1CFDISK(8) System Administration CFDISK(8)
2
6 cfdisk - display or manipulate disk partition table
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9 cfdisk [-agvz] [-c cylinders] [-h heads] [-s sectors-per-track] [-P
10 opt] [device]
11
13 cfdisk is a curses-based program for partitioning any hard disk drive.
14 Typical values of the device argument are:
15 /dev/hda [default]
17 /dev/hdb
18 /dev/sda
19 /dev/sdb
20 /dev/sdc
21 /dev/sdd
22 Note that cfdisk does not align partitions to block device I/O limits.
24 This functionality is provided by fdisk(8).
25 In order to write the partition table cfdisk needs something called the
27 `geometry' of the disk: the number of `heads' and the number of `sec‐
28 tors per track'. Linux does not use any geometry, so if the disk will
29 not be accessed by other operating systems, you can safely accept the
30 defaults that cfdisk chooses for you. The geometry used by cfdisk is
31 found as follows. First the partition table is examined, to see what
32 geometry was used by the previous program that changed it. If the par‐
33 tition table is empty, or contains garbage, or does not point at a con‐
34 sistent geometry, the kernel is asked for advice. If nothing works 255
35 heads and 63 sectors/track is assumed. The geometry can be overridden
36 on the command line or by use of the `g' command. When partitioning an
37 empty large modern disk, picking 255 heads and 63 sectors/track is
38 always a good idea. There is no need to set the number of cylinders,
39 since cfdisk knows the disk size.
40 Next, cfdisk tries to read the current partition table from the disk
42 drive. If it is unable to figure out the partition table, an error is
43 displayed and the program will exit. This might also be caused by
44 incorrect geometry information, and can be overridden on the command
45 line. Another way around this problem is with the -z option. This
46 will ignore the partition table on the disk.
47 The main display is composed of four sections, from top to bottom: the
49 header, the partitions, the command line and a warning line. The
50 header contains the program name and version number followed by the
51 disk drive and its geometry. The partitions section always displays
52 the current partition table. The command line is the place where com‐
53 mands and text are entered. The available commands are usually dis‐
54 played in brackets. The warning line is usually empty except when
55 there is important information to be displayed. The current partition
56 is highlighted with reverse video (or an arrow if the -a option is
57 given). All partition specific commands apply to the current parti‐
58 tion.
59 The format of the partition table in the partitions section is, from
61 left to right: Name, Flags, Partition Type, Filesystem Type and Size.
62 The name is the partition device name. The flags can be Boot, which
63 designates a bootable partition or NC, which stands for "Not Compatible
64 with DOS or OS/2". DOS, OS/2 and possibly other operating systems
65 require the first sector of the first partition on the disk and all
66 logical partitions to begin on the second head. This wastes the second
67 through the last sector of the first track of the first head (the first
68 sector is taken by the partition table itself). cfdisk allows you to
69 recover these "lost" sectors with the maximize command (m). Note:
70 fdisk(8) and some early versions of DOS create all partitions with the
71 number of sectors already maximized. For more information, see the
72 maximize command below. The partition type can be one of Primary or
73 Logical. For unallocated space on the drive, the partition type can
74 also be Pri/Log, or empty (if the space is unusable). The filesystem
75 type section displays the name of the filesystem used on the partition,
76 if known. If it is unknown, then Unknown and the hex value of the
77 filesystem type are displayed. A special case occurs when there are
78 sections of the disk drive that cannot be used (because all of the pri‐
79 mary partitions are used). When this is detected, the filesystem type
80 is displayed as Unusable. The size field displays the size of the par‐
81 tition in megabytes (by default). It can also display the size in sec‐
82 tors and cylinders (see the change units command below). If an aster‐
83 isk (*) appears after the size, this means that the partition is not
84 aligned on cylinder boundaries.
85
87 The DOS 6.x FORMAT command looks for some information in the first sec‐
88 tor of the data area of the partition, and treats this information as
89 more reliable than the information in the partition table. DOS FORMAT
90 expects DOS FDISK to clear the first 512 bytes of the data area of a
91 partition whenever a size change occurs. DOS FORMAT will look at this
92 extra information even if the /U flag is given -- we consider this a
93 bug in DOS FORMAT and DOS FDISK.
94 The bottom line is that if you use cfdisk or fdisk to change the size
96 of a DOS partition table entry, then you must also use dd to zero the
97 first 512 bytes of that partition before using DOS FORMAT to format the
98 partition. For example, if you were using cfdisk to make a DOS parti‐
99 tion table entry for /dev/hda1, then (after exiting fdisk or cfdisk and
100 rebooting Linux so that the partition table information is valid) you
101 would use the command "dd if=/dev/zero of=/dev/hda1 bs=512 count=1" to
102 zero the first 512 bytes of the partition. Note:
103 BE EXTREMELY CAREFUL if you use the dd command, since a small typo can
105 make all of the data on your disk useless.
