fixparts - MBR partition table repair utility
FixParts (aka fixparts) is a text-mode menu-driven program for repairing
certain types of problems with Master Boot Record (MBR) partition tables. The
program has three design goals, although a few additional features are
supported, as well:
- It can remove stray GUID Partition Table (GPT) data, which can be left
behind on a disk that was once used as a GPT disk but then incompletely
converted to the more common (as of 2011) MBR form.
- It can repair mis-sized extended partitions -- either partitions that
extend beyond the physical end of the disk or that overlap with nearby
primary partitions. FixParts is designed in such a way that this type of
repair occurs automatically, so if it's the only problem with your disk,
you can launch the program and then immediately save the partition table,
making no manual changes, and the program will fix the problem.
- You can change primary partitions into logical partitions or vice-versa,
within constraints imposed by the MBR data structures.
Additional features include the ability to change partition type
codes or boot/active flags, to delete partitions, and to recompute CHS
values. With the possible exception of recomputing CHS values, these
secondary features are better performed with fdisk, because
fixparts' design means that it's likely to alter partition numbering
even when such changes are not requested.
The fixparts program employs a user interface similar to
that of Linux's fdisk, but fixparts is much more specialized.
Most importantly, you can't create new partitions with fixparts,
although you can change primary/logical assignment.
In the MBR scheme, partitions come in three varieties:
- These partitions are defined in the first sector of the hard disk and are
limited in number to four. Some OSes, such as Windows and FreeBSD, must
boot from a primary partition.
- Extended partitions are specialized primary partitions. They serve as
holding areas for logical partitions.
- A disk can contain an arbitrary number of logical partitions
(fixparts, however, imposes a limit of 124 logical partitions). All
the logical partitions reside inside a single extended partition, and are
defined using a linked-list data structure. This fact means that every
logical partition must be preceded by at least one sector of unallocated
space to hold its defining data structure (an Extended Boot Record, or
These distinctions mean that primary and logical partitions cannot
be arbitrarily interspersed. A disk can contain one to three primary
partitions, a block of one or more logical partitions, and one to three more
primary partitions (for a total of three primary partitions, not counting
the extended partition). Primary partitions may not be sandwiched between
logical partitions, since this would mean placing a primary partition within
an extended partition (which is just a specific type of primary
Unlike most disk utilities, fixparts' user interface
ignores extended partitions. Internally, the program discards the
information on the original extended partition and, when you tell it to save
its changes, it generates a new extended partition to contain the
then-defined logical partitions. This is done because most of the repairs
and manipulations the tool performs require generating a fresh extended
partition, so keeping the original in the user interface would only be a
Another unusual feature of fixparts' user interface is that
partition numbers do not necessarily correlate with primary/logical status.
In most utilities, partitions 1-4 correspond to primary partitions, whereas
partitions 5 and up are logical partitions. In fixparts, any
partition number may be assigned primary or logical status, so long as the
rules for layout described earlier are obeyed. When the partition table is
saved, partitions will be assigned appropriately and then tools such as the
Linux kernel and fdisk will give them conventional numbers.
When it first starts, fixparts performs a scan for GPT
data. If the disk looks like a conventional GPT disk, fixparts
refuses to run. If the disk appears to be a conventional MBR disk but GPT
signatures are present in the GPT primary or secondary header areas,
fixparts offers to delete this extraneous data. If you tell it to do
so, the program immediately wipes the GPT header or headers. (If only one
header was found, only that one header will be erased, to minimize the risk
of damaging a boot loader or other data that might have overwritten just one
of the GPT headers.)
With the exception of optionally erasing leftover GPT data when it
first starts, fixparts keeps all changes in memory until the user
writes changes with the w command. Thus, you can adjust your
partitions in the user interface and abort those changes by typing q
to quit without saving changes.
The fixparts utility supports no command-line options, except for
specification of the target device.
Most interactions with fixparts occur with its interactive
text-mode menu. Specific functions are:
Known bugs and limitations include:
- Toggle the active/boot flag. This flag is required by some boot loaders
- Recompute the cylinder/head/sector (CHS) values for all partitions. CHS
addressing mode is largely obsolete, but some OSes and utilities complain
if they don't like the CHS values. Note that fixparts' CHS values
are likely to be incorrect on disks smaller than about 8 GiB except on
- Change a partition's status to logical. This option will only work if the
current partition layout supports such a change. Note that if changing a
partition's status in this way is not currently possible, making some
other change may make it possible. For instance, omitting a partition that
precedes the target partition may enable converting a partition to logical
form if there had been no free sectors between the two partitions.
- Omit a partition. Once omitted, the partition will still appear in the
fixparts partition list, but it will be flagged as omitted. You can
subsequently convert it to primary or logical form with the r or
l commands, respectively. When you save your changes with w,
though, the partition will be lost.
- Display basic partition summary data. This includes partition's number,
the boot/active flag's status, starting and ending sector numbers,
primary/logical/omitted status, whether or not the partition may be
converted to logical form, and the partition's MBR types code.
- Quit from the program without saving your changes. Use this option
if you just wanted to view information or if you make a mistake and want
to back out of all your changes.
- Change a partition's status to primary. This option will only work if the
current partition layout supports such a change. Note that every partition
can theoretically become a primary partition, although in some
configurations, making this change will require omitting some partitions.
If fixparts refuses to allow changing a partition to primary, you
may need to convert other partitions to logical form or omit them
- Sort partition entries. This option orders partitions in the display to
match their on-disk positions, which can make understanding the disk
layout easier in some cases. This option has no effect on the ultimate
ordering of logical partitions, which are sorted before being saved. The
order of primary partitions in the final saved partition table may be
affected by this option. In both cases, as already noted, the partition
numbers displayed by fixparts may not be the same as those used by
the kernel or displayed by other partitioning tools.
- Change a partition's type code. You enter the type code using a one-byte
- Write data. Use this command to save your changes and exit from the
- Print the menu. Type this command (or any other unrecognized command) to
see a summary of available options.
Primary author: Roderick W. Smith (firstname.lastname@example.org)
- The program compiles correctly only on Linux, FreeBSD, Mac OS X, and
Windows. 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. Under FreeBSD, 32-bit (x86) and 64-bit (x86-64) versions have
been tested. Only 32-bit versions for Mac OS X and Windows have been
- 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 program can load only up to 128 partitions (4 primary partitions and
124 logical partitions). This limit can be raised by changing the
#define MAX_MBR_PARTS line in the basicmbr.h source code
file and recompiling.
- The program can read partitions 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.
- The program makes no effort to preserve partition numbers. This can have
consequences for boot loaders and for mounting filesystems via
/etc/fstab. It may be necessary to edit configuration files or even
to re-install your boot loader.
The program may change the order of partitions in the
* Yves Blusseau (email@example.com)
* David Hubbard (firstname.lastname@example.org)
* Justin Maggard (email@example.com)
* Dwight Schauer (firstname.lastname@example.org)
* Florian Zumbiehl (email@example.com)
cfdisk (8), cgdisk (8), fdisk (8), mkfs (8),
parted (8), sfdisk (8) gdisk (8) sgdisk (8)
The fixparts command is part of the GPT fdisk package and is
available from Rod Smith.