disk-utils/fdisk.8

   1 .\" Copyright 1992, 1993 Rickard E. Faith (faith@cs.unc.edu)
   2 .\" Copyright 1998 Andries E. Brouwer (aeb@cwi.nl)
   3 .\" Copyright 2012 Davidlohr Bueso <dave@gnu.org>
   4 .\" Copyright (C) 2013 Karel Zak <kzak@redhat.com>
   5 .\" May be distributed under the GNU General Public License
   6 .TH FDISK 8 "February 2016" "util-linux" "System Administration"
   7
   8 .SH NAME
   9 fdisk \- manipulate disk partition table
  10
  11 .SH SYNOPSIS
  12 .B fdisk
  13 [options]
  14 .I device
  15 .sp
  16 .B fdisk \-l
  17 .RI [ device ...]
  18
  19 .SH DESCRIPTION
  20 .B fdisk
  21 is a dialog-driven program for creation and manipulation of partition tables.
  22 It understands GPT, MBR, Sun, SGI and BSD partition tables.
  23
  24 Block devices can be divided into one or more logical disks called
  25 .IR partitions .
  26 This division is recorded in the
  27 .IR "partition table" ,
  28 usually found in sector 0 of the disk.
  29 (In the BSD world one talks about `disk slices' and a `disklabel'.)
  30
  31 All partitioning is driven by device I/O limits (the topology) by default.
  32 .B fdisk
  33 is able to optimize the disk layout for a 4K-sector size and use an alignment offset on
  34 modern devices for MBR and GPT.  It is always a good idea to follow \fBfdisk\fR's defaults
  35 as the default values (e.g. first and last partition sectors) and partition
  36 sizes specified by the +/-<size>{M,G,...} notation are always aligned according
  37 to the device properties.
  38
  39 Note that
  40 .BR partx (8)
  41 provides a rich interface for scripts to print disk layouts,
  42 .B fdisk
  43 is mostly designed for humans.  Backward compatibility in the output of
  44 .B fdisk
  45 is not guaranteed.  The input (the commands) should always be backward compatible.
  46
  47 .SH OPTIONS
  48 .TP
  49 \fB\-b\fR, \fB\-\-sector\-size\fR \fIsectorsize\fP
  50 Specify the sector size of the disk.  Valid values are 512, 1024, 2048, and 4096.
  51 (Recent kernels know the sector size.  Use this option only on old kernels or
  52 to override the kernel's ideas.)  Since util-linux-2.17, \fBfdisk\fR differentiates
  53 between logical and physical sector size.  This option changes both sector sizes to
  54 .IB sectorsize .
  55 .TP
  56 \fB\-B\fR, \fB\-\-protect\-boot\fP
  57 Don't erase the begin of the first disk sector when create a new disk label.  This
  58 feature is supported for GPT and MBR.
  59 .TP
  60 \fB\-c\fR, \fB\-\-compatibility\fR[=\fImode\fR]
  61 Specify the compatibility mode, 'dos' or 'nondos'.  The default is non-DOS
  62 mode.  For backward compatibility, it is possible to use the option without
  63 the \fImode\fR argument -- then the default is used.  Note that the optional
  64 \fImode\fR argument cannot be separated from the \fB-c\fR option by a space,
  65 the correct form is for example '-c=dos'.
  66 .TP
  67 \fB\-h\fR, \fB\-\-help\fR
  68 Display a help text and exit.
  69 .TP
  70 \fB\-L\fR, \fB\-\-color\fR[=\fIwhen\fR]
  71 Colorize the output.  The optional argument \fIwhen\fP
  72 can be \fBauto\fR, \fBnever\fR or \fBalways\fR.  If the \fIwhen\fR argument is omitted,
  73 it defaults to \fBauto\fR.  The colors can be disabled; for the current built-in default
  74 see the \fB\-\-help\fR output.  See also the \fBCOLORS\fR section.
  75 .TP
  76 \fB\-l\fR, \fB\-\-list\fR
  77 List the partition tables for the specified devices and then exit.
  78 If no devices are given, those mentioned in
  79 .I /proc/partitions
  80 (if that file exists) are used.
  81 .TP
  82 .BR \-o , " \-\-output " \fIlist\fP
  83 Specify which output columns to print.  Use
  84 .B \-\-help
  85 to get a list of all supported columns.
  86
  87 The default list of columns may be extended if \fIlist\fP is
  88 specified in the format \fI+list\fP (e.g. \fB-o +UUID\fP).
