     qemu-nbd [OPTION]... FILENAME

     qemu-nbd -L [OPTION]...

     qemu-nbd -d DEV

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.

FILENAME is a disk image filename, or a set of block driver options if --image-opts is specified.

DEV is an NBD device.

--object type,id=ID,...props...
     Define a new instance of the TYPE object class identified by ID. See the 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.

-p, --port=PORT
     The TCP port to listen on as a server, or connect to as a client (default 10809).

-o, --offset=OFFSET
     The offset into the image.

-b, --bind=IFACE
     The interface to bind to as a server, or connect to as a client (default 0.0.0.0).

-k, --socket=PATH
     Use a unix socket with path PATH.

--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 'format=' option should be set.

-f, --format=FMT
     Force the use of the block driver for format FMT instead of auto-detecting.

-r, --read-only
     Export the disk as read-only.

-P, --partition=NUM
     Deprecated: Only expose MBR partition NUM.  Understands physical partitions 1-4 and logical partition 5. New code should instead use --image-opts with the raw driver wrapping a subset of the original image.

-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.

-s, --snapshot
     Use FILENAME as an external snapshot, create a temporary file with backing_file=FILENAME, redirect the write to the temporary one.

-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]'

-n, --nocache
--cache=CACHE
     The cache mode to be used with the file.  See the documentation of the emulator's -drive cache=... option for allowed values.

--aio=AIO
     Set the asynchronous I/O mode between threads (the default) and native (Linux only).

--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.

--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.

-c, --connect=DEV
     Connect FILENAME to NBD device DEV (Linux only).

-d, --disconnect
     Disconnect the device DEV (Linux only).

-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.

-t, --persistent
     Don't exit on the last connection.

-x, --export-name=NAME
     Set the NBD volume export name (default of a zero-length string).

-D, --description=DESCRIPTION
     Set the NBD volume export description, as a human-readable string.

-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 --export-name, --offset, ...).

--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.

--fork
     Fork off the server process and exit the parent once the server is running.

--pid-file=PATH
     Store the server's process ID in the given file.

--tls-authz=ID
     Specify the ID of a qauthz object previously created with the --object option. This will be used to authorize connecting users against their x509 distinguished name.

-v, --verbose
     Display extra debugging information.

-h, --help
     Display this help and exit.

-V, --version
     Display version information and exit.

-T, --trace [[enable=]PATTERN][,events=FILE][,file=FILE]
          [file qemu-option-trace.texi not included]

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 just the first MBR partition 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 \
       --partition=1 --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