1===================================== 2QEMU Disk Network Block Device Server 3===================================== 4 5Synopsis 6-------- 7 8**qemu-nbd** [*OPTION*]... *filename* 9 10**qemu-nbd** -L [*OPTION*]... 11 12**qemu-nbd** -d *dev* 13 14Description 15----------- 16 17Export a QEMU disk image using the NBD protocol. 18 19Other uses: 20 21- Bind a /dev/nbdX block device to a QEMU server (on Linux). 22- As a client to query exports of a remote NBD server. 23 24Options 25------- 26 27.. program:: qemu-nbd 28 29*filename* is a disk image filename, or a set of block 30driver options if ``--image-opts`` is specified. 31 32*dev* is an NBD device. 33 34.. option:: --object type,id=ID,...props... 35 36 Define a new instance of the *type* object class identified by *ID*. 37 See the :manpage:`qemu(1)` manual page for full details of the properties 38 supported. The common object types that it makes sense to define are the 39 ``secret`` object, which is used to supply passwords and/or encryption 40 keys, and the ``tls-creds`` object, which is used to supply TLS 41 credentials for the qemu-nbd server or client. 42 43.. option:: -p, --port=PORT 44 45 TCP port to listen on as a server, or connect to as a client 46 (default ``10809``). 47 48.. option:: -o, --offset=OFFSET 49 50 The offset into the image. 51 52.. option:: -b, --bind=IFACE 53 54 The interface to bind to as a server, or connect to as a client 55 (default ``0.0.0.0``). 56 57.. option:: -k, --socket=PATH 58 59 Use a unix socket with path *PATH*. 60 61.. option:: --image-opts 62 63 Treat *filename* as a set of image options, instead of a plain 64 filename. If this flag is specified, the ``-f`` flag should 65 not be used, instead the :option:`format=` option should be set. 66 67.. option:: -f, --format=FMT 68 69 Force the use of the block driver for format *FMT* instead of 70 auto-detecting. 71 72.. option:: -r, --read-only 73 74 Export the disk as read-only. 75 76.. option:: -A, --allocation-depth 77 78 Expose allocation depth information via the 79 ``qemu:allocation-depth`` metadata context accessible through 80 NBD_OPT_SET_META_CONTEXT. 81 82.. option:: -B, --bitmap=NAME 83 84 If *filename* has a qcow2 persistent bitmap *NAME*, expose 85 that bitmap via the ``qemu:dirty-bitmap:NAME`` metadata context 86 accessible through NBD_OPT_SET_META_CONTEXT. 87 88.. option:: -s, --snapshot 89 90 Use *filename* as an external snapshot, create a temporary 91 file with ``backing_file=``\ *filename*, redirect the write to 92 the temporary one. 93 94.. option:: -l, --load-snapshot=SNAPSHOT_PARAM 95 96 Load an internal snapshot inside *filename* and export it 97 as an read-only device, SNAPSHOT_PARAM format is 98 ``snapshot.id=[ID],snapshot.name=[NAME]`` or ``[ID_OR_NAME]`` 99 100.. option:: --cache=CACHE 101 102 The cache mode to be used with the file. See the documentation of 103 the emulator's ``-drive cache=...`` option for allowed values. 104 105.. option:: -n, --nocache 106 107 Equivalent to :option:`--cache=none`. 108 109.. option:: --aio=AIO 110 111 Set the asynchronous I/O mode between ``threads`` (the default), 112 ``native`` (Linux only), and ``io_uring`` (Linux 5.1+). 113 114.. option:: --discard=DISCARD 115 116 Control whether ``discard`` (also known as ``trim`` or ``unmap``) 117 requests are ignored or passed to the filesystem. *DISCARD* is one of 118 ``ignore`` (or ``off``), ``unmap`` (or ``on``). The default is 119 ``ignore``. 120 121.. option:: --detect-zeroes=DETECT_ZEROES 122 123 Control the automatic conversion of plain zero writes by the OS to 124 driver-specific optimized zero write commands. *DETECT_ZEROES* is one of 125 ``off``, ``on``, or ``unmap``. ``unmap`` 126 converts a zero write to an unmap operation and can only be used if 127 *DISCARD* is set to ``unmap``. The default is ``off``. 128 129.. option:: -c, --connect=DEV 130 131 Connect *filename* to NBD device *DEV* (Linux only). 132 133.. option:: -d, --disconnect 134 135 Disconnect the device *DEV* (Linux only). 