106 For best results, you should always use an OS-specific partition table
108 program. For example, you should make DOS partitions with the DOS
109 FDISK program and Linux partitions with the Linux fdisk or Linux cfdisk
110 program.
111
114 cfdisk commands can be entered by pressing the desired key (pressing
115 Enter after the command is not necessary). Here is a list of the
116 available commands:
117 b Toggle bootable flag of the current partition. This allows you
119 to select which primary partition is bootable on the drive.
120 d Delete the current partition. This will convert the current
122 partition into free space and merge it with any free space imme‐
123 diately surrounding the current partition. A partition already
124 marked as free space or marked as unusable cannot be deleted.
125 g Change the disk geometry (cylinders, heads, or sectors-per-
127 track). WARNING: This option should only be used by people who
128 know what they are doing. A command line option is also avail‐
129 able to change the disk geometry. While at the change disk
130 geometry command line, you can choose to change cylinders (c),
131 heads (h), and sectors per track (s). The default value will be
132 printed at the prompt which you can accept by simply pressing
133 the Enter key, or you can exit without changes by pressing the
134 ESC key. If you want to change the default value, simply enter
135 the desired value and press Enter. The altered disk parameter
136 values do not take effect until you return to the main menu (by
137 pressing Enter or ESC at the change disk geometry command line).
138 If you change the geometry such that the disk appears larger,
139 the extra sectors are added at the end of the disk as free
140 space. If the disk appears smaller, the partitions that are
141 beyond the new last sector are deleted and the last partition on
142 the drive (or the free space at the end of the drive) is made to
143 end at the new last sector.
144 h Print the help screen.
146 m Maximize disk usage of the current partition. This command will
148 recover the unused space between the partition table and the
149 beginning of the partition, but at the cost of making the parti‐
150 tion incompatible with DOS, OS/2 and possibly other operating
151 systems. This option will toggle between maximal disk usage and
152 DOS, OS/2, etc. compatible disk usage. The default when creat‐
153 ing a partition is to create DOS, OS/2, etc. compatible parti‐
154 tions.
155 n Create new partition from free space. If the partition type is
157 Primary or Logical, a partition of that type will be created,
158 but if the partition type is Pri/Log, you will be prompted for
159 the type you want to create. Be aware that (1) there are only
160 four slots available for primary partitions and (2) since there
161 can be only one extended partition, which contains all of the
162 logical drives, all of the logical drives must be contiguous
163 (with no intervening primary partition). cfdisk next prompts
164 you for the size of the partition you want to create. The
165 default size, equal to the entire free space of the current par‐
166 tition, is displayed in megabytes. You can either press the
167 Enter key to accept the default size or enter a different size
168 at the prompt. cfdisk accepts size entries in megabytes (M)
169 [default], kilobytes (K), cylinders (C) and sectors (S) by
170 entering the number immediately followed by one of (M, K, C or
171 S). If the partition fills the free space available, the parti‐
172 tion is created and you are returned to the main command line.
173 Otherwise, the partition can be created at the beginning or the
174 end of the free space, and cfdisk will ask you to choose where
175 to place the partition. After the partition is created, cfdisk
176 automatically adjusts the other partitions' partition types if
177 all of the primary partitions are used.
178 p Print the partition table to the screen or to a file. There are
180 several different formats for the partition that you can choose
181 from:
182 r Raw data format (exactly what would be written to disk)
185 s Partition table in sector order format
187 t Partition table in raw format
189 The raw data format will print the sectors that would be written
191 to disk if a write command is selected. First, the primary par‐
192 tition table is printed, followed by the partition tables asso‐
193 ciated with each logical partition. The data is printed in hex
194 byte by byte with 16 bytes per line.
195 The partition table in sector order format will print the parti‐
197 tion table ordered by sector number. The fields, from left to
198 right, are the number of the partition, the partition type, the
199 first sector, the last sector, the offset from the first sector
200 of the partition to the start of the data, the length of the
201 partition, the filesystem type (with the hex value in parenthe‐
202 sis), and the flags (with the hex value in parenthesis). In
203 addition to the primary and logical partitions, free and unus‐
204 able space is printed and the extended partition is printed
205 before the first logical partition.
