CGDISK(8)                    (1.0.8)                    CGDISK(8)

          cgdisk - Curses-based GUID partition table (GPT) manipulator

          cgdisk [ -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 con-
          vert 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 interac-
          tive 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
 or consult Wikipedia.

          The cgdisk program employs a user interface similar to that
          of Linux's cfdisk, but cgdisk modifies GPT partitions. It
          also has the capability of transforming MBR partitions or
          BSD disklabels into GPT partitions. Like the original cfdisk
          program, cgdisk does not 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
          partitions unmodified.

          Ordinarily, cgdisk operates on disk device files, such as
          /dev/sda or /dev/hda under Linux, /dev/disk0 under Mac OS X,
          or /dev/ad0 or /dev/da0 under FreeBSD. The program can also
          operate on disk image files, which can be either copies of
          whole disks (made with dd, 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

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          first and/or final partitions because they overlap with the
          GPT data structures, though.) Upon exiting with the 'w'
          option, cgdisk replaces the MBR or disklabel with a GPT.
          This action is potentially dangerous! 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 considera-
          tions may be in order:

          *    For data (non-boot) disks, and for boot disks used on
               BIOS-based computers with GRUB as the boot loader, par-
               titions may be created in whatever order and in what-
               ever 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

          *    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 cre-
               ate 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 (typi-
               cally 128 MiB) after each partition. The intent is to
               enable future disk utilities to use this space. Such

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               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 (specify-
               ing the starting sector as '+128M', for instance) to
               simplify creating such gaps.

          Only one command-line option is accepted, aside from the
          device filename: -a. 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 tele-
          types and screen readers.

          Interactions with cgdisk occur with its interactive
          text-mode menus.  The display is broken into two interactive

          *    The partition display area, in which partitions and
               gaps between them (marked as "free space") are summa-

          *    The option selection area, in which buttons for the
               main options appear.

          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 among them:

          up arrow
               This key moves the partition selection up by one parti-

          down arrow
               This key moves the partition selection down by one par-

          Page Up
               This key moves the partition selection up by one

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          Page Down
               This key moves the partition selection down by one

          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
          provides a much more limited set of options than its sibling
          gdisk. If you need to perform partition table recovery,
          hybrid MBR modification, or other advanced operations, you
          should consult the gdisk documentation.)

               Change the sector alignment value. Disks with more log-
               ical 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 1 MiB boundaries (2048-sectors on
               disks with 512-byte sectors) by default, which opti-
               mizes 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

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               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 parti-
               tion on the disk. If a corresponding hybrid MBR parti-
               tion exists, gdisk deletes it, as well, and expands any
               adjacent 0xEE (EFI GPT) MBR protective partition to
               fill the new free space.

          Help Print brief descriptions of all the options.

          Info Show detailed partition information. The summary infor-
               mation 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 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.

          naMe Change the GPT name of a partition. This name is
               encoded as a UTF-16 string, but proper entry and dis-
               play 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 impor-
               tant 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 option....

          New  Create a new partition. You enter a starting sector, a

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               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 preced-
               ing 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 avail-
               able block for the start sector and the full available
               size for the size.

          Quit 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

          Type 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.  The type code list may optionally be fil-
               tered by a search string; for instance, entering linux
               shows only partition type codes with descriptions that
               include the string Linux. This search is performed

               Verify disk. This option checks for a variety of prob-
               lems, 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,

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               and Mac OS X. In theory, it should compile under Win-
               dows 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 parti-
               tions 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 typ-
               ing sysctl kern.geom.debugflags=16 at a shell prompt.

          *    The program can load only up to 128 partitions (4 pri-
               mary partitions and 124 logical partitions) when con-
               verting 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 cho-
               sen because that number equals the 128 partitions sup-
               ported 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 some-
               times 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

          *    MBR conversions work only if the disk has correct LBA
               partition descriptors. These descriptors should be pre-
               sent on any disk over 8 GiB in size or on smaller disks
               partitioned with any but very ancient software.

          *    BSD disklabel support can create first and/or last par-
               titions 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.

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          *    Because of the highly variable nature of BSD disklabel
               structures, conversions from this form may be unreli-
               able -- partitions may be dropped, converted in a way
               that creates overlaps with other partitions, or con-
               verted 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 list-
               ing 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 limi-
               tation is a minor cosmetic blemish that does not affect

          Primary author: Roderick W. Smith (


          * Yves Blusseau (

          * David Hubbard (

          * Justin Maggard (

          * Dwight Schauer (

          * Florian Zumbiehl (

          cfdisk(8), fdisk(8), gdisk(8), mkfs(8), parted(8),
          sfdisk(8), sgdisk(8), fixparts(8).

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          The cgdisk command is part of the GPT fdisk package and is
          available from Rod Smith.

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