1SGDISK(8) GPT fdisk Manual SGDISK(8)
2
6 sgdisk - Command-line GUID partition table (GPT) manipulator for Linux
7 and Unix
8
10 sgdisk [ options ] device
11
14 GPT fdisk is a text-mode menu-driven package for creation and manipula‐
15 tion of partition tables. It consists of two programs: the text-mode
16 interactive gdisk and the command-line sgdisk. Either program will
17 automatically convert an old-style Master Boot Record (MBR) partition
18 table or BSD disklabel stored without an MBR carrier partition to the
19 newer Globally Unique Identifier (GUID) Partition Table (GPT) format,
20 or will load a GUID partition table. This man page documents the com‐
21 mand-line sgdisk program.
22 Some advanced data manipulation and recovery options require you to
24 understand the distinctions between the main and backup data, as well
25 as between the GPT headers and the partition tables. For information on
26 MBR vs. GPT, as well as GPT terminology and structure, see the extended
27 gdisk documentation at http://www.rodsbooks.com/gdisk/ or consult
28 Wikipedia.
29 The sgdisk program employs a user interface that's based entirely on
31 the command line, making it suitable for use in scripts or by experts
32 who want to make one or two quick changes to a disk. (The program may
33 query the user when certain errors are encountered, though.) The pro‐
34 gram's name is based on sfdisk, but the user options of the two pro‐
35 grams are entirely different from one another.
36 Ordinarily, sgdisk operates on disk device files, such as /dev/sda or
38 /dev/hda under Linux, /dev/disk0 under Mac OS X, or /dev/ad0 or
39 /dev/da0 under FreeBSD. The program can also operate on disk image
40 files, which can be either copies of whole disks (made with dd, for
41 instance) or raw disk images used by emulators such as QEMU or VMWare.
42 Note that only raw disk images are supported; sgdisk cannot work on
43 compressed or other advanced disk image formats.
44 The MBR partitioning system uses a combination of cylinder/head/sector
46 (CHS) addressing and logical block addressing (LBA). The former is
47 klunky and limiting. GPT drops CHS addressing and uses 64-bit LBA mode
48 exclusively. Thus, GPT data structures, and therefore sgdisk, do not
49 need to deal with CHS geometries and all the problems they create.
50 For best results, you should use an OS-specific partition table program
52 whenever possible. For example, you should make Mac OS X partitions
53 with the Mac OS X Disk Utility program and Linux partitions with the
54 Linux gdisk, sgdisk, or GNU Parted programs.
55 Upon start, sgdisk attempts to identify the partition type in use on
57 the disk. If it finds valid GPT data, sgdisk will use it. If sgdisk
58 finds a valid MBR or BSD disklabel but no GPT data, it will attempt to
59 convert the MBR or disklabel into GPT form. (BSD disklabels are likely
60 to have unusable first and/or final partitions because they overlap
61 with the GPT data structures, though.) GPT fdisk can identify, but not
62 use data in, Apple Partition Map (APM) disks, which are used on 680x0-
63 and PowerPC-based Macintoshes. If you specify any option that results
64 in changes to an MBR or BSD disklabel, sgdisk ignores those changes
65 unless the -g (--mbrtogpt), -z (--zap), or -Z (--zap-all) option is
66 used. If you use the -g option, sgdisk replaces the MBR or disklabel
67 with a GPT. This action is potentially dangerous! Your system may
68 become unbootable, and partition type codes may become corrupted if the
69 disk uses unrecognized type codes. Boot problems are particularly
70 likely if you're multi-booting with any GPT-unaware OS.
71 The MBR-to-GPT conversion will leave at least one gap in the partition
73 numbering if the original MBR used logical partitions. These gaps are
74 harmless, but you can eliminate them by using the -s (--sort) option,
75 if you like. (Doing this may require you to update your /etc/fstab
76 file.)
77 When creating a fresh partition table, certain considerations may be in
79 order:
80 * For data (non-boot) disks, and for boot disks used on BIOS-based
83 computers with GRUB as the boot loader, partitions may be cre‐
84 ated in whatever order and in whatever sizes are desired.
