cgdisk

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 manipula-
       tion 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  Ta-
       ble (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  struc-
       ture,  see  the  extended  GPT  fdisk documentation at http://www.rods-
       books.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 struc-
       tures until you explicitly write them to disk, so if you  make  a  mis-
       take,  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 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 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  cre-
              ated 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  rec-
              ommended  size  of  this  partition  is between 100 and 300 MiB.
              Boot-related files are stored here. (Note that GNU Parted  iden-
              tifies 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 docu-
              mentation for details.

       *      If Windows is to boot from a GPT disk, a partition of  type  Mi-
              crosoft  Reserved  (GPT  fdisk  internal  code 0x0C01) is recom-
              mended. This partition should be about 128 MiB in size. It ordi-
              narily 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.

OPTIONS
       Only  one  command-line option is accepted, aside from the device file-
       name: -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 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 options
              appear.

       In  addition,  the top of the display shows the program's name and ver-
       sion 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 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 modifcation, or other
       advanced operations, you should consult the gdisk documentation.)

       Align  Change the sector alignment value. Disks with more logical  sec-
              tors  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 prop-
              erly 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 perfor-
              mance 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 cur-
              rent 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 pro-
              gram,  make  changes,  and then use this option, the backup will
              reflect your changes.

       Delete Delete a partition. This action deletes the entry from the  par-
              tition  table  but  does not disturb the data within the sectors
              originally allocated to the partition on the disk. If  a  corre-
              sponding 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 parti-
              tions' sector-exact start and end points. The Info  option  dis-
              plays 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 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
              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 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 speci-
              fies 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 changes.

       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.

       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 problems, 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 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
              prompt.

       *      The program can load only up to 128 partitions (4 primary parti-
              tions and 124 logical partitions) when converting from MBR  for-
              mat.   This   limit  can  be  raised  by  changing  the  #define
              MAX_MBR_PARTS line in the basicmbr.h source code file and recom-
              piling;   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 sup-
              ported by the most common partition table size.)

       *      Converting from MBR format sometimes fails because  of  insuffi-
              cient 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 parti-
              tion 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 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  table  size,  but in
              extreme cases the affected partition(s) may need to be deleted.

       *      Because of the highly variable nature of  BSD  disklabel  struc-
              tures,  conversions  from  this form may be unreliable -- parti-
              tions 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  load-
              ers.  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 & transforma-
              tion 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@rodsbooks.com)

       Contributors:

       * Yves Blusseau (1otnwmz02@sneakemail.com)

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

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

       * Dwight Schauer (dschauer@gmail.com)

       * Florian Zumbiehl (florz@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                    1.0.3                           CGDISK(8)
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