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@c man begin SYNOPSIS
@command{qemu-nbd} [OPTION]... @var{filename}
@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.
@c man end
@c man begin OPTIONS
@var{filename} is a disk image filename, or a set of block
driver options if @var{--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.
@item -p, --port=@var{port}
The TCP port to listen on (default @samp{10809})
@item -o, --offset=@var{offset}
The offset into the image
@item -b, --bind=@var{iface}
The interface to bind to (default @samp{})
@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
@item -r, --read-only
Export the disk as read-only
@item -P, --partition=@var{num}
Only expose partition @var{num}
@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
'[ID],[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
@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}
@item -d, --disconnect
Disconnect the device @var{dev}
@item -e, --shared=@var{num}
Allow up to @var{num} clients to share the device (default @samp{1})
@item -t, --persistent
Don't exit on the last connection
@item -x NAME, --export-name=NAME
Set the NBD volume export name. This switches the server to use
the new style NBD protocol negotiation
@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
@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
@setfilename qemu-nbd
@settitle QEMU Disk Network Block Device Server
@c man begin AUTHOR
Copyright (C) 2006 Anthony Liguori <>.
This is free software; see the source for copying conditions. There is NO
@c man end
@c man begin SEEALSO
qemu(1), qemu-img(1)
@c man end
@end ignore