85 * Boot disks for EFI-based systems require an EFI System Partition
88 (gdisk internal code 0xEF00) formatted as FAT-32. I recommended
89 making this partition 550 MiB. (Smaller ESPs are common, but
90 some EFIs have flaky FAT drivers that necessitate a larger par‐
91 tition for reliable operation.) Boot-related files are stored
92 here. (Note that GNU Parted identifies such partitions as having
93 the "boot flag" set.)
94 * Some boot loaders for BIOS-based systems make use of a BIOS Boot
97 Partition (gdisk internal code 0xEF02), in which the secondary
98 boot loader is stored, possibly without the benefit of a
99 filesystem. (GRUB2 may optionally use such a partition.) This
100 partition can typically be quite small (roughly 32 to 200 KiB,
101 although 1 MiB is more common in practice), but you should con‐
102 sult your boot loader documentation for details.
103 * If Windows is to boot from a GPT disk, a partition of type Mi‐
106 crosoft Reserved (sgdisk internal code 0x0C01) is recommended.
107 This partition should be about 128 MiB in size. It ordinarily
108 follows the EFI System Partition and immediately precedes the
109 Windows data partitions. (Note that GNU Parted creates all FAT
110 partitions as this type, which actually makes the partition
111 unusable for normal file storage in both Windows and Mac OS X.)
112 * Some OSes' GPT utilities create some blank space (typically 128
115 MiB) after each partition. The intent is to enable future disk
116 utilities to use this space. Such free space is not required of
117 GPT disks, but creating it may help in future disk maintenance.
118
121 Some options take no arguments, others take one argument (typically a
122 partition number), and others take compound arguments with colon delim‐
123 itation. For instance, -n (--new) takes a partition number, a starting
124 sector number, and an ending sector number, as in sgdisk -n
125 2:2000:50000 /dev/sdc, which creates a new partition, numbered 2,
126 starting at sector 2000 an ending at sector 50,000, on /dev/sdc.
127 Unrelated options may be combined; however, some such combinations will
129 be nonsense (such as deleting a partition and then changing its GUID
130 type code). sgdisk interprets options in the order in which they're
131 entered, so effects can vary depending on order. For instance, sgdisk
132 -s -d 2 sorts the partition table entries and then deletes partition 2
133 from the newly-sorted list; but sgdisk -d 2 -s deletes the original
134 partition 2 and then sorts the modified partition table.
135 Error checking and opportunities to correct mistakes in sgdisk are min‐
137 imal. Although the program endeavors to keep the GPT data structures
138 legal, it does not prompt for verification before performing its
139 actions. Unless you require a command-line-driven program, you should
140 use the interactive gdisk instead of sgdisk, since gdisk allows you to
141 quit without saving your changes, should you make a mistake.
142 Although sgdisk is based on the same partition-manipulation code as
144 gdisk, sgdisk implements fewer features than its interactive sibling.
145 Options available in sgdisk are:
146 -a, --set-alignment=value
149 Set the sector alignment multiple. GPT fdisk aligns the start of
150 partitions to sectors that are multiples of this value, which
151 defaults to 1 MiB (2048 on disks with 512-byte sectors) on
152 freshly formatted disks. This alignment value is necessary to
153 obtain optimum performance with Western Digital Advanced Format
154 and similar drives with larger physical than logical sector
155 sizes, with some types of RAID arrays, and with SSD devices.
156 -A, --attributes=list|[partnum:show|or|nand|xor|=|set|clear|tog‐
159 gle|get[:bitnum|hexbitmask]]
160 View or set partition attributes. Use list to see defined
161 (known) attribute values. Omit the partition number (and even
162 the device filename) when using this option. The others require
163 a partition number. The show and get options show the current
164 attribute settings (all attributes or for a particular bit,
165 respectively). The or, nand, xor, =, set, clear, and toggle
166 options enable you to change the attribute bit value. The set,
167 clear, toggle, and get options work on a bit number; the others
168 work on a hexadecimal bit mask. For example, type sgdisk -A
169 4:set:2 /dev/sdc to set the bit 2 attribute (legacy BIOS
170 bootable) on partition 4 on /dev/sdc.
171 -b, --backup=file
174 Save partition data to a backup file. You can back up your cur‐
175 rent in-memory partition table to a disk file using this option.