206 If a partition does not start or end on a cylinder boundary or
208 if the partition length is not divisible by the cylinder size,
209 an asterisk (*) is printed after the non-aligned sector num‐
210 ber/count. This usually indicates that a partition was created
211 by an operating system that either does not align partitions to
212 cylinder boundaries or that used different disk geometry infor‐
213 mation. If you know the disk geometry of the other operating
214 system, you could enter the geometry information with the change
215 geometry command (g).
216 For the first partition on the disk and for all logical parti‐
218 tions, if the offset from the beginning of the partition is not
219 equal to the number of sectors per track (i.e., the data does
220 not start on the first head), a number sign (#) is printed after
221 the offset. For the remaining partitions, if the offset is not
222 zero, a number sign will be printed after the offset. This cor‐
223 responds to the NC flag in the partitions section of the main
224 display.
225 The partition table in raw format will print the partition table
227 ordered by partition number. It will leave out all free and
228 unusable space. The fields, from left to right, are the number
229 of the partition, the flags (in hex), the starting head, sector
230 and cylinder, the filesystem ID (in hex), the ending head, sec‐
231 tor and cylinder, the starting sector in the partition and the
232 number of sectors in the partition. The information in this ta‐
233 ble can be directly translated to the raw data format.
234 The partition table entries only have 10 bits available to rep‐
236 resent the starting and ending cylinders. Thus, when the abso‐
237 lute starting (ending) sector number is on a cylinder greater
238 than 1023, the maximal values for starting (ending) head, sector
239 and cylinder are printed. This is the method used by OS/2, and
240 thus fixes the problems associated with OS/2's fdisk rewriting
241 the partition table when it is not in this format. Since Linux
242 and OS/2 use absolute sector counts, the values in the starting
243 and ending head, sector and cylinder are not used.
244 q Quit program. This will exit the program without writing any
246 data to disk.
247 t Change the filesystem type. By default, new partitions are cre‐
249 ated as Linux partitions, but since cfdisk can create partitions
250 for other operating systems, change partition type allows you to
251 enter the hex value of the filesystem you desire. A list of the
252 know filesystem types is displayed. You can type in the
253 filesystem type at the prompt or accept the default filesystem
254 type [Linux].
255 u Change units of the partition size display. It will rotate
257 through megabytes, sectors and cylinders.
258 W Write partition table to disk (must enter an upper case W).
260 Since this might destroy data on the disk, you must either con‐
261 firm or deny the write by entering `yes' or `no'. If you enter
262 `yes', cfdisk will write the partition table to disk and the
263 tell the kernel to re-read the partition table from the disk.
264 The re-reading of the partition table does not work in some
265 cases, for example for device-mapper devices. In particular
266 case you need to inform kernel about new partitions by part‐
267 probe(8), kpartx(8) or reboot the system.
268 Up Arrow
270 Down Arrow
272 Move cursor to the previous or next partition. If there are
273 more partitions than can be displayed on a screen, you can dis‐
274 play the next (previous) set of partitions by moving down (up)
275 at the last (first) partition displayed on the screen.
276 CTRL-L Redraws the screen. In case something goes wrong and you cannot
278 read anything, you can refresh the screen from the main command
279 line.
280 ? Print the help screen.
282 All of the commands can be entered with either upper or lower case let‐
284 ters (except for Writes). When in a sub-menu or at a prompt to enter a
285 filename, you can hit the ESC key to return to the main command line.
286
288 -a Use an arrow cursor instead of reverse video for highlighting
289 the current partition.
290 -g Do not use the geometry given by the disk driver, but try to
292 guess a geometry from the partition table.
293 -v Print the version number and copyright.
295 -z Start with zeroed partition table. This option is useful when
297 you want to repartition your entire disk. Note: this option
298 does not zero the partition table on the disk; rather, it simply
299 starts the program without reading the existing partition table.
300 -c cylinders
302 -h heads
304 -s sectors-per-track
306 Override the number of cylinders, heads and sectors per track
307 read from the BIOS. If your BIOS or adapter does not supply
308 this information or if it supplies incorrect information, use
309 these options to set the disk geometry values.
310 -P opt Prints the partition table in specified formats. opt can be one
312 or more of "r", "s" or "t". See the print command (above) for
313 more information on the print formats.
314
316 0: No errors; 1: Invocation error; 2: I/O error; 3: cannot get geome‐
317 try; 4: bad partition table on disk.
318
320 fdisk(8), sfdisk(8), mkfs(8), parted(8), partprobe(8), kpartx(8)
321
323 The current version does not support multiple disks.
324
326 Kevin E. Martin (martin@cs.unc.edu)
327
330 The cfdisk command is part of the util-linux package and is available
331 from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
332util-linux July 2009 CFDISK(8)