cgdisk - Curses-based GUID partition table (GPT) manipulator
[ -a ] device
GPT fdisk is a text-mode family of programs for creation and manipulation of
partition tables. The cgdisk
member of this family employs a
curses-based user interface for interaction using a text-mode menuing system.
It will automatically convert an old-style Master Boot Record (MBR) partition
table or BSD disklabel stored without an MBR carrier partition to the newer
Globally Unique Identifier (GUID) Partition Table (GPT) format, or will load a
GUID partition table. Other members of this program family are gdisk
(the most feature-rich program of the group, with a non-curses-based
interactive user interface) and sgdisk
(which is driven via
command-line options for use by experts or in scripts). FixParts is a related
program for fixing a limited set of problems with MBR disks.
For information on MBR vs. GPT, as well as GPT terminology and structure, see
the extended GPT fdisk documentation at http://www.rodsbooks.com/gdisk/
or consult Wikipedia.
program employs a user interface similar to that of Linux's
, but cgdisk
modifies GPT partitions. It also has the
capability of transforming MBR partitions or BSD disklabels into GPT
partitions. Like the original cfdisk
modify disk structures until you explicitly write them to disk, so if you make
a mistake, you can exit from the program with the Quit option to leave your
operates on disk device files, such as /dev/sda
under Linux, /dev/disk0
under Mac OS X, or
under FreeBSD. The program can also operate
on disk image files, which can be either copies of whole disks (made with
, for instance) or raw disk images used by emulators such as QEMU or
VMWare. Note that only raw
disk images are supported; cgdisk
cannot work on compressed or other advanced disk image formats.
Upon start, cgdisk
attempts to identify the partition type in use on the
disk. If it finds valid GPT data, cgdisk
will use it. If cgdisk
finds a valid MBR or BSD disklabel but no GPT data, it will attempt to convert
the MBR or disklabel into GPT form. (BSD disklabels are likely to have
unusable first and/or final partitions because they overlap with the GPT data
structures, though.) Upon exiting with the 'w' option, cgdisk
the MBR or disklabel with a GPT. This action is potentially
Your system may become unbootable, and partition type codes may
become corrupted if the disk uses unrecognized type codes. Boot problems are
particularly likely if you're multi-booting with any GPT-unaware OS. If you
mistakenly launch cgdisk
on an MBR disk, you can safely exit the
program without making any changes by using the Quit option.
When creating a fresh partition table, certain considerations may be in order:
- For data (non-boot) disks, and for boot disks used on
BIOS-based computers with GRUB as the boot loader, partitions may be
created in whatever order and in whatever sizes are desired.
- Boot disks for EFI-based systems require an EFI
System Partition (GPT fdisk internal code 0xEF00) formatted as
FAT-32. The recommended size of this partition is between 100 and 300 MiB.
Boot-related files are stored here. (Note that GNU Parted identifies such
partitions as having the "boot flag" set.)
- The GRUB 2 boot loader for BIOS-based systems makes use of
a BIOS Boot Partition (GPT fdisk internal code 0xEF02), in
which the secondary boot loader is stored, without the benefit of a
filesystem. This partition can typically be quite small (roughly 32 KiB to
1 MiB), but you should consult your boot loader documentation for details.
- If Windows is to boot from a GPT disk, a partition of type
Microsoft Reserved (GPT fdisk internal code 0x0C01) is
recommended. This partition should be about 128 MiB in size. It ordinarily
follows the EFI System Partition and immediately precedes the Windows data
partitions. (Note that old versions of GNU Parted create all FAT
partitions as this type, which actually makes the partition unusable for
normal file storage in both Windows and Mac OS X.)
- Some OSes' GPT utilities create some blank space (typically
128 MiB) after each partition. The intent is to enable future disk
utilities to use this space. Such free space is not required of GPT disks,
but creating it may help in future disk maintenance. You can use GPT
fdisk's relative partition positioning option (specifying the starting
sector as '+128M', for instance) to simplify creating such gaps.
