1CGDISK(8) GPT fdisk Manual CGDISK(8)
2
6 cgdisk - Curses-based GUID partition table (GPT) manipulator
7
9 cgdisk [ -a ] device
10
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 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 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 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 in‐
42 stance) 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 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' op‐
52 tion, 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 us‐
58 ing the Quit option.
59 When creating a fresh partition table, certain considerations may be in
61 order:
62 * 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.
67 * 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.)
74 * 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 * 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.)
92 * 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.
101
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.
110 Interactions with cgdisk occur with its interactive text-mode menus.
112 The display is broken into two interactive parts:
113 * The partition display area, in which partitions and gaps between
116 them (marked as "free space") are summarized.
117 * The option selection area, in which buttons for the main options
120 appear.
121 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).
126 You can use the following keys to move among the various options and to
128 select among them:
129 up arrow
132 This key moves the partition selection up by one partition.
133 down arrow
136 This key moves the partition selection down by one partition.
137 Page Up
140 This key moves the partition selection up by one screen.
141 Page Down
144 This key moves the partition selection down by one screen.
145 right arrow
148 This key moves the option selection to the right by one item.
149 left arrow
152 This key moves the option selection to the left by one item.
153 Enter This key activates the currently selected option. You can also
156 activate an option by typing the capitalized letter in the op‐
157 tion's name on the keyboard, such as a to activate the Align op‐
158 tion.
159 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 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 modification, or other ad‐
168 vanced operations, you should consult the gdisk documentation.)
169 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 1 MiB boundaries (2048-sectors
177 on disks with 512-byte sectors) by default, which optimizes per‐
178 formance for all of these disk types. On pre-partitioned disks,
179 GPT 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. The alignment value
183 also affects the default end sector value when creating a new
184 partition; it will be aligned to one less than a multiple of the
185 alignment value, when possible. This should keep partitions a
186 multiple of the alignment value in size. Some disk encryption
187 tools require partitions to be sized to some value, typically
188 4096 bytes, so the default alignment of 1 MiB works well for
189 them.
190 Backup Save partition data to a backup file. You can back up your cur‐
193 rent in-memory partition table to a disk file using this option.
194 The resulting file is a binary file consisting of the protective
195 MBR, the main GPT header, the backup GPT header, and one copy of
196 the partition table, in that order. Note that the backup is of
197 the current in-memory data structures, so if you launch the pro‐
198 gram, make changes, and then use this option, the backup will
199 reflect your changes.
200 Delete Delete a partition. This action deletes the entry from the par‐
203 tition table but does not disturb the data within the sectors
204 originally allocated to the partition on the disk. If a corre‐
205 sponding hybrid MBR partition exists, gdisk deletes it, as well,
206 and expands any adjacent 0xEE (EFI GPT) MBR protective partition
207 to fill the new free space.
208 Help Print brief descriptions of all the options.
211 Info Show detailed partition information. The summary information
214 shown in the partition display area necessarily omits many de‐
215 tails, such as the partitions' unique GUIDs and the partitions'
216 sector-exact start and end points. The Info option displays this
217 information for a single partition.
218 Load Load partition data from a backup file. This option is the re‐
221 verse of the Backup option. Note that restoring partition data
222 from anything but the original disk is not recommended.
223 naMe Change the GPT name of a partition. This name is encoded as a
226 UTF-16 string, but proper entry and display of anything beyond
227 basic ASCII values requires suitable locale and font support.
228 For the most part, Linux ignores the partition name, but it may
229 be important in some OSes. GPT fdisk sets a default name based
230 on the partition type code. Note that the GPT partition name is
231 different from the filesystem name, which is encoded in the
232 filesystem's data structures. Note also that to activate this
233 item by typing its alphabetic equivalent, you must use M, not
234 the more obvious N, because the latter is used by the next op‐
235 tion....
236 New Create a new partition. You enter a starting sector, a size, a
239 type code, and a name. The start sector can be specified in ab‐
240 solute terms as a sector number or as a position measured in
241 kibibytes (K), mebibytes (M), gibibytes (G), tebibytes (T), or
242 pebibytes (P); for instance, 40M specifies a position 40MiB from
243 the start of the disk. You can specify locations relative to the
244 start or end of the specified default range by preceding the
245 number by a '+' symbol, as in +2G to specify a point 2GiB after
246 the default start sector. The size value can use the K, M, G, T,
247 and P suffixes, too. Pressing the Enter key with no input speci‐
248 fies the default value, which is the start of the largest avail‐
249 able block for the start sector and the full available size for
250 the size.
251 Quit Quit from the program without saving your changes. Use this op‐
254 tion if you just wanted to view information or if you make a
255 mistake and want to back out of all your changes.
