fixparts man page

fixparts — MBR partition table repair utility

Synopsis

fixparts device

Description

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:

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:

primary

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

Extended partitions are specialized primary partitions. They serve as holding areas for logical partitions.

logical

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 EBR).

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 partition).

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 complication.

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.

Options

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:

a

Toggle the active/boot flag. This flag is required by some boot loaders and OSes.

c

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 Linux.

l

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.

o

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.

p

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.

q

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.

r

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 entirely.

s

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.

t

Change a partition's type code. You enter the type code using a one-byte hexadecimal number.

w

Write data. Use this command to save your changes and exit from the program.

?

Print the menu. Type this command (or any other unrecognized command) to see a summary of available options.

Bugs

Known bugs and limitations include:

Authors

Primary author: Roderick W. Smith (rodsmith@rodsbooks.com)

Contributors:

* Yves Blusseau (1otnwmz02@sneakemail.com)

* David Hubbard (david.c.hubbard@gmail.com)

* Justin Maggard (justin.maggard@netgear.com)

* Dwight Schauer (dschauer@gmail.com)

* Florian Zumbiehl (florz@florz.de)

See Also

cfdisk (8), cgdisk (8), fdisk (8), mkfs (8), parted (8), sfdisk (8) gdisk (8) sgdisk (8)

http://en.wikipedia.org/wiki/Master_boot_record

http://www.rodsbooks.com/fixparts/

Availability

The fixparts command is part of the GPT fdisk package and is available from Rod Smith.

Referenced By

cgdisk(8), gdisk(8), sgdisk(8).

1.0.1 Roderick W. Smith FixParts Manual