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 CHS (Cylinder-Head-Sector) addressing is deprecated and not used by default.
  40 Please, do not follow old articles and recommendations with "fdisk -S <n> -H
  41 <n>" advices for SSD or 4K-sector devices.
  42
  43 Note that
  44 .BR partx (8)
  45 provides a rich interface for scripts to print disk layouts,
  46 .B fdisk
  47 is mostly designed for humans.  Backward compatibility in the output of
  48 .B fdisk
  49 is not guaranteed.  The input (the commands) should always be backward compatible.
  50
  51 .SH OPTIONS
  52 .TP
  53 \fB\-b\fR, \fB\-\-sector\-size\fR \fIsectorsize\fP
  54 Specify the sector size of the disk.  Valid values are 512, 1024, 2048, and 4096.
  55 (Recent kernels know the sector size.  Use this option only on old kernels or
  56 to override the kernel's ideas.)  Since util-linux-2.17, \fBfdisk\fR differentiates
  57 between logical and physical sector size.  This option changes both sector sizes to
  58 .IB sectorsize .
  59 .TP
  60 \fB\-B\fR, \fB\-\-protect\-boot\fP
  61 Don't erase the begin of the first disk sector when create a new disk label.  This
  62 feature is supported for GPT and MBR.
  63 .TP
  64 \fB\-c\fR, \fB\-\-compatibility\fR[=\fImode\fR]
  65 Specify the compatibility mode, 'dos' or 'nondos'.  The default is non-DOS
  66 mode.  For backward compatibility, it is possible to use the option without
  67 the \fImode\fR argument -- then the default is used.  Note that the optional
  68 \fImode\fR argument cannot be separated from the \fB-c\fR option by a space,
  69 the correct form is for example '-c=dos'.
  70 .TP
  71 \fB\-h\fR, \fB\-\-help\fR
  72 Display a help text and exit.
  73 .TP
  74 \fB\-L\fR, \fB\-\-color\fR[=\fIwhen\fR]
  75 Colorize the output.  The optional argument \fIwhen\fP
  76 can be \fBauto\fR, \fBnever\fR or \fBalways\fR.  If the \fIwhen\fR argument is omitted,
  77 it defaults to \fBauto\fR.  The colors can be disabled; for the current built-in default
  78 see the \fB\-\-help\fR output.  See also the \fBCOLORS\fR section.
  79 .TP
  80 \fB\-l\fR, \fB\-\-list\fR
  81 List the partition tables for the specified devices and then exit.
  82 If no devices are given, those mentioned in
  83 .I /proc/partitions
  84 (if that file exists) are used.
  85 .TP
  86 .BR \-o , " \-\-output " \fIlist\fP
  87 Specify which output columns to print.  Use
  88 .B \-\-help
  89 to get a list of all supported columns.
  90
  91 The default list of columns may be extended if \fIlist\fP is
  92 specified in the format \fI+list\fP (e.g. \fB-o +UUID\fP).
  93 .TP
  94 \fB\-s\fR, \fB\-\-getsz\fR
  95 Print the size in 512-byte sectors of each given block device.  This option is DEPRECATED
  96 in favour of
  97 .BR blockdev (1).
  98 .TP
  99 \fB\-t\fR, \fB\-\-type\fR \fItype\fR
 100 Enable support only for disklabels of the specified \fItype\fP, and disable
 101 support for all other types.
 102 .TP
 103 \fB\-u\fR, \fB\-\-units\fR[=\fIunit\fR]
 104 When listing partition tables, show sizes in 'sectors' or in 'cylinders'.  The
 105 default is to show sizes in sectors.  For backward compatibility, it is possible
 106 to use the option without the \fIunit\fR argument -- then the default is used.
 107 Note that the optional \fIunit\fR argument cannot be separated from the \fB-u\fR
 108 option by a space, the correct form is for example '-u=cylinders'.
 109
 110 .TP
 111 \fB\-C\fR, \fB\-\-cylinders\fR \fInumber\fR
 112 Specify the number of cylinders of the disk.
 113 I have no idea why anybody would want to do so.
 114 .TP
 115 \fB\-H\fR, \fB\-\-heads\fR \fInumber\fR
 116 Specify the number of heads of the disk.  (Not the physical number,
 117 of course, but the number used for partition tables.)
