1CGDISK(8)                      GPT fdisk Manual                      CGDISK(8)
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NAME

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

9       cgdisk [ -a ] device
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11

DESCRIPTION

13       GPT  fdisk is a text-mode family of programs for creation and manipula‐
14       tion of partition tables. The cgdisk member of this  family  employs  a
15       curses-based  user  interface for interaction using a text-mode menuing
16       system. It will automatically convert an old-style Master  Boot  Record
17       (MBR)  partition  table  or BSD disklabel stored without an MBR carrier
18       partition to the newer Globally Unique Identifier (GUID) Partition  Ta‐
19       ble (GPT) format, or will load a GUID partition table. Other members of
20       this program family are gdisk (the most  feature-rich  program  of  the
21       group,  with  a non-curses-based interactive user interface) and sgdisk
22       (which is driven via command-line options for  use  by  experts  or  in
23       scripts).   FixParts  is  a related program for fixing a limited set of
24       problems with MBR disks.
25
26       For information on MBR vs. GPT, as well as GPT terminology  and  struc‐
27       ture,  see  the  extended  GPT  fdisk documentation at http://www.rods
28       books.com/gdisk/ or consult Wikipedia.
29
30       The cgdisk program employs a user interface similar to that of  Linux's
31       cfdisk,  but cgdisk modifies GPT partitions. It also has the capability
32       of transforming MBR partitions or BSD disklabels into  GPT  partitions.
33       Like  the  original  cfdisk program, cgdisk does not modify disk struc‐
34       tures until you explicitly write them to disk, so if you  make  a  mis‐
35       take,  you can exit from the program with the Quit option to leave your
36       partitions unmodified.
37
38       Ordinarily, cgdisk operates on disk device files, such as  /dev/sda  or
39       /dev/hda  under  Linux,  /dev/disk0  under  Mac  OS  X,  or /dev/ad0 or
40       /dev/da0 under FreeBSD. The program can  also  operate  on  disk  image
41       files,  which  can  be  either copies of whole disks (made with dd, for
42       instance) or raw disk images used by emulators such as QEMU or  VMWare.
43       Note  that  only  raw  disk images are supported; cgdisk cannot work on
44       compressed or other advanced disk image formats.
45
46       Upon start, cgdisk attempts to identify the partition type  in  use  on
47       the  disk.  If  it  finds valid GPT data, cgdisk will use it. If cgdisk
48       finds a valid MBR or BSD disklabel but no GPT data, it will attempt  to
49       convert  the MBR or disklabel into GPT form. (BSD disklabels are likely
50       to have unusable first and/or final  partitions  because  they  overlap
51       with  the  GPT  data  structures,  though.)  Upon  exiting with the 'w'
52       option, cgdisk replaces the MBR or disklabel with a GPT. This action is
53       potentially dangerous! Your system may become unbootable, and partition
54       type codes may become corrupted if  the  disk  uses  unrecognized  type
55       codes.   Boot  problems are particularly likely if you're multi-booting
56       with any GPT-unaware OS. If you mistakenly  launch  cgdisk  on  an  MBR
57       disk,  you  can  safely  exit the program without making any changes by
58       using the Quit option.
59
60       When creating a fresh partition table, certain considerations may be in
61       order:
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63
64       *      For data (non-boot) disks, and for boot disks used on BIOS-based
65              computers with GRUB as the boot loader, partitions may  be  cre‐
66              ated in whatever order and in whatever sizes are desired.
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68
69       *      Boot disks for EFI-based systems require an EFI System Partition
70              (GPT fdisk internal code 0xEF00) formatted as FAT-32.  The  rec‐
71              ommended  size  of  this  partition  is between 100 and 300 MiB.
72              Boot-related files are stored here. (Note that GNU Parted  iden‐
73              tifies such partitions as having the "boot flag" set.)
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75
76       *      The  GRUB  2  boot  loader for BIOS-based systems makes use of a
77              BIOS Boot Partition (GPT fdisk internal code 0xEF02),  in  which
78              the  secondary  boot  loader is stored, without the benefit of a
79              filesystem. This partition can typically be quite small (roughly
80              32  KiB to 1 MiB), but you should consult your boot loader docu‐
81              mentation for details.
82
83
84       *      If Windows is to boot from a GPT disk, a partition of  type  Mi‐
85              crosoft  Reserved  (GPT  fdisk  internal  code 0x0C01) is recom‐
86              mended. This partition should be about 128 MiB in size. It ordi‐
87              narily follows the EFI System Partition and immediately precedes
88              the Windows data partitions. (Note  that  old  versions  of  GNU
89              Parted  create  all  FAT partitions as this type, which actually
90              makes the partition unusable for normal  file  storage  in  both
91              Windows and Mac OS X.)
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93
94       *      Some  OSes' GPT utilities create some blank space (typically 128
95              MiB) after each partition. The intent is to enable  future  disk
96              utilities  to use this space. Such free space is not required of
97              GPT disks, but creating it may help in future disk  maintenance.
98              You  can  use  GPT fdisk's relative partition positioning option
99              (specifying the starting sector as  '+128M',  for  instance)  to
100              simplify creating such gaps.
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102

