Manpages

NAME

nbdinfo - display information and metadata about NBD servers and exports

SYNOPSIS

nbdinfo [--json] NBD

"NBD" is an NBD URI or subprocess:

NBD := nbd://... | nbd+unix:// (or other URI formats)
| [ CMD ARGS ... ]

nbdinfo --size [--json] NBD

nbdinfo --uri [--json] NBD

nbdinfo --is read-only|rotational NBD
nbdinfo --isnt read-only|rotational NBD

nbdinfo --can cache|connect|... NBD
nbdinfo --cannot cache|connect|... NBD

nbdinfo --map [--totals] [--json] NBD

nbdinfo -L|--list [--json] NBD

nbdinfo --help

nbdinfo --version

DESCRIPTION

nbdinfo displays information and metadata about an NBD server.

The single required parameter can be the NBD URI of the server (see https://github.com/NetworkBlockDevice/nbd/blob/master/doc/uri.md):

$ nbdinfo nbd://localhost
protocol: newstyle-fixed without TLS, using structured packets
export="":
export-size: 1048576 (1M)
content: data
uri: nbd://localhost:10809/
is_rotational: false
is_read_only: false
can_cache: true
can_df: true
can_fast_zero: true
can_flush: true
can_fua: true
can_multi_conn: true
can_trim: true
can_zero: true
block_size_minimum: 1
block_size_preferred: 4096 (4K)
block_size_maximum: 33554432 (32M)

For an NBD server on a local Unix domain socket you would use a command such as this (with similar output to above):

$ nbdinfo "nbd+unix:///?socket=/tmp/unixsock";

Or you can run the NBD server as a subprocess (see section "Subprocess" below):

$ nbdinfo -- [ qemu-nbd -r -f qcow2 file.qcow2 ]

JSON output
To display the output as JSON (eg. for scripting with jq(1)) add the --json parameter:

$ nbdinfo --json nbd://localhost | jq .
{
"protocol": "newstyle-fixed",
"TLS": false,
"structured": true,
"extended": false,
"exports": [
{
"export-name": "",
"content": "DOS/MBR boot sector; partition 1 : ID=0xc, start-CHS (0x3ff,254,63), end-CHS (0x3ff,254,63), startsector 2048, 4148704 sectors",
"uri": "nbd://localhost:10809/",
"is_rotational": false,
"is_read_only": true,
"can_cache": true,
"can_df": true,
"can_fast_zero": false,
"can_flush": false,
"can_fua": false,
"can_multi_conn": true,
"can_trim": false,
"can_zero": false,
"block_size_minimum": 1,
"block_size_preferred": 4096,
"block_size_maximum": 33554432,
"export-size": 2125119488,
"export-size-str": "2075312K"
}
]
}

Size
To display only the size in bytes of the NBD export (useful for scripting) use the --size parameter:

$ nbdinfo --size nbd://localhost
1048576

$ nbdinfo --size [ nbdkit null 1M ]
1048576

URI
To display the canonical URI:

$ nbdinfo --uri nbd://localhost
nbd://localhost:10809/

Test for flags
Use one of the --can, --is or --has options below to test NBD flags. The command does not print anything. Instead it exits with success (exit code 0) if true, or failure (exit code 2) if false. (Other exit codes indicate an error querying the flag).

--cannot, --isnt and --hasnt negate the test.

You can use it in shell scripts like this:

if nbdinfo --is read-only nbd://localhost ||
nbdinfo --cannot trim nbd://localhost
then
error "the device must support writing and trimming"
fi
nbdinfo --is read-only URI

Test if the server export is read-only.

nbdinfo --can write URI

For convenience this is the opposite of --is read-only.

nbdinfo --can read URI

All NBD servers must support read, so this always exits with success (unless there is a failure connecting to the URI).

nbdinfo --can connect URI

Test if we can connect to the NBD URI.

nbdinfo --is tls URI

Test if the NBD URI connection is using TLS.

nbdinfo --has structured-reply URI

Test if server has support for structured replies (a prerequisite for supporting block status commands).

nbdinfo --has extended-headers URI

Test if server supports extended headers (a prerequisite for supporting 64-bit commands; implies structured replies as well).

nbdinfo --is rotational URI

Test if the server export is backed by something which behaves like a rotating disk: accessing nearby blocks may be faster than random access and requests should be sorted to improve performance. Many servers do not or cannot report this accurately.

nbdinfo --can block-status-payload URI

Test if the server export has support for passing a client payload to limit the response to a block status command.

nbdinfo --can cache URI
nbdinfo --can df URI
nbdinfo --can fast-zero URI
nbdinfo --can flush URI
nbdinfo --can fua URI
nbdinfo --can multi-conn URI
nbdinfo --can trim URI
nbdinfo --can zero URI

Test other properties of the NBD server export.

In fact --can/--is/--has, and --cannot/--isnt/--hasnt are synonyms, you can use them interchangeably.

Map
To show a map of which areas of the disk are allocated and sparse, use the --map option:

$ nbdinfo --map nbd://localhost/
0 1048576 0 data
1048576 1048576 3 hole,zero

The fields are: start, size, type, description (optional).

The type field is an integer showing the raw value from the NBD protocol. For some maps nbdinfo knows how to translate the type into a printable description.

To get parseable JSON output, add --json:

$ nbdinfo --map --json nbd://localhost/
[{ "offset": 0, "length": 1048576,
"type": 0, "description": "data" },
{ "offset": 1048576, "length": 1048576,
"type": 3, "description": "hole,zero" }]

By default this shows the "base:allocation" map, but you can show other maps too:

$ nbdinfo --map=qemu:dirty-bitmap:bitmap nbd://localhost/
0 1048576 1 dirty

For more information on NBD maps, see Metadata querying in the NBD protocol.

