1nbdinfo(1) LIBNBD nbdinfo(1)
2
6 nbdinfo - display information and metadata about NBD servers and
7 exports
8
10 nbdinfo [--json] NBD
11 "NBD" is an NBD URI or subprocess:
13 NBD := nbd://... | nbd+unix:// (or other URI formats)
15 | [ CMD ARGS ... ]
16 nbdinfo --size [--json] NBD
18 nbdinfo --is read-only|rotational NBD
20 nbdinfo --can cache|connect|... NBD
22 nbdinfo --map [--totals] [--json] NBD
24 nbdinfo -L|--list [--json] NBD
26 nbdinfo --help
28 nbdinfo --version
30
32 nbdinfo displays information and metadata about an NBD server.
33 The single required parameter can be the NBD URI of the server (see
35 https://github.com/NetworkBlockDevice/nbd/blob/master/doc/uri.md):
36 $ nbdinfo nbd://localhost
38 protocol: newstyle-fixed without TLS, using structured packets
39 export="":
40 export-size: 1048576 (1M)
41 content: data
42 uri: nbd://localhost:10809/
43 is_rotational: false
44 is_read_only: false
45 can_cache: true
46 can_df: true
47 can_fast_zero: true
48 can_flush: true
49 can_fua: true
50 can_multi_conn: true
51 can_trim: true
52 can_zero: true
53 block_size_minimum: 1
54 block_size_preferred: 4096
55 block_size_maximum: 33554432
56 For an NBD server on a local Unix domain socket you would use a command
58 such as this (with similar output to above):
59 $ nbdinfo "nbd+unix:///?socket=/tmp/unixsock"
61 Or you can run the NBD server as a subprocess (see section "Subprocess"
63 below):
64 $ nbdinfo -- [ qemu-nbd -r -f qcow2 file.qcow2 ]
66 JSON output
68 To display the output as JSON (eg. for scripting with jq(1)) add the
69 --json parameter:
70 $ nbdinfo --json nbd://localhost | jq .
72 {
73 "protocol": "newstyle-fixed",
74 "TLS": false,
75 "structured": true,
76 "exports": [
77 {
78 "export-name": "",
79 "content": "DOS/MBR boot sector; partition 1 : ID=0xc, start-CHS (0x3ff,254,63), end-CHS (0x3ff,254,63), startsector 2048, 4148704 sectors",
80 "uri": "nbd://localhost:10809/",
81 "is_rotational": false,
82 "is_read_only": true,
83 "can_cache": true,
84 "can_df": true,
85 "can_fast_zero": false,
86 "can_flush": false,
87 "can_fua": false,
88 "can_multi_conn": true,
89 "can_trim": false,
90 "can_zero": false,
91 "block_size_minimum": 1,
92 "block_size_preferred": 4096,
93 "block_size_maximum": 33554432,
94 "export-size": 2125119488,
95 "export-size-str": "2075312K"
96 }
97 ]
98 }
99 Size
101 To display only the size in bytes of the NBD export (useful for
102 scripting) use the --size parameter:
103 $ nbdinfo --size nbd://localhost
105 1048576
106 $ nbdinfo --size [ nbdkit null 1M ]
108 1048576
109 Test for flags
111 Use one of the options below to test NBD flags. The command does not
112 print anything. Instead it exits with success (exit code 0) if true,
113 or failure (exit code 2) if false. (Other exit codes indicate an error
114 querying the flag). You can use it in shell scripts like this:
115 if nbdinfo --is read-only nbd://localhost ||
117 ! nbdinfo --can trim nbd://localhost
118 then
119 error "the device must support writing and trimming"
120 fi
121 nbdinfo --is read-only URI
123 Test if the server export is read-only.
124 nbdinfo --can write URI
126 For convenience this is the opposite of --is read-only.
127 nbdinfo --can read URI
129 All NBD servers must support read, so this always exits with
130 success (unless there is a failure connecting to the URI).
