fdisk(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | DEVICES | SIZES | SCRIPT FILES | DISK LABELS | DOS mode and DOS 6.x WARNING | COLORS | ENVIRONMENT | AUTHORS | SEE ALSO | AVAILABILITY | COLOPHON

FDISK(8)                  System Administration                 FDISK(8)

NAME         top

       fdisk - manipulate disk partition table

SYNOPSIS         top

       fdisk [options] device

       fdisk -l [device...]

DESCRIPTION         top

       fdisk is a dialog-driven program for creation and manipulation of
       partition tables.  It understands GPT, MBR, Sun, SGI and BSD
       partition tables.

       Block devices can be divided into one or more logical disks
       called partitions.  This division is recorded in the partition
       table, usually found in sector 0 of the disk.  (In the BSD world
       one talks about `disk slices' and a `disklabel'.)

       All partitioning is driven by device I/O limits (the topology) by
       default.  fdisk is able to optimize the disk layout for a 4K-
       sector size and use an alignment offset on modern devices for MBR
       and GPT.  It is always a good idea to follow fdisk's defaults as
       the default values (e.g., first and last partition sectors) and
       partition sizes specified by the +/-<size>{M,G,...} notation are
       always aligned according to the device properties.

       CHS (Cylinder-Head-Sector) addressing is deprecated and not used
       by default.  Please, do not follow old articles and
       recommendations with "fdisk -S <n> -H <n>" advices for SSD or 4K-
       sector devices.

       Note that partx(8) provides a rich interface for scripts to print
       disk layouts, fdisk is mostly designed for humans.  Backward
       compatibility in the output of fdisk is not guaranteed.  The
       input (the commands) should always be backward compatible.

OPTIONS         top

       -b, --sector-size sectorsize
              Specify the sector size of the disk.  Valid values are
              512, 1024, 2048, and 4096.  (Recent kernels know the
              sector size.  Use this option only on old kernels or to
              override the kernel's ideas.)  Since util-linux-2.17,
              fdisk differentiates between logical and physical sector
              size.  This option changes both sector sizes to
              sectorsize.

       -B, --protect-boot
              Don't erase the beginning of the first disk sector when
              creating a new disk label.  This feature is supported for
              GPT and MBR.

       -c, --compatibility[=mode]
              Specify the compatibility mode, 'dos' or 'nondos'.  The
              default is non-DOS mode.  For backward compatibility, it
              is possible to use the option without the mode argument --
              then the default is used.  Note that the optional mode
              argument cannot be separated from the -c option by a
              space, the correct form is for example '-c=dos'.

       -h, --help
              Display a help text and exit.

       -L, --color[=when]
              Colorize the output.  The optional argument when can be
              auto, never or always.  If the when argument is omitted,
              it defaults to auto.  The colors can be disabled; for the
              current built-in default see the --help output.  See also
              the COLORS section.

       -l, --list
              List the partition tables for the specified devices and
              then exit.  If no devices are given, those mentioned in
              /proc/partitions (if that file exists) are used.

       -x, --list-details
              Like --list, but provides more details.

       --lock[=mode]
              Use exclusive BSD lock for device or file it operates.
              The optional argument mode can be yes, no (or 1 and 0) or
              nonblock.  If the mode argument is omitted, it defaults to
              "yes".  This option overwrites environment variable
              $LOCK_BLOCK_DEVICE.  The default is not to use any lock at
              all, but it's recommended to avoid collisions with udevd
              or other tools.

       -n, --noauto-pt
              Don't automatically create a default partition table on
              empty device.  The partition table has to be explicitly
              created by user (by command like 'o', 'g', etc.).

       -o, --output list
              Specify which output columns to print.  Use --help to get
              a list of all supported columns.

              The default list of columns may be extended if list is
              specified in the format +list (e.g., -o +UUID).

       -s, --getsz
              Print the size in 512-byte sectors of each given block
              device.  This option is DEPRECATED in favour of
              blockdev(8).

       -t, --type type
              Enable support only for disklabels of the specified type,
              and disable support for all other types.

       -u, --units[=unit]
              When listing partition tables, show sizes in 'sectors' or
              in 'cylinders'.  The default is to show sizes in sectors.
              For backward compatibility, it is possible to use the
              option without the unit argument -- then the default is
              used.  Note that the optional unit argument cannot be
              separated from the -u option by a space, the correct form
              is for example '-u=cylinders'.

       -C, --cylinders number
              Specify the number of cylinders of the disk.  I have no
              idea why anybody would want to do so.

       -H, --heads number
              Specify the number of heads of the disk.  (Not the
              physical number, of course, but the number used for
              partition tables.)  Reasonable values are 255 and 16.

       -S, --sectors number
              Specify the number of sectors per track of the disk.  (Not
              the physical number, of course, but the number used for
              partition tables.) A reasonable value is 63.

       -w, --wipe when
              Wipe filesystem, RAID and partition-table signatures from
              the device, in order to avoid possible collisions.  The
              argument when can be auto, never or always.  When this
              option is not given, the default is auto, in which case
              signatures are wiped only when in interactive mode.  In
              all cases detected signatures are reported by warning
              messages before a new partition table is created.  See
              also wipefs(8) command.

       -W, --wipe-partitions when
              Wipe filesystem, RAID and partition-table signatures from
              a newly created partitions, in order to avoid possible
              collisions.  The argument when can be auto, never or
              always.  When this option is not given, the default is
              auto, in which case signatures are wiped only when in
              interactive mode and after confirmation by user.  In all
              cases detected signatures are reported by warning messages
              before a new partition is created.  See also wipefs(8)
              command.

       -V, --version
              Display version information and exit.

DEVICES         top

       The device is usually /dev/sda, /dev/sdb or so.  A device name
       refers to the entire disk.  Old systems without libata (a library
       used inside the Linux kernel to support ATA host controllers and
       devices) make a difference between IDE and SCSI disks.  In such
       cases the device name will be /dev/hd* (IDE) or /dev/sd* (SCSI).

       The partition is a device name followed by a partition number.
       For example, /dev/sda1 is the first partition on the first hard
       disk in the system.  See also Linux kernel documentation (the
       Documentation/admin-guide/devices.txt file).

SIZES         top

       The "last sector" dialog accepts partition size specified by
       number of sectors or by +/-<size>{K,B,M,G,...} notation.

       If the size is prefixed by  '+' then it is interpreted as
       relative to the partition first sector.  If the size is prefixed
       by  '-' then it is interpreted as relative to the high limit
       (last available sector for the partition).

       In the case the size is specified in bytes than the number may be
       followed by the multiplicative suffixes KiB=1024, MiB=1024*1024,
       and so on for GiB, TiB, PiB, EiB, ZiB and YiB. The "iB" is
       optional, e.g., "K" has the same meaning as "KiB".

       The relative sizes are always aligned according to device I/O
       limits.  The +/-<size>{K,B,M,G,...} notation is recommended.

       For backward compatibility fdisk also accepts the suffixes
       KB=1000, MB=1000*1000, and so on for GB, TB, PB, EB, ZB and YB.
       These 10^N suffixes are deprecated.

SCRIPT FILES         top

       fdisk allows reading (by 'I' command) sfdisk compatible script
       files.  The script is applied to in-memory partition table, and
       then it is possible to modify the partition table before you
       write it to the device.

       And vice-versa it is possible to write the current in-memory disk
       layout to the script file by command 'O'.

       The script files are compatible between cfdisk, sfdisk, fdisk and
       other libfdisk applications. For more details see sfdisk(8).

DISK LABELS         top

       GPT (GUID Partition Table)
              GPT is modern standard for the layout of the partition
              table.  GPT uses 64-bit logical block addresses,
              checksums, UUIDs and names for partitions and an unlimited
              number of partitions (although the number of partitions is
              usually restricted to 128 in many partitioning tools).

              Note that the first sector is still reserved for a
              protective MBR in the GPT specification.  It prevents MBR-
              only partitioning tools from mis-recognizing and
              overwriting GPT disks.

              GPT is always a better choice than MBR, especially on
              modern hardware with a UEFI boot loader.

       DOS-type (MBR)
              A DOS-type partition table can describe an unlimited
              number of partitions.  In sector 0 there is room for the
              description of 4 partitions (called `primary').  One of
              these may be an extended partition; this is a box holding
              logical partitions, with descriptors found in a linked
              list of sectors, each preceding the corresponding logical
              partitions.  The four primary partitions, present or not,
              get numbers 1-4.  Logical partitions are numbered starting
              from 5.

              In a DOS-type partition table the starting offset and the
              size of each partition is stored in two ways: as an
              absolute number of sectors (given in 32 bits), and as a
              Cylinders/Heads/Sectors triple (given in 10+8+6 bits).
              The former is OK -- with 512-byte sectors this will work
              up to 2 TB.  The latter has two problems.  First, these
              C/H/S fields can be filled only when the number of heads
              and the number of sectors per track are known.  And
              second, even if we know what these numbers should be, the
              24 bits that are available do not suffice.  DOS uses C/H/S
              only, Windows uses both, Linux never uses C/H/S.  The
              C/H/S addressing is deprecated and may be unsupported in
              some later fdisk version.

              Please, read the DOS-mode section if you want DOS-
              compatible partitions.  fdisk does not care about cylinder
              boundaries by default.

       BSD/Sun-type
              A BSD/Sun disklabel can describe 8 partitions, the third
              of which should be a `whole disk' partition.  Do not start
              a partition that actually uses its first sector (like a
              swap partition) at cylinder 0, since that will destroy the
              disklabel.  Note that a BSD label is usually nested within
              a DOS partition.

       IRIX/SGI-type
              An IRIX/SGI disklabel can describe 16 partitions, the
              eleventh of which should be an entire `volume' partition,
              while the ninth should be labeled `volume header'.  The
              volume header will also cover the partition table, i.e.,
              it starts at block zero and extends by default over five
              cylinders.  The remaining space in the volume header may
              be used by header directory entries.  No partitions may
              overlap with the volume header.  Also do not change its
              type or make some filesystem on it, since you will lose
              the partition table.  Use this type of label only when
              working with Linux on IRIX/SGI machines or IRIX/SGI disks
              under Linux.

       A sync() and an ioctl(BLKRRPART) (rereading the partition table
       from disk) are performed before exiting when the partition table
       has been updated.

DOS mode and DOS 6.x WARNING         top

       Note that all this is deprecated. You don't have to care about
       things like geometry and cylinders on modern operating systems.
       If you really want DOS-compatible partitioning then you have to
       enable DOS mode and cylinder units by using the '-c=dos
       -u=cylinders' fdisk command-line options.

       The DOS 6.x FORMAT command looks for some information in the
       first sector of the data area of the partition, and treats this
       information as more reliable than the information in the
       partition table.  DOS FORMAT expects DOS FDISK to clear the first
       512 bytes of the data area of a partition whenever a size change
       occurs.  DOS FORMAT will look at this extra information even if
       the /U flag is given -- we consider this a bug in DOS FORMAT and
       DOS FDISK.

       The bottom line is that if you use fdisk or cfdisk to change the
       size of a DOS partition table entry, then you must also use dd(1)
       to zero the first 512 bytes of that partition before using DOS
       FORMAT to format the partition.  For example, if you were using
       fdisk to make a DOS partition table entry for /dev/sda1, then
       (after exiting fdisk and rebooting Linux so that the partition
       table information is valid) you would use the command "dd
       if=/dev/zero of=/dev/sda1 bs=512 count=1" to zero the first 512
       bytes of the partition.

       fdisk usually obtains the disk geometry automatically.  This is
       not necessarily the physical disk geometry (indeed, modern disks
       do not really have anything like a physical geometry, certainly
       not something that can be described in the simplistic
       Cylinders/Heads/Sectors form), but it is the disk geometry that
       MS-DOS uses for the partition table.

       Usually all goes well by default, and there are no problems if
       Linux is the only system on the disk.  However, if the disk has
       to be shared with other operating systems, it is often a good
       idea to let an fdisk from another operating system make at least
       one partition.  When Linux boots it looks at the partition table,
       and tries to deduce what (fake) geometry is required for good
       cooperation with other systems.

       Whenever a partition table is printed out in DOS mode, a
       consistency check is performed on the partition table entries.
       This check verifies that the physical and logical start and end
       points are identical, and that each partition starts and ends on
       a cylinder boundary (except for the first partition).

       Some versions of MS-DOS create a first partition which does not
       begin on a cylinder boundary, but on sector 2 of the first
       cylinder.  Partitions beginning in cylinder 1 cannot begin on a
       cylinder boundary, but this is unlikely to cause difficulty
       unless you have OS/2 on your machine.

       For best results, you should always use an OS-specific partition
       table program.  For example, you should make DOS partitions with
       the DOS FDISK program and Linux partitions with the Linux fdisk
       or Linux cfdisk programs.

COLORS         top

       Implicit coloring can be disabled by an empty file /etc/terminal-
       colors.d/fdisk.disable.

       See terminal-colors.d(5) for more details about colorization
       configuration. The logical color names supported by fdisk are:

       header The header of the output tables.

       help-title
              The help section titles.

       warn   The warning messages.

       welcome
              The welcome message.

ENVIRONMENT         top

       FDISK_DEBUG=all
              enables fdisk debug output.

       LIBFDISK_DEBUG=all
              enables libfdisk debug output.

       LIBBLKID_DEBUG=all
              enables libblkid debug output.

       LIBSMARTCOLS_DEBUG=all
              enables libsmartcols debug output.

       LIBSMARTCOLS_DEBUG_PADDING=on
              use visible padding characters. Requires enabled
              LIBSMARTCOLS_DEBUG.

       LOCK_BLOCK_DEVICE=<mode>
              use exclusive BSD lock.  The mode is "1" or "0".  See
              --lock for more details.

AUTHORS         top

       Karel Zak ⟨kzak@redhat.com⟩
       Davidlohr Bueso ⟨dave@gnu.org⟩

       The original version was written by Andries E. Brouwer, A. V. Le
       Blanc and others.

SEE ALSO         top

       cfdisk(8), mkfs(8), partx(8), sfdisk(8)

AVAILABILITY         top

       The fdisk command is part of the util-linux package and is
       available from
       https://www.kernel.org/pub/linux/utils/util-linux/.

COLOPHON         top

       This page is part of the util-linux (a random collection of Linux
       utilities) project.  Information about the project can be found
       at ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩.  If you
       have a bug report for this manual page, send it to
       util-linux@vger.kernel.org.  This page was obtained from the
       project's upstream Git repository
       ⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
       2020-12-18.  (At that time, the date of the most recent commit
       that was found in the repository was 2020-12-17.)  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to man-pages@man7.org

util-linux                    February 2016                     FDISK(8)

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