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)