
367 The DOS 6.x FORMAT command looks for some information in the first sec‐
368 tor of the data area of the partition, and treats this information as
369 more reliable than the information in the partition table. DOS FORMAT
370 expects DOS FDISK to clear the first 512 bytes of the data area of a
371 partition whenever a size change occurs. DOS FORMAT will look at this
372 extra information even if the /U flag is given -- we consider this a
373 bug in DOS FORMAT and DOS FDISK.
374 The bottom line is that if you use sfdisk to change the size of a DOS
376 partition table entry, then you must also use dd to zero the first 512
377 bytes of that partition before using DOS FORMAT to format the parti‐
378 tion. For example, if you were using sfdisk to make a DOS partition
379 table entry for /dev/hda1, then (after exiting sfdisk and rebooting
380 Linux so that the partition table information is valid) you would use
381 the command "dd if=/dev/zero of=/dev/hda1 bs=512 count=1" to zero the
382 first 512 bytes of the partition. BE EXTREMELY CAREFUL if you use the
383 dd command, since a small typo can make all of the data on your disk
384 useless.
385 For best results, you should always use an OS-specific partition table
387 program. For example, you should make DOS partitions with the DOS
388 FDISK program and Linux partitions with the Linux sfdisk program.
389
392 Stephen Tweedie reported (930515): `Most reports of superblock corrup‐
393 tion turn out to be due to bad partitioning, with one filesystem over‐
394 running the start of the next and corrupting its superblock. I have
395 even had this problem with the supposedly-reliable DRDOS. This was
396 quite possibly due to DRDOS-6.0's FDISK command. Unless I created a
397 blank track or cylinder between the DRDOS partition and the immediately
398 following one, DRDOS would happily stamp all over the start of the next
399 partition. Mind you, as long as I keep a little free disk space after
400 any DRDOS partition, I don't have any other problems with the two coex‐
401 isting on the one drive.'
402 A. V. Le Blanc writes in README.efdisk: `Dr. DOS 5.0 and 6.0 has been
404 reported to have problems cooperating with Linux, and with this version
405 of efdisk in particular. This efdisk sets the system type to hexadeci‐
406 mal 81. Dr. DOS seems to confuse this with hexadecimal 1, a DOS code.
407 If you use Dr. DOS, use the efdisk command 't' to change the system
408 code of any Linux partitions to some number less than hexadecimal 80; I
409 suggest 41 and 42 for the moment.'
410 A. V. Le Blanc writes in his README.fdisk: `DR-DOS 5.0 and 6.0 are
412 reported to have difficulties with partition ID codes of 80 or more.
413 The Linux `fdisk' used to set the system type of new partitions to
414 hexadecimal 81. DR-DOS seems to confuse this with hexadecimal 1, a DOS
415 code. The values 82 for swap and 83 for file systems should not cause
416 problems with DR-DOS. If they do, you may use the `fdisk' command `t'
417 to change the system code of any Linux partitions to some number less
418 than hexadecimal 80; I suggest 42 and 43 for the moment.'
419 In fact, it seems that only 4 bits are significant for the DRDOS FDISK,
421 so that for example 11 and 21 are listed as DOS 2.0. However, DRDOS
422 itself seems to use the full byte. I have not been able to reproduce
423 any corruption with DRDOS or its fdisk.
424
427 A corresponding interactive cfdisk (with curses interface) is still
428 lacking.
429 There are too many options.
431 There is no support for non-DOS partition types.
433
436 cfdisk(8), fdisk(8), mkfs(8), parted(8)
437Linux 1 September 1995 SFDISK(8)