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 (sgdisk internal code 0xEF00) formatted
as FAT-32. The recommended size of this partition is between 100 and 300
MiB. Boot-related files are stored here. (Note that GNU Parted identifies
such partitions as having the "boot flag" set.)
- *
- Some boot loaders for BIOS-based systems make use of a
BIOS Boot Partition (sgdisk internal code 0xEF02), in
which the secondary boot loader is stored, possibly without the benefit of
a filesystem. This partition can typically be quite small (roughly 32 to
200 KiB), but you should consult your boot loader documentation for
details.
- *
- If Windows is to boot from a GPT disk, a partition of type
Microsoft Reserved (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 2048 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.
GPT fdisk sets a default name based on the partition type code. 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.
- -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.
- -N, --largest-new=num
- Create a new partition that fills the largest available
block of space on the disk. Note that if used on a completely blank disk,
this is likely to result in a sector-moved warning, since the first
available sector (normally 34) doesn't fall on a 2048-sector boundary (the
default for alignment). 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.
- -p, --print
- Display basic 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
- 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¶
As of May 2012 (version 0.8.5),
sgdisk should be considered beta
software. Known bugs and limitations include:
- *
- The program compiles correctly only on Linux, FreeBSD, and
Mac OS X. Linux versions for x86-64 (64-bit), x86 (32-bit), and PowerPC
(32-bit) have been tested, with the x86-64 version having seen the most
testing.
- *
- The 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@ti.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.