Provided by: gdisk_1.0.5-1_amd64 
NAME
sgdisk - Command-line GUID partition table (GPT) manipulator for Linux and Unix
SYNOPSIS
sgdisk [ options ] device
DESCRIPTION
GPT fdisk is a text-mode menu-driven package for creation and manipulation of partition tables. It
consists of two programs: the text-mode interactive gdisk and the command-line sgdisk. Either program
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. This man page documents the command-line sgdisk program.
Some advanced data manipulation and 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 sgdisk program employs a user interface that's based entirely on the command line, making it suitable
for use in scripts or by experts who want to make one or two quick changes to a disk. (The program may
query the user when certain errors are encountered, though.) The program's name is based on sfdisk, but
the user options of the two programs are entirely different from one another.
Ordinarily, sgdisk 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; sgdisk 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 limiting. GPT drops CHS addressing and uses 64-bit LBA mode
exclusively. Thus, GPT data structures, and therefore sgdisk, do not need to deal with CHS geometries and
all the problems they create.
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, sgdisk, or GNU Parted programs.
Upon start, sgdisk attempts to identify the partition type in use on the disk. If it finds valid GPT
data, sgdisk will use it. If sgdisk 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.
If you specify any option that results in changes to an MBR or BSD disklabel, sgdisk ignores those
changes unless the -g (--mbrtogpt), -z (--zap), or -Z (--zap-all) option is used. If you use the -g
option, sgdisk replaces the MBR or disklabel with a GPT. This action is potentially 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.
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 (--sort) 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. I recommended making this partition 550 MiB. (Smaller ESPs are common, but
some EFIs have flaky FAT drivers that necessitate a larger partition for reliable 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 optionally use such a partition.) This partition can typically 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 (sgdisk 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 creates 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.
OPTIONS
Some options take no arguments, others take one argument (typically a partition number), and others take
compound arguments with colon delimitation. For instance, -n (--new) takes a partition number, a starting
sector number, and an ending sector number, as in sgdisk -n 2:2000:50000 /dev/sdc, which creates a new
partition, numbered 2, starting at sector 2000 an ending at sector 50,000, on /dev/sdc.
Unrelated options may be combined; however, some such combinations will be nonsense (such as deleting a
partition and then changing its GUID type code). sgdisk interprets options in the order in which they're
entered, so effects can vary depending on order. For instance, sgdisk -s -d 2 sorts the partition table
entries and then deletes partition 2 from the newly-sorted list; but sgdisk -d 2 -s deletes the original
partition 2 and then sorts the modified partition table.
Error checking and opportunities to correct mistakes in sgdisk are minimal. Although the program
endeavors to keep the GPT data structures legal, it does not prompt for verification before performing
its actions. Unless you require a command-line-driven program, you should use the interactive gdisk
instead of sgdisk, since gdisk allows you to quit without saving your changes, should you make a mistake.
Although sgdisk is based on the same partition-manipulation code as gdisk, sgdisk implements fewer
features than its interactive sibling. Options available in sgdisk are:
-a, --set-alignment=value
Set the sector alignment multiple. GPT fdisk aligns the start of partitions to sectors that are
multiples of this value, which defaults to 1 MiB (2048 on disks with 512-byte sectors) on freshly
formatted disks. This alignment value is necessary to obtain optimum performance with Western
Digital Advanced Format and similar drives with larger physical than logical sector sizes, with
some types of RAID arrays, and with SSD devices.
-A, --attributes=list|[partnum:show|or|nand|xor|=|set|clear|toggle|get[:bitnum|hexbitmask]]
View or set partition attributes. Use list to see defined (known) attribute values. Omit the
partition number (and even the device filename) when using this option. The others require a
partition number. The show and get options show the current attribute settings (all attributes or
for a particular bit, respectively). The or, nand, xor, =, set, clear, and toggle options enable
you to change the attribute bit value. The set, clear, toggle, and get options work on a bit
number; the others work on a hexadecimal bit mask. For example, type sgdisk -A 4:set:2 /dev/sdc to
set the bit 2 attribute (legacy BIOS bootable) on partition 4 on /dev/sdc.
-b, --backup=file
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. If the GPT data
structures are damaged, the backup may not accurately reflect the damaged state; instead, they
will reflect GPT fdisk's first-pass interpretation of the GPT.