 118 Reasonable values are 255 and 16.
 119 .TP
 120 \fB\-S\fR, \fB\-\-sectors\fR \fInumber\fR
 121 Specify the number of sectors per track of the disk.
 122 (Not the physical number, of course, but the number used for
 123 partition tables.) A reasonable value is 63.
 124
 125 .TP
 126 \fB\-w\fR, \fB\-\-wipe\fR \fIwhen\fR
 127 Wipe filesystem, RAID and partition-table signatures from the device, in order
 128 to avoid possible collisions.  The argument \fIwhen\fR can be \fBauto\fR,
 129 \fBnever\fR or \fBalways\fR.  When this option is not given, the default is
 130 \fBauto\fR, in which case signatures are wiped only when in interactive mode.
 131 In all cases detected signatures are reported by warning messages
 132 before a new partition table is created.  See also
 133 .BR wipefs (8)
 134 command.
 135
 136 .TP
 137 \fB\-W\fR, \fB\-\-wipe-partition\fR \fIwhen\fR
 138 Wipe filesystem, RAID and partition-table signatures from a newly created
 139 partitions, in order to avoid possible collisions.  The argument \fIwhen\fR can
 140 be \fBauto\fR, \fBnever\fR or \fBalways\fR.  When this option is not given, the
 141 default is \fBauto\fR, in which case signatures are wiped only when in
 142 interactive mode and after confirmation by user.  In all cases detected
 143 signatures are reported by warning messages before a new partition is
 144 created.  See also
 145 .BR wipefs (8)
 146 command.
 147
 148 .TP
 149 \fB\-V\fR, \fB\-\-version\fR
 150 Display version information and exit.
 151
 152 .SH DEVICES
 153 The
 154 .I device
 155 is usually /dev/sda, /dev/sdb or so.  A device name refers to the entire disk.
 156 Old systems without libata (a library used inside the Linux kernel to support
 157 ATA host controllers and devices) make a difference between IDE and SCSI disks.
 158 In such cases the device name will be /dev/hd* (IDE) or /dev/sd* (SCSI).
 159
 160 The
 161 .I partition
 162 is a device name followed by a partition number.  For example, /dev/sda1 is the
 163 first partition on the first hard disk in the system.  See also Linux kernel
 164 documentation (the Documentation/devices.txt file).
 165
 166 .SH SIZES
 167 The "last sector" dialog accepts partition size specified by number of sectors
 168 or by +/-<size>{K,B,M,G,...} notation.
 169
 170 If the size is prefixed by  '+' then it is interpreted as relative to the
 171 partition first sector.  If the size is prefixed by  '-' then it is interpreted
 172 as relative to the high limit (last available sector for the partition).
 173
 174 In the case the size is specified in bytes than the number may be followed by
 175 the multiplicative suffixes KiB=1024, MiB=1024*1024, and so on for GiB, TiB,
 176 PiB, EiB, ZiB and YiB. The "iB" is optional, e.g. "K" has the same meaning as
 177 "KiB".
 178
 179 The relative sizes are always aligned according to device I/O limits.  The
 180 +/-<size>{K,B,M,G,...} notation is recommended.
 181
 182 For backward compatibility fdisk also accepts the suffixes KB=1000,
 183 MB=1000*1000, and so on for GB, TB, PB, EB, ZB and YB. These 10^N suffixes
 184 are deprecated.
 185
 186 .SH SCRIPT FILES
 187 .B fdisk
 188 allows to read (by 'I' command) sfdisk compatible script files. The script is
 189 applied to in-memory partition table, and then it is possible to modify the
 190 partition table before you write it to the device.
 191 .PP
 192 And vice-versa it is possible to write the current in-memory disk layout
 193 to the script file by command 'O'.
 194 .PP
 195 The script files are compatible between cfdisk, sfdisk, fdisk and another
 196 libfdisk applications. For more details see
 197 .BR sfdisk (8).
