GDISK(8)                     (1.0.8)                     GDISK(8)

          gdisk - Interactive GUID partition table (GPT) manipulator

          gdisk [ -l ] device

          GPT fdisk (aka gdisk) is a text-mode menu-driven program for
          creation and manipulation of partition tables. It will auto-
          matically convert an old-style Master Boot Record (MBR) par-
          tition 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 pro-
          gram 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
 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 pro-
          gram, 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 leave your
          partitions unmodified.

          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

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          cylinder/head/sector (CHS) addressing and logical block
          addressing (LBA). The former is klunky and limiting. 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 cre-
          ate. 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 pro-
          gram and Linux partitions with the Linux gdisk or GNU Parted

          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 potentially dangerous! Your system may
          become unbootable, and partition type codes may become cor-
          rupted if the disk uses unrecognized type codes. Boot prob-
          lems 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 without 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 parti-
          tions. 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 considera-
          tions may be in order:

          *    For data (non-boot) disks, and for boot disks used on
               BIOS-based computers with GRUB as the boot loader, par-
               titions may be created in whatever order and in what-
               ever sizes are desired.

          *    Boot disks for EFI-based systems require an EFI System
               Partition (gdisk internal code 0xEF00) formatted as
               FAT-32. I recommended making this partition 550 MiB.
               (Smaller ESPs are common, but some EFIs have flaky FAT

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               drivers that necessitate a larger partition for reli-
               able operation.) 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. (GRUB2 may option-
               ally use such a partition.) This partition can typi-
               cally be quite small (roughly 32 to 200 KiB, although 1
               MiB is more common in practice), 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 old versions of GNU Parted create all FAT
               partitions as this type, which actually makes the par-
               tition unusable for normal file storage in both Windows
               and Mac OS X.)

          *    Some OSes' GPT utilities create some blank space (typi-
               cally 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 (specify-
               ing the starting sector as '+128M', for instance) to
               simplify creating such gaps.

          -l   List the partition table for the specified device and
               then exits.

          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 partitions, 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

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               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 encour-
               age its use.

          c    Change the GPT name of a partition. This name is
               encoded as a UTF-16 string, but proper entry and dis-
               play 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 impor-
               tant 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.

          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 parti-
               tion on the disk. If a corresponding hybrid MBR parti-
               tion exists, gdisk deletes it, as well, and expands any
               adjacent 0xEE (EFI GPT) MBR protective partition to
               fill the new free space.

          i    Show detailed partition information. The summary infor-
               mation 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 compresses
               these into two-byte (four-digit hexadecimal) values
               that are related to their equivalent MBR codes. Specif-
               ically, 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 impossible, though. Most notably, the
               codes for all varieties of FAT and NTFS partition cor-
               respond to a single GPT code (entered as 0x0700 in

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               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. The type code list may optionally be filtered by
               a search string; for instance, entering linux shows
               only partition type codes with descriptions that
               include the string Linux. This search is performed

          n    Create a new partition. This command is modeled 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 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 preced-
               ing the number by a '+' or '-' symbol, as in +2G to
               specify a point 2GiB after the default start sector, or
               -200M to specify a point 200MiB before the last avail-
               able sector. Pressing the Enter key with no input spec-
               ifies the default value, which is the start of the
               largest available block for the start sector and the
               end of the same block for the end sector.

          o    Clear out all partition data. This includes GPT header
               data, all partition definitions, and the protective
               MBR. The sector alignment is reset to the default (1
               MiB, or 2048 sectors on a disk with 512-byte sectors).

          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

          r    Enter the recovery & transformation menu. This menu
               includes emergency recovery options (to fix damaged GPT

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               data structures) and options to transform to or from
               other partitioning systems, including creating hybrid

          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 prob-
               lems, such as incorrect CRCs and mismatched main and
               backup data. This option does not automatically correct
               most problems, though; for that, you must use options
               on the recovery & transformation menu. If no problems
               are found, this command displays a summary of unallo-
               cated 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 unrec-
               ognized 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 parti-
          tioning schemes (converting BSD disklabels into GPT parti-
          tions 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

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               header was damaged or destroyed (say, by sloppy use of

          c    Load backup partition table. Ordinarily, gdisk uses
               only the main partition table (although the backup's
               integrity is checked when you launch the program). 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 con-
               verted 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 use-
               ful if you've tried to use the backup partition table
               (via 'c') but it's in worse shape then the main parti-
               tion 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 as
               many partitions as possible 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 partitions or three primary parti-
               tions and as many logical partitions as can be gener-
               ated. Each logical partition requires at least one
               unallocated block immediately before its first block.
               Therefore, it may be possible to convert a maximum of
               four partitions on disks with tightly-packed parti-
               tions; however, if free space was inserted between par-
               titions when they were created, and if the disk is
               under 2 TiB in size, it should be possible to convert
               all the partitions to MBR form.  See also the 'h'

          h    Create a hybrid MBR. This is an ugly workaround that

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               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, particularly when hybrid-unaware GPT
               utilities are used to edit the disk.  Thus, you may
               need to re-create the hybrid MBR if you use such tools.
               Unlike the 'g' option, this option does not support
               converting any partitions into MBR logical partitions.