131 nbdinfo --can connect URI
133 Test if we can connect to the NBD URI.
134 nbdinfo --is tls URI
136 Test if the NBD URI connection is using TLS.
137 nbdinfo --can structured-reply URI
139 Test if server can respond with structured replies (a prerequisite
140 for supporting block status commands).
141 nbdinfo --is rotational URI
143 Test if the server export is backed by something which behaves like
144 a rotating disk: accessing nearby blocks may be faster than random
145 access and requests should be sorted to improve performance. Many
146 servers do not or cannot report this accurately.
147 nbdinfo --can cache URI
149 nbdinfo --can df URI
150 nbdinfo --can fast-zero URI
151 nbdinfo --can flush URI
152 nbdinfo --can fua URI
153 nbdinfo --can multi-conn URI
154 nbdinfo --can trim URI
155 nbdinfo --can zero URI
156 Test other properties of the NBD server export.
157 Map
159 To show a map of which areas of the disk are allocated and sparse, use
160 the --map option:
161 $ nbdinfo --map nbd://localhost/
163 0 1048576 0 data
164 1048576 1048576 3 hole,zero
165 The fields are: start, size, type, description (optional).
167 The type field is an integer showing the raw value from the NBD
169 protocol. For some maps nbdinfo knows how to translate the type into a
170 printable description.
171 To get parseable JSON output, add --json:
173 $ nbdinfo --map --json nbd://localhost/
175 [{ "offset": 0, "length": 1048576,
176 "type": 0, "description": "data" },
177 { "offset": 1048576, "length": 1048576,
178 "type": 3, "description": "hole,zero" }]
179 By default this shows the "base:allocation" map, but you can show other
181 maps too:
182 $ nbdinfo --map=qemu:dirty-bitmap:bitmap nbd://localhost/
184 0 1048576 1 dirty
185 For more information on NBD maps, see Metadata querying in the NBD
187 protocol.
188 Map totals
190 Using --map --totals performs the same operation as --map but displays
191 a summary of the total size of each type of allocation, in bytes and as
192 a percentage (of the virtual size of the export). This is useful for
193 estimating how much real storage is used on the server, or might be
194 required when copying a sparse image with nbdcopy(1).
195 In the example below, half (50.0%) of the disk is allocated data and
197 half is unallocated:
198 $ nbdinfo --map --totals nbd://localhost/
200 1048576 50.0% 0 data
201 1048576 50.0% 3 hole,zero
202 The fields are: total size in bytes, percentage of the virtual size,
204 type, description (optional).
205 You can also get the same information in parseable form using --json:
207 $ nbdinfo --map --totals --json nbd://localhost/
209 [{ "size": 1048576, "percent": 50,
210 "type": 0, "description": "data" },
211 { "size": 1048576, "percent": 50,
212 "type": 3, "description": "hole,zero" }]
213 As with the --map option, by default this shows the "base:allocation"
215 map, but you can show the summary for other maps.
216 List all exports
218 To list all the exports available on an NBD server use the --list (-L)
219 option. To get parseable JSON output, add --json.
220 For example:
222 $ nbdkit file dir=. --run 'nbdinfo --list "$uri"'
224 protocol: newstyle-fixed without TLS
225 export="Fedora-Workstation-Live-x86_64-29-1.2.iso":
226 export-size: 1931476992 (1842M)
227 uri: nbd://localhost:10809/Fedora-Workstation-Live-x86_64-29-1.2.iso
228 [...]
229 export="debian-10.4.0-amd64-DVD-1.iso":
230 export-size: 3955556352 (3862848K)
231 uri: nbd://localhost:10809/debian-10.4.0-amd64-DVD-1.iso
232 [...]
233 Subprocess
235 nbdinfo can also run an NBD server as a subprocess. This requires an
236 NBD server which understands systemd socket activation, such as
237 qemu-nbd(8) or nbdkit(1). All the usual nbdinfo modes can be used.
238 For example, to give general information or display the map of a qcow2
240 file:
241 nbdinfo -- [ qemu-nbd -r -f qcow2 file.qcow2 ]
243 nbdinfo --map -- [ qemu-nbd -r -f qcow2 file.qcow2 ]
245 Note that "[ ... ]" are separate parameters, and must be surrounded by
247 spaces. "--" separates nbdinfo parameters from subprocess parameters.
248 Alternative tools
250 You could use "qemu-img info" (see qemu-img(1)) to query a single
251 export from an NBD server. "qemu-nbd -L" (see qemu-nbd(8)) can list
252 NBD exports. nbdsh(1) or the libnbd(3) API can be used for more
253 complex queries.
254
256 --help
257 Display brief command line help and exit.
258 --can cache
260 --can connect
261 --can df
262 --can fast-zero
263 --can flush
264 --can fua
265 --can multi-conn
266 --can read
267 --can structured-reply
268 --can trim
269 --can write
270 --can zero
271 Test properties of the NBD server export or the connection itself.
272 The command does not print anything. Instead it exits with success
273 (exit code 0) if true, or failure (exit code 2) if false. (Other
274 exit codes indicate an error querying the flag).
275 For further information see the NBD protocol and the following
277 libnbd functions: nbd_can_cache(3), nbd_can_df(3),
278 nbd_can_fast_zero(3), nbd_can_flush(3), nbd_can_fua(3),
279 nbd_can_multi_conn(3), nbd_can_trim(3), nbd_can_zero(3),
280 nbd_is_read_only(3), nbd_get_structured_replies_negotiated(3).
281 --color
283 --colour
284 --no-color
285 --no-colour
286 Enable or disable ANSI colours in output. By default we use
287 colours if the output seems to be a terminal, and disable them if
288 not.
289 --content
291 --no-content
292 Mostly the information displayed comes from the metadata sent by
293 the NBD server during the handshake. However nbdinfo also
294 downloads a small amount of data from the beginning of the export
295 to try to probe the content with file(1).
296 When not using --list, the default is --content, ie. probing the
298 content. To prevent content probing, use --no-content.
299 When using --list, the default is --no-content (since downloading
301 from each export is expensive). To enable content probing use
302 --list --content.
303 --is read-only
305 --is rotational
306 --is tls
307 Test if the NBD server export is read-only and rotational, or
308 whether the connection itself is using TLS. The command does not
309 print anything. Instead it exits with success (exit code 0) if
310 true, or failure (exit code 2) if false. (Other exit codes
311 indicate an error querying the flag).
312 For further information see the NBD protocol and the following
314 libnbd functions: nbd_is_read_only(3), nbd_is_rotational(3),
315 nbd_get_tls_negotiated(3).
316 --json
318 The output is displayed in JSON format.
319 -L
321 --list
322 List all the exports on an NBD server. The export name in the NBD
323 URI is ignored.
324 --map
326 --map=MAP
327 Display the map (usually whether parts of the disk are allocated or
328 sparse) of the given export. This displays the "base:allocation"
329 map by default, you can choose a different map with the optional
330 parameter.
331 See the "Map" section above.
333 --map --totals
335 --map=MAP --totals
336 The same as --map, but displays a summary of the total size of each
337 type of allocation.
338 See the "Map totals" section above.
340 --size
342 Display only the size in bytes of the export.
343 -V
345 --version
346 Display the package name and version and exit.
347
349 libnbd(3), nbdcopy(1), nbddump(1), nbdfuse(1), nbdsh(1), file(1),
350 jq(1), qemu-img(1), qemu-nbd(8).
351
353 Richard W.M. Jones
354 Eric Blake
356
358 Copyright (C) 2020-2021 Red Hat Inc.
359
361 This library is free software; you can redistribute it and/or modify it
362 under the terms of the GNU Lesser General Public License as published
363 by the Free Software Foundation; either version 2 of the License, or
364 (at your option) any later version.
365 This library is distributed in the hope that it will be useful, but
367 WITHOUT ANY WARRANTY; without even the implied warranty of
368 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
369 Lesser General Public License for more details.
370 You should have received a copy of the GNU Lesser General Public
372 License along with this library; if not, write to the Free Software
373 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
374 02110-1301 USA
375libnbd-1.14.2 2023-01-03 nbdinfo(1)