Provided by: libnbd-bin_1.14.2-1_amd64 
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 --is read-only|rotational NBD
nbdinfo --can 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
block_size_maximum: 33554432
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,
"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
Test for flags
Use one of the 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). You can use it in shell scripts
like this:
if nbdinfo --is read-only nbd://localhost ||
! nbdinfo --can 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 --can structured-reply URI
Test if server can respond with structured replies (a prerequisite for supporting
block status commands).
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 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.
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 cache
--can connect
--can df
--can fast-zero
--can flush
--can fua
--can multi-conn
--can read
--can structured-reply
--can trim
--can write
--can zero
Test properties of the NBD server export or the connection itself. 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_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), nbd_get_structured_replies_negotiated(3).
--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.
--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).
--json
The output is displayed in JSON format.
-L
--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.
-V
--version
Display the package name and version and exit.
SEE ALSO
libnbd(3), nbdcopy(1), nbddump(1), nbdfuse(1), nbdsh(1), file(1), jq(1), qemu-img(1),
qemu-nbd(8).
AUTHORS
Richard W.M. Jones
Eric Blake
COPYRIGHT
Copyright (C) 2020-2021 Red Hat Inc.
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