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> advice 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. The kernel is aware
of the sector size for regular block devices. Use this option only on very old kernels, when working
with disk images, or to override the kernel’s default sector size. Since util-linux-2.17, fdisk
distinguishes between logical and physical sector size. This option changes both sector sizes to the
specified 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.

-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.

-h, --help
Display help text and exit.

-V, --version
Display version 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, then the number may be followed by the multiplicative
       suffixes KiB (1024 bytes), MiB (1024*1024 bytes), 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 if specified with multiplicative suffixes (e.g. +100MiB) are always aligned according
       to device I/O limits. The +/-<size>{K,B,M,G,...} notation is recommended.

       The last sector of the partition is strictly calculated as <start> + <size> (without -1) if the size is
       specified by the +<sectors> notation. In this case, the size is not aligned to the device I/O limits.

       For backward compatibility fdisk also accepts the suffixes KB (1000 bytes), MB (1000*1000 bytes), 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

       Since version 2.41, the $NO_COLOR environment variable is also supported to disable output colorization
       unless explicitly enabled by a command-line option.

       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 <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 2.41                                    2025-03-17                                           FDISK(8)