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 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.
SEE ALSO
cfdisk(8), mkfs(8), partx(8), sfdisk(8)
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/>.
util-linux 2.38.1 2022-05-11 FDISK(8)
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