man gdisk Command

Man page for apt-get gdisk Command

Man Page for gdisk in Linux

Ubuntu Man Command : man gdisk

Man Gdisk  Command

This tutorial shows the man page for man gdisk in linux.

Open terminal with 'su' access and type the command as shown below:
man gdisk

Result of the Command Execution shown below:

GDISK(8)                                                                  GPT fdisk Manual                                                                  GDISK(8)



NAME
gdisk GUID partition table (GPT) manipulator for Linux and Unix

SYNOPSIS
gdisk [ l ] device


DESCRIPTION
GPT fdisk (aka gdisk) is a text mode menu driven program for creation and manipulation of partition tables. 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 Table
(GPT) format, or will load a GUID partition table. When used with the l command line option, the program displays the current partition table and then
exits.

GPT fdisk operates mainly on the GPT headers and partition tables; however, it can and will generate a fresh protective MBR, when required. (Any boot loader
code in the protective MBR will not be disturbed.) If you've created an unusual protective MBR, such as a hybrid MBR created by gptsync or gdisk's own hybrid
MBR creation feature, this should not be disturbed by most ordinary actions. Some advanced data recovery options require you to understand the distinctions
between the main and backup data, as well as between the GPT headers and the partition tables. For information on MBR vs. GPT, as well as GPT terminology and
structure, see the extended gdisk documentation at http://www.rodsbooks.com/gdisk/ or consult Wikipedia.

The gdisk program employs a user interface similar to that of Linux's fdisk, but gdisk modifies GPT partitions. It also has the capability of transforming
MBR partitions or BSD disklabels into GPT partitions. Like the original fdisk program, gdisk does not modify disk structures until you explicitly write them
to disk, so if you make a mistake, you can exit from the program with the 'q' option to save your partitions.

Ordinarily, gdisk 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; gdisk cannot work on compressed or other advanced disk image formats.

The MBR partitioning system uses a combination of cylinder/head/sector (CHS) addressing and logical block addressing (LBA). The former is klunky and limit Äê
ing. GPT drops CHS addressing and uses 64 bit LBA mode exclusively. Thus, GPT data structures, and therefore gdisk, do not need to deal with CHS geometries
and all the problems they create. Users of fdisk will note that gdisk lacks the options and limitations associated with CHS geometries.

For best results, you should use an OS specific partition table program whenever possible. For example, you should make Mac OS X partitions with the Mac OS X
Disk Utility program and Linux partitions with the Linux gdisk or GNU Parted program.

Upon start, gdisk attempts to identify the partition type in use on the disk. If it finds valid GPT data, gdisk will use it. If gdisk 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.) GPT fdisk can identify, but not use data in, Apple Partition Map (APM) disks, which
are used on 680x0 and PowerPC based Macintoshes. Upon exiting with the 'w' option, gdisk replaces the MBR or disklabel with a GPT. This action is poten Äê
tially 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 gdisk on an MBR disk, you can safely exit the program with Äê
out making any changes by using the 'q' option.

The MBR to GPT conversion will leave at least one gap in the partition numbering if the original MBR used logical partitions. These gaps are harmless, but
you can eliminate them by using the 's' option, if you like. (Doing this may require you to update your /etc/fstab file.)

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 created in whatever order
and in whatever sizes are desired.


* Boot disks for EFI based systems require an EFI System Partition (gdisk internal code 0xEF00) formatted as FAT 32. The recommended size of this par Äê
tition is between 100 and 200 MiB. Boot related files are stored here. (Note that GNU Parted identifies such partitions as having the "boot flag"
set.)


* Some boot loaders for BIOS based systems make use of a BIOS Boot Partition (gdisk internal code 0xEF02), in which the secondary boot loader is stored,
possibly without the benefit of a filesystem. This partition can typically be quite small (roughly 32 to 200 KiB), 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 (gdisk 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 GNU Parted cre Äê
ates 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
l List the partition tables for the specified devices and then exit.

Most interactions with gdisk occur with its interactive text mode menus. Three menus exist: the main menu, the recovery & transformation menu, and the
experts' menu. The main menu provides the functions that are most likely to be useful for typical partitioning tasks, such as creating and deleting parti Äê
tions, changing partition type codes, and so on. Specific functions are:


b 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 current in memory data structures, so if you launch the program, make changes, and then use this option, the backup will
reflect your changes. Note also that the restore option is on the recovery & transformation menu; the backup option is on the main menu to encourage
its use.



c Change the GPT name of a partition. This name is encoded as a UTF 16 string, but gdisk supports only ASCII characters as names. 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.


d 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 pro Äê
tective partition to fill the new free space.


i Show detailed partition information. The summary information produced by the 'p' command necessarily omits many details, such as the partition's
unique GUID and the translation of gdisk's internal partition type code to a plain type name. The 'i' option displays this information for a single
partition.


l Display a summary of partition types. GPT uses a GUID to identify partition types for particular OSes and purposes. For ease of data entry, gdisk com Äê
presses these into two byte (four digit hexadecimal) values that are related to their equivalent MBR codes. Specifically, the MBR code is multiplied
by hexadecimal 0x0100. For instance, the code for Linux swap space in MBR is 0x82, and it's 0x8200 in gdisk. A one to one correspondence is impossi Äê
ble, though. Most notably, many DOS, Windows, and Linux data partition codes correspond to a single GPT code (entered as 0x0700 in gdisk). Some OSes
use a single MBR code but employ many more codes in GPT. For these, gdisk adds code numbers sequentially, such as 0xa500 for a FreeBSD disklabel,
0xa501 for FreeBSD boot, 0xa502 for FreeBSD swap, and so on. Note that these two byte codes are unique to gdisk.


n Create a new partition. This command is modelled after the equivalent fdisk option, although some differences exist. You enter a partition number,
starting sector, and an ending sector. Both start and end sectors can be specified in absolute terms as sector numbers or as positions measured in
kilobytes (K), megabytes (M), gigabytes (G), or terabytes (T); for instance, 40M specifies a position 40MiB from the start of the disk. You can spec Äê
ify locations relative to the start or end of the specified range by preceding the number by a '+' or ' ' symbol, as in +2G to specify a point 2GiB
after the first available sector, or 200M to specify a point 200MiB before the last available sector. 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 last available block for the end sector.


o Clear out all partition data. This includes GPT header data, all partition definitions, and the protective MBR.


p Display basic partition summary data. This includes partition numbers, starting and ending sector numbers, partition sizes, gdisk's partition types
codes, and partition names. For additional information, use the 'i' command.


q 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.


r Enter the recovery & transformation menu. This menu includes emergency recovery options (to fix damaged GPT data structures) and options to transform
to or from other partitioning systems, including creating hybrid MBRs.


s Sort partition entries. GPT partition numbers need not match the order of partitions on the disk. If you want them to match, you can use this option.
Note that some partitioning utilities sort partitions whenever they make changes. Such changes will be reflected in your device filenames, so you may
need to edit /etc/fstab if you use this option.


t Change a single partition's type code. You enter the type code using a two byte hexadecimal number, as described earlier. You may also enter a GUID
directly, if you have one and gdisk doesn't know it.


v Verify disk. This option checks for a variety of problems, such as incorrect CRCs and mismatched main and backup data. This option does not automati Äê
cally correct most problems, though; for that, you must use options on the recovery & transformation menu. If no problems are found, this command dis Äê
plays a summary of unallocated disk space.


w Write data. Use this command to save your changes.


x Enter the experts' menu. Using this option provides access to features you can use to get into even more trouble than the main menu allows.

? Print the menu. Type this command (or any other unrecognized command) to see a summary of available options.


The second gdisk menu is the recovery & transformation menu, which provides access to data recovery options and features related to the transformation of
partitions between partitioning schemes (converting BSD disklabels into GPT partitions or creating hybrid MBRs, for instance). A few options on this menu
duplicate functionality on the main menu, for the sake of convenience. The options on this menu are:


b Rebuild GPT header from backup. You can use the backup GPT header to rebuild the main GPT header with this option. It's likely to be useful if your
main GPT header was damaged or destroyed (say, by sloppy use of dd).


c Load backup partition table. Ordinarily, gdisk uses only the main partition table (although the backup's integrity is checked when you launch the pro Äê
gram). If the main partition table has been damaged, you can use this option to load the backup from disk and use it instead. Note that this will
almost certainly produce no or strange partition entries if you've just converted an MBR disk to GPT format, since there will be no backup partition
table on disk.


d Use main GPT header and rebuild the backup. This option is likely to be useful if the backup GPT header has been damaged or destroyed.


e Load main partition table. This option reloads the main partition table from disk. It's only likely to be useful if you've tried to use the backup
partition table (via 'c') but it's in worse shape then the main partition table.


f Load MBR and build fresh GPT from it. Use this option if your GPT is corrupt or conflicts with the MBR and you want to use the MBR as the basis for a
new set of GPT partitions.


g Convert GPT into MBR and exit. This option converts up to four GPT partitions into MBR form, destroys the GPT data structures, saves the new MBR, and
exits. Use this option if you've tried GPT and find that MBR works better for you. Note that this function generates up to four primary MBR parti Äê
tions; it cannot generate logical partitions, and so it cannot transform more than four partitions. If four or fewer partitions exist, and if they can
be represented in the 32 bit MBR LBA scheme, this function converts them all. If more than four partitions exist, you'll be asked to select which ones
to convert. See also the 'h' option.


h Create a hybrid MBR. This is an ugly workaround that enables GPT unaware OSes, or those that can't boot from a GPT disk, to access up to three of the
partitions on the disk by creating MBR entries for them. Note that these hybrid MBR entries can easily go out of sync with the GPT entries, particu Äê
larly when hybrid unaware GPT utilities are used to edit the disk. Thus, you may need to recreate the hybrid MBR if you use such tools.


i Show detailed partition information. This option is identical to the 'i' option on the main menu.


l Load partition data from a backup file. This option is the reverse of the 'b' option on the main menu. Note that restoring partition data from any Äê
thing but the original disk is not recommended.


m Return to the main menu. This option enables you to enter main menu commands.


o Print protective MBR data. You can see a summary of the protective MBR's partitions with this option. This may enable you to spot glaring problems or
help identify the partitions in a hybrid MBR.


p Print the partition table. This option is identical to the 'p' option in the main menu.


q Quit without saving changes. This option is identical to the 'q' option in the main menu.


t Transform BSD partitions into GPT partitions. This option works on BSD disklabels held within GPT (or converted MBR) partitions. Converted partitions'
type codes are likely to need manual adjustment. gdisk will attempt to convert BSD disklabels stored on the main disk when launched, but this conver Äê
sion is likely to produce first and/or last partitions that are unusable. The many BSD variants means that the probability of gdisk being unable to
convert a BSD disklabel is high compared to the likelihood of problems with an MBR conversion.


v Verify disk. This option is identical to the 'v' option in the main menu.


w Write table to disk and exit. This option is identical to the 'w' option in the main menu.


x Enter the experts' menu. This option is identical to the 'x' option in the main menu.


? Print the menu. This option (or any unrecognized entry) displays a summary of the menu options.


The third gdisk menu is the experts' menu. This menu provides advanced options that aren't closely related to recovery or transformation between partitioning
systems. Its options are:


a Set attributes. GPT provides a 64 bit attributes field that can be used to set features for each partition. gdisk supports four attributes: system
partition, read only, hidden, and do not automount. You can set other attributes, but their numbers aren't translated into anything useful. In prac Äê
tice, most OSes seem to ignore these attributes.


c Change partition GUID. You can enter a custom unique GUID for a partition using this option. (Note this refers to the GUID that uniquely identifies a
partition, not to its type code, which you can change with the 't' main menu option.) Ordinarily, gdisk assigns this number randomly; however, you
might want to adjust the number manually if you've wound up with the same GUID on two partitions because of buggy GUID assignments (hopefully not in
gdisk) or sheer incredible coincidence.


e Move backup GPT data structures to the end of the disk. Use this command if you've added disks to a RAID array, thus creating a virtual disk with
space that follows the backup GPT data structures. This command moves the backup GPT data structures to the end of the disk, where they belong.


g Change disk GUID. Each disk has a unique GUID code, which gdisk assigns randomly upon creation of the GPT data structures. You can generate a fresh
random GUID or enter one manually with this option.


i Show detailed partition information. This option is identical to the 'i' option on the main menu.


m Return to the main menu. This option enables you to enter main menu commands.


n Create a new protective MBR. Use this option if the current protective MBR is damaged in a way that gdisk doesn't automatically detect and correct, or
if you want to convert a hybrid MBR into a "pure" GPT with a conventional protective MBR.


o Print protective MBR data. You can see a summary of the protective MBR's partitions with this option. This may enable you to spot glaring problems or
help identify the partitions in a hybrid MBR.


p Print the partition table. This option is identical to the 'p' option in the main menu.


q Quit without saving changes. This option is identical to the 'q' option in the main menu.


r Enter the recovery & transformations menu. This option is identical to the 'r' option on the main menu.


s Resize partition table. The default partition table size is 128 entries. Officially, sizes of less than 16KB (128 entries, given the normal entry
size) are unsupported by the GPT specification; however, in practice they seem to work, and can sometimes be useful in converting MBR disks. Larger
sizes also work fine. OSes may impose their own limits on the number of partitions, though.


v Verify disk. This option is identical to the 'v' option in the main menu.


z Zap (destroy) the GPT data structures and exit. Use this option if you want to repartition a GPT disk using fdisk or some other GPT unaware program.
You'll be given the choice of preserving the existing MBR, in case it's a hybrid MBR with salvageable partitions or if you've already created new MBR
partitions and want to erase the remnants of your GPT partitions. If you've already created new MBR partitions, it's conceivable that this option will
damage the first and/or last MBR partitions! Such an event is unlikely, but could occur if your new MBR partitions overlap the old GPT data struc Äê
tures.


? Print the menu. This option (or any unrecognized entry) displays a summary of the menu options.


In many cases, you can press the Enter key to select a default option when entering data. When only one option is possible, gdisk usually bypasses the prompt
entirely.


BUGS
As of November 2009 (version 0.5.1), gdisk should be considered beta software. Known bugs and limitations include:


* The program compiles correctly only on Linux, FreeBSD, and Mac OS X. 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. The Mac OS X support was added with version 0.3.1 and has not been as thoroughly tested.
FreeBSD support was added with version 0.4.0 and has seen even less testing.


* 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.)


* The fields used to display the start and end sector numbers for partitions in the 'p' command are 14 characters wide. This translates to a limitation
of about 45 PiB. On larger disks, the displayed columns will go out of alignment.


* Only ASCII characters are supported in the partition name field. If an existing partition uses non ASCII UTF 16 characters, they're likely to be cor Äê
rupted in the 'i' and 'p' menu options' displays; however, they should be preserved when loading and saving partitions.


* The program can load only up to 128 partitions (4 primary partitions and 124 logical partitions) when converting from MBR format. This limit can be
raised by changing the


Related Topics

Apt Get Commands