Only one command-line option is accepted, aside from the device filename:
. This option alters the highlighting of partitions and blocks of
free space: Instead of using ncurses, when -a
is used cgdisk
uses a ">" symbol to the left of the selected partition or free
space. This option is intended for use on limited display devices such as
teletypes and screen readers.
Interactions with cgdisk
occur with its interactive text-mode menus. The
display is broken into two interactive parts:
- The partition display area, in which partitions and gaps
between them (marked as "free space") are summarized.
- The option selection area, in which buttons for the main
In addition, the top of the display shows the program's name and version number,
the device filename associated with the disk, and the disk's size in both
sectors and IEEE-1541 units (GiB, TiB, and so on).
You can use the following keys to move among the various options and to select
- up arrow
- This key moves the partition selection up by one partition.
- down arrow
- This key moves the partition selection down by one
- Page Up
- This key moves the partition selection up by one screen.
- Page Down
- This key moves the partition selection down by one screen.
- right arrow
- This key moves the option selection to the right by one
- left arrow
- This key moves the option selection to the left by one
- This key activates the currently selected option. You can
also activate an option by typing the capitalized letter in the option's
name on the keyboard, such as a to activate the Align option.
If more partitions exist than can be displayed in one screen, you can scroll
between screens using the partition selection keys, much as in a text editor.
Available options are as described below. (Note that cgdisk
much more limited set of options than its sibling gdisk
. If you need to
perform partition table recovery, hybrid MBR modifcation, or other advanced
operations, you should consult the gdisk
- Change the sector alignment value. Disks with more logical
sectors than physical sectors (such as modern Advanced Format drives),
some RAID configurations, and many SSD devices, can suffer performance
problems if partitions are not aligned properly for their internal data
structures. On new disks, GPT fdisk attempts to align partitions on 1MiB
boundaries (2048-sectors on disks with 512-byte sectors) by default, which
optimizes performance for all of these disk types. On pre-partitioned
disks, GPT fdisk attempts to identify the alignment value used on that
disk, but will set 8-sector alignment on disks larger than 300 GB even if
lesser alignment values are detected. In either case, it can be changed by
using this option.
- Save partition data to a backup file. You can back up your
current in-memory partition table to a disk file using this option. The
resulting file is a binary file consisting of the protective MBR, the main
GPT header, the backup GPT header, and one copy of the partition table, in
that order. Note that the backup is of the current in-memory data
structures, so if you launch the program, make changes, and then use this
option, the backup will reflect your changes.
- Delete a partition. This action deletes the entry from the
partition table but does not disturb the data within the sectors
originally allocated to the partition on the disk. If a corresponding
hybrid MBR partition exists, gdisk deletes it, as well, and expands
any adjacent 0xEE (EFI GPT) MBR protective partition to fill the new free
- Print brief descriptions of all the options.
- Show detailed partition information. The summary
information shown in the partition display area necessarily omits many
details, such as the partitions' unique GUIDs and the partitions'
sector-exact start and end points. The Info option displays this
information for a single partition.
- Load partition data from a backup file. This option is the
reverse of the Backup option. Note that restoring partition data from
anything but the original disk is not recommended.
- Change the GPT name of a partition. This name is encoded as
a UTF-16 string, but proper entry and display of anything beyond basic
ASCII values requires suitable locale and font support. For the most part,
Linux ignores the partition name, but it may be important in some OSes.
GPT fdisk sets a default name based on the partition type code. Note that
the GPT partition name is different from the filesystem name, which is
encoded in the filesystem's data structures. Note also that to activate
this item by typing its alphabetic equivalent, you must use M, not
the more obvious N, because the latter is used by the next
- Create a new partition. You enter a starting sector, a
size, a type code, and a name. The start sector can be specified in
absolute terms as a sector number or as a position measured in kibibytes
(K), mebibytes (M), gibibytes (G), tebibytes (T), or pebibytes (P); for
instance, 40M specifies a position 40MiB from the start of
the disk. You can specify locations relative to the start or end of the
specified default range by preceding the number by a '+' symbol, as in
+2G to specify a point 2GiB after the default start sector.
