fdisk

FDISK(8)                     System Administration                    FDISK(8)



NAME
       fdisk - manipulate disk partition table


SYNOPSIS
       fdisk [options] device

       fdisk -l [device...]


DESCRIPTION
       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
       -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 begin of the first disk sector when create 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.

       -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-partition 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
       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
       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
       fdisk allows to read (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
       another libfdisk applications. For more details see sfdisk(8).


DISK LABELS
       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
       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
       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.


AUTHORS
       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.


ENVIRONMENT
       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.


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


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



util-linux                       February 2016                        FDISK(8)