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 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 1MiB (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. The
created hybrid MBR places an EFI GPT (type 0xEE) partition first
in the table, 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 AT rodsbooks.com)
Contributors:
* Yves Blusseau (1otnwmz02 AT sneakemail.com)
* David Hubbard (david.c.hubbard AT gmail.com)
* Justin Maggard (justin.maggard AT netgear.com)
* Dwight Schauer (dschauer AT gmail.com)
* Florian Zumbiehl (florz AT 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.
Roderick W. Smith 1.0.3 SGDISK(8)
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