@example @c man begin SYNOPSIS @command{qemu-nbd} [OPTION]... @var{filename} @command{qemu-nbd} @option{-L} [OPTION]... @command{qemu-nbd} @option{-d} @var{dev} @c man end @end example @c man begin DESCRIPTION Export a QEMU disk image using the NBD protocol. Other uses: @itemize @item Bind a /dev/nbdX block device to a QEMU server (on Linux). @item As a client to query exports of a remote NBD server. @end itemize @c man end @c man begin OPTIONS @var{filename} is a disk image filename, or a set of block driver options if @option{--image-opts} is specified. @var{dev} is an NBD device. @table @option @item --object type,id=@var{id},...props... Define a new instance of the @var{type} object class identified by @var{id}. See the @code{qemu(1)} manual page for full details of the properties supported. The common object types that it makes sense to define are the @code{secret} object, which is used to supply passwords and/or encryption keys, and the @code{tls-creds} object, which is used to supply TLS credentials for the qemu-nbd server or client. @item -p, --port=@var{port} The TCP port to listen on as a server, or connect to as a client (default @samp{10809}). @item -o, --offset=@var{offset} The offset into the image. @item -b, --bind=@var{iface} The interface to bind to as a server, or connect to as a client (default @samp{0.0.0.0}). @item -k, --socket=@var{path} Use a unix socket with path @var{path}. @item --image-opts Treat @var{filename} as a set of image options, instead of a plain filename. If this flag is specified, the @var{-f} flag should not be used, instead the '@code{format=}' option should be set. @item -f, --format=@var{fmt} Force the use of the block driver for format @var{fmt} instead of auto-detecting. @item -r, --read-only Export the disk as read-only. @item -P, --partition=@var{num} Deprecated: Only expose MBR partition @var{num}. Understands physical partitions 1-4 and logical partition 5. New code should instead use @option{--image-opts} with the raw driver wrapping a subset of the original image. @item -B, --bitmap=@var{name} If @var{filename} has a qcow2 persistent bitmap @var{name}, expose that bitmap via the ``qemu:dirty-bitmap:@var{name}'' context accessible through NBD_OPT_SET_META_CONTEXT. @item -s, --snapshot Use @var{filename} as an external snapshot, create a temporary file with backing_file=@var{filename}, redirect the write to the temporary one. @item -l, --load-snapshot=@var{snapshot_param} Load an internal snapshot inside @var{filename} and export it as an read-only device, @var{snapshot_param} format is 'snapshot.id=[ID],snapshot.name=[NAME]' or '[ID_OR_NAME]' @item -n, --nocache @itemx --cache=@var{cache} The cache mode to be used with the file. See the documentation of the emulator's @code{-drive cache=...} option for allowed values. @item --aio=@var{aio} Set the asynchronous I/O mode between @samp{threads} (the default) and @samp{native} (Linux only). @item --discard=@var{discard} Control whether @dfn{discard} (also known as @dfn{trim} or @dfn{unmap}) requests are ignored or passed to the filesystem. @var{discard} is one of @samp{ignore} (or @samp{off}), @samp{unmap} (or @samp{on}). The default is @samp{ignore}. @item --detect-zeroes=@var{detect-zeroes} Control the automatic conversion of plain zero writes by the OS to driver-specific optimized zero write commands. @var{detect-zeroes} is one of @samp{off}, @samp{on} or @samp{unmap}. @samp{unmap} converts a zero write to an unmap operation and can only be used if @var{discard} is set to @samp{unmap}. The default is @samp{off}. @item -c, --connect=@var{dev} Connect @var{filename} to NBD device @var{dev} (Linux only). @item -d, --disconnect Disconnect the device @var{dev} (Linux only). @item -e, --shared=@var{num} Allow up to @var{num} clients to share the device (default @samp{1}). Safe for readers, but for now, consistency is not guaranteed between multiple writers. @item -t, --persistent Don't exit on the last connection. @item -x, --export-name=@var{name} Set the NBD volume export name (default of a zero-length string). @item -D, --description=@var{description} Set the NBD volume export description, as a human-readable string. @item -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}, ...). @item --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. @item --fork Fork off the server process and exit the parent once the server is running. @item --pid-file=PATH Store the server's process ID in the given file. @item --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. @item -v, --verbose Display extra debugging information. @item -h, --help Display this help and exit. @item -V, --version Display version information and exit. @item -T, --trace [[enable=]@var{pattern}][,events=@var{file}][,file=@var{file}] @findex --trace @include qemu-option-trace.texi @end table @c man end @c man begin 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: @example qemu-nbd -f qcow2 file.qcow2 @end example 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': @example 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 @end example 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: @example qemu-nbd --fork --persistent --shared=5 --socket=/path/to/sock \ --partition=1 --read-only --format=qcow2 file.qcow2 @end example 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 @code{modprobe nbd} to enable the kernel NBD client module. @emph{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. @example qemu-nbd -c /dev/nbd0 -f qcow2 file.qcow2 qemu-nbd -d /dev/nbd0 @end example Query a remote server to see details about what export(s) it is serving on port 10809, and authenticating via PSK: @example qemu-nbd \ --object tls-creds-psk,id=tls0,dir=/tmp/keys,username=eblake,endpoint=client \ --tls-creds tls0 -L -b remote.example.com @end example @c man end @ignore @setfilename qemu-nbd @settitle QEMU Disk Network Block Device Server @c man begin AUTHOR Copyright (C) 2006 Anthony Liguori <anthony@codemonkey.ws>. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. @c man end @c man begin SEEALSO qemu(1), qemu-img(1) @c man end @end ignore