Ubuntu Manpage: fdisk - manipulate disk partition table

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 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 help text and exit.

-V, --version
Print version 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, the devices mentioned in /proc/partitions (if this file
exists) are used. Devices are always listed in the order in which they are specified
on the command-line, or by the kernel listed in /proc/partitions.

-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
systemd-udevd(8) 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.

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/admin-guide/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 reading (by 'I' command) sfdisk(8) 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(8), sfdisk(8), fdisk and other 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(2) 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(8) 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(8) programs.

COLORS

       The output colorization is implemented by terminal-colors.d(5) functionality. Implicit
       coloring can be disabled by an empty file

          /etc/terminal-colors.d/fdisk.disable

       for the fdisk command or for all tools by

          /etc/terminal-colors.d/disable

       The user-specific $XDG_CONFIG_HOME/terminal-colors.d or $HOME/.config/terminal-colors.d
       overrides the global setting.

       Note that the output colorization may be enabled by default, and in this case
       terminal-colors.d directories do not have to exist yet.

       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.

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.

       LOCK_BLOCK_DEVICE=<mode>
           use exclusive BSD lock. The mode is "1" or "0". See --lock for more details.

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.

REPORTING BUGS

       For bug reports, use the issue tracker at https://github.com/util-linux/util-linux/issues.

AVAILABILITY

       The fdisk command is part of the util-linux package which can be downloaded from Linux
       Kernel Archive <https://www.kernel.org/pub/linux/utils/util-linux/>.