  89 .TP
  90 \fB\-s\fR, \fB\-\-getsz\fR
  91 Print the size in 512-byte sectors of each given block device.  This option is DEPRECATED
  92 in favour of
  93 .BR blockdev (1).
  94 .TP
  95 \fB\-t\fR, \fB\-\-type\fR \fItype\fR
  96 Enable support only for disklabels of the specified \fItype\fP, and disable
  97 support for all other types.
  98 .TP
  99 \fB\-u\fR, \fB\-\-units\fR[=\fIunit\fR]
 100 When listing partition tables, show sizes in 'sectors' or in 'cylinders'.  The
 101 default is to show sizes in sectors.  For backward compatibility, it is possible
 102 to use the option without the \fIunit\fR argument -- then the default is used.
 103 Note that the optional \fIunit\fR argument cannot be separated from the \fB-u\fR
 104 option by a space, the correct form is for example '-u=cylinders'.
 105
 106 .TP
 107 \fB\-C\fR, \fB\-\-cylinders\fR \fInumber\fR
 108 Specify the number of cylinders of the disk.
 109 I have no idea why anybody would want to do so.
 110 .TP
 111 \fB\-H\fR, \fB\-\-heads\fR \fInumber\fR
 112 Specify the number of heads of the disk.  (Not the physical number,
 113 of course, but the number used for partition tables.)
 114 Reasonable values are 255 and 16.
 115 .TP
 116 \fB\-S\fR, \fB\-\-sectors\fR \fInumber\fR
 117 Specify the number of sectors per track of the disk.
 118 (Not the physical number, of course, but the number used for
 119 partition tables.) A reasonable value is 63.
 120
 121 .TP
 122 \fB\-w\fR, \fB\-\-wipe\fR \fIwhen\fR
 123 Wipe filesystem, RAID and partition-table signatures from the device, in order
 124 to avoid possible collisions.  The argument \fIwhen\fR can be \fBauto\fR,
 125 \fBnever\fR or \fBalways\fR.  When this option is not given, the default is
 126 \fBauto\fR, in which case signatures are wiped only when in interactive mode.
 127 In all cases detected signatures are reported by warning messages
 128 before a new partition table is created.  See also
 129 .BR wipefs (8)
 130 command.
 131
 132 .TP
 133 \fB\-W\fR, \fB\-\-wipe-partition\fR \fIwhen\fR
 134 Wipe filesystem, RAID and partition-table signatures from a newly created
 135 partitions, in order to avoid possible collisions.  The argument \fIwhen\fR can
 136 be \fBauto\fR, \fBnever\fR or \fBalways\fR.  When this option is not given, the
 137 default is \fBauto\fR, in which case signatures are wiped only when in
 138 interactive mode and after confirmation by user.  In all cases detected
 139 signatures are reported by warning messages before a new partition is
 140 created.  See also
 141 .BR wipefs (8)
 142 command.
 143
 144 .TP
 145 \fB\-V\fR, \fB\-\-version\fR
 146 Display version information and exit.
 147
 148 .SH DEVICES
 149 The
 150 .I device
 151 is usually /dev/sda, /dev/sdb or so.  A device name refers to the entire disk.
 152 Old systems without libata (a library used inside the Linux kernel to support
 153 ATA host controllers and devices) make a difference between IDE and SCSI disks.
 154 In such cases the device name will be /dev/hd* (IDE) or /dev/sd* (SCSI).
 155
 156 The
 157 .I partition
 158 is a device name followed by a partition number.  For example, /dev/sda1 is the
 159 first partition on the first hard disk in the system.  See also Linux kernel
 160 documentation (the Documentation/devices.txt file).
 161
 162 .SH SIZES
 163 The "last sector" dialog accepts partition size specified by number of sectors
 164 or by +/-<size>{K,B,M,G,...} notation.
 165
 166 If the size is prefixed by  '+' then it is interpreted as relative to the
 167 partition first sector.  If the size is prefixed by  '-' then it is interpreted
 168 as relative to the high limit (last available sector for the partition).
 169
 170 In the case the size is specified in bytes than the number may be followed by
 171 the multiplicative suffixes KiB=1024, MiB=1024*1024, and so on for GiB, TiB,
 172 PiB, EiB, ZiB and YiB. The "iB" is optional, e.g. "K" has the same meaning as
 173 "KiB".
 174
 175 The relative sizes are always aligned according to device I/O limits.  The
 176 +/-<size>{K,B,M,G,...} notation is recommended.
