The ip address the server should listen on. This may
be an IPv4 address, an IPv6 address, or a hostname. In the
latter case, nbd-server will do a hostname lookup for the
name specified, and will listen on the first address that is
returned. For compatibility with past versions of
nbd-server, if an IPv4 address is specified, the @ sign that
serves as separator between the address and port may be
replaced by a colon.
If this parameter is not specified, nbd-server will listen on all local addresses on both IPv4 and IPv6. To limit to IPv4, specify the address as 0.0.0.0; to limit to IPv6, specify it as ::.
|port||The port the server should listen to. A valid port is any number between 1 and 65536; if 0 is used, nbd-server will listen on stdin (so that nbd-server can be ran from inetd)|
|The filename of the file that should be exported. This can be any file, including "real" blockdevices (i.e. a file from /dev). If the filename includes the literal string "%s", then this %s will be substituded with the IP-address of the client trying to connect.|
The size of the block device at the client side. This
is especially useful in conjunction with the -m
Can optionally be followed by one of K,k,M or m, in which case the size will be multiplied by 1024 (K or k) or 1048576 (M or m)
|-r||Export the file read-only. If a client tries to write to a read-only exported file, it will receive an error, but the connection will stay up.|
Work with multiple files. This can be used to export
blockdevices that are larger than the maximum allowed
filesize on a given filesystem; i.e. when the filesystem
does not allow files larger than 2GB (which is true for
Linux 2.2 and below), you can use this option to store the
data in multiple files and export a larger filesystem, if
To use this option, you must create a number of files with names in the format "name.X", where "name" is given as the filename argument to nbd-server, and "X" is a number starting by 0 and going up for each file.
Allowing more flexibility for this option is planned for future versions.
|-c||Copy on write. When this option is provided, write-operations are not done to the exported file, but to a separate file. This separate file is removed when the connection is closed, which means that serving this way will make nbd-server slow down (especially on large block devices with lots of writes), and that after disconnecting and reconnecting the client or the server, all changes are lost.|
Specify configuration file. The default configuration
file, if this parameter is not specified, is
Note that the configuration file is always parsed and the entries in the file used, even if an extra server is specified on the command line. To disable the configuration file entirely, either move it away or use the -C option to point nbd-server(1) to a non-existing or empty configuration file.
Also note that if an empty, incomplete, or invalid configuration file is specified, nbd-server will produce a warning about failure to parse the config file. If the command line contains a fully specified configuration, this warning is harmless and may be ignored.
|-M||Specify the maximum number of opened connections. If this parameter is not specified, no limit is set.|
|-d||Do not fork. Useful for debugging.|
|host list filename|
|This argument should contain a list of IP-addresses for hosts that may connect to the server. Wildcards are not allowed. If the file does not exist, it is ignored (and any host can connect); If the file does exist, but is empty, no host can connect. By default, the name nbd_server.allow is used, and looked for in the current directory, unless nbd-server is compiled as a daemon, in which case it is looked for in the root-directory.|
|If the -o argument is given on the command line, then nbd-server will output a configuration file section with this as the header that is functionally equivalent to the other options specified on the command line, and exit. This is useful for migrating pre-2.9 nbd-server initscript configuration files to the new format.|
Some examples of nbd-server usage:
o To export a file /export/nbd/exp-bl-dev on port 2000:
nbd-server 2000 /export/nbd/exp-bl-dev
o To export a the same file read-only:
nbd-server 2000 /export/nbd/exp-bl-dev -r
o To export the same file read-write, but make sure changes are lost after restarting the client or the server:
nbd-server 2000 /export/nbd/exp-bl-dev -c
The NBD kernel module and the NBD tools were originally written by Pavel Machek (firstname.lastname@example.org)
On The Hurd there is a regular translator available to perform the client side of the protocol, and the use of nbd-client is not required. Please see the relevant documentation for more information.
This manual page was written by Wouter Verhelst (<email@example.com>) for the Debian GNU/Linux system (but may be used by others). Permission is granted to copy, distribute and/or modify this document under the terms of the GNU General Public License, version 2, as published by the Free Software Foundation.