 198
 199 .SH DISK LABELS
 200 .B GPT (GUID Partition Table)
 201 .RS
 202 GPT is modern standard for the layout of the partition table.  GPT uses 64-bit
 203 logical block addresses, checksums, UUIDs and names for partitions and an
 204 unlimited number of partitions (although the number of partitions is
 205 usually restricted to 128 in many partitioning tools).
 206
 207 Note that the first sector is still reserved for a
 208 .B protective MBR
 209 in the GPT specification.  It prevents MBR-only partitioning tools
 210 from mis-recognizing and overwriting GPT disks.
 211
 212 GPT is always a better choice than MBR, especially on modern hardware with a UEFI
 213 boot loader.
 214 .RE
 215
 216 .B DOS-type (MBR)
 217 .RS
 218 A DOS-type partition table can describe an unlimited number of partitions.  In sector 0
 219 there is room for the description of 4 partitions (called `primary').  One of
 220 these may be an extended partition; this is a box holding logical partitions,
 221 with descriptors found in a linked list of sectors, each preceding the
 222 corresponding logical partitions.  The four primary partitions, present or not,
 223 get numbers 1-4.  Logical partitions are numbered starting from 5.
 224
 225 In a DOS-type partition table the starting offset and the size of each
 226 partition is stored in two ways: as an absolute number of sectors (given in 32
 227 bits), and as a
 228 .B Cylinders/Heads/Sectors
 229 triple (given in 10+8+6 bits).  The former is OK -- with 512-byte sectors this
 230 will work up to 2 TB.  The latter has two problems.  First, these C/H/S fields
 231 can be filled only when the number of heads and the number of sectors per track
 232 are known.  And second, even if we know what these numbers should be, the 24
 233 bits that are available do not suffice.  DOS uses C/H/S only, Windows uses
 234 both, Linux never uses C/H/S.  The
 235 .B C/H/S addressing is deprecated
 236 and may be unsupported in some later fdisk version.
 237
 238 .B Please, read the DOS-mode section if you want DOS-compatible partitions.
 239 .B fdisk
 240 does not care about cylinder boundaries by default.
 241 .RE
 242
 243 .B BSD/Sun-type
 244 .RS
 245 A BSD/Sun disklabel can describe 8 partitions, the third of which should be a `whole
 246 disk' partition.  Do not start a partition that actually uses its first sector
 247 (like a swap partition) at cylinder 0, since that will destroy the disklabel.
 248 Note that a
 249 .B BSD label
 250 is usually nested within a DOS partition.
 251 .RE
 252
 253 .B IRIX/SGI-type
 254 .RS
 255 An IRIX/SGI disklabel can describe 16 partitions, the eleventh of which should be an entire
 256 `volume' partition, while the ninth should be labeled `volume header'.  The
 257 volume header will also cover the partition table, i.e., it starts at block
 258 zero and extends by default over five cylinders.  The remaining space in the
 259 volume header may be used by header directory entries.  No partitions may
 260 overlap with the volume header.  Also do not change its type or make some
 261 filesystem on it, since you will lose the partition table.  Use this type of
 262 label only when working with Linux on IRIX/SGI machines or IRIX/SGI disks under
 263 Linux.
 264 .RE
 265
 266 A sync() and an ioctl(BLKRRPART) (rereading the partition table from disk)
 267 are performed before exiting when the partition table has been updated.
 268
 269 .SH "DOS mode and DOS 6.x WARNING"
 270 .B Note that all this is deprecated.  You don't have to care about things like
 271 .B geometry and cylinders on modern operating systems.  If you really want
 272 .B DOS-compatible partitioning then you have to enable DOS mode and cylinder
 273 .B units by using the '-c=dos -u=cylinders' fdisk command-line options.
 274
 275 The DOS 6.x FORMAT command looks for some information in the first sector of
 276 the data area of the partition, and treats this information as more reliable
 277 than the information in the partition table.  DOS FORMAT expects DOS FDISK to
 278 clear the first 512 bytes of the data area of a partition whenever a size
 279 change occurs.  DOS FORMAT will look at this extra information even if the /U
 280 flag is given -- we consider this a bug in DOS FORMAT and DOS FDISK.
