Provided by: fdisk_2.34-0.1ubuntu9.6_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.
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(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.
-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/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
Davidlohr Bueso
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)