176 The resulting file is a binary file consisting of the protective
177 MBR, the main GPT header, the backup GPT header, and one copy of
178 the partition table, in that order. Note that the backup is of
179 the current in-memory data structures, so if you launch the pro‐
180 gram, make changes, and then use this option, the backup will
181 reflect your changes. If the GPT data structures are damaged,
182 the backup may not accurately reflect the damaged state;
183 instead, they will reflect GPT fdisk's first-pass interpretation
184 of the GPT.
185 -c, --change-name=partnum:name
188 Change the GPT name of a partition. This name is encoded as a
189 UTF-16 string, but proper entry and display of anything beyond
190 basic ASCII values requires suitable locale and font support.
191 For the most part, Linux ignores the partition name, but it may
192 be important in some OSes. If you want to set a name that
193 includes a space, enclose it in quotation marks, as in sgdisk -c
194 1:"Sample Name" /dev/sdb. Note that the GPT name of a partition
195 is distinct from the filesystem name, which is encoded in the
196 filesystem's data structures.
197 -C, --recompute-chs
200 Recompute CHS values in protective or hybrid MBR. This option
201 can sometimes help if a disk utility, OS, or BIOS doesn't like
202 the CHS values used by the partitions in the protective or
203 hybrid MBR. In particular, the GPT specification requires a CHS
204 value of 0xFFFFFF for over-8GiB partitions, but this value is
205 technically illegal by the usual standards. Some BIOSes hang if
206 they encounter this value. This option will recompute a more
207 normal CHS value -- 0xFEFFFF for over-8GiB partitions, enabling
208 these BIOSes to boot.
209 -d, --delete=partnum
212 Delete a partition. This action deletes the entry from the par‐
213 tition table but does not disturb the data within the sectors
214 originally allocated to the partition on the disk. If a corre‐
215 sponding hybrid MBR partition exists, gdisk deletes it, as well,
216 and expands any adjacent 0xEE (EFI GPT) MBR protective partition
217 to fill the new free space.
218 -D, --display-alignment
221 Display current sector alignment value. Partitions will be cre‐
222 ated on multiples of the sector value reported by this option.
223 You can change the alignment value with the -a option.
224 -e, --move-second-header
227 Move backup GPT data structures to the end of the disk. Use this
228 option if you've added disks to a RAID array, thus creating a
229 virtual disk with space that follows the backup GPT data struc‐
230 tures. This command moves the backup GPT data structures to the
231 end of the disk, where they belong.
232 -E, --end-of-largest
235 Displays the sector number of the end of the largest available
236 block of sectors on the disk. A script may store this value and
237 pass it back as part of -n's option to create a partition. If no
238 unallocated sectors are available, this function returns the
239 value 0.
240 -f, --first-in-largest
243 Displays the sector number of the start of the largest available
244 block of sectors on the disk. A script may store this value and
245 pass it back as part of -n's option to create a partition. If no
246 unallocated sectors are available, this function returns the
247 value 0. Note that this parameter is blind to partition align‐
248 ment; when you actually create a partition, its start point
249 might be changed from this value.
250 -F, --first-aligned-in-largest
253 Similar to -f (--first-in-largest), except returns the sector
254 number with the current alignment correction applied. Use this
255 function if you need to compute the actual partition start point
256 rather than a theoretical start point or the actual start point
257 if you set the alignment value to 1.
258 -g, --mbrtogpt
261 Convert an MBR or BSD disklabel disk to a GPT disk. As a safety
262 measure, use of this option is required on MBR or BSD disklabel
263 disks if you intend to save your changes, in order to prevent
264 accidentally damaging such disks.
265 -G, --randomize-guids
268 Randomize the disk's GUID and all partitions' unique GUIDs (but
269 not their partition type code GUIDs). This function may be used
270 after cloning a disk in order to render all GUIDs once again
271 unique.
272 -h, --hybrid
275 Create a hybrid MBR. This option takes from one to three parti‐
276 tion numbers, separated by colons, as arguments. You may option‐
277 ally specify a final partition "EE" to indicate that the EFI GPT
278 (type 0xEE) should be placed last in the table, otherwise it
279 will be placed first, followed by the partition(s) you specify.
280 Their type codes are based on the GPT fdisk type codes divided
281 by 0x0100, which is usually correct for Windows partitions. If
282 the active/bootable flag should be set, you must do so in
283 another program, such as fdisk. The gdisk program offers addi‐
284 tional hybrid MBR creation options.
