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12 <!-- Fill in your name for FIRSTNAME and SURNAME. -->
13 <!ENTITY dhfirstname "<firstname>Wouter</firstname>">
14 <!ENTITY dhsurname "<surname>Verhelst</surname>">
15 <!-- Please adjust the date whenever revising the manpage. -->
16 <!ENTITY dhdate "<date>$Date$</date>">
17 <!-- SECTION should be 1-8, maybe w/ subsection other parameters are
18 allowed: see man(7), man(1). -->
19 <!ENTITY dhsection "<manvolnum>1</manvolnum>">
20 <!ENTITY dhemail "<email>wouter@debian.org</email>">
21 <!ENTITY dhusername "Wouter Verhelst">
22 <!ENTITY dhucpackage "<refentrytitle>NBD-SERVER</refentrytitle>">
23 <!ENTITY dhpackage "nbd-server">
25 <!ENTITY debian "<productname>Debian GNU/Linux</productname>">
26 <!ENTITY gnu "<acronym>GNU</acronym>">
40 <holder>&dhusername;</holder>
50 <refname>&dhpackage;</refname>
52 <refpurpose>serve a file as a block device to other computers
53 running the &gnu;/Linux(tm) or &gnu;/Hurd Operating
58 <command>&dhpackage; </command>
60 <arg choice=plain><replaceable>[ip@]port</replaceable</arg>
61 <arg choice=plain><replaceable>filename</replaceable></arg>
62 <arg><replaceable>size</replaceable></arg>
63 <arg><option>-r</option></arg>
64 <arg><option>-m</option></arg>
65 <arg><option>-c</option></arg>
66 <arg><option>-l <replaceable>host list filename</replaceable></option></arg>
67 <arg><option>-o <replaceable>section name</replaceable></option></arg>
68 <arg><option>-C <replaceable>config file</replaceable></option></arg>
69 <arg><option>-M <replaceable>max connections</replaceable></option></arg>
73 <title>DESCRIPTION</title>
75 <para><command>&dhpackage;</command> is the server for the Linux
76 Network Block Device (NBD). With NBD, a client can use a file,
77 exported over the network from a server, as a block device. It can
78 then be used for whatever purpose a normal block device (harddisk,
79 CD-ROM, ...) can be used for.</para>
81 <para>NBD can be useful for diskless clients that need swapspace,
82 but you can also create a filesystem on it and use it as though it
83 were a local filesystem.</para>
85 <para><command>&dhpackage;</command> implements some security
86 through a file called "$sysconfdir/nbd-server/allow" (by default; a
87 different file can be chosen with the '-l' option or through a
88 config file specification). This file must list the IP-addresses or
89 network masks of clients that are allowed to connect. If it does not
90 exist, all clients are able to connect. If the file is empty, no
91 clients can connect.</para>
93 <para>Note that while the command line allows for specifying an
94 export, the use of this option is deprecated. It is preferred to
95 make use of a configuration file instead, the format of which is
96 defined in nbd-server(5).</para>
99 <title>OPTIONS</title>
105 <para>The ip address the server should listen on. This may
106 be an IPv4 address, an IPv6 address, or a hostname. In the
107 latter case, nbd-server will do a hostname lookup for the
108 name specified, and will listen on the first address that is
109 returned. For compatibility with past versions of
110 nbd-server, if an IPv4 address is specified, the @ sign that
111 serves as separator between the address and port may be
112 replaced by a colon.</para>
113 <para>If this parameter is not specified, nbd-server will
114 listen on all local addresses on both IPv4 and IPv6. To
115 limit to IPv4, specify the address as 0.0.0.0; to limit to
116 IPv6, specify it as ::.</para>
120 <term><option>port</option>
123 <para>The port the server should listen to. A valid port is
124 any number between 1 and 65536; if 0 is used, nbd-server
125 will listen on stdin (so that nbd-server can be ran from
130 <term><option>filename</option></term>
132 <para>The filename of the file that should be exported. This
133 can be any file, including "real" blockdevices (i.e. a file
134 from /dev). If the filename includes the literal string
135 "%s", then this %s will be substituded with the IP-address
136 of the client trying to connect.</para>
140 <term><option>size</option></term>
142 <para>The size of the block device at the client side. This
143 is especially useful in conjunction with the -m
145 <para>Can optionally be followed by one of K,k,M or
146 m, in which case the size will be multiplied by 1024 (K
147 or k) or 1048576 (M or m)</para>
151 <term><option>-r</option></term>
153 <para>Export the file read-only. If a client tries to write
154 to a read-only exported file, it will receive an error, but
155 the connection will stay up.</para>
159 <term><option>-m</option></term>
161 <para>Work with multiple files. This can be used to export
162 blockdevices that are larger than the maximum allowed
163 filesize on a given filesystem; i.e. when the filesystem
164 does not allow files larger than 2GB (which is true for
165 Linux 2.2 and below), you can use this option to store the
166 data in multiple files and export a larger filesystem, if
169 To use this option, you must create a number of files
170 with names in the format "name.X", where "name" is given as
171 the filename argument to nbd-server, and "X" is a number
172 starting by 0 and going up for each file.
175 Allowing more flexibility for this option is planned for
176 future versions.</para>
180 <term><option>-c</option></term>
182 <para>Copy on write. When this option is provided,
183 write-operations are not done to the exported file, but to a
184 separate file. This separate file is removed when the
185 connection is closed, which means that serving this way will
186 make nbd-server slow down (especially on large block devices
187 with lots of writes), and that after disconnecting and
188 reconnecting the client or the server, all changes are
193 <term><option>-C</option></term>
195 <para>Specify configuration file. The default configuration
196 file, if this parameter is not