Ubuntu Manpage: fdisk - manipulate disk partition table

Provided by: util-linux_2.27.1-6ubuntu3.10_amd64

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.

       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 --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(1).

-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.

-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/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. In this case the size is expected in bytes and 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.

AVAILABILITY

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