285 -i, --info=partnum
288 Show detailed partition information. The summary information
289 produced by the -p command necessarily omits many details, such
290 as the partition's unique GUID and the translation of sgdisk's
291 internal partition type code to a plain type name. The -i option
292 displays this information for a single partition.
293 -j, --adjust-main-table=sector
296 Adjust the location of the main partition table. This value is
297 normally 2, but it may need to be increased in some cases, such
298 as when a system-on-chip (SoC) is hard-coded to read boot code
299 from sector 2. I recommend against adjusting this value unless
300 doing so is absolutely necessary.
301 -l, --load-backup=file
304 Load partition data from a backup file. This option is the
305 reverse of the -b option. Note that restoring partition data
306 from anything but the original disk is not recommended. This
307 option will work even if the disk's original partition table is
308 bad; however, most other options on the same command line will
309 be ignored.
310 -L, --list-types
313 Display a summary of partition types. GPT uses a GUID to iden‐
314 tify partition types for particular OSes and purposes. For ease
315 of data entry, sgdisk compresses these into two-byte (four-digit
316 hexadecimal) values that are related to their equivalent MBR
317 codes. Specifically, the MBR code is multiplied by hexadecimal
318 0x0100. For instance, the code for Linux swap space in MBR is
319 0x82, and it's 0x8200 in gdisk. A one-to-one correspondence is
320 impossible, though. Most notably, the codes for all varieties of
321 FAT and NTFS partition correspond to a single GPT code (entered
322 as 0x0700 in sgdisk). Some OSes use a single MBR code but employ
323 many more codes in GPT. For these, sgdisk adds code numbers
324 sequentially, such as 0xa500 for a FreeBSD disklabel, 0xa501 for
325 FreeBSD boot, 0xa502 for FreeBSD swap, and so on. Note that
326 these two-byte codes are unique to gdisk and sgdisk. This option
327 does not require you to specify a valid disk device filename.
328 -m, --gpttombr
331 Convert disk from GPT to MBR form. This option takes from one to
332 four partition numbers, separated by colons, as arguments. Their
333 type codes are based on the GPT fdisk type codes divided by
334 0x0100. If the active/bootable flag should be set, you must do
335 so in another program, such as fdisk. The gdisk program offers
336 additional MBR conversion options. It is not possible to convert
337 more than four partitions from GPT to MBR form or to convert
338 partitions that start above the 2TiB mark or that are larger
339 than 2TiB.
340 -n, --new=partnum:start:end
343 Create a new partition. You enter a partition number, starting
344 sector, and an ending sector. Both start and end sectors can be
345 specified in absolute terms as sector numbers or as positions
346 measured in kibibytes (K), mebibytes (M), gibibytes (G),
347 tebibytes (T), or pebibytes (P); for instance, 40M specifies a
348 position 40MiB from the start of the disk. You can specify loca‐
349 tions relative to the start or end of the specified default
350 range by preceding the number by a '+' or '-' symbol, as in +2G
351 to specify a point 2GiB after the default start sector, or -200M
352 to specify a point 200MiB before the last available sector. A
353 start or end value of 0 specifies the default value, which is
354 the start of the largest available block for the start sector
355 and the end of the same block for the end sector. A partnum
356 value of 0 causes the program to use the first available parti‐
357 tion number. Subsequent uses of the -A, -c, -t, and -u options
358 may also use 0 to refer to the same partition.
359 -N, --largest-new=num
362 Create a new partition that fills the largest available block of
363 space on the disk. You can use the -a (--set-alignment) option
364 to adjust the alignment, if desired. A num value of 0 causes the
365 program to use the first available partition number.
366 -o, --clear
369 Clear out all partition data. This includes GPT header data, all
370 partition definitions, and the protective MBR. Note that this
371 operation will, like most other operations, fail on a damaged
372 disk. If you want to prepare a disk you know to be damaged for
373 GPT use, you should first wipe it with -Z and then partition it
374 normally. This option will work even if the disk's original par‐
375 tition table is bad; however, most other options on the same
376 command line will be ignored.
377 -O, --print-mbr
380 Display basic MBR partition summary data. This includes parti‐
381 tion numbers, starting and ending sector numbers, partition
382 sizes, MBR partition types codes, and partition names. This
383 option is useful mainly for diagnosing partition table problems,
384 particularly on disks with hybrid MBRs.
385 -p, --print
388 Display basic GPT partition summary data. This includes parti‐
389 tion numbers, starting and ending sector numbers, partition
390 sizes, sgdisk's partition types codes, and partition names. For
391 additional information, use the -i (--info) option.
392 -P, --pretend
395 Pretend to make specified changes. In-memory GPT data structures
396 are altered according to other parameters, but changes are not
397 written to disk.
398 -r, --transpose
401 Swap two partitions' entries in the partition table. One or both
402 partitions may be empty, although swapping two empty partitions
403 is pointless. For instance, if partitions 1-4 are defined,
404 transposing 1 and 5 results in a table with partitions numbered
405 from 2-5. Transposing partitions in this way has no effect on
406 their disk space allocation; it only alters their order in the
407 partition table.
408 -R, --replicate=second_device_filename
411 Replicate the main device's partition table on the specified
412 second device. Note that the replicated partition table is an
413 exact copy, including all GUIDs; if the device should have its
414 own unique GUIDs, you should use the -G option on the new disk.
415 -s, --sort
418 Sort partition entries. GPT partition numbers need not match the
419 order of partitions on the disk. If you want them to match, you
420 can use this option. Note that some partitioning utilities sort
421 partitions whenever they make changes. Such changes will be
422 reflected in your device filenames, so you may need to edit
423 /etc/fstab if you use this option.
424 -t, --typecode=partnum:{hexcode|GUID}
427 Change a single partition's type code. You enter the type code
428 using either a two-byte hexadecimal number, as described ear‐
429 lier, or a fully-specified GUID value, such as
430 EBD0A0A2-B9E5-4433-87C0-68B6B72699C7.
431 -T, --transform-bsd=partnum
434 Transform BSD partitions into GPT partitions. This option works
435 on BSD disklabels held within GPT (or converted MBR) partitions.
436 Converted partitions' type codes are likely to need manual
437 adjustment. sgdisk will attempt to convert BSD disklabels stored
438 on the main disk when launched, but this conversion is likely to
439 produce first and/or last partitions that are unusable. The many
440 BSD variants means that the probability of sgdisk being unable
441 to convert a BSD disklabel is high compared to the likelihood of
442 problems with an MBR conversion.
443 -u, --partition-guid=partnum:guid
446 Set the partition unique GUID for an individual partition. The
447 GUID may be a complete GUID or 'R' to set a random GUID.
448 -U, --disk-guid=guid
451 Set the GUID for the disk. The GUID may be a complete GUID or
452 'R' to set a random GUID.
453 --usage
456 Print a brief summary of available options.
457 -v, --verify
460 Verify disk. This option checks for a variety of problems, such
461 as incorrect CRCs and mismatched main and backup data. This
462 option does not automatically correct most problems, though; for
463 that, you must use options on the recovery & transformation
464 menu. If no problems are found, this command displays a summary
465 of unallocated disk space. This option will work even if the
466 disk's original partition table is bad; however, most other
467 options on the same command line will be ignored.
468 -V, --version
471 Display program version information. This option may be used
472 without specifying a device filename.
473 -z, --zap
476 Zap (destroy) the GPT data structures and then exit. Use this
477 option if you want to repartition a GPT disk using fdisk or some
478 other GPT-unaware program. This option destroys only the GPT
479 data structures; it leaves the MBR intact. This makes it useful
480 for wiping out GPT data structures after a disk has been repar‐
481 titioned for MBR using a GPT-unaware utility; however, there's a
482 risk that it will damage boot loaders or even the start of the
483 first or end of the last MBR partition. If you use it on a valid
484 GPT disk, the MBR will be left with an inappropriate EFI GPT
485 (0xEE) partition definition, which you can delete using another
486 utility.
487 -Z, --zap-all
490 Zap (destroy) the GPT and MBR data structures and then exit.
491 This option works much like -z, but as it wipes the MBR as well
492 as the GPT, it's more suitable if you want to repartition a disk
493 after using this option, and completely unsuitable if you've
494 already repartitioned the disk.
495 -?, --help
498 Print a summary of options.
499
502 sgdisk returns various values depending on its success or failure:
503 0 Normal program execution
506 1 Too few arguments
509 2 An error occurred while reading the partition table
512 3 Non-GPT disk detected and no -g option, but operation requires a
515 write action
516 4 An error prevented saving changes
519 5 An error occurred while reading standard input (should never
522 occur with sgdisk, but may with gdisk)
523 8 Disk replication operation (-R) failed
526
529 Known bugs and limitations include:
530 * The program compiles correctly only on Linux, FreeBSD, and Mac
533 OS X. Linux versions for x86-64 (64-bit), x86 (32-bit), and Pow‐
534 erPC (32-bit) have been tested, with the x86-64 version having
535 seen the most testing.
536 * The FreeBSD version of the program can't write changes to the
539 partition table to a disk when existing partitions on that disk
540 are mounted. (The same problem exists with many other FreeBSD
541 utilities, such as gpt, fdisk, and dd.) This limitation can be
542 overcome by typing sysctl kern.geom.debugflags=16 at a shell
543 prompt.
544 * The fields used to display the start and end sector numbers for
547 partitions in the -p option are 14 characters wide. This trans‐
548 lates to a limitation of about 45 PiB. On larger disks, the dis‐
549 played columns will go out of alignment.
550 * The program can load only up to 128 partitions (4 primary parti‐
553 tions and 124 logical partitions) when converting from MBR for‐
554 mat. This limit can be raised by changing the #define
555 MAX_MBR_PARTS line in the basicmbr.h source code file and recom‐
556 piling; however, such a change will require using a
557 larger-than-normal partition table. (The limit of 128 partitions
558 was chosen because that number equals the 128 partitions sup‐
559 ported by the most common partition table size.)
560 * Converting from MBR format sometimes fails because of insuffi‐
563 cient space at the start or (more commonly) the end of the disk.
564 Resizing the partition table (using the 's' option in the
565 experts' menu) can sometimes overcome this problem; however, in
566 extreme cases it may be necessary to resize a partition using
567 GNU Parted or a similar tool prior to conversion with gdisk.
568 * MBR conversions work only if the disk has correct LBA partition
571 descriptors. These descriptors should be present on any disk
572 over 8 GiB in size or on smaller disks partitioned with any but
573 very ancient software.
574 * BSD disklabel support can create first and/or last partitions
577 that overlap with the GPT data structures. This can sometimes be
578 compensated by adjusting the partition table size, but in
579 extreme cases the affected partition(s) may need to be deleted.
580 * Because of the highly variable nature of BSD disklabel struc‐
583 tures, conversions from this form may be unreliable -- parti‐
584 tions may be dropped, converted in a way that creates overlaps
585 with other partitions, or converted with incorrect start or end
586 values. Use this feature with caution!
587 * Booting after converting an MBR or BSD disklabel disk is likely
590 to be disrupted. Sometimes re-installing a boot loader will fix
591 the problem, but other times you may need to switch boot load‐
592 ers. Except on EFI-based platforms, Windows through at least
593 Windows 7 RC doesn't support booting from GPT disks. Creating a
594 hybrid MBR (using the 'h' option on the recovery & transforma‐
595 tion menu) or abandoning GPT in favor of MBR may be your only
596 options in this case.
597
600 Primary author: Roderick W. Smith (rodsmith@rodsbooks.com)
601 Contributors:
603 * Yves Blusseau (1otnwmz02@sneakemail.com)
605 * David Hubbard (david.c.hubbard@gmail.com)
607 * Justin Maggard (justin.maggard@netgear.com)
609 * Dwight Schauer (dschauer@gmail.com)
611 * Florian Zumbiehl (florz@florz.de)
613
617 cfdisk(8), cgdisk(8), fdisk(8), gdisk(8), mkfs(8), parted(8),
618 sfdisk(8), fixparts(8).
619 http://en.wikipedia.org/wiki/GUID_Partition_Table
621 http://developer.apple.com/technotes/tn2006/tn2166.html
623 http://www.rodsbooks.com/gdisk/
625
628 The sgdisk command is part of the GPT fdisk package and is available
629 from Rod Smith.
630Roderick W. Smith 1.0.5 SGDISK(8)