The size value can use the K, M, G, T, and P suffixes, too. Pressing the
Enter key with no input specifies the default value, which is the start of
the largest available block for the start sector and the full available
size for the size.
- Quit from the program without saving your changes.
Use this option if you just wanted to view information or if you make a
mistake and want to back out of all your changes.
- Change a single partition's type code. You enter the type
code using a two-byte hexadecimal number. You may also enter a GUID
directly, if you have one and cgdisk doesn't know it. If you don't
know the type code for your partition, you can type L to see a list
of known type codes.
- Verify disk. This option checks for a variety of problems,
such as incorrect CRCs and mismatched main and backup data. This option
does not automatically correct most problems, though; for that, you must
use gdisk. If no problems are found, this command displays a
summary of unallocated disk space.
- Write data. Use this command to save your changes.
Known bugs and limitations include:
- The program compiles correctly only on Linux, FreeBSD, and
Mac OS X. In theory, it should compile under Windows if the Ncurses
library for Windows is installed, but I have not tested this capability.
Linux versions for x86-64 (64-bit), x86 (32-bit), and PowerPC (32-bit)
have been tested, with the x86-64 version having seen the most testing.
Under FreeBSD, 32-bit (x86) and 64-bit (x86-64) versions have been tested.
Only 32-bit versions for Mac OS X has been tested by the author.
- The FreeBSD version of the program can't write changes to
the partition table to a disk when existing partitions on that disk are
mounted. (The same problem exists with many other FreeBSD utilities, such
as gpt, fdisk, and dd.) This limitation can be
overcome by typing sysctl kern.geom.debugflags=16 at a shell
- The program can load only up to 128 partitions (4 primary
partitions and 124 logical partitions) when converting from MBR format.
This limit can be raised by changing the #define MAX_MBR_PARTS line
in the basicmbr.h source code file and recompiling; however, such a
change will require using a larger-than-normal partition table. (The limit
of 128 partitions was chosen because that number equals the 128 partitions
supported by the most common partition table size.)
- Converting from MBR format sometimes fails because of
insufficient space at the start or (more commonly) the end of the disk.
Resizing the partition table (using the 's' option in the experts' menu in
gdisk) can sometimes overcome this problem; however, in extreme
cases it may be necessary to resize a partition using GNU Parted or a
similar tool prior to conversion with GPT fdisk.
- MBR conversions work only if the disk has correct LBA
partition descriptors. These descriptors should be present on any disk
over 8 GiB in size or on smaller disks partitioned with any but very
- BSD disklabel support can create first and/or last
partitions that overlap with the GPT data structures. This can sometimes
be compensated by adjusting the partition table size, but in extreme cases
the affected partition(s) may need to be deleted.
- Because of the highly variable nature of BSD disklabel
structures, conversions from this form may be unreliable -- partitions may
be dropped, converted in a way that creates overlaps with other
partitions, or converted with incorrect start or end values. Use this
feature with caution!
- Booting after converting an MBR or BSD disklabel disk is
likely to be disrupted. Sometimes re-installing a boot loader will fix the
problem, but other times you may need to switch boot loaders. Except on
EFI-based platforms, Windows through at least Windows 7 doesn't support
booting from GPT disks. Creating a hybrid MBR (using the 'h' option on the
recovery & transformation menu in gdisk) or abandoning GPT in
favor of MBR may be your only options in this case.
- The cgdisk Verify function and the partition type
listing obtainable by typing L in the Type function (or when
specifying a partition type while creating a new partition) both currently
exit ncurses mode. This limitation is a minor cosmetic blemish that does
not affect functionality.
Primary author: Roderick W. Smith (firstname.lastname@example.org)
* Yves Blusseau (email@example.com)
* David Hubbard (firstname.lastname@example.org)
* Justin Maggard (email@example.com)
* Dwight Schauer (firstname.lastname@example.org)
* Florian Zumbiehl (email@example.com)
, fdisk (8)
, gdisk (8)
, mkfs (8)
, sfdisk (8) sgdisk (8) fixparts (8)
command is part of the GPT fdisk
package and is
available from Rod Smith.