OPTIONS

104       Only  one  command-line option is accepted, aside from the device file‐
105       name: -a. This option alters the highlighting of partitions and  blocks
106       of  free space: Instead of using ncurses, when -a is used cgdisk uses a
107       ">" symbol to the left of the selected partition or free  space.   This
108       option is intended for use on limited display devices such as teletypes
109       and screen readers.
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111       Interactions with cgdisk occur with its  interactive  text-mode  menus.
112       The display is broken into two interactive parts:
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114
115       *      The partition display area, in which partitions and gaps between
116              them (marked as "free space") are summarized.
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118
119       *      The option selection area, in which buttons for the main options
120              appear.
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122
123       In  addition,  the top of the display shows the program's name and ver‐
124       sion number, the device filename associated  with  the  disk,  and  the
125       disk's size in both sectors and IEEE-1541 units (GiB, TiB, and so on).
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127       You can use the following keys to move among the various options and to
128       select among them:
129
130
131       up arrow
132              This key moves the partition selection up by one partition.
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134
135       down arrow
136              This key moves the partition selection down by one partition.
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138
139       Page Up
140              This key moves the partition selection up by one screen.
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143       Page Down
144              This key moves the partition selection down by one screen.
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147       right arrow
148              This key moves the option selection to the right by one item.
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150
151       left arrow
152              This key moves the option selection to the left by one item.
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154
155       Enter  This key activates the currently selected option. You  can  also
156              activate  an  option  by  typing  the  capitalized letter in the
157              option's name on the keyboard, such as a to activate  the  Align
158              option.
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160
161       If  more  partitions exist than can be displayed in one screen, you can
162       scroll between screens using the partition selection keys, much as in a
163       text editor.
164
165       Available  options are as described below. (Note that cgdisk provides a
166       much more limited set of options than its sibling gdisk. If you need to
167       perform  partition  table  recovery,  hybrid  MBR modifcation, or other
168       advanced operations, you should consult the gdisk documentation.)
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170
171       Align  Change the sector alignment value. Disks with more logical  sec‐
172              tors  than  physical  sectors  (such  as  modern Advanced Format
173              drives), some RAID configurations, and  many  SSD  devices,  can
174              suffer  performance problems if partitions are not aligned prop‐
175              erly for their internal data structures. On new disks, GPT fdisk
176              attempts to align partitions on 1MiB boundaries (2048-sectors on
177              disks with 512-byte sectors) by default, which optimizes perfor‐
178              mance for all of these disk types. On pre-partitioned disks, GPT
179              fdisk attempts to identify the  alignment  value  used  on  that
180              disk,  but  will set 8-sector alignment on disks larger than 300
181              GB even if lesser alignment values are detected. In either case,
182              it can be changed by using this option.
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184
185       Backup Save  partition data to a backup file. You can back up your cur‐
186              rent in-memory partition table to a disk file using this option.
187              The resulting file is a binary file consisting of the protective
188              MBR, the main GPT header, the backup GPT header, and one copy of
189              the  partition  table, in that order. Note that the backup is of
