fdisk - manipulate disk partition table
fdisk [options] device
fdisk -l [device...]
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.
- -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 beginning of the first disk sector when creating 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.
- -x, --list-details
- Like --list, but provides more details.
- --lock[=mode]
- Use exclusive BSD lock for device or file it operates. The optional
argument mode can be yes, no (or 1 and 0) or
nonblock. If the mode argument is omitted, it defaults to
"yes". This option overwrites environment variable
$LOCK_BLOCK_DEVICE. The default is not to use any lock at all, but
it's recommended to avoid collisions with udevd or other tools.
- -n, --noauto-pt
- Don't automatically create a default partition table on empty device. The
partition table has to be explicitly created by user (by command like 'o',
'g', etc.).
- -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-partitions 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.
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).
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.
fdisk allows reading (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
other libfdisk applications. For more details see sfdisk(8).
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.
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.
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.
- 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.
- LOCK_BLOCK_DEVICE=<mode>
- use exclusive BSD lock. The mode is "1" or "0". See
--lock for more details.
cfdisk(8), mkfs(8), partx(8), sfdisk(8)
The fdisk command is part of the util-linux package and is available from
https://www.kernel.org/pub/linux/utils/util-linux/.