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 certain errors are encountered, though.) The program's name is based on sfdisk, but the user options of the two programs are entirely dif‐
   ferent 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  op‐
   erate  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 identi‐
          fies 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 ben‐
          efit 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  prac‐
          tice), 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 physi‐
          cal 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 partitions 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 current in-memory data struc‐
          tures,  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.

   -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  or‐
          der 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, enclose it  in  quota‐
          tion  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  pro‐
          tective  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 stan‐
          dards. 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 op‐
          tion.

   -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 par‐
          tition, 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  parti‐
          tion 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 or‐
          der 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.

   -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 being 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 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 par‐
          tition 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 se‐
          quentially,  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 op‐
          tions. 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 num‐
          ber. 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 (--typecode),  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 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 partition‐
          ing 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 parti‐
          tions 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 #de‐
          fine 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 con‐
          version 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 (das@teegra.net)

   * Florian Zumbiehl (florz@florz.de)