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 divi-
sion 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 guaran-
teed. 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 sector-
size.
-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 argu-
ment -- 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 DEP-
RECATED 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) com-
mand.
-W, --wipe-partition when
Wipe filesystem, RAID and partition-table signatures from a newly created parti-
tions, 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 sig-
natures 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 parti-
tion 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 documen-
tation (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 ta-
ble 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 appli-
cations. 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 log-
ical 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 speci-
fication. It prevents MBR-only partitioning tools from mis-recognizing and over-
writing 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 sec-
tor 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 sec-
tor (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 physi-
cal disk geometry (indeed, modern disks do not really have anything like a physical geome-
try, certainly not something that can be described in the simplistic Cylinders/Heads/Sec-
tors 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 bound-
ary, 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 exam-
ple, 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.ker-
nel.org/pub/linux/utils/util-linux/.
util-linux February 2016 FDISK(8)
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