| nbdinfo(1) | LIBNBD | nbdinfo(1) |
nbdinfo - display information and metadata about NBD servers and exports
nbdinfo [--json] [--map] [--size] NBD-URI nbdinfo -L|--list NBD-URI nbdinfo --help nbdinfo --version
nbdinfo displays information and metadata about an NBD server. The only required parameter is 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
export="":
export-size: 1048576
content: data
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 the same output as above):
$ nbdinfo "nbd+unix:///?socket=/tmp/unixsock"
To display only the size in bytes of the NBD export (useful for scripting) use the --size parameter:
$ nbdinfo --size nbd://localhost 1048576
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,
"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",
"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
}
]
}
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 allocated
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": "allocated" },
{ "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.
To list all the exports available on an NBD server use the --list (-L) option.
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.
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.
libnbd(3), nbdcopy(1), nbdfuse(1), nbdsh(1), file(1), jq(1), qemu-img(1), qemu-nbd(8).
Richard W.M. Jones
Eric Blake
Copyright (C) 2020 Red Hat Inc.
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
| 2021-02-09 | libnbd-1.6.1 |