 177
 178 For backward compatibility fdisk also accepts the suffixes KB=1000,
 179 MB=1000*1000, and so on for GB, TB, PB, EB, ZB and YB. These 10^N suffixes
 180 are deprecated.
 181
 182 .SH SCRIPT FILES
 183 .B fdisk
 184 allows to read (by 'I' command) sfdisk compatible script files. The script is
 185 applied to in-memory partition table, and then it is possible to modify the
 186 partition table before you write it to the device.
 187 .PP
 188 And vice-versa it is possible to write the current in-memory disk layout
 189 to the script file by command 'O'.
 190 .PP
 191 The script files are compatible between cfdisk, sfdisk, fdisk and another
 192 libfdisk applications. For more details see
 193 .BR sfdisk (8).
 194
 195 .SH DISK LABELS
 196 .B GPT (GUID Partition Table)
 197 .RS
 198 GPT is modern standard for the layout of the partition table.  GPT uses 64-bit
 199 logical block addresses, checksums, UUIDs and names for partitions and an
 200 unlimited number of partitions (although the number of partitions is
 201 usually restricted to 128 in many partitioning tools).
 202
 203 Note that the first sector is still reserved for a
 204 .B protective MBR
 205 in the GPT specification.  It prevents MBR-only partitioning tools
 206 from mis-recognizing and overwriting GPT disks.
 207
 208 GPT is always a better choice than MBR, especially on modern hardware with a UEFI
 209 boot loader.
 210 .RE
 211
 212 .B DOS-type (MBR)
 213 .RS
 214 A DOS-type partition table can describe an unlimited number of partitions.  In sector 0
 215 there is room for the description of 4 partitions (called `primary').  One of
 216 these may be an extended partition; this is a box holding logical partitions,
 217 with descriptors found in a linked list of sectors, each preceding the
 218 corresponding logical partitions.  The four primary partitions, present or not,
 219 get numbers 1-4.  Logical partitions are numbered starting from 5.
 220
 221 In a DOS-type partition table the starting offset and the size of each
 222 partition is stored in two ways: as an absolute number of sectors (given in 32
 223 bits), and as a
 224 .B Cylinders/Heads/Sectors
 225 triple (given in 10+8+6 bits).  The former is OK -- with 512-byte sectors this
 226 will work up to 2 TB.  The latter has two problems.  First, these C/H/S fields
 227 can be filled only when the number of heads and the number of sectors per track
 228 are known.  And second, even if we know what these numbers should be, the 24
 229 bits that are available do not suffice.  DOS uses C/H/S only, Windows uses
 230 both, Linux never uses C/H/S.  The
 231 .B C/H/S addressing is deprecated
 232 and may be unsupported in some later fdisk version.
 233
 234 .B Please, read the DOS-mode section if you want DOS-compatible partitions.
 235 .B fdisk
 236 does not care about cylinder boundaries by default.
 237 .RE
 238
 239 .B BSD/Sun-type
 240 .RS
 241 A BSD/Sun disklabel can describe 8 partitions, the third of which should be a `whole
 242 disk' partition.  Do not start a partition that actually uses its first sector
 243 (like a swap partition) at cylinder 0, since that will destroy the disklabel.
 244 Note that a
 245 .B BSD label
 246 is usually nested within a DOS partition.
 247 .RE
 248
 249 .B IRIX/SGI-type
 250 .RS
 251 An IRIX/SGI disklabel can describe 16 partitions, the eleventh of which should be an entire
 252 `volume' partition, while the ninth should be labeled `volume header'.  The
 253 volume header will also cover the partition table, i.e., it starts at block
 254 zero and extends by default over five cylinders.  The remaining space in the
 255 volume header may be used by header directory entries.  No partitions may
 256 overlap with the volume header.  Also do not change its type or make some
 257 filesystem on it, since you will lose the partition table.  Use this type of
 258 label only when working with Linux on IRIX/SGI machines or IRIX/SGI disks under
 259 Linux.
 260 .RE
 261
 262 A sync() and an ioctl(BLKRRPART) (rereading the partition table from disk)
 263 are performed before exiting when the partition table has been updated.
 264
 265 .SH "DOS mode and DOS 6.x WARNING"
 266 .B Note that all this is deprecated.  You don't have to care about things like
 267 .B geometry and cylinders on modern operating systems.  If you really want
 268 .B DOS-compatible partitioning then you have to enable DOS mode and cylinder
 269 .B units by using the '-c=dos -u=cylinders' fdisk command-line options.
