1NBD-SERVER(1) NBD-SERVER(1)
2
6 nbd-server - serve a file as a block device to other computers run‐
7 ning the GNU/Linux(tm) or GNU/Hurd Operating System
8
10 nbd-server [ip@]port filename [ size ] [ -r ] [ -m ] [ -c ] [ -l host
11 list filename ] [ -o section name ] [ -C config file ] [ -M max connec‐
12 tions ]
13
16 nbd-server is the server for the Linux Network Block Device (NBD). With
17 NBD, a client can use a file, exported over the network from a server,
18 as a block device. It can then be used for whatever purpose a normal
19 block device (harddisk, CD-ROM, ...) can be used for.
20 NBD can be useful for diskless clients that need swapspace, but you can
22 also create a filesystem on it and use it as though it were a local
23 filesystem.
24 nbd-server implements some security through a file called "/etc/nbd-
26 server/allow" (by default; a different file can be chosen with the '-l'
27 option or through a config file specification). This file must list the
28 IP-addresses or network masks of clients that are allowed to connect.
29 If it does not exist, all clients are able to connect. If the file is
30 empty, no clients can connect.
31 Note that while the command line allows for specifying an export, the
33 use of this option is deprecated. It is preferred to make use of a con‐
34 figuration file instead, the format of which is defined in nbd-
35 server(5).
36
38 ip The ip address the server should listen on. This may be an IPv4
39 address, an IPv6 address, or a hostname. In the latter case,
40 nbd-server will do a hostname lookup for the name specified, and
41 will listen on the first address that is returned. For compati‐
42 bility with past versions of nbd-server, if an IPv4 address is
43 specified, the @ sign that serves as separator between the
44 address and port may be replaced by a colon.
45 If this parameter is not specified, nbd-server will listen on
47 all local addresses on both IPv4 and IPv6. To limit to IPv4,
48 specify the address as 0.0.0.0; to limit to IPv6, specify it as
49 ::.
50 port The port the server should listen to. A valid port is any number
52 between 1 and 65536; if 0 is used, nbd-server will listen on
53 stdin (so that nbd-server can be ran from inetd)
54 filename
56 The filename of the file that should be exported. This can be
57 any file, including "real" blockdevices (i.e. a file from /dev).
58 If the filename includes the literal string "%s", then this %s
59 will be substituded with the IP-address of the client trying to
60 connect.
61 size The size of the block device at the client side. This is espe‐
63 cially useful in conjunction with the -m option
64 Can optionally be followed by one of K,k,M or m, in which case
66 the size will be multiplied by 1024 (K or k) or 1048576 (M or m)
67 -r Export the file read-only. If a client tries to write to a read-
69 only exported file, it will receive an error, but the connection
70 will stay up.
71 -m Work with multiple files. This can be used to export blockde‐
73 vices that are larger than the maximum allowed filesize on a
74 given filesystem; i.e. when the filesystem does not allow files
75 larger than 2GB (which is true for Linux 2.2 and below), you can
76 use this option to store the data in multiple files and export a
77 larger filesystem, if needed.
78 To use this option, you must create a number of files with names
80 in the format "name.X", where "name" is given as the filename
81 argument to nbd-server, and "X" is a number starting by 0 and
82 going up for each file.
83 Allowing more flexibility for this option is planned for future
85 versions.
86 -c Copy on write. When this option is provided, write-operations
88 are not done to the exported file, but to a separate file. This
89 separate file is removed when the connection is closed, which
90 means that serving this way will make nbd-server slow down
91 (especially on large block devices with lots of writes), and
92 that after disconnecting and reconnecting the client or the
93 server, all changes are lost.
94 -C Specify configuration file. The default configuration file, if
96 this parameter is not specified, is /etc/nbd-server/config.
97 Note that the configuration file is always parsed and the
99 entries in the file used, even if an extra server is specified
100 on the command line. To disable the configuration file entirely,
101 either move it away or use the -C option to point nbd-server(1)
102 to a non-existing or empty configuration file.
103 Also note that if an empty, incomplete, or invalid configuration
105 file is specified, nbd-server will produce a warning about fail‐
106 ure to parse the config file. If the command line contains a
107 fully specified configuration, this warning is harmless and may
108 be ignored.
109 -M Specify the maximum number of opened connections. If this param‐
111 eter is not specified, no limit is set.
112 host list filename
114 This argument should contain a list of IP-addresses for hosts
115 that may connect to the server. Wildcards are not allowed. If
116 the file does not exist, it is ignored (and any host can con‐
117 nect); If the file does exist, but is empty, no host can con‐
118 nect. By default, the name 'nbd_server.allow' is used, and
119 looked for in the current directory, unless nbd-server is com‐
120 piled as a daemon, in which case it is looked for in the root-
121 directory.
122 section name
124 If the -o argument is given on the command line, then nbd-server
125 will output a configuration file section with this as the header
126 that is functionally equivalent to the other options specified
127 on the command line, and exit. This is useful for migrating
128 pre-2.9 nbd-server initscript configuration files to the new
129 format.
130
132 Some examples of nbd-server usage:
133 · To export a file /export/nbd/exp-bl-dev on port 2000:
135 nbd-server 2000 /export/nbd/exp-bl-dev
137 · To export a the same file read-only:
139 nbd-server 2000 /export/nbd/exp-bl-dev -r
141 · To export the same file read-write, but make sure changes are lost
143 after restarting the client or the server:
144 nbd-server 2000 /export/nbd/exp-bl-dev -c
146
148 nbd-client (8), nbd-server (5)
149
151 The NBD kernel module and the NBD tools were originally written by
152 Pavel Machek (pavel@ucw.cz)
153 The Linux kernel module is now maintained by Paul Clements
155 (Paul.Clements@steeleye.com), while the userland tools are maintained
156 by Wouter Verhelst (<wouter@debian.org>)
157 On The Hurd there is a regular translator available to perform the
159 client side of the protocol, and the use of nbd-client is not required.
160 Please see the relevant documentation for more information.
161 This manual page was written by Wouter Verhelst (<wouter@debian.org>)
163 for the Debian GNU/Linux system (but may be used by others). Permis‐
164 sion is granted to copy, distribute and/or modify this document under
165 the terms of the GNU General Public License, version 2, as published by
166 the Free Software Foundation.
167 27 January 2011 NBD-SERVER(1)