Manual: 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 manipulation 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 automatiā
cally 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 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 structure, see the extended GPT fdisk documentation at
https://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 misā
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 overā
lap 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 beā
come corrupted if the disk uses unrecognized type codes. Boot problems are particularly likely if you're multi-bootā
ing 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, parā
titions 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 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 filename: -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 teleā
types 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 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 activate the Align option.
If more partitions exist than can be displayed in one screen, you can scroll between screens using the partition seā
lection 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 sibā
ling 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 sectors (such as modern Adā
vanced Format drives), some RAID configurations, and many SSD devices, can suffer performance problems if parā
titions 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 perā
formance 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. The alignment value also affects
the default end sector value when creating a new partition; it will be aligned to one less than a multiple of
the alignment value, when possible. This should keep partitions a multiple of the alignment value in size.
Some disk encryption tools require partitions to be sized to some value, typically 4096 bytes, so the default
alignment of 1 MiB works well for them.
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 curā
rent 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 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 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 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. The type code list may optionally be filā
tered 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 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 Winā
dows 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 verā
sions 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 partiā
tions 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 convertā
ing 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; however, such a change will require using a larger-than-normal partition taā
ble. (The limit of 128 partitions was chosen because that number equals the 128 partitions supported 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 someā
times 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 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 partiā
tion(s) may need to be deleted.
* Because of the highly variable nature of BSD disklabel structures, conversions from this form may be unreliā
able -- partitions may be dropped, converted in a way that creates overlaps with other partitions, or conā
verted 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 loaders. 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 & 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@rodsbooks.com)
Contributors:
* Yves Blusseau (1otnwmz02@sneakemail.com)
* David Hubbard (david.c.hubbard@gmail.com)
* Justin Maggard (justin.maggard@netgear.com)
* Dwight Schauer (das@teegra.net)
* Florian Zumbiehl (florz@florz.de)
SEE ALSO
cfdisk(8), fdisk(8), gdisk(8), mkfs(8), parted(8), sfdisk(8), sgdisk(8), fixparts(8).
https://en.wikipedia.org/wiki/GUID_Partition_Table
https://developer.apple.com/technotes/tn2006/tn2166.html
https://www.rodsbooks.com/gdisk/
AVAILABILITY
The cgdisk command is part of the GPT fdisk package and is available from Rod Smith.
Roderick W. Smith 1.0.10 CGDISK(8)