190              the current in-memory data structures, so if you launch the pro‐
191              gram,  make  changes,  and then use this option, the backup will
192              reflect your changes.
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194
195       Delete Delete a partition. This action deletes the entry from the  par‐
196              tition  table  but  does not disturb the data within the sectors
197              originally allocated to the partition on the disk. If  a  corre‐
198              sponding hybrid MBR partition exists, gdisk deletes it, as well,
199              and expands any adjacent 0xEE (EFI GPT) MBR protective partition
200              to fill the new free space.
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202
203       Help   Print brief descriptions of all the options.
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205
206       Info   Show  detailed  partition  information.  The summary information
207              shown in the  partition  display  area  necessarily  omits  many
208              details,  such  as  the  partitions' unique GUIDs and the parti‐
209              tions' sector-exact start and end points. The Info  option  dis‐
210              plays this information for a single partition.
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212
213       Load   Load  partition  data  from  a  backup  file. This option is the
214              reverse of the Backup option. Note that restoring partition data
215              from anything but the original disk is not recommended.
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217
218       naMe   Change  the  GPT  name of a partition. This name is encoded as a
219              UTF-16 string, but proper entry and display of  anything  beyond
220              basic  ASCII  values  requires suitable locale and font support.
221              For the most part, Linux ignores the partition name, but it  may
222              be  important  in some OSes. GPT fdisk sets a default name based
223              on the partition type code. Note that the GPT partition name  is
224              different  from  the  filesystem  name,  which is encoded in the
225              filesystem's data structures. Note also that  to  activate  this
226              item  by  typing  its alphabetic equivalent, you must use M, not
227              the more obvious N, because the  latter  is  used  by  the  next
228              option....
229
230
231       New    Create  a  new partition. You enter a starting sector, a size, a
232              type code, and a name. The start  sector  can  be  specified  in
233              absolute  terms  as a sector number or as a position measured in
234              kibibytes (K), mebibytes (M), gibibytes (G), tebibytes  (T),  or
235              pebibytes (P); for instance, 40M specifies a position 40MiB from
236              the start of the disk. You can specify locations relative to the
237              start  or  end  of  the specified default range by preceding the
238              number by a '+' symbol, as in +2G to specify a point 2GiB  after
239              the default start sector. The size value can use the K, M, G, T,
240              and P suffixes, too. Pressing the Enter key with no input speci‐
241              fies the default value, which is the start of the largest avail‐
242              able block for the start sector and the full available size  for
243              the size.
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245
246       Quit   Quit  from  the  program  without saving your changes.  Use this
247              option if you just wanted to view information or if you  make  a
248              mistake and want to back out of all your changes.
249
250
251       Type   Change  a  single partition's type code. You enter the type code
252              using a two-byte hexadecimal number. You may also enter  a  GUID
253              directly,  if  you  have  one and cgdisk doesn't know it. If you
254              don't know the type code for your partition, you can type  L  to
255              see a list of known type codes.
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257
258       Verify Verify  disk. This option checks for a variety of problems, such
259              as incorrect CRCs and mismatched  main  and  backup  data.  This
260              option does not automatically correct most problems, though; for
261              that, you must use gdisk. If no problems are found, this command
262              displays a summary of unallocated disk space.
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264
265       Write  Write data. Use this command to save your changes.
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267

