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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, OS X, and Solaris, libuuid must be installed. This is | |
the standard for Linux and OS X, 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 not 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 OS X, but you may need to | |
install the development headers (libicu-dev or something similar in | |
Linux; or the libicu36-dev Fink package in OS X). 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. These files were installed | |
already on my Mac OS X development system; however, they may have been | |
installed as dependencies of other programs I've installed. 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. Mac OS 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), or | |
Fink (http://www.finkproject.org); however, you'll first need to install | |
DarwinPorts, MacPorts, or Fink (instructions exist on the relevant | |
projects' pages). Alternatively, you can compile gdisk and/or cgdisk | |
alone, without sgdisk; gdisk doesn'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 may need to type "make -f Makefile.mac" on Mac OS | |
X, "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 | |
------- | |
THIS SOFTWARE IS BETA SOFTWARE! IF IT WIPES OUT YOUR HARD DISK OR EATS YOUR | |
CAT, DON'T BLAME ME! To date, I've tested the software on several USB flash | |
drives, physical hard disks, and virtual disks in the QEMU and VirtualBox | |
environments. Many others have now used the software on their computers, as | |
well. 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; my only direct testing with such disks is with | |
virtual QEMU and VirtualBox disks. I've received user reports of success with | |
RAID arrays over 2TiB in size, though. | |
My main development platform is a system running the 64-bit version of | |
Gentoo Linux. I've also tested on several other 32- and 64-bit Linux | |
distributions, Intel-based Mac OS X 10.5 and 10.6, 64-bit FreeBSD 7.1, and | |
Windows 7. | |
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) |