136 137.. option:: -e, --shared=NUM 138 139 Allow up to *NUM* clients to share the device (default 140 ``1``), 0 for unlimited. Safe for readers, but for now, 141 consistency is not guaranteed between multiple writers. 142 143.. option:: -t, --persistent 144 145 Don't exit on the last connection. 146 147.. option:: -x, --export-name=NAME 148 149 Set the NBD volume export name (default of a zero-length string). 150 151.. option:: -D, --description=DESCRIPTION 152 153 Set the NBD volume export description, as a human-readable 154 string. 155 156.. option:: -L, --list 157 158 Connect as a client and list all details about the exports exposed by 159 a remote NBD server. This enables list mode, and is incompatible 160 with options that change behavior related to a specific export (such as 161 :option:`--export-name`, :option:`--offset`, ...). 162 163.. option:: --tls-creds=ID 164 165 Enable mandatory TLS encryption for the server by setting the ID 166 of the TLS credentials object previously created with the --object 167 option; or provide the credentials needed for connecting as a client 168 in list mode. 169 170.. option:: --fork 171 172 Fork off the server process and exit the parent once the server is running. 173 174.. option:: --pid-file=PATH 175 176 Store the server's process ID in the given file. 177 178.. option:: --tls-authz=ID 179 180 Specify the ID of a qauthz object previously created with the 181 :option:`--object` option. This will be used to authorize connecting users 182 against their x509 distinguished name. 183 184.. option:: -v, --verbose 185 186 Display extra debugging information. 187 188.. option:: -h, --help 189 190 Display this help and exit. 191 192.. option:: -V, --version 193 194 Display version information and exit. 195 196.. option:: -T, --trace [[enable=]PATTERN][,events=FILE][,file=FILE] 197 198 .. include:: ../qemu-option-trace.rst.inc 199 200Examples 201-------- 202 203Start a server listening on port 10809 that exposes only the 204guest-visible contents of a qcow2 file, with no TLS encryption, and 205with the default export name (an empty string). The command is 206one-shot, and will block until the first successful client 207disconnects: 208 209:: 210 211 qemu-nbd -f qcow2 file.qcow2 212 213Start a long-running server listening with encryption on port 10810, 214and whitelist clients with a specific X.509 certificate to connect to 215a 1 megabyte subset of a raw file, using the export name 'subset': 216 217:: 218 219 qemu-nbd \ 220 --object tls-creds-x509,id=tls0,endpoint=server,dir=/path/to/qemutls \ 221 --object 'authz-simple,id=auth0,identity=CN=laptop.example.com,,\ 222 O=Example Org,,L=London,,ST=London,,C=GB' \ 223 --tls-creds tls0 --tls-authz auth0 \ 224 -t -x subset -p 10810 \ 225 --image-opts driver=raw,offset=1M,size=1M,file.driver=file,file.filename=file.raw 226 227Serve a read-only copy of a guest image over a Unix socket with as 228many as 5 simultaneous readers, with a persistent process forked as a 229daemon: 230 231:: 232 233 qemu-nbd --fork --persistent --shared=5 --socket=/path/to/sock \ 234 --read-only --format=qcow2 file.qcow2 235 236Expose the guest-visible contents of a qcow2 file via a block device 237/dev/nbd0 (and possibly creating /dev/nbd0p1 and friends for 238partitions found within), then disconnect the device when done. 239Access to bind qemu-nbd to an /dev/nbd device generally requires root 240privileges, and may also require the execution of ``modprobe nbd`` 241to enable the kernel NBD client module. *CAUTION*: Do not use 242this method to mount filesystems from an untrusted guest image - a 243malicious guest may have prepared the image to attempt to trigger 244kernel bugs in partition probing or file system mounting. 245 246:: 247 248 qemu-nbd -c /dev/nbd0 -f qcow2 file.qcow2 249 qemu-nbd -d /dev/nbd0 250 251Query a remote server to see details about what export(s) it is 252serving on port 10809, and authenticating via PSK: 253 254:: 255 256 qemu-nbd \ 257 --object tls-creds-psk,id=tls0,dir=/tmp/keys,username=eblake,endpoint=client \ 258 --tls-creds tls0 -L -b remote.example.com 259 260See also 261-------- 262 263:manpage:`qemu(1)`, :manpage:`qemu-img(1)` 264