1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
|
QEMU Disk Network Block Device Server
=====================================
Synopsis
--------
**qemu-nbd** [*OPTION*]... *filename*
**qemu-nbd** -L [*OPTION*]...
**qemu-nbd** -d *dev*
Description
-----------
Export a QEMU disk image using the NBD protocol.
Other uses:
- Bind a /dev/nbdX block device to a QEMU server (on Linux).
- As a client to query exports of a remote NBD server.
Options
-------
.. program:: qemu-nbd
*filename* is a disk image filename, or a set of block
driver options if ``--image-opts`` is specified.
*dev* is an NBD device.
.. option:: --object type,id=ID,...props...
Define a new instance of the *type* object class identified by *ID*.
See the :manpage:`qemu(1)` manual page for full details of the properties
supported. The common object types that it makes sense to define are the
``secret`` object, which is used to supply passwords and/or encryption
keys, and the ``tls-creds`` object, which is used to supply TLS
credentials for the qemu-nbd server or client.
.. option:: -p, --port=PORT
TCP port to listen on as a server, or connect to as a client
(default ``10809``).
.. option:: -o, --offset=OFFSET
The offset into the image.
.. option:: -b, --bind=IFACE
The interface to bind to as a server, or connect to as a client
(default ``0.0.0.0``).
.. option:: -k, --socket=PATH
Use a unix socket with path *PATH*.
.. option:: --image-opts
Treat *filename* as a set of image options, instead of a plain
filename. If this flag is specified, the ``-f`` flag should
not be used, instead the :option:`format=` option should be set.
.. option:: -f, --format=FMT
Force the use of the block driver for format *FMT* instead of
auto-detecting.
.. option:: -r, --read-only
Export the disk as read-only.
.. option:: -B, --bitmap=NAME
If *filename* has a qcow2 persistent bitmap *NAME*, expose
that bitmap via the ``qemu:dirty-bitmap:NAME`` context
accessible through NBD_OPT_SET_META_CONTEXT.
.. option:: -s, --snapshot
Use *filename* as an external snapshot, create a temporary
file with ``backing_file=``\ *filename*, redirect the write to
the temporary one.
.. option:: -l, --load-snapshot=SNAPSHOT_PARAM
Load an internal snapshot inside *filename* and export it
as an read-only device, SNAPSHOT_PARAM format is
``snapshot.id=[ID],snapshot.name=[NAME]`` or ``[ID_OR_NAME]``
.. option:: --cache=CACHE
The cache mode to be used with the file. See the documentation of
the emulator's ``-drive cache=...`` option for allowed values.
.. option:: -n, --nocache
Equivalent to :option:`--cache=none`.
.. option:: --aio=AIO
Set the asynchronous I/O mode between ``threads`` (the default),
``native`` (Linux only), and ``io_uring`` (Linux 5.1+).
.. option:: --discard=DISCARD
Control whether ``discard`` (also known as ``trim`` or ``unmap``)
requests are ignored or passed to the filesystem. *DISCARD* is one of
``ignore`` (or ``off``), ``unmap`` (or ``on``). The default is
``ignore``.
.. option:: --detect-zeroes=DETECT_ZEROES
Control the automatic conversion of plain zero writes by the OS to
driver-specific optimized zero write commands. *DETECT_ZEROES* is one of
``off``, ``on``, or ``unmap``. ``unmap``
converts a zero write to an unmap operation and can only be used if
*DISCARD* is set to ``unmap``. The default is ``off``.
.. option:: -c, --connect=DEV
Connect *filename* to NBD device *DEV* (Linux only).
.. option:: -d, --disconnect
Disconnect the device *DEV* (Linux only).
.. option:: -e, --shared=NUM
Allow up to *NUM* clients to share the device (default
``1``). Safe for readers, but for now, consistency is not
guaranteed between multiple writers.
.. option:: -t, --persistent
Don't exit on the last connection.
.. option:: -x, --export-name=NAME
Set the NBD volume export name (default of a zero-length string).
.. option:: -D, --description=DESCRIPTION
Set the NBD volume export description, as a human-readable
string.
.. option:: -L, --list
Connect as a client and list all details about the exports exposed by
a remote NBD server. This enables list mode, and is incompatible
with options that change behavior related to a specific export (such as
:option:`--export-name`, :option:`--offset`, ...).
.. option:: --tls-creds=ID
Enable mandatory TLS encryption for the server by setting the ID
of the TLS credentials object previously created with the --object
option; or provide the credentials needed for connecting as a client
in list mode.
.. option:: --fork
Fork off the server process and exit the parent once the server is running.
.. option:: --pid-file=PATH
Store the server's process ID in the given file.
.. option:: --tls-authz=ID
Specify the ID of a qauthz object previously created with the
:option:`--object` option. This will be used to authorize connecting users
against their x509 distinguished name.
.. option:: -v, --verbose
Display extra debugging information.
.. option:: -h, --help
Display this help and exit.
.. option:: -V, --version
Display version information and exit.
.. option:: -T, --trace [[enable=]PATTERN][,events=FILE][,file=FILE]
.. include:: qemu-option-trace.rst.inc
Examples
--------
Start a server listening on port 10809 that exposes only the
guest-visible contents of a qcow2 file, with no TLS encryption, and
with the default export name (an empty string). The command is
one-shot, and will block until the first successful client
disconnects:
::
qemu-nbd -f qcow2 file.qcow2
Start a long-running server listening with encryption on port 10810,
and whitelist clients with a specific X.509 certificate to connect to
a 1 megabyte subset of a raw file, using the export name 'subset':
::
qemu-nbd \
--object tls-creds-x509,id=tls0,endpoint=server,dir=/path/to/qemutls \
--object 'authz-simple,id=auth0,identity=CN=laptop.example.com,,\
O=Example Org,,L=London,,ST=London,,C=GB' \
--tls-creds tls0 --tls-authz auth0 \
-t -x subset -p 10810 \
--image-opts driver=raw,offset=1M,size=1M,file.driver=file,file.filename=file.raw
Serve a read-only copy of a guest image over a Unix socket with as
many as 5 simultaneous readers, with a persistent process forked as a
daemon:
::
qemu-nbd --fork --persistent --shared=5 --socket=/path/to/sock \
--read-only --format=qcow2 file.qcow2
Expose the guest-visible contents of a qcow2 file via a block device
/dev/nbd0 (and possibly creating /dev/nbd0p1 and friends for
partitions found within), then disconnect the device when done.
Access to bind qemu-nbd to an /dev/nbd device generally requires root
privileges, and may also require the execution of ``modprobe nbd``
to enable the kernel NBD client module. *CAUTION*: Do not use
this method to mount filesystems from an untrusted guest image - a
malicious guest may have prepared the image to attempt to trigger
kernel bugs in partition probing or file system mounting.
::
qemu-nbd -c /dev/nbd0 -f qcow2 file.qcow2
qemu-nbd -d /dev/nbd0
Query a remote server to see details about what export(s) it is
serving on port 10809, and authenticating via PSK:
::
qemu-nbd \
--object tls-creds-psk,id=tls0,dir=/tmp/keys,username=eblake,endpoint=client \
--tls-creds tls0 -L -b remote.example.com
See also
--------
:manpage:`qemu(1)`, :manpage:`qemu-img(1)`
|
