gpt(8)

NAME

gpt - GUID partition table maintenance utility

SYNOPSIS

gpt [general_options] command [command_options] device ...

DESCRIPTION

The gpt utility provides the necessary functionality to ma

nipulate GUID
partition tables (GPTs), but see BUGS below for how and

where functionality is missing. The basic usage model of the gpt tool fol

lows that of
the cvs(1) tool. The general options are described in the

following
paragraph. The remaining paragraphs describe the individual

commands
with their options. Here we conclude by mentioning that a

device is
either a special file corresponding to a disk-like device or

a regular
file. The command is applied to each device listed on the

command line.

General Options

The general options allow the user to change default set

tings or otherwise change the behaviour that is applicable to all com

mands. Not all
commands use all default settings, so some general options

may not have
an effect on all commands.

The -p count option allows the user to change the number of

partitions
the GPT can accomodate. This is used whenever a new GPT is

created. By
default, the gpt utility will create space for 128 parti

tions (or 32 sectors of 512 bytes).

The -r option causes the gpt utility to open the device for

reading only.
Currently this option is primarily useful for the show com

mand, but the
intent is to use it to implement dry-run behaviour.

The -v option controls the verbosity level. The level in

creases with
every occurrence of this option. There is no formalized

definition of
the different levels yet.

Commands

gpt add [-b number] [-i index] [-s count] [-t type] device

...

The add command allows the user to add a new parti

tion to an
existing table. By default, it will create a UFS

partition covering the first available block of an unused disk

space. The
command-specific options can be used to control this

behaviour.

The -b number option allows the user to specify the

starting
(beginning) sector number of the partition. The

minimum sector
number is 1, but has to fall inside an unused region

of disk
space that is covered by the GPT.

The -i index option allows the user to specify which

(free) entry
in the GPT table is to be used for the new parti

tion. By
default, the first free entry is selected.

The -s count option allows the user to specify the

size of the
partition in sectors. The minimum size is 1.

The -t type option allows the user to specify the

partition type.
The type is given as an UUID, but gpt accepts efi,

swap, ufs,
linux and windows as aliases for the most commonly

used partition
types.

gpt create [-fp] device ...

The create command allows the user to create a new

(empty) GPT.
By default, one cannot create a GPT when the device

contains a
MBR, however this can be overridden with the -f op

tion. If the
-f option is specified, an existing MBR is destroyed

and any partitions described by the MBR are lost.

The -p option tells gpt to create only the primary

table and not
the backup table. This option is only useful for

debugging and
should not be used otherwise.

gpt destroy [-r] device ...

The destroy command allows the user to destroy an

existing, possibly not empty GPT.

The -r option instructs gpt to destroy the table in

a way that it
can be recovered.

gpt label [-a] <-f file | -l label> device ...

gpt label [-b number] [-i index] [-s count] [-t type] <-f

file | -l

label> device ...
The label command allows the user to label any par

titions that
match the selection. At least one of the following

selection
options must be specified.

The -a option specifies that all partitions should

be labeled.
It is mutually exclusive with all other selection

options.

The -b number option selects the partition that

starts at the
given block number.

The -i index option selects the partition with the

given partition number.

The -s count option selects all partitions that have

the given
size. This can cause multiple partitions to be re

moved.

The -t type option selects all partitions that have

the given
type. The type is given as an UUID or by the alias

es that the
add command accepts. This can cause multiple parti

tions to be
removed.

The -f file or -l label options specify the new la

bel to be
assigned to the selected partitions. The -f file

option is used
to read the label from the specified file. Only the

first line
is read from the file and the trailing newline char

acter is
stripped. If the file name is the dash or minus

sign (-), the
label is read from the standard input. The -l label

option is
used to specify the label in the command line. The

label is
assumed to be encoded in UTF-8.

gpt migrate [-fs] device ...

The migrate command allows the user to migrate an

MBR-based disk
partitioning into a GPT-based partitioning. By de

fault, the MBR
is not migrated when it contains partitions of an

unknown type.
This can be overridden with the -f option. Specify

ing the -f
option will cause unknown partitions to be ignored

and any data
in it to be lost.

The -s option prevents migrating BSD disk labels in

to GPT partitions by creating the GPT equivalent of a slice.

gpt remove [-a] device ...

gpt remove [-b number] [-i index] [-s count] [-t type]

device ...

The remove command allows the user to remove any and

all partitions that match the selection. It uses the same

selection
options as the label command. See above for a de

scription of
these options. Partitions are removed by clearing

the partition
type. No other information is changed.

gpt show [-lu] device ...

The show command displays the current partitioning

on the listed
devices and gives an overall view of the disk con

tents. With the
-l option the GPT partition label will be displayed

instead of
the GPT partition type. The option has no effect on

non-GPT partitions. With the -u option the GPT partition type

is displayed
as an UUID instead of in an user friendly form. The

-l option
takes precedence over the -u option.

SEE ALSO

fdisk(8), mount(8), newfs(8), swapon(8)

HISTORY

The gpt utility appeared in FreeBSD 5.0 for ia64.

BUGS

The development of the gpt utility is still work in

progress. Many necessary features are missing or partially implemented. In

practice this
means that the manual page, supposed to describe these fea

tures, is farther removed from being complete or useful. As such, miss

ing functionality is not even documented as missing. However, it is be

lieved that the
currently present functionality is reliable and stable

enough that this
tool can be used without bullet-proof footware if one thinks

one does not
make mistakes.

It is expected that the basic usage model does not change,

but it is possible that future versions will not be compatible in the

strictest sense
of the word. For example, the -p count option may be

changed to a command option rather than a generic option. There are only

two commands
that use it so there is a chance that the natural tendency

for people is
to use it as a command option. Also, options primarily in

tended for
diagnostic or debug purposes may be removed in future ver

sions.

Another possibility is that the current usage model is ac

companied by
other interfaces to make the tool usable as a back-end.

This all depends
on demand and thus feedback.

BSD August 31, 2005

BSD