-c, --change-name=partnum: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. If you want to
set a name that includes a space, enclose it in quotation marks, as in sgdisk -c 1:"Sample Name"
/dev/sdb. Note that the GPT name of a partition is distinct from the filesystem name, which is
encoded in the filesystem's data structures.
-C, --recompute-chs
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
partitions, enabling these BIOSes to boot.
-d, --delete=partnum
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.
-D, --display-alignment
Display current sector alignment value. Partitions will be created on multiples of the sector
value reported by this option. You can change the alignment value with the -a option.
-e, --move-second-header
Move backup GPT data structures to the end of the disk. Use this option 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.
-E, --end-of-largest
Displays the sector number of the end of the largest available block of sectors on the disk. A
script may store this value and pass it back as part of -n's option to create a partition. If no
unallocated sectors are available, this function returns the value 0.
-f, --first-in-largest
Displays the sector number of the start of the largest available block of sectors on the disk. A
script may store this value and pass it back as part of -n's option to create a partition. If no
unallocated sectors are available, this function returns the value 0. Note that this parameter is
blind to partition alignment; when you actually create a partition, its start point might be
changed from this value.
-F, --first-aligned-in-largest
Similar to -f (--first-in-largest), except returns the sector number with the current alignment
correction applied. Use this function if you need to compute the actual partition start point
rather than a theoretical start point or the actual start point if you set the alignment value to
1.
-g, --mbrtogpt
Convert an MBR or BSD disklabel disk to a GPT disk. As a safety measure, use of this option is
required on MBR or BSD disklabel disks if you intend to save your changes, in order to prevent
accidentally damaging such disks.
-G, --randomize-guids
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 in order to render all GUIDs once again
unique.
-h, --hybrid
Create a hybrid MBR. This option takes from one to three partition numbers, separated by colons,
as arguments. You may optionally specify a final partition "EE" to indicate that the EFI GPT (type
0xEE) should be placed last in the table, otherwise it will be placed first, followed by the
partition(s) you specify. Their type codes are based on the GPT fdisk type codes divided by
0x0100, which is usually correct for Windows partitions. If the active/bootable flag should be
set, you must do so in another program, such as fdisk. The gdisk program offers additional hybrid
MBR creation options.
-i, --info=partnum
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
sgdisk's internal partition type code to a plain type name. The -i option displays this
information for a single partition.
-j, --adjust-main-table=sector
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 absolutely necessary.
-l, --load-backup=file
Load partition data from a backup file. This option is the reverse of the -b option. Note that
restoring partition data from anything but the original disk is not recommended. This option will
work even if the disk's original partition table is bad; however, most other options on the same
command line will be ignored.
-L, --list-types
Display a summary of partition types. GPT uses a GUID to identify partition types for particular
OSes and purposes. For ease of data entry, sgdisk compresses 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 impossible, though. Most notably, the codes
for all varieties of FAT and NTFS partition correspond to a single GPT code (entered as 0x0700 in
sgdisk). Some OSes use a single MBR code but employ many more codes in GPT. For these, sgdisk 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 and sgdisk. This
option does not require you to specify a valid disk device filename.
-m, --gpttombr
Convert disk from GPT to MBR form. This option takes from one to four partition numbers, separated
by colons, as arguments. Their type codes are based on the GPT fdisk type codes divided by 0x0100.
If the active/bootable flag should be set, you must do so in another program, such as fdisk. The
gdisk program offers additional MBR conversion options. It is not possible to convert more than
four partitions from GPT to MBR form or to convert partitions that start above the 2TiB mark or
that are larger than 2TiB.
-n, --new=partnum:start:end
Create a new partition. 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 preceding 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 available sector. A start or end value of 0 specifies 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. A partnum value of 0 causes the program to use the first available
partition number. Subsequent uses of the -A, -c, -t, and -u options may also use 0 to refer to the
same partition.
-N, --largest-new=num
Create a new partition that fills the largest available block of space on the disk. You can use
the -a (--set-alignment) option to adjust the alignment, if desired. A num value of 0 causes the
program to use the first available partition number.
-o, --clear
Clear out all partition data. This includes GPT header data, all partition definitions, and the
protective MBR. Note that this operation will, like most other operations, fail on a damaged disk.
If you want to prepare a disk you know to be damaged for GPT use, you should first wipe it with -Z
and then partition it normally. This option will work even if the disk's original partition table
is bad; however, most other options on the same command line will be ignored.
