1CGDISK(8) GPT fdisk Manual CGDISK(8)
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6 cgdisk - Curses-based GUID partition table (GPT) manipulator
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9 cgdisk device
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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
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 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 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 Interactions with cgdisk occur with its interactive text-mode menus.
105 The display is broken into two interactive parts:
106 * The partition display area, in which partitions and gaps between
109 them (marked as "free space") are summarized.
110 * The option selection area, in which buttons for the main options
113 appear.
114 In addition, the top of the display shows the program's name and ver‐
117 sion number, the device filename associated with the disk, and the
118 disk's size in both sectors and IEEE-1541 units (GiB, TiB, and so on).
119 You can use the following keys to move among the various options and to
121 select among them:
122 up arrow
125 This key moves the partition selection up by one partition.
126 down arrow
129 This key moves the partition selection down by one partition.
130 Page Up
133 This key moves the partition selection up by one screen.
134 Page Down
137 This key moves the partition selection down by one screen.
138 right arrow
141 This key moves the option selection to the right by one item.
142 left arrow
145 This key moves the option selection to the left by one item.
146 Enter This key activates the currently selected option. You can also
149 activate an option by typing the capitalized letter in the
150 option's name on the keyboard, such as a to activate the Align
151 option.
152 If more partitions exist than can be displayed in one screen, you can
155 scroll between screens using the partition selection keys, much as in a
156 text editor.
157 Available options are as described below. (Note that cgdisk provides a
159 much more limited set of options than its sibling gdisk. If you need to
160 perform partition table recovery, hybrid MBR modifcation, or other
161 advanced operations, you should consult the gdisk documentation.)
162 Align Change the sector alignment value. Disks with more logical sec‐
165 tors than physical sectors (such as modern Advanced Format
166 drives), some RAID configurations, and many SSD devices, can
167 suffer performance problems if partitions are not aligned prop‐
168 erly for their internal data structures. On new disks, GPT fdisk
169 attempts to align partitions on 2048-sector (1MiB) boundaries by
170 default, which optimizes performance for all of these disk
171 types. On pre-partitioned disks, GPT fdisk attempts to identify
172 the alignment value used on that disk, but will set 8-sector
173 alignment on disks larger than 300 GB even if lesser alignment
174 values are detected. In either case, it can be changed by using
175 this option.
176 Backup Save partition data to a backup file. You can back up your cur‐
179 rent in-memory partition table to a disk file using this option.
180 The resulting file is a binary file consisting of the protective
181 MBR, the main GPT header, the backup GPT header, and one copy of
182 the partition table, in that order. Note that the backup is of
183 the current in-memory data structures, so if you launch the pro‐
184 gram, make changes, and then use this option, the backup will
185 reflect your changes.
186 Delete Delete a partition. This action deletes the entry from the par‐
189 tition table but does not disturb the data within the sectors
190 originally allocated to the partition on the disk. If a corre‐
191 sponding hybrid MBR partition exists, gdisk deletes it, as well,
192 and expands any adjacent 0xEE (EFI GPT) MBR protective partition
193 to fill the new free space.
194 Help Print brief descriptions of all the options.
197 Info Show detailed partition information. The summary information
200 shown in the partition display area necessarily omits many
201 details, such as the partitions' unique GUIDs and the parti‐
202 tions' sector-exact start and end points. The Info option dis‐
203 plays this information for a single partition.
204 Load Load partition data from a backup file. This option is the
207 reverse of the Backup option. Note that restoring partition data
208 from anything but the original disk is not recommended.
209 naMe Change the GPT name of a partition. This name is encoded as a
212 UTF-16 string, but proper entry and display of anything beyond
213 basic ASCII values requires suitable locale and font support.
214 For the most part, Linux ignores the partition name, but it may
215 be important in some OSes. GPT fdisk sets a default name based
216 on the partition type code. Note that the GPT partition name is
217 different from the filesystem name, which is encoded in the
218 filesystem's data structures. Note also that to activate this
219 item by typing its alphabetic equivalent, you must use M, not
220 the more obvious N, because the latter is used by the next
221 option....
222 New Create a new partition. You enter a starting sector, a size, a
225 type code, and a name. The start sector can be specified in
226 absolute terms as a sector number or as a position measured in
227 kibibytes (K), mebibytes (M), gibibytes (G), tebibytes (T), or
228 pebibytes (P); for instance, 40M specifies a position 40MiB from
229 the start of the disk. You can specify locations relative to the
230 start or end of the specified default range by preceding the
231 number by a '+' symbol, as in +2G to specify a point 2GiB after
232 the default start sector. The size value can use the K, M, G, T,
233 and P suffixes, too. Pressing the Enter key with no input speci‐
234 fies the default value, which is the start of the largest avail‐
235 able block for the start sector and the full available size for
236 the size.
237 Quit Quit from the program without saving your changes. Use this
240 option if you just wanted to view information or if you make a
241 mistake and want to back out of all your changes.
242 Type Change a single partition's type code. You enter the type code
245 using a two-byte hexadecimal number. You may also enter a GUID
246 directly, if you have one and cgdisk doesn't know it. If you
247 don't know the type code for your partition, you can type L to
248 see a list of known type codes.
249 Verify Verify disk. This option checks for a variety of problems, such
252 as incorrect CRCs and mismatched main and backup data. This
253 option does not automatically correct most problems, though; for
254 that, you must use gdisk. If no problems are found, this command
255 displays a summary of unallocated disk space.
256 Write Write data. Use this command to save your changes.
259
262 As of September 2011 (version 0.8.1), cgdisk should be considered beta
263 software. Although the underlying partition manipulation code is much
264 older, the cgdisk ncurses user interface is brand new with GPT fdisk
265 version 0.8.0. Known bugs and limitations include:
266 * The program compiles correctly only on Linux, FreeBSD, and Mac
269 OS X. In theory, it should compile under Windows if the Ncurses
270 library for Windows is installed, but I have not tested this
271 capability. Linux versions for x86-64 (64-bit), x86 (32-bit),
272 and PowerPC (32-bit) have been tested, with the x86-64 version
273 having seen the most testing. Under FreeBSD, 32-bit (x86) and
274 64-bit (x86-64) versions have been tested. Only 32-bit versions
275 for Mac OS X has been tested by the author.
276 * The FreeBSD version of the program can't write changes to the
279 partition table to a disk when existing partitions on that disk
280 are mounted. (The same problem exists with many other FreeBSD
281 utilities, such as gpt, fdisk, and dd.) This limitation can be
282 overcome by typing sysctl kern.geom.debugflags=16 at a shell
283 prompt.
284 * The program can load only up to 128 partitions (4 primary parti‐
287 tions and 124 logical partitions) when converting from MBR for‐
288 mat. This limit can be raised by changing the #define
289 MAX_MBR_PARTS line in the basicmbr.h source code file and recom‐
290 piling; however, such a change will require using a
291 larger-than-normal partition table. (The limit of 128 partitions
292 was chosen because that number equals the 128 partitions sup‐
293 ported by the most common partition table size.)
294 * Converting from MBR format sometimes fails because of insuffi‐
297 cient space at the start or (more commonly) the end of the disk.
298 Resizing the partition table (using the 's' option in the
299 experts' menu in gdisk) can sometimes overcome this problem;
300 however, in extreme cases it may be necessary to resize a parti‐
301 tion using GNU Parted or a similar tool prior to conversion with
302 GPT fdisk.
303 * MBR conversions work only if the disk has correct LBA partition
306 descriptors. These descriptors should be present on any disk
307 over 8 GiB in size or on smaller disks partitioned with any but
308 very ancient software.
309 * BSD disklabel support can create first and/or last partitions
312 that overlap with the GPT data structures. This can sometimes be
313 compensated by adjusting the partition table size, but in
314 extreme cases the affected partition(s) may need to be deleted.
315 * Because of the highly variable nature of BSD disklabel struc‐
318 tures, conversions from this form may be unreliable -- parti‐
319 tions may be dropped, converted in a way that creates overlaps
320 with other partitions, or converted with incorrect start or end
321 values. Use this feature with caution!
322 * Booting after converting an MBR or BSD disklabel disk is likely
325 to be disrupted. Sometimes re-installing a boot loader will fix
326 the problem, but other times you may need to switch boot load‐
327 ers. Except on EFI-based platforms, Windows through at least
328 Windows 7 doesn't support booting from GPT disks. Creating a
329 hybrid MBR (using the 'h' option on the recovery & transforma‐
330 tion menu in gdisk) or abandoning GPT in favor of MBR may be
331 your only options in this case.
332 * The cgdisk Verify function and the partition type listing
335 obtainable by typing L in the Type function (or when specifying
336 a partition type while creating a new partition) both currently
337 exit ncurses mode. This limitation is a minor cosmetic blemish
338 that does not affect functionality.
339
342 Primary author: Roderick W. Smith (rodsmith@rodsbooks.com)
343 Contributors:
345 * Yves Blusseau (1otnwmz02@sneakemail.com)
347 * David Hubbard (david.c.hubbard@gmail.com)
349 * Justin Maggard (justin.maggard@netgear.com)
351 * Dwight Schauer (dschauer@ti.com)
353 * Florian Zumbiehl (florz@florz.de)
355
359 cfdisk (8), fdisk (8), gdisk (8), mkfs (8), parted (8), sfdisk (8)
360 sgdisk (8) fixparts (8)
361 http://en.wikipedia.org/wiki/GUID_Partition_Table
363 http://developer.apple.com/technotes/tn2006/tn2166.html
365 http://www.rodsbooks.com/gdisk/
367
370 The cgdisk command is part of the GPT fdisk package and is available
371 from Rod Smith.
372Roderick W. Smith 0.8.1 CGDISK(8)