1 GPT fdisk (aka gdisk, cgdisk, and sgdisk) and FixParts
2 by Roderick W. Smith, rodsmith@rodsbooks.com
7 This package includes the source code for four related disk partitioning
10 - gdisk -- This program is modeled after Linux fdisk, but it operates on
11 GUID Partition Table (GPT) disks rather than the Master Boot Record (MBR)
12 disks that fdisk modifies. As such, gdisk is an interactive text-mode
13 tool for manipulating partitions, but it does nothing to the contents of
14 those partitions (usually filesystems, but sometimes swap space or other
17 - cgdisk -- This program is modeled after Linux cfdisk, but it operates on
18 GPT disks rather than the MBR disks that cfdisk modifies. As such, cgdisk
19 is a curses-based text-mode tool for manipulating partitions, which is to
20 say that it uses an interface that relies on arrow keys and a dynamic
21 display rather than the command letters and a scrolling display like
24 - sgdisk -- This program is conceptually similar to the Linux sfdisk and
25 FreeBSD gpt programs, but its operational details differ. It enables
26 manipulation of GPT disks using command-line options, so it's suitable
27 for use in scripts or by experts to perform specific tasks that might
28 take several commands in gdisk to accomplish.
30 - fixparts -- This program, unlike the preceding three, operates on MBR
31 disks. It's intended to fix certain problems that can be created by
32 various utilities. Specifically, it can fix mis-sized extended partitions
33 and primary partitions located in the middle of extended partitions. It
34 also enables changing primary vs. logical partition status (within limits
35 of what's legal in the MBR scheme) and making a few other minor changes.
36 It does NOT support creating new partitions; for that, you should use
37 fdisk, parted, or some other tool.
39 More details about the abilities of these tools follows.
41 All four programs rely on the same set of underlying code base; they differ
42 only in their control interfaces (defined in gdisk.cc, cgdisk.cc,
43 sgdisk.cc, and fixparts.cc, respectively) and in which support code they
46 GPT fdisk (gdisk, cgdisk, and sgdisk) Details
47 ---------------------------------------------
49 The gdisk program is intended as a (somewhat) fdisk-workalike program for
50 GPT-partitioned disks, cgdisk is similarly a workalike for fdisk, and
51 sgdisk provides most of gdisk's functionality in a more script-friendly
52 program. Although libparted and programs that use it (GNU Parted, gparted,
53 etc.) provide the ability to handle GPT disks, they have certain
54 limitations that gdisk overcomes. Specific advantages of gdisk, cgdisk, and
57 * The ability to convert MBR-partitioned disks in-place to GPT format,
60 * The ability to convert BSD disklabels in-place to create GPT
61 partitions, without losing data
63 * The ability to convert from GPT format to MBR format without data loss
64 (gdisk and sgdisk only)
66 * More flexible specification of filesystem type code GUIDs, which
67 GNU Parted tends to corrupt
69 * Clear identification of the number of unallocated sectors on a
72 * A user interface that's familiar to long-time users of Linux
73 fdisk and cfdisk (gdisk and cgdisk only)
75 * The MBR boot loader code is left alone
77 * The ability to create a hybrid MBR, which permits GPT-unaware OSes to
78 access up to three GPT partitions on the disk (gdisk and sgdisk only)
80 Of course, GPT fdisk isn't without its limitations. Most notably, it lacks
81 the filesystem awareness and filesystem-related features of GNU Parted. You
82 can't resize a partition's filesystem or create a partition with a
83 filesystem already in place with gdisk, for instance. There's no GUI
86 The GPT fdisk package provides three program files: the interactive
87 text-mode gdisk, the curses-based interactive cgdisk, and the
88 command-line-driven sgdisk. The first two are intended for use in manually
89 partitioning disks or changing partitioning details; sgdisk is intended for
90 use in scripts to help automate tasks such as disk cloning or preparing
91 multiple disks for Linux installation.
96 This program's creation was motivated by cries for help I've seen in online
97 forums from users who have found their partition tables to be corrupted by
98 various buggy partitioning tools. Although most OSes can handle the
99 afflicted disks fine, libparted-based tools (GParted, parted, most Linux
100 installers, etc.) tend to flake out when presented with these disks.
101 Typically, the symptom is a disk that appears to hold no partitions;
102 however, sometimes the libparted tool presents partitions other than those
105 I've observed four causes of these symptoms, three of which FixParts can
108 * Old GPT data -- If a disk is used as a GPT disk and then re-used as an
109 MBR disk, the GPT data may be incompletely erased. This happens if the
110 disk is repartitioned with fdisk or the Microsoft Windows installer, for
111 instance. (Tools based on libparted correctly remove the old GPT data
112 when converting from GPT to MBR format.) FixParts checks for this problem
113 when it starts and offers to correct it. If you opt to erase the GPT
114 data, this erasure occurs immediately, unlike other changes the program
117 * Mis-sized extended partitions -- Some tools create an extended partition
118 that's too large, typically ending after the last sector of the disk.
119 FixParts automatically corrects this problem (if you use the 'w' option
120 to save the partition table).
122 * Primary partitions inside an extended partition -- Some utilities create
123 or move primary partitions to within the range covered by the extended
124 partition. FixParts can usually correct this problem by turning the
125 primary partition into a logical partition or by changing one or more
126 other logical partitions into primaries. Such corrections aren't always
127 possible, though, at least not without deleting or resizing other
130 * Leftover RAID data -- If a disk is used in a RAID array and then re-used
131 as a non-RAID disk, some utilities can become confused and fail to see
132 the disk. FixParts can NOT correct this problem. You must destroy the old
133 RAID data, or possibly remove the dmraid package from the system, to fix
136 When run, FixParts presents an fdisk-like interface, enabling you to adjust
137 partition types (primary, logical, or omitted), change type codes, change
138 the bootable flag, and so on. Although you can delete a partition (by
139 omitting it), you can't create new partitions with the program. If you're
140 used to partitioning disks, particularly with Linux fdisk, two unusual
141 features of FixParts require elaboration:
143 * No extended partitions -- Internally, FixParts reads the partition table
144 and discards data on any extended partition(s) it finds. When you save
145 the partition table, the program generates a new extended partition. This
146 design means that the program automatically corrects many problems
147 related to the extended partition. It also means that you'll see no
148 evidence of extended partitions in the FixParts user interface, although
149 it keeps track of the requirements and prevents you from creating illegal
150 layouts, such as a primary between two logicals.
152 * Partition numbering -- In most Linux tools, partitions 1-4 are primaries
153 and partitions 5 and up are logicals. Although a legal partition table
154 loaded into FixParts will initially conform to this convention, some
155 types of damaged table might not, and various changes you make can also
156 cause deviations. When FixParts writes the partition table, its numbering
157 will be altered to conform to the standard MBR conventions, but you
158 should use the explicit labeling of partitions as primary or logical
159 rather than the partition numbers to determine a partition's status.
164 To compile GPT fdisk, you must have appropriate development tools
165 installed, most notably the GNU Compiler Collection (GCC) and its g++
166 compiler for C++. (Under Windows, Microsoft Visual C++ 2008 can also be
167 used.) In addition, note these requirements:
169 * On Linux, FreeBSD, and OS X, libuuid must be installed. This is the
170 standard for Linux and OS X, although you may need to install a package
171 called uuid-dev or something similar to get the headers. On FreeBSD, the
172 e2fsprogs-libuuid port must be installed.
174 * The ICU library (http://site.icu-project.org), which provides support for
175 Unicode partition names, is recommended on all
176 platforms except Windows. This library is normally installed in Linux and
177 OS X, but you may need to install the development headers (libicu-dev or
178 something similar in Linux; or the libicu36-dev Fink package in OS X). To
179 compile without ICU support, you must modify the Makefile: Remove the
180 "-D USE_UTF16" part from the CXXFLAGS line and remove references to
181 -licuio, -licuuc, -licudata, and -licucore (details vary between
182 platforms) from the compilation options. Suitable lines are present, but
183 commented out, in the Makefile, Makefile.mac, and Makefile.bsd files.
185 * The cgdisk program requires the ncurses library and its development files
186 (headers). Most Linux distributions install ncurses by default, but you
187 may need to install a package called libncurses5-dev, ncurses-devel, or
188 something similar to obtain the header files. These files were installed
189 already on my Mac OS X development system; however, they may have been
190 installed as dependencies of other programs I've installed. If you're
191 having problems installing ncurses, you can compile gdisk and/or sgdisk
192 without cgdisk by specifying only the targets you want to compile to
195 * The sgdisk program requires the popt library and its development files
196 (headers). Most Linux distributions install popt by default, but you may
197 need to install a package called popt-dev, popt-devel, or something
198 similar to obtain the header files. Mac OS users can find a version of
199 popt for Mac OS from Darwin Ports (http://popt.darwinports.com) or Fink
200 (http://www.finkproject.org); however, you'll first need to install
201 DarwinPorts or Fink (instructions exist on the relevant projects' pages).
202 Alternatively, you can compile gdisk and/or cgdisk alone, without sgdisk;
203 gdisk doesn't require popt.
205 When all the necessary development tools and libraries are installed, you
206 can uncompress the package and type "make" at the command prompt in the
207 resulting directory. (You may need to type "make -f Makefile.mac" on Mac OS
208 X, "make -f Makefile.freebsd" on FreeBSD, or "make -f Makefile.mingw" to
209 compile using MinGW for Windows.) You may also need to add header (include)
210 directories or library directories by setting the CXXFLAGS environment
211 variable or by editing the Makefile. The result should be program files
212 called gdisk, sgdisk, and fixparts. Typing "make gdisk", "make cgdisk",
213 "make sgdisk", or "make fixparts" will compile only the requested programs.
214 You can use these programs in place or copy the files to a suitable
215 directory, such as /usr/local/sbin. You can copy the man pages (gdisk.8,
216 cgdisk.8, sgdisk.8, and fixparts.8) to /usr/local/man/man8 to make them
222 THIS SOFTWARE IS BETA SOFTWARE! IF IT WIPES OUT YOUR HARD DISK OR EATS YOUR
223 CAT, DON'T BLAME ME! To date, I've tested the software on several USB flash
224 drives, physical hard disks, and virtual disks in the QEMU and VirtualBox
225 environments. Many others have now used the software on their computers, as
226 well. I believe all data-corruption bugs to be squashed, but I know full well
227 that the odds of my missing something are high. This is particularly true for
228 large (over-2TiB) drives; my only direct testing with such disks is with
229 virtual QEMU and VirtualBox disks. I've received user reports of success with
230 RAID arrays over 2TiB in size, though.
232 My main development platform is a system running the 64-bit version of
233 Gentoo Linux (previously Ubuntu 8.04). I've also tested on several other
234 32- and 64-bit Linux distributions, Intel-based Mac OS X 10.5 and 10.6,
235 64-bit FreeBSD 7.1, and Windows 7.
240 This program is licensed under terms of the GNU GPL (see the file COPYING).
245 This code is mostly my own; however, I've used three functions from two
246 other GPLed programs:
248 - The code used to generate CRCs is taken from the efone program by
249 Krzysztof Dabrowski and ElysiuM deeZine. (See the crc32.h and
250 crc32.cc source code files.)
252 - A function to find the disk size is taken from Linux fdisk by A. V. Le
253 Blanc. This code has subsequently been heavily modified.
255 Additional code contributors include:
257 - Yves Blusseau (1otnwmz02@sneakemail.com)
259 - David Hubbard (david.c.hubbard@gmail.com)
261 - Justin Maggard (justin.maggard@netgear.com)
263 - Dwight Schauer (dschauer@ti.com)
265 - Florian Zumbiehl (florz@florz.de)
267 - Guillaume Delacour (contributed the gdisk_test.sh script)