qemu-nbd.rst (7743B)
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. Valid values are: 103 ``none``, ``writeback`` (the default), ``writethrough``, 104 ``directsync`` and ``unsafe``. See the documentation of 105 the emulator's ``-drive cache=...`` option for more info. 106 107.. option:: -n, --nocache 108 109 Equivalent to :option:`--cache=none`. 110 111.. option:: --aio=AIO 112 113 Set the asynchronous I/O mode between ``threads`` (the default), 114 ``native`` (Linux only), and ``io_uring`` (Linux 5.1+). 115 116.. option:: --discard=DISCARD 117 118 Control whether ``discard`` (also known as ``trim`` or ``unmap``) 119 requests are ignored or passed to the filesystem. *DISCARD* is one of 120 ``ignore`` (or ``off``), ``unmap`` (or ``on``). The default is 121 ``ignore``. 122 123.. option:: --detect-zeroes=DETECT_ZEROES 124 125 Control the automatic conversion of plain zero writes by the OS to 126 driver-specific optimized zero write commands. *DETECT_ZEROES* is one of 127 ``off``, ``on``, or ``unmap``. ``unmap`` 128 converts a zero write to an unmap operation and can only be used if 129 *DISCARD* is set to ``unmap``. The default is ``off``. 130 131.. option:: -c, --connect=DEV 132 133 Connect *filename* to NBD device *DEV* (Linux only). 134 135.. option:: -d, --disconnect 136 137 Disconnect the device *DEV* (Linux only). 138 139.. option:: -e, --shared=NUM 140 141 Allow up to *NUM* clients to share the device (default 142 ``1``), 0 for unlimited. Safe for readers, but for now, 143 consistency is not guaranteed between multiple writers. 144 145.. option:: -t, --persistent 146 147 Don't exit on the last connection. 148 149.. option:: -x, --export-name=NAME 150 151 Set the NBD volume export name (default of a zero-length string). 152 153.. option:: -D, --description=DESCRIPTION 154 155 Set the NBD volume export description, as a human-readable 156 string. 157 158.. option:: -L, --list 159 160 Connect as a client and list all details about the exports exposed by 161 a remote NBD server. This enables list mode, and is incompatible 162 with options that change behavior related to a specific export (such as 163 :option:`--export-name`, :option:`--offset`, ...). 164 165.. option:: --tls-creds=ID 166 167 Enable mandatory TLS encryption for the server by setting the ID 168 of the TLS credentials object previously created with the --object 169 option; or provide the credentials needed for connecting as a client 170 in list mode. 171 172.. option:: --fork 173 174 Fork off the server process and exit the parent once the server is running. 175 176.. option:: --pid-file=PATH 177 178 Store the server's process ID in the given file. 179 180.. option:: --tls-authz=ID 181 182 Specify the ID of a qauthz object previously created with the 183 :option:`--object` option. This will be used to authorize connecting users 184 against their x509 distinguished name. 185 186.. option:: -v, --verbose 187 188 Display extra debugging information. 189 190.. option:: -h, --help 191 192 Display this help and exit. 193 194.. option:: -V, --version 195 196 Display version information and exit. 197 198.. option:: -T, --trace [[enable=]PATTERN][,events=FILE][,file=FILE] 199 200 .. include:: ../qemu-option-trace.rst.inc 201 202Examples 203-------- 204 205Start a server listening on port 10809 that exposes only the 206guest-visible contents of a qcow2 file, with no TLS encryption, and 207with the default export name (an empty string). The command is 208one-shot, and will block until the first successful client 209disconnects: 210 211:: 212 213 qemu-nbd -f qcow2 file.qcow2 214 215Start a long-running server listening with encryption on port 10810, 216and whitelist clients with a specific X.509 certificate to connect to 217a 1 megabyte subset of a raw file, using the export name 'subset': 218 219:: 220 221 qemu-nbd \ 222 --object tls-creds-x509,id=tls0,endpoint=server,dir=/path/to/qemutls \ 223 --object 'authz-simple,id=auth0,identity=CN=laptop.example.com,,\ 224 O=Example Org,,L=London,,ST=London,,C=GB' \ 225 --tls-creds tls0 --tls-authz auth0 \ 226 -t -x subset -p 10810 \ 227 --image-opts driver=raw,offset=1M,size=1M,file.driver=file,file.filename=file.raw 228 229Serve a read-only copy of a guest image over a Unix socket with as 230many as 5 simultaneous readers, with a persistent process forked as a 231daemon: 232 233:: 234 235 qemu-nbd --fork --persistent --shared=5 --socket=/path/to/sock \ 236 --read-only --format=qcow2 file.qcow2 237 238Expose the guest-visible contents of a qcow2 file via a block device 239/dev/nbd0 (and possibly creating /dev/nbd0p1 and friends for 240partitions found within), then disconnect the device when done. 241Access to bind qemu-nbd to an /dev/nbd device generally requires root 242privileges, and may also require the execution of ``modprobe nbd`` 243to enable the kernel NBD client module. *CAUTION*: Do not use 244this method to mount filesystems from an untrusted guest image - a 245malicious guest may have prepared the image to attempt to trigger 246kernel bugs in partition probing or file system mounting. 247 248:: 249 250 qemu-nbd -c /dev/nbd0 -f qcow2 file.qcow2 251 qemu-nbd -d /dev/nbd0 252 253Query a remote server to see details about what export(s) it is 254serving on port 10809, and authenticating via PSK: 255 256:: 257 258 qemu-nbd \ 259 --object tls-creds-psk,id=tls0,dir=/tmp/keys,username=eblake,endpoint=client \ 260 --tls-creds tls0 -L -b remote.example.com 261 262See also 263-------- 264 265:manpage:`qemu(1)`, :manpage:`qemu-img(1)`