Provided by: util-linux_2.20.1-1ubuntu3_amd64 bug

NAME

       fdisk - manipulate disk partition table

SYNOPSIS

       fdisk [-uc] [-b sectorsize] [-C cyls] [-H heads] [-S sects] device

       fdisk -l [-u] [device...]

       fdisk -s partition...

       fdisk -v

       fdisk -h

DESCRIPTION

       fdisk  (in  the  first  form  of  invocation)  is  a  menu-driven program for creation and
       manipulation of partition tables.  It understands DOS-type partition tables  and  BSD-  or
       SUN-type disklabels.

       fdisk  does  not  understand GUID partition tables (GPTs) and it is not designed for large
       partitions.  In these cases, use the more advanced GNU parted(8).

       fdisk does not use DOS-compatible mode and cylinders as display units by default.  The old
       deprecated  DOS  behavior  can  be  enabled  with  the  '-c=dos -u=cylinders' command-line
       options.

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

       Linux needs at least one partition, namely for its root file  system.   It  can  use  swap
       files  and/or  swap  partitions,  but the latter are more efficient.  So, usually one will
       want a second Linux partition dedicated as swap partition.  On Intel-compatible  hardware,
       the BIOS that boots the system can often only access the first 1024 cylinders of the disk.
       For this reason people with large disks often create a third  partition,  just  a  few  MB
       large,  typically  mounted  on  /boot, to store the kernel image and a few auxiliary files
       needed at boot time, so as to make sure that this stuff is accessible to the BIOS.   There
       may  be  reasons  of  security, ease of administration and backup, or testing, to use more
       than the minimum number of partitions.

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/devices.txt file).

DISK LABELS

       A  BSD/SUN-type 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.

       An  IRIX/SGI-type 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 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  start  numbering
       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.

       If  possible,  fdisk will obtain 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  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,  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.

       A  sync()  and an ioctl(BLKRRPART) (reread partition table from disk) are performed before
       exiting when the partition table has been updated.  Long ago it used to  be  necessary  to
       reboot  after  the  use  of  fdisk.   I  do  not think this is the case anymore -- indeed,
       rebooting too quickly might cause loss of not-yet-written data.  Note that both the kernel
       and the disk hardware may buffer data.

DOS 6.x WARNING

       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 cfdisk or fdisk to change the size of a  DOS  partition
       table  entry,  then  you  must  also  use dd to zero the first 512 bytes of that partition
       before using DOS FORMAT to format the partition.  For example, if you were using cfdisk to
       make  a  DOS  partition table entry for /dev/sda1, then (after exiting fdisk or cfdisk 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.

       BE EXTREMELY CAREFUL if you use the dd command, since a small typo can  make  all  of  the
       data on your disk useless.

       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 program.

OPTIONS

       -b sectorsize
              Specify  the  sector  size  of the disk.  Valid values are 512, 1024, 2048 or 4096.
              (Recent kernels know the sector size.  Use this 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.

       -c[=mode]
              Specify the compatiblity 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'.

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

       -H heads
              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 sects
              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.

       -h     Print help and then exit.

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

       -s partition...
              Print the size (in blocks) of each given partition.

       -u[=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 <units> 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'.

       -v     Print version number of fdisk program and exit.

BUGS

       There are several *fdisk programs around.  Each has its problems and strengths.  Try  them
       in  the  order  cfdisk,  fdisk,  sfdisk.   (Indeed, cfdisk is a beautiful program that has
       strict requirements on  the  partition  tables  it  accepts,  and  produces  high  quality
       partition  tables.   Use it if you can.  fdisk is a buggy program that does fuzzy things -
       usually it happens to produce reasonable results.  Its single advantage  is  that  it  has
       some support for BSD disk labels and other non-DOS partition tables.  Avoid it if you can.
       sfdisk is for hackers only -- the user interface is terrible, but it is more correct  than
       fdisk  and  more  powerful  than  both  fdisk  and  cfdisk.   Moreover,  it  can  be  used
       noninteractively.)

       These days there also is parted.  The cfdisk interface is  nicer,  but  parted  does  much
       more: it not only resizes partitions, but also the filesystems that live in them.

       The  IRIX/SGI-type disklabel is currently not supported by the kernel.  Moreover, IRIX/SGI
       header directories are not fully supported yet.

       The option `dump partition table to file' is missing.

SEE ALSO

       cfdisk(8), sfdisk(8), mkfs(8), parted(8), partprobe(8), kpartx(8)

AVAILABILITY

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