Manual: sgdisk
SGDISK(8) GPT fdisk Manual SGDISK(8)
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 https://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 cerā
tain 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 overā
lap 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) opā
tion 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 unrecogā
nized 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, 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 (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 arā
guments 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.
When the -I option is used, this same alignment value is used to determine partition end points; but partiā
tions end at one less than a multiple of this value, to keep the partition length a multiple of this value.
-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 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. If the GPT data structures are damaged, the backup may not accurately reā
flect the damaged state; instead, they will reflect GPT fdisk's first-pass interpretation of the GPT.
-B, --byte-swap-name=partnum
Swap the byte order for the name of the specified partition. 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 feature corrects this problem.
-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, enā
close 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 ilā
legal 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 apā
plied. 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 partiā
tions. 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.
-I, --align-end
When possible, align the end points of partitions to one less than a multiple of the alignment value. When
both start and end points are aligned, partitions should be multiples of the alignment value in size, which is
necessary for some partition encryption tools to function correctly. This option applies to all partitions
created after this option on the command line. Note that this alignment is not always possible; for instance,
if the free space at the end of a disk is less than the alignment value, with the current final partition beā
ing aligned, and if sgdisk is asked to create a partition in that space, then it will not be end-aligned.
-j, --move-main-table=sector
Sets the start sector 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.
-k, --move-backup-table=sector
Sets the start sector of the second/backup partition table. The backup table is usually placed just before the
last sector, which holds the backup header. The default value is thus the size of the disk, minus one, minus
the total size of the partition table (in sectors, usually 32). There are probably very few reasons to ever
change this, and while the EFI standard does not mandate it, most tooling assumes the backup table to be at
the very end of the disk.
-l, --load-backup=file
Load partition data from a backup file. This option is the reverse of the -b option. Note that restoring parā
tition 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 purā
poses. 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 inā
stance, 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 (--attributes), -c (--change-name), -t (--typecode), and -u
(--partition-guid) 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. Subsequent uses of the -A (--attributes), -c (--change-name), -t (--typeā
code), and -u (--partition-guid) options may also use 0 to refer to the same partition.
-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 partiā
tion 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 conā
verted MBR) partitions. Converted partitions' type codes are likely to need manual adjustment. sgdisk will atā
tempt to convert BSD disklabels stored on the main disk when launched, but this conversion is likely to proā
duce 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 conā
version.
-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 unalloā
cated 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 usā
ing 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 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 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 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) can sometimes overā
come 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 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 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 (das@teegra.net)
* Florian Zumbiehl (florz@florz.de)
SEE ALSO
cfdisk(8), cgdisk(8), fdisk(8), gdisk(8), mkfs(8), parted(8), sfdisk(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 sgdisk command is part of the GPT fdisk package and is available from Rod Smith.
Roderick W. Smith 1.0.10 SGDISK(8)