256 Type Change a single partition's type code. You enter the type code
259 using a two-byte hexadecimal number. You may also enter a GUID
260 directly, if you have one and cgdisk doesn't know it. If you
261 don't know the type code for your partition, you can type L to
262 see a list of known type codes. The type code list may option‐
263 ally be filtered by a search string; for instance, entering
264 linux shows only partition type codes with descriptions that in‐
265 clude the string Linux. This search is performed case-insensi‐
266 tively.
267 Verify Verify disk. This option checks for a variety of problems, such
270 as incorrect CRCs and mismatched main and backup data. This op‐
271 tion does not automatically correct most problems, though; for
272 that, you must use gdisk. If no problems are found, this command
273 displays a summary of unallocated disk space.
274 Write Write data. Use this command to save your changes.
277
280 Known bugs and limitations include:
281 * The program compiles correctly only on Linux, FreeBSD, and Mac
284 OS X. In theory, it should compile under Windows if the Ncurses
285 library for Windows is installed, but I have not tested this ca‐
286 pability. Linux versions for x86-64 (64-bit), x86 (32-bit), and
287 PowerPC (32-bit) have been tested, with the x86-64 version hav‐
288 ing seen the most testing. Under FreeBSD, 32-bit (x86) and
289 64-bit (x86-64) versions have been tested. Only 32-bit versions
290 for Mac OS X has been tested by the author.
291 * The FreeBSD version of the program can't write changes to the
294 partition table to a disk when existing partitions on that disk
295 are mounted. (The same problem exists with many other FreeBSD
296 utilities, such as gpt, fdisk, and dd.) This limitation can be
297 overcome by typing sysctl kern.geom.debugflags=16 at a shell
298 prompt.
299 * The program can load only up to 128 partitions (4 primary parti‐
302 tions and 124 logical partitions) when converting from MBR for‐
303 mat. This limit can be raised by changing the #define
304 MAX_MBR_PARTS line in the basicmbr.h source code file and recom‐
305 piling; however, such a change will require using a
306 larger-than-normal partition table. (The limit of 128 partitions
307 was chosen because that number equals the 128 partitions sup‐
308 ported by the most common partition table size.)
309 * Converting from MBR format sometimes fails because of insuffi‐
312 cient space at the start or (more commonly) the end of the disk.
313 Resizing the partition table (using the 's' option in the ex‐
314 perts' menu in gdisk) can sometimes overcome this problem; how‐
315 ever, in extreme cases it may be necessary to resize a partition
316 using GNU Parted or a similar tool prior to conversion with GPT
317 fdisk.
318 * MBR conversions work only if the disk has correct LBA partition
321 descriptors. These descriptors should be present on any disk
322 over 8 GiB in size or on smaller disks partitioned with any but
323 very ancient software.
324 * BSD disklabel support can create first and/or last partitions
327 that overlap with the GPT data structures. This can sometimes be
328 compensated by adjusting the partition table size, but in ex‐
329 treme cases the affected partition(s) may need to be deleted.
330 * Because of the highly variable nature of BSD disklabel struc‐
333 tures, conversions from this form may be unreliable -- parti‐
334 tions may be dropped, converted in a way that creates overlaps
335 with other partitions, or converted with incorrect start or end
336 values. Use this feature with caution!
337 * Booting after converting an MBR or BSD disklabel disk is likely
340 to be disrupted. Sometimes re-installing a boot loader will fix
341 the problem, but other times you may need to switch boot load‐
342 ers. Except on EFI-based platforms, Windows through at least
343 Windows 7 doesn't support booting from GPT disks. Creating a hy‐
344 brid MBR (using the 'h' option on the recovery & transformation
345 menu in gdisk) or abandoning GPT in favor of MBR may be your
346 only options in this case.
347 * The cgdisk Verify function and the partition type listing ob‐
350 tainable by typing L in the Type function (or when specifying a
351 partition type while creating a new partition) both currently
352 exit ncurses mode. This limitation is a minor cosmetic blemish
353 that does not affect functionality.
354
357 Primary author: Roderick W. Smith (rodsmith@rodsbooks.com)
358 Contributors:
360 * Yves Blusseau (1otnwmz02@sneakemail.com)
362 * David Hubbard (david.c.hubbard@gmail.com)
364 * Justin Maggard (justin.maggard@netgear.com)
366 * Dwight Schauer (das@teegra.net)
368 * Florian Zumbiehl (florz@florz.de)
370
374 cfdisk(8), fdisk(8), gdisk(8), mkfs(8), parted(8), sfdisk(8),
375 sgdisk(8), fixparts(8).
376 http://en.wikipedia.org/wiki/GUID_Partition_Table
378 http://developer.apple.com/technotes/tn2006/tn2166.html
380 http://www.rodsbooks.com/gdisk/
382
385 The cgdisk command is part of the GPT fdisk package and is available
386 from Rod Smith.
387Roderick W. Smith 1.0.9 CGDISK(8)