 281
 282 The bottom line is that if you use \fBfdisk\fR or \fBcfdisk\fR to change the
 283 size of a DOS partition table entry, then you must also use
 284 .BR dd "(1) to " "zero the first 512 bytes"
 285 of that partition before using DOS FORMAT to format the partition.  For
 286 example, if you were using \fBfdisk\fR to make a DOS partition table entry for
 287 /dev/sda1, then (after exiting \fBfdisk\fR and rebooting Linux so that the
 288 partition table information is valid) you would use the command "dd
 289 if=/dev/zero of=/dev/sda1 bs=512 count=1" to zero the first 512 bytes of the
 290 partition.
 291
 292 .B fdisk
 293 usually obtains the disk geometry automatically.  This is not necessarily the
 294 physical disk geometry (indeed, modern disks do not really have anything like a
 295 physical geometry, certainly not something that can be described in the simplistic
 296 Cylinders/Heads/Sectors form), but it is the disk geometry that MS-DOS uses for
 297 the partition table.
 298
 299 Usually all goes well by default, and there are no problems if Linux is the
 300 only system on the disk.  However, if the disk has to be shared with other
 301 operating systems, it is often a good idea to let an fdisk from another
 302 operating system make at least one partition.  When Linux boots it looks at the
 303 partition table, and tries to deduce what (fake) geometry is required for good
 304 cooperation with other systems.
 305
 306 Whenever a partition table is printed out in DOS mode, a consistency check is
 307 performed on the partition table entries.  This check verifies that the
 308 physical and logical start and end points are identical, and that each
 309 partition starts and ends on a cylinder boundary (except for the first
 310 partition).
 311
 312 Some versions of MS-DOS create a first partition which does not begin
 313 on a cylinder boundary, but on sector 2 of the first cylinder.
 314 Partitions beginning in cylinder 1 cannot begin on a cylinder boundary, but
 315 this is unlikely to cause difficulty unless you have OS/2 on your machine.
 316
 317 For best results, you should always use an OS-specific partition table
 318 program.  For example, you should make DOS partitions with the DOS FDISK
 319 program and Linux partitions with the Linux fdisk or Linux cfdisk programs.
 320 .SH COLORS
 321 Implicit coloring can be disabled by an empty file \fI/etc/terminal-colors.d/fdisk.disable\fR.
 322
 323 See
 324 .BR terminal-colors.d (5)
 325 for more details about colorization configuration. The logical color names
 326 supported by
 327 .B fdisk
 328 are:
 329 .TP
 330 .B header
 331 The header of the output tables.
 332 .TP
 333 .B help-title
 334 The help section titles.
 335 .TP
 336 .B warn
 337 The warning messages.
 338 .TP
 339 .B welcome
 340 The welcome message.
 341
 342 .SH AUTHORS
 343 .MT kzak@redhat.com
 344 Karel Zak
 345 .ME
 346 .br
 347 .MT dave@gnu.org
 348 Davidlohr Bueso
 349 .ME
 350 .br
 351 .PP
 352 The original version was written by
 353 Andries E. Brouwer, A. V. Le Blanc and others.
 354
 355 .SH ENVIRONMENT
 356 .IP FDISK_DEBUG=all
 357 enables fdisk debug output.
 358 .IP LIBFDISK_DEBUG=all
 359 enables libfdisk debug output.
 360 .IP LIBBLKID_DEBUG=all
 361 enables libblkid debug output.
 362 .IP LIBSMARTCOLS_DEBUG=all
 363 enables libsmartcols debug output.
 364 .IP LIBSMARTCOLS_DEBUG_PADDING=on
 365 use visible padding characters. Requires enabled LIBSMARTCOLS_DEBUG.
 366
 367 .SH "SEE ALSO"
 368 .BR cfdisk (8),
 369 .BR mkfs (8),
 370 .BR partx (8),
 371 .BR sfdisk (8)
 372
 373 .SH AVAILABILITY
 374 The fdisk command is part of the util-linux package and is available from
 375 https://www.kernel.org/pub/linux/utils/util-linux/.