 270
 271 The DOS 6.x FORMAT command looks for some information in the first sector of
 272 the data area of the partition, and treats this information as more reliable
 273 than the information in the partition table.  DOS FORMAT expects DOS FDISK to
 274 clear the first 512 bytes of the data area of a partition whenever a size
 275 change occurs.  DOS FORMAT will look at this extra information even if the /U
 276 flag is given -- we consider this a bug in DOS FORMAT and DOS FDISK.
 277
 278 The bottom line is that if you use \fBfdisk\fR or \fBcfdisk\fR to change the
 279 size of a DOS partition table entry, then you must also use
 280 .BR dd "(1) to " "zero the first 512 bytes"
 281 of that partition before using DOS FORMAT to format the partition.  For
 282 example, if you were using \fBfdisk\fR to make a DOS partition table entry for
 283 /dev/sda1, then (after exiting \fBfdisk\fR and rebooting Linux so that the
 284 partition table information is valid) you would use the command "dd
 285 if=/dev/zero of=/dev/sda1 bs=512 count=1" to zero the first 512 bytes of the
 286 partition.
 287
 288 .B fdisk
 289 usually obtains the disk geometry automatically.  This is not necessarily the
 290 physical disk geometry (indeed, modern disks do not really have anything like a
 291 physical geometry, certainly not something that can be described in the simplistic
 292 Cylinders/Heads/Sectors form), but it is the disk geometry that MS-DOS uses for
 293 the partition table.
 294
 295 Usually all goes well by default, and there are no problems if Linux is the
 296 only system on the disk.  However, if the disk has to be shared with other
 297 operating systems, it is often a good idea to let an fdisk from another
 298 operating system make at least one partition.  When Linux boots it looks at the
 299 partition table, and tries to deduce what (fake) geometry is required for good
 300 cooperation with other systems.
 301
 302 Whenever a partition table is printed out in DOS mode, a consistency check is
 303 performed on the partition table entries.  This check verifies that the
 304 physical and logical start and end points are identical, and that each
 305 partition starts and ends on a cylinder boundary (except for the first
 306 partition).
 307
 308 Some versions of MS-DOS create a first partition which does not begin
 309 on a cylinder boundary, but on sector 2 of the first cylinder.
 310 Partitions beginning in cylinder 1 cannot begin on a cylinder boundary, but
 311 this is unlikely to cause difficulty unless you have OS/2 on your machine.
 312
 313 For best results, you should always use an OS-specific partition table
 314 program.  For example, you should make DOS partitions with the DOS FDISK
 315 program and Linux partitions with the Linux fdisk or Linux cfdisk programs.
 316 .SH COLORS
 317 Implicit coloring can be disabled by an empty file \fI/etc/terminal-colors.d/fdisk.disable\fR.
 318
 319 See
 320 .BR terminal-colors.d (5)
 321 for more details about colorization configuration. The logical color names
 322 supported by
 323 .B fdisk
 324 are:
 325 .TP
 326 .B header
 327 The header of the output tables.
 328 .TP
 329 .B help-title
 330 The help section titles.
 331 .TP
 332 .B warn
 333 The warning messages.
 334 .TP
 335 .B welcome
 336 The welcome message.
 337
 338 .SH AUTHORS
 339 .MT kzak@redhat.com
 340 Karel Zak
 341 .ME
 342 .br
 343 .MT dave@gnu.org
 344 Davidlohr Bueso
 345 .ME
 346 .br
 347 .PP
 348 The original version was written by
 349 Andries E. Brouwer, A. V. Le Blanc and others.
 350
 351 .SH ENVIRONMENT
 352 .IP FDISK_DEBUG=all
 353 enables fdisk debug output.
 354 .IP LIBFDISK_DEBUG=all
 355 enables libfdisk debug output.
 356 .IP LIBBLKID_DEBUG=all
 357 enables libblkid debug output.
 358 .IP LIBSMARTCOLS_DEBUG=all
 359 enables libsmartcols debug output.
 360 .IP LIBSMARTCOLS_DEBUG_PADDING=on
 361 use visible padding characters. Requires enabled LIBSMARTCOLS_DEBUG.
 362
 363 .SH "SEE ALSO"
 364 .BR cfdisk (8),
 365 .BR mkfs (8),
 366 .BR partx (8),
 367 .BR sfdisk (8)
 368
 369 .SH AVAILABILITY
 370 The fdisk command is part of the util-linux package and is available from
 371 https://www.kernel.org/pub/linux/utils/util-linux/.