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 ] [ -V ] [ -n ] [ -d ]
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 While nbd-server is running, new exports can be added by re-writing
38 configuration files and then sending SIGHUP to nbd-server. SIGHUP
39 causes nbd-server to re-read its configuration files and to start serv‐
40 ing all new exports which were not served earlier. Reconfiguration does
41 not modify any existing export, it only appends new ones.
42
44 ip The ip address the server should listen on. This may be an IPv4
45 address, an IPv6 address, or a hostname. In the latter case,
46 nbd-server will do a hostname lookup for the name specified, and
47 will listen on the first address that is returned. For compati‐
48 bility with past versions of nbd-server, if an IPv4 address is
49 specified, the @ sign that serves as separator between the ad‐
50 dress and port may be replaced by a colon.
51 If this parameter is not specified, nbd-server will listen on
53 all local addresses on both IPv4 and IPv6. To limit to IPv4,
54 specify the address as 0.0.0.0; to limit to IPv6, specify it as
55 ::.
56 port The port the server should listen to. A valid port is any number
58 between 1 and 65536; if 0 is used, nbd-server will listen on
59 stdin (so that nbd-server can be ran from inetd)
60 filename
62 The filename of the file that should be exported. This can be
63 any file, including "real" blockdevices (i.e. a file from /dev).
64 If the filename includes the literal string "%s", then this %s
65 will be substituded with the IP-address of the client trying to
66 connect.
67 size The size of the block device at the client side. This is espe‐
69 cially useful in conjunction with the -m option
70 Can optionally be followed by one of K,k,M or m, in which case
72 the size will be multiplied by 1024 (K or k) or 1048576 (M or m)
73 -r Export the file read-only. If a client tries to write to a read-
75 only exported file, it will receive an error, but the connection
76 will stay up.
77 -m Work with multiple files. This can be used to export blockde‐
79 vices that are larger than the maximum allowed filesize on a
80 given filesystem; i.e. when the filesystem does not allow files
81 larger than 2GB (which is true for Linux 2.2 and below), you can
82 use this option to store the data in multiple files and export a
83 larger filesystem, if needed.
84 To use this option, you must create a number of files with names
86 in the format "name.X", where "name" is given as the filename
87 argument to nbd-server, and "X" is a number starting by 0 and
88 going up for each file.
89 Allowing more flexibility for this option is planned for future
91 versions.
92 -c Copy on write. When this option is provided, write-operations
94 are not done to the exported file, but to a separate file. This
95 separate file is removed when the connection is closed, which
96 means that serving this way will make nbd-server slow down (es‐
97 pecially on large block devices with lots of writes), and that
98 after disconnecting and reconnecting the client or the server,
99 all changes are lost.
100 -C Specify configuration file. The default configuration file, if
102 this parameter is not specified, is /etc/nbd-server/config.
103 Note that the configuration file is always parsed and the en‐
105 tries in the file used, even if an extra server is specified on
106 the command line. To disable the configuration file entirely,
107 either move it away or use the -C option to point nbd-server(1)
108 to a non-existing or empty configuration file.
109 Also note that if an empty, incomplete, or invalid configuration
111 file is specified, nbd-server will produce a warning about fail‐
112 ure to parse the config file. If the command line contains a
113 fully specified configuration, this warning is harmless and may
114 be ignored.
115 -M Specify the maximum number of opened connections. If this param‐
117 eter is not specified, no limit is set.
118 -V Output the version of nbd-server, and exit.
120 -n Do not daemonize the main process. In contrast to -d, this still
122 allows to fork the serving process for a client from the main
123 process.
124 -d Do not fork. Useful for debugging. Implies -n.
126 host list filename
128 This argument should contain a list of IP-addresses for hosts
129 that may connect to the server. Wildcards are not allowed. If
130 the file does not exist, it is ignored (and any host can con‐
131 nect); If the file does exist, but is empty, no host can con‐
132 nect. By default, the name 'nbd_server.allow' is used, and
133 looked for in the current directory, unless nbd-server is com‐
134 piled as a daemon, in which case it is looked for in the root-
135 directory.
136 section name
138 If the -o argument is given on the command line, then nbd-server
139 will output a configuration file section with this as the header
140 that is functionally equivalent to the other options specified
141 on the command line, and exit. This is useful for migrating
142 pre-2.9 nbd-server initscript configuration files to the new
143 format.
144
146 Some examples of nbd-server usage:
147 • To export a file /export/nbd/exp-bl-dev on port 2000:
149 nbd-server 2000 /export/nbd/exp-bl-dev
151 • To export a the same file read-only:
153 nbd-server 2000 /export/nbd/exp-bl-dev -r
155 • To export the same file read-write, but make sure changes are lost
157 after restarting the client or the server:
158 nbd-server 2000 /export/nbd/exp-bl-dev -c
160
162 nbd-client (8), nbd-server (5), nbd-trdump (8)
163
165 The NBD kernel module and the NBD tools were originally written by
166 Pavel Machek (pavel@ucw.cz)
167 The Linux kernel module is now maintained by Paul Clements
169 (Paul.Clements@steeleye.com), while the userland tools are maintained
170 by Wouter Verhelst (<wouter@debian.org>)
171 On The Hurd there is a regular translator available to perform the
173 client side of the protocol, and the use of nbd-client is not required.
174 Please see the relevant documentation for more information.
175 This manual page was written by Wouter Verhelst (<wouter@debian.org>)
177 for the Debian GNU/Linux system (but may be used by others). Permis‐
178 sion is granted to copy, distribute and/or modify this document under
179 the terms of the GNU General Public License, version 2, as published by
180 the Free Software Foundation.
181 $ NBD-SERVER(1)