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CGDISK(8)                                 GPT fdisk Manual                                 CGDISK(8)



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

SYNOPSIS
       cgdisk [ -a ] device


DESCRIPTION
       GPT  fdisk  is  a text-mode family of programs for creation and manipulation of partition ta‐
       bles. 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  pro‐
       gram  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.

       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 oper‐
       ate on disk image files, which can be either copies of whole disks (made  with  dd,  for  in‐
       stance)  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 replaces the MBR  or  disklabel
       with a GPT. This action is potentially dangerous! Your system may become unbootable, and par‐
       tition type codes may become corrupted if the disk uses unrecognized type codes.  Boot  prob‐
       lems  are particularly likely if you're multi-booting with any GPT-unaware OS. If you mistak‐
       enly 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 Win‐
              dows 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 parti‐
              tion. 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.


OPTIONS
       Only one command-line option is accepted, aside from the device filename: -a. This option al‐
       ters  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 read‐
       ers.

       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 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 partition.


       down arrow
              This key moves the partition selection down by one partition.


       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 item.


       left arrow
              This key moves the option selection to the left by one item.


       Enter  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 acti‐
              vate 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.)


       Align  Change  the sector alignment value. Disks with more logical sectors than physical sec‐
              tors (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
              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.


       Backup 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 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
              space.


       Help   Print brief descriptions of all the options.


       Info   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  in‐
              formation for a single partition.


       Load   Load  partition  data from a backup file. This option is the reverse of the Backup op‐
              tion. 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 display of anything beyond basic ASCII values requires  suitable  lo‐
              cale 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 option....


       New    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 posi‐
              tion measured in kibibytes (K), mebibytes (M), gibibytes (G), tebibytes  (T),  or  pe‐
              bibytes  (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   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.


       Type   Change a single partition's type code. You enter the type code using a two-byte  hexa‐
              decimal 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 filtered by a search
              string; for instance, entering linux shows only partition type codes with descriptions
              that include the string Linux. This search is performed case-insensitively.


       Verify 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 prob‐
              lems,  though;  for  that,  you must use gdisk. If no problems are found, this command
              displays a summary of unallocated disk space.


       Write  Write data. Use this command to save your changes.


BUGS
       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 test‐
              ing. 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 prompt.


       *      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;  how‐
              ever,  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  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 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 de‐
              scriptors should be present on any disk over 8 GiB in size or on smaller disks  parti‐
              tioned with any but very ancient software.


       *      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  ta‐
              ble 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 cre‐
              ates  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. Some‐
              times  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  Win‐
              dows  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.


AUTHORS
       Primary author: Roderick W. Smith (rodsmith AT rodsbooks.com)

       Contributors:

       * Yves Blusseau (1otnwmz02 AT sneakemail.com)

       * David Hubbard (david.c.hubbard AT gmail.com)

       * Justin Maggard (justin.maggard AT netgear.com)

       * Dwight Schauer (das AT teegra.net)

       * Florian Zumbiehl (florz AT florz.de)



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

       http://en.wikipedia.org/wiki/GUID_Partition_Table

       http://developer.apple.com/technotes/tn2006/tn2166.html

       http://www.rodsbooks.com/gdisk/


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



Roderick W. Smith                               1.0.8                                      CGDISK(8)