GPT(8)

System Manager's Manual

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 manipulate GUID partition tables (GPTs), but see BUGS below for how and where functionality is missing. The basic usage model of the gpt tool follows 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 settings or otherwise change the behaviour that is applicable to all commands. 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 accommodate. This is used whenever a new GPT is created. By default, the gpt utility will create space for 128 partitions (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 command, but the intent is to use it to implement dry-run behaviour.

The -v option controls the verbosity level. The level increases 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 partition 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 partition. 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, hfs, linux, raid, lfs, ccd, cgd, bios, ffs, and windows as aliases for the most commonly used partition types.

gpt biosboot [-c bootcode] [-i index] device ...

The biosboot command allows the user to configure the partition that contains the primary bootstrap program, used during boot(8).

The -c option allows the user to specify the filename that gpt should read the bootcode from. The default is to read from /usr/mdec/gptmbr.bin.

The -i option selects the partition that should contain the primary bootstrap code, as installed via installboot(8).

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 option. 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 partitions 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 removed.

The -t type option selects all partitions that have the given type. The type is given as an UUID or by the aliases that the add command accepts. This can cause multiple partitions to be removed.

The -f file or -l label options specify the new label 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 character 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 default, the MBR is not migrated when it contains partitions of an unknown type. This can be overridden with the -f option. Specifying 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 into GPT partitions by creating the GPT equivalent of a slice.

gpt recover device ...

The recover command tries to restore the GPT partition label from the backup near the end of the disk. It is very useful in case the primary label was deleted.

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 description 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 contents. 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 a user friendly form. The -l option takes precedence over the -u option.

EXAMPLES

nas# gpt show wd3 
       start        size  index  contents 
           0           1         PMBR 
           1  3907029167 
nas# gpt create wd3 
nas# gpt show wd3 
       start        size  index  contents 
           0           1         PMBR 
           1           1         Pri GPT header 
           2          32         Pri GPT table 
          34  3907029101 
  3907029135          32         Sec GPT table 
  3907029167           1         Sec GPT header 
nas# gpt add -s 10486224 -t swap -i 1 wd3 
Partition added, use: 
        dkctl rwd3d addwedge dk<N> 34 10486224 <type> 
to create a wedge for it 
nas# gpt label -i 1 -l swap_1 wd3 
parition 1 on rwd3d labeled swap_1 
nas# gpt show wd3 
       start        size  index  contents 
           0           1         PMBR 
           1           1         Pri GPT header 
           2          32         Pri GPT table 
          34    10486224      1  GPT part - NetBSD swap 
    10486258  3896542877 
  3907029135          32         Sec GPT table 
  3907029167           1         Sec GPT header 
nas#

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 features, is farther removed from being complete or useful. As such, missing functionality is not even documented as missing. However, it is believed 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 intended for diagnostic or debug purposes may be removed in future versions.

Another possibility is that the current usage model is accompanied by other interfaces to make the tool usable as a back-end. This all depends on demand and thus feedback.

March 9, 2012

NetBSD 6.1