-O, --print-mbr
Display basic MBR partition summary data. This includes partition numbers, starting and ending
sector numbers, partition sizes, MBR partition types codes, and partition names. This option is
useful mainly for diagnosing partition table problems, particularly on disks with hybrid MBRs.
-p, --print
Display basic GPT partition summary data. This includes partition numbers, starting and ending
sector numbers, partition sizes, sgdisk's partition types codes, and partition names. For
additional information, use the -i (--info) option.
-P, --pretend
Pretend to make specified changes. In-memory GPT data structures are altered according to other
parameters, but changes are not written to disk.
-r, --transpose
Swap two partitions' entries in the partition table. One or both partitions may be empty, although
swapping two empty partitions is pointless. For instance, if partitions 1-4 are defined,
transposing 1 and 5 results in a table with partitions numbered from 2-5. Transposing partitions
in this way has no effect on their disk space allocation; it only alters their order in the
partition table.
-R, --replicate=second_device_filename
Replicate the main device's partition table on the specified second device. 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 -G option on the new disk.
-s, --sort
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, --typecode=partnum:{hexcode|GUID}
Change a single partition's type code. You enter the type code using either a two-byte hexadecimal
number, as described earlier, or a fully-specified GUID value, such as
EBD0A0A2-B9E5-4433-87C0-68B6B72699C7.
-T, --transform-bsd=partnum
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. sgdisk 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 sgdisk being unable to convert a BSD disklabel is high
compared to the likelihood of problems with an MBR conversion.
-u, --partition-guid=partnum:guid
Set the partition unique GUID for an individual partition. The GUID may be a complete GUID or 'R'
to set a random GUID.
-U, --disk-guid=guid
Set the GUID for the disk. The GUID may be a complete GUID or 'R' to set a random GUID.
--usage
Print a brief summary of available options.
-v, --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 options on the recovery & transformation menu. If no problems are found, this command
displays a summary of unallocated disk space. This option will work even if the disk's original
partition table is bad; however, most other options on the same command line will be ignored.
-V, --version
Display program version information. This option may be used without specifying a device filename.
-z, --zap
Zap (destroy) the GPT data structures and then exit. Use this option if you want to repartition a
GPT disk using fdisk or some other GPT-unaware program. This option destroys only the GPT data
structures; it leaves the MBR intact. This makes it useful for wiping out GPT data structures
after a disk has been repartitioned for MBR using a GPT-unaware utility; however, there's a risk
that it will damage boot loaders or even the start of the first or end of the last MBR partition.
If you use it on a valid GPT disk, the MBR will be left with an inappropriate EFI GPT (0xEE)
partition definition, which you can delete using another utility.
-Z, --zap-all
Zap (destroy) the GPT and MBR data structures and then exit. This option works much like -z, but
as it wipes the MBR as well as the GPT, it's more suitable if you want to repartition a disk after
using this option, and completely unsuitable if you've already repartitioned the disk.
-?, --help
Print a summary of options.
RETURN VALUES
sgdisk returns various values depending on its success or failure:
0 Normal program execution
1 Too few arguments
2 An error occurred while reading the partition table
3 Non-GPT disk detected and no -g option, but operation requires a write action
4 An error prevented saving changes
5 An error occurred while reading standard input (should never occur with sgdisk, but may with
gdisk)
8 Disk replication operation (-R) failed
BUGS
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 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.) This limitation can be overcome by typing 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 option are 14
characters wide. This translates to a limitation of about 45 PiB. On larger disks, the displayed
columns will go out of alignment.
* 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 #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 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) 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 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 partition(s) may need to be deleted.
* Because of the highly variable nature of BSD disklabel structures, conversions from this form may
be unreliable -- partitions may be dropped, converted in a way that creates overlaps with other
partitions, or converted 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 RC 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.
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 (dschauer@gmail.com)
* Florian Zumbiehl (florz@florz.de)
SEE ALSO
cfdisk(8), cgdisk(8), fdisk(8), gdisk(8), mkfs(8), parted(8), sfdisk(8), fixparts(8).
http://en.wikipedia.org/wiki/GUID_Partition_Table
http://developer.apple.com/technotes/tn2006/tn2166.html
http://www.rodsbooks.com/gdisk/
AVAILABILITY
The sgdisk command is part of the GPT fdisk package and is available from Rod Smith.