BUGS

269       Known bugs and limitations include:
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271
272       *      The  program  compiles correctly only on Linux, FreeBSD, and Mac
273              OS X. In theory, it should compile under Windows if the  Ncurses
274              library  for  Windows  is  installed, but I have not tested this
275              capability. Linux versions for x86-64  (64-bit),  x86  (32-bit),
276              and  PowerPC  (32-bit) have been tested, with the x86-64 version
277              having seen the most testing. Under FreeBSD,  32-bit  (x86)  and
278              64-bit  (x86-64) versions have been tested. Only 32-bit versions
279              for Mac OS X has been tested by the author.
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281
282       *      The FreeBSD version of the program can't write  changes  to  the
283              partition  table to a disk when existing partitions on that disk
284              are mounted. (The same problem exists with  many  other  FreeBSD
285              utilities,  such  as gpt, fdisk, and dd.) This limitation can be
286              overcome by typing sysctl  kern.geom.debugflags=16  at  a  shell
287              prompt.
288
289
290       *      The program can load only up to 128 partitions (4 primary parti‐
291              tions and 124 logical partitions) when converting from MBR  for‐
292              mat.   This   limit  can  be  raised  by  changing  the  #define
293              MAX_MBR_PARTS line in the basicmbr.h source code file and recom‐
294              piling;   however,   such   a   change   will  require  using  a
295              larger-than-normal partition table. (The limit of 128 partitions
296              was  chosen  because  that number equals the 128 partitions sup‐
297              ported by the most common partition table size.)
298
299
300       *      Converting from MBR format sometimes fails because  of  insuffi‐
301              cient space at the start or (more commonly) the end of the disk.
302              Resizing the partition  table  (using  the  's'  option  in  the
303              experts'  menu  in  gdisk)  can sometimes overcome this problem;
304              however, in extreme cases it may be necessary to resize a parti‐
305              tion using GNU Parted or a similar tool prior to conversion with
306              GPT fdisk.
307
308
309       *      MBR conversions work only if the disk has correct LBA  partition
310              descriptors.  These  descriptors  should  be present on any disk
311              over 8 GiB in size or on smaller disks partitioned with any  but
312              very ancient software.
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314
315       *      BSD  disklabel  support  can create first and/or last partitions
316              that overlap with the GPT data structures. This can sometimes be
317              compensated  by  adjusting  the  partition  table  size,  but in
318              extreme cases the affected partition(s) may need to be deleted.
319
320
321       *      Because of the highly variable nature of  BSD  disklabel  struc‐
322              tures,  conversions  from  this form may be unreliable -- parti‐
323              tions may be dropped, converted in a way that  creates  overlaps
324              with  other partitions, or converted with incorrect start or end
325              values. Use this feature with caution!
326
327
328       *      Booting after converting an MBR or BSD disklabel disk is  likely
329              to  be disrupted. Sometimes re-installing a boot loader will fix
330              the problem, but other times you may need to switch  boot  load‐
331              ers.  Except  on  EFI-based  platforms, Windows through at least
332              Windows 7 doesn't support booting from  GPT  disks.  Creating  a
333              hybrid  MBR  (using the 'h' option on the recovery & transforma‐
334              tion menu in gdisk) or abandoning GPT in favor  of  MBR  may  be
335              your only options in this case.
336
337
338       *      The  cgdisk  Verify  function  and  the  partition  type listing
339              obtainable by typing L in the Type function (or when  specifying
340              a  partition type while creating a new partition) both currently
341              exit ncurses mode. This limitation is a minor  cosmetic  blemish
342              that does not affect functionality.
343
344

AUTHORS

346       Primary author: Roderick W. Smith (rodsmith@rodsbooks.com)
347
348       Contributors:
349
350       * Yves Blusseau (1otnwmz02@sneakemail.com)
351
352       * David Hubbard (david.c.hubbard@gmail.com)
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354       * Justin Maggard (justin.maggard@netgear.com)
355
356       * Dwight Schauer (dschauer@gmail.com)
357
358       * Florian Zumbiehl (florz@florz.de)
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360
361

SEE ALSO

363       cfdisk  (8),  fdisk  (8),  gdisk  (8), mkfs (8), parted (8), sfdisk (8)
364       sgdisk (8) fixparts (8)
365
366       http://en.wikipedia.org/wiki/GUID_Partition_Table
367
368       http://developer.apple.com/technotes/tn2006/tn2166.html
369
370       http://www.rodsbooks.com/gdisk/
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372

AVAILABILITY

374       The cgdisk command is part of the GPT fdisk package  and  is  available
375       from Rod Smith.
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378
379Roderick W. Smith                    1.0.3                           CGDISK(8)
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