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GPT fdisk (aka gdisk, cgdisk, and sgdisk) and FixParts by Roderick W. Smith, rodsmith@rodsbooks.com Introduction ------------ This package includes the source code for four related disk partitioning programs: - gdisk -- This program is modeled after Linux fdisk, but it operates on GUID Partition Table (GPT) disks rather than the Master Boot Record (MBR) disks that fdisk modifies. As such, gdisk is an interactive text-mode tool for manipulating partitions, but it does nothing to the contents of those partitions (usually filesystems, but sometimes swap space or other data). - cgdisk -- This program is modeled after Linux cfdisk, but it operates on GPT disks rather than the MBR disks that cfdisk modifies. As such, cgdisk is a curses-based text-mode tool for manipulating partitions, which is to say that it uses an interface that relies on arrow keys and a dynamic display rather than the command letters and a scrolling display like gdisk uses. - sgdisk -- This program is conceptually similar to the Linux sfdisk and FreeBSD gpt programs, but its operational details differ. It enables manipulation of GPT disks using command-line options, so it's suitable for use in scripts or by experts to perform specific tasks that might take several commands in gdisk to accomplish. - fixparts -- This program, unlike the preceding three, operates on MBR disks. It's intended to fix certain problems that can be created by various utilities. Specifically, it can fix mis-sized extended partitions and primary partitions located in the middle of extended partitions. It also enables changing primary vs. logical partition status (within limits of what's legal in the MBR scheme) and making a few other minor changes. It does NOT support creating new partitions; for that, you should use fdisk, parted, or some other tool. More details about the abilities of these tools follows. All four programs rely on the same set of underlying code base; they differ only in their control interfaces (defined in gdisk.cc, cgdisk.cc, sgdisk.cc, and fixparts.cc, respectively) and in which support code they use. GPT fdisk (gdisk, cgdisk, and sgdisk) Details --------------------------------------------- The gdisk program is intended as a (somewhat) fdisk-workalike program for GPT-partitioned disks, cgdisk is similarly a workalike for fdisk, and sgdisk provides most of gdisk's functionality in a more script-friendly program. Although libparted and programs that use it (GNU Parted, gparted, etc.) provide the ability to handle GPT disks, they have certain limitations that gdisk overcomes. Specific advantages of gdisk, cgdisk, and sgdisk include: * The ability to convert MBR-partitioned disks in-place to GPT format, without losing data * The ability to convert BSD disklabels in-place to create GPT partitions, without losing data * The ability to convert from GPT format to MBR format without data loss (gdisk and sgdisk only) * More flexible specification of filesystem type code GUIDs, which GNU Parted tends to corrupt * Clear identification of the number of unallocated sectors on a disk * A user interface that's familiar to long-time users of Linux fdisk and cfdisk (gdisk and cgdisk only) * The MBR boot loader code is left alone * The ability to create a hybrid MBR, which permits GPT-unaware OSes to access up to three GPT partitions on the disk (gdisk and sgdisk only) Of course, GPT fdisk isn't without its limitations. Most notably, it lacks the filesystem awareness and filesystem-related features of GParted. You can't resize a partition's filesystem or create a partition with a filesystem already in place with gdisk, for instance. There's no GUI version of gdisk. The GPT fdisk package provides three program files: the interactive text-mode gdisk, the curses-based interactive cgdisk, and the command-line-driven sgdisk. The first two are intended for use in manually partitioning disks or changing partitioning details; sgdisk is intended for use in scripts to help automate tasks such as disk cloning or preparing multiple disks for Linux installation. FixParts Details ---------------- This program's creation was motivated by cries for help I've seen in online forums from users who have found their partition tables to be corrupted by various buggy partitioning tools. Although most OSes can handle the afflicted disks fine, libparted-based tools (GParted, parted, most Linux installers, etc.) tend to flake out when presented with these disks. Typically, the symptom is a disk that appears to hold no partitions; however, sometimes the libparted tool presents partitions other than those that the OS sees. I've observed four causes of these symptoms, three of which FixParts can correct: * Old GPT data -- If a disk is used as a GPT disk and then re-used as an MBR disk, the GPT data may be incompletely erased. This happens if the disk is repartitioned with fdisk or the Microsoft Windows installer, for instance. (Tools based on libparted correctly remove the old GPT data when converting from GPT to MBR format.) FixParts checks for this problem when it starts and offers to correct it. If you opt to erase the GPT data, this erasure occurs immediately, unlike other changes the program makes. * Mis-sized extended partitions -- Some tools create an extended partition that's too large, typically ending after the last sector of the disk. FixParts automatically corrects this problem (if you use the 'w' option to save the partition table). * Primary partitions inside an extended partition -- Some utilities create or move primary partitions to within the range covered by the extended partition. FixParts can usually correct this problem by turning the primary partition into a logical partition or by changing one or more other logical partitions into primaries. Such corrections aren't always possible, though, at least not without deleting or resizing other partitions. * Leftover RAID data -- If a disk is used in a RAID array and then re-used as a non-RAID disk, some utilities can become confused and fail to see the disk. FixParts can NOT correct this problem. You must destroy the old RAID data, or possibly remove the dmraid package from the system, to fix this problem. When run, FixParts presents an fdisk-like interface, enabling you to adjust partition types (primary, logical, or omitted), change type codes, change the bootable flag, and so on. Although you can delete a partition (by omitting it), you can't create new partitions with the program. If you're used to partitioning disks, particularly with Linux fdisk, two unusual features of FixParts require elaboration: * No extended partitions -- Internally, FixParts reads the partition table and discards data on any extended partition(s) it finds. When you save the partition table, the program generates a new extended partition. This design means that the program automatically corrects many problems related to the extended partition. It also means that you'll see no evidence of extended partitions in the FixParts user interface, although it keeps track of the requirements and prevents you from creating illegal layouts, such as a primary between two logicals. * Partition numbering -- In most Linux tools, partitions 1-4 are primaries and partitions 5 and up are logicals. Although a legal partition table loaded into FixParts will initially conform to this convention, some types of damaged table might not, and various changes you make can also cause deviations. When FixParts writes the partition table, its numbering will be altered to conform to the standard MBR conventions, but you should use the explicit labeling of partitions as primary or logical rather than the partition numbers to determine a partition's status. Installing ---------- To compile GPT fdisk, you must have appropriate development tools installed, most notably the GNU Compiler Collection (GCC) and its g++ compiler for C++. I've also tested compilation with Clang, which seems to work; however, I've not done extensive testing of the resulting binaries, beyond checking a few basics. Under Windows, Microsoft Visual C++ 2008 can be used instead. In addition, note these requirements: * On Linux, FreeBSD, macOS, and Solaris, libuuid must be installed. This is the standard for Linux and macOS, although you may need to install a package called uuid-dev or something similar to get the headers. On FreeBSD, the e2fsprogs-libuuid port must be installed. * The ICU library (http://site.icu-project.org), which provides support for Unicode partition names, is optional on all platforms except Windows, on which it's not supported. Using this library was required to get proper UTF-16 partition name support in GPT fdisk versions prior to 0.8.9, but as of that version it should no longer be required. Nonetheless, you can use it if you're having problems with the new UTF-16 support. This library is normally installed in Linux and macOS, but you may need to install the development headers (libicu-dev or something similar in Linux; or the libicu36-dev Fink package in macOS). To compile with ICU support, you must modify the Makefile: Look for commented-out lines that refer to USE_UTF16, -licuuc, -licudata, or -licucore. Uncomment them and comment out the equivalents that lack these lines. * The cgdisk program requires the ncurses library and its development files (headers). Most Linux distributions install ncurses by default, but you may need to install a package called libncurses5-dev, ncurses-devel, or something similar to obtain the header files. On my macOS development system, I installed the nurses Homebrew ("brew") package; however, other Unix-style software repositories are available and may work for you (see the next item). If you're having problems installing ncurses, you can compile gdisk and/or sgdisk without cgdisk by specifying only the targets you want to compile to make. * The sgdisk program requires the popt library and its development files (headers). Most Linux distributions install popt by default, but you may need to install a package called popt-dev, popt-devel, or something similar to obtain the header files. MacOS users can find a version of popt for Mac OS from Darwin Ports (http://popt.darwinports.com), MacPorts (https://trac.macports.org/browser/trunk/dports/devel/popt/Portfile), Fink (http://www.finkproject.org), or brew (http://macappstore.org/popt/); however, you'll first need to install the relevant environment (instructions exist on the relevant projects' pages). When I re-built my Mac build environment in February of 2020, I found that brew was, by far, the easiest of these to install. Some of the others seem to have been abandoned, but I didn't investigate thoroughly. I'm leaving the references in case they might be useful in the future. Instead of installing one of These ports, you can compile gdisk and/or cgdisk alone, without sgdisk; gdisk and cgdisk don't require popt. When all the necessary development tools and libraries are installed, you can uncompress the package and type "make" at the command prompt in the resulting directory. (You must type "make -f Makefile.mac" on macOS, "make -f Makefile.freebsd" on FreeBSD, "make -f Makefile.solaris" on Solaris, or "make -f Makefile.mingw" to compile using MinGW for Windows.) You may also need to add header (include) directories or library directories by setting the CXXFLAGS environment variable or by editing the Makefile. The result should be program files called gdisk, cgdisk, sgdisk, and fixparts. Typing "make gdisk", "make cgdisk", "make sgdisk", or "make fixparts" will compile only the requested programs. You can use these programs in place or copy the files to a suitable directory, such as /usr/local/sbin. You can copy the man pages (gdisk.8, cgdisk.8, sgdisk.8, and fixparts.8) to /usr/local/man/man8 to make them available. Caveats ------- DISK PARTITIONING SOFTWARE IS DANGEROUS! Although the GPT fdisk project has existed since 2009, I do not claim it is entirely bug-free; in fact a glance at the revision history shows recent bug fixes. I believe all data-corruption bugs to be squashed, but I know full well that the odds of my missing something are high. This is particularly true for large (over-2TiB) drives and use in exotic environments. My main development platform is a system running the 64-bit version of Ubuntu Linux. I've also tested on several other 32- and 64-bit Linux distributions, Intel-based macOS 10 and 11, 64-bit FreeBSD 7.1, and Windows 7 and 10. Other environments qualify as "exotic," and even macOS and Windows are borderline exotic in this context, since I use Linux almost exclusively, and my impression is that GPT fdisk is far more commonly used on Linux than in other OSes. Redistribution -------------- This program is licensed under terms of the GNU GPL (see the file COPYING). Acknowledgements ---------------- This code is mostly my own; however, I've used three functions from two other GPLed programs: - The code used to generate CRCs is taken from the efone program by Krzysztof Dabrowski and ElysiuM deeZine. (See the crc32.h and crc32.cc source code files.) - A function to find the disk size is taken from Linux fdisk by A. V. Le Blanc. This code has subsequently been heavily modified. Additional code contributors include: - 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) - Guillaume Delacour (contributed the gdisk_test.sh script)