          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 anything 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 con-
               verted 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 conversion 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 con-

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          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 pro-
          vides advanced options that aren't closely related to recov-
          ery 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 practice, most OSes seem to
               ignore these attributes.

          b    Swap the byte order for the name of the specified par-
               tition. Some partitioning tools, including GPT fdisk
               1.0.7 and earlier, can write the partition name in the
               wrong byte order on big-endian computers, such as the
               IBM s390 mainframes and PowerPC-based Macs. This fea-
               ture corrects this problem.

          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 parti-
               tion, 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 assign-
               ments (hopefully not in gdisk) or sheer incredible

          d    Display the sector alignment value. See the description

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               of the 'l' option for more details.

          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.

          f    Randomize the disk's GUID and all partitions' unique
               GUIDs (but not their partition type code GUIDs). This
               function may be used after cloning a disk with another
               utility in order to render all GUIDs once again unique.

          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.

          h    Recompute CHS values in protective or hybrid MBR. This
               option can sometimes help if a disk utility, OS, or
               BIOS doesn't like the CHS values used by the partitions
               in the protective or hybrid MBR. In particular, the GPT
               specification requires a CHS value of 0xFFFFFF for
               over-8GiB partitions, but this value is technically
               illegal by the usual standards. Some BIOSes hang if
               they encounter this value. This option will recompute a
               more normal CHS value -- 0xFEFFFF for over-8GiB parti-
               tions, enabling these BIOSes to boot.

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

          j    Adjust the location of the main partition table. This
               value is normally 2, but it may need to be increased in
               some cases, such as when a system-on-chip (SoC) is
               hard-coded to read boot code from sector 2. I recommend
               against adjusting this value unless doing so is abso-
               lutely necessary.

          l    Change the sector alignment value. Disks with more log-
               ical sectors per physical sectors (such as modern
               Advanced Format drives), some RAID configurations, and
               many SSD devices, can suffer performance problems if
               partitions are not aligned properly for their internal

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               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 opti-
               mizes performance 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.

          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 prac-
               tice 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 parti-
               tions, though.

          t    Swap two partitions' entries in the partition table.
               One partition may be empty. For instance, if partitions

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               1-4 are defined, transposing 1 and 5 results in a table
               with partitions numbered from 2-5. Transposing parti-
               tions in this way has no effect on their disk space
               allocation; it only alters their order in the partition

          u    Replicate the current device's partition table on
               another device. You will be prompted to type the new
               device's filename. After the write operation completes,
               you can continue editing the original device's parti-
               tion table.  Note that the replicated partition table
               is an exact copy, including all GUIDs; if the device
               should have its own unique GUIDs, you should use the f
               option on the new disk.

          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

          ?    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.

          Known bugs and limitations include:

          *    The program compiles correctly only on Linux, FreeBSD,
               Mac OS X, and Windows.  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

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               testing. Under FreeBSD, 32-bit (x86) and 64-bit
               (x86-64) versions have been tested. Only 32-bit ver-
               sions for Mac OS X and Windows have been tested by the
               author, although I've heard of 64-bit versions being
               successfully compiled.

          *    The FreeBSD version of the program can't write changes
               to the partition table to a disk when existing parti-
               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 typ-
               ing sysctl kern.geom.debugflags=16 at a shell prompt.

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

          *    In the Windows version, only ASCII characters are sup-
               ported in the partition name field. If an existing par-
               tition uses non-ASCII UTF-16 characters, they're likely
               to be corrupted in the 'i' and 'p' menu options' dis-
               plays; however, they should be preserved when loading
               and saving partitions. Binaries for Linux, FreeBSD, and
               OS X support full UTF-16 partition names.

          *    The program can load only up to 128 partitions (4 pri-
               mary partitions and 124 logical partitions) when con-
               verting 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 table. (The limit of 128 partitions was cho-
               sen because that number equals the 128 partitions sup-
               ported 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) can sometimes
               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 gdisk.

          *    MBR conversions work only if the disk has correct LBA

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               partition descriptors. These descriptors should be pre-
               sent 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 par-
               titions that overlap with the GPT data structures. This
               can sometimes be compensated by adjusting the partition
               table size, but in extreme cases the affected
               partition(s) may need to be deleted.

          *    Because of the highly variable nature of BSD disklabel
               structures, conversions from this form may be unreli-
               able -- partitions may be dropped, converted in a way
               that creates overlaps with other partitions, or con-
               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) or abandoning GPT in favor of MBR may be your
               only options in this case.

          Primary author: Roderick W. Smith (


          * Yves Blusseau (

          * David Hubbard (

          * Justin Maggard (

          * Dwight Schauer (

          * Florian Zumbiehl (

          cfdisk(8), cgdisk(8), fdisk(8), mkfs(8), parted(8),
          sfdisk(8), sgdisk(8), fixparts(8).

     Page 14                 Roderick W. Smith       (printed 5/24/22)

     GDISK(8)                     (1.0.8)                     GDISK(8)

          The gdisk command is part of the GPT fdisk package and is
          available from Rod Smith.

     Page 15                 Roderick W. Smith       (printed 5/24/22)