Map totals
Using --map --totals performs the same operation as --map but displays a summary of the total size of each type of allocation, in bytes and as a percentage (of the virtual size of the export). This is useful for estimating how much real storage is used on the server, or might be required when copying a sparse image with nbdcopy(1).

In the example below, half (50.0%) of the disk is allocated data and half is unallocated:

$ nbdinfo --map --totals nbd://localhost/
1048576 50.0% 0 data
1048576 50.0% 3 hole,zero

The fields are: total size in bytes, percentage of the virtual size, type, description (optional).

You can also get the same information in parseable form using --json:

$ nbdinfo --map --totals --json nbd://localhost/
[{ "size": 1048576, "percent": 50,
"type": 0, "description": "data" },
{ "size": 1048576, "percent": 50,
"type": 3, "description": "hole,zero" }]

As with the --map option, by default this shows the "base:allocation" map, but you can show the summary for other maps.

List all exports
To list all the exports available on an NBD server use the --list (-L) option. To get parseable JSON output, add --json.

For example:

$ nbdkit file dir=. --run 'nbdinfo --list "$uri"'
protocol: newstyle-fixed without TLS
export="Fedora-Workstation-Live-x86_64-29-1.2.iso":
export-size: 1931476992 (1842M)
uri: nbd://localhost:10809/Fedora-Workstation-Live-x86_64-29-1.2.iso
[...]
export="debian-10.4.0-amd64-DVD-1.iso":
export-size: 3955556352 (3862848K)
uri: nbd://localhost:10809/debian-10.4.0-amd64-DVD-1.iso
[...]

Subprocess
nbdinfo can also run an NBD server as a subprocess. This requires an NBD server which understands systemd socket activation, such as qemu-nbd(8) or nbdkit(1). All the usual nbdinfo modes can be used.

For example, to give general information or display the map of a qcow2 file:

nbdinfo -- [ qemu-nbd -r -f qcow2 file.qcow2 ]

nbdinfo --map -- [ qemu-nbd -r -f qcow2 file.qcow2 ]

Note that "[ ... ]" are separate parameters, and must be surrounded by spaces. "--" separates nbdinfo parameters from subprocess parameters.

Alternative tools
You could use "qemu-img info" (see qemu-img(1)) to query a single export from an NBD server. "qemu-nbd -L" (see qemu-nbd(8)) can list NBD exports. nbdsh(1) or the libnbd(3) API can be used for more complex queries.

OPTIONS

--help

Display brief command line help and exit.

--can block-status-payload
--can cache
--can connect
--can df
--can fast-zero
--can flush
--can fua
--can multi-conn
--can read
--can trim
--can write
--can zero

Test properties of the NBD server export. The command does not print anything. Instead it exits with success (exit code 0) if true, or failure (exit code 2) if false. (Other exit codes indicate an error querying the flag).

For further information see the NBD protocol and the following libnbd functions: nbd_can_block_status_payload(3), nbd_can_cache(3), nbd_can_df(3), nbd_can_fast_zero(3), nbd_can_flush(3), nbd_can_fua(3), nbd_can_multi_conn(3), nbd_can_trim(3), nbd_can_zero(3), nbd_is_read_only(3).

--cannot flag

Test the negation of flag.

--color
--colour
--no-color
--no-colour

Enable or disable ANSI colours in output. By default we use colours if the output seems to be a terminal, and disable them if not.

--content
--no-content

Mostly the information displayed comes from the metadata sent by the NBD server during the handshake. However nbdinfo also downloads a small amount of data from the beginning of the export to try to probe the content with file(1).

When not using --list, the default is --content, ie. probing the content. To prevent content probing, use --no-content.

When using --list, the default is --no-content (since downloading from each export is expensive). To enable content probing use --list --content.

--has extended-headers
--has structured-reply

Test properties of the NBD server connection. The command does not print anything. Instead it exits with success (exit code 0) if true, or failure (exit code 2) if false. (Other exit codes indicate an error querying the flag).

For further information see the NBD protocol and the following libnbd functions: nbd_get_extended_headers_negotiated(3), nbd_get_structured_replies_negotiated(3).

--hasnt flag

Test the negation of flag.

--is read-only
--is rotational
--is tls

Test if the NBD server export is read-only and rotational, or whether the connection itself is using TLS. The command does not print anything. Instead it exits with success (exit code 0) if true, or failure (exit code 2) if false. (Other exit codes indicate an error querying the flag).

For further information see the NBD protocol and the following libnbd functions: nbd_is_read_only(3), nbd_is_rotational(3), nbd_get_tls_negotiated(3).

--isnt flag

Test the negation of flag.

--json

The output is displayed in JSON format.

--list

List all the exports on an NBD server. The export name in the NBD URI is ignored.

--map
--map=MAP

Display the map (usually whether parts of the disk are allocated or sparse) of the given export. This displays the "base:allocation" map by default, you can choose a different map with the optional parameter.

See the "Map" section above.

--map --totals
--map=MAP --totals

The same as --map, but displays a summary of the total size of each type of allocation.

See the "Map totals" section above.

--size

Display only the size in bytes of the export.

--uri

Display only the canonical URI. If combined with --json then the output is a JSON-quoted string.

--version

Display the package name and version and exit.

SEE ALSO

libnbd(3), nbdcopy(1), nbddump(1), nbdfuse(1), nbdsh(1), nbdublk(1), file(1), jq(1), qemu-img(1), qemu-nbd(8).

AUTHORS

Richard W.M. Jones

Eric Blake

COPYRIGHT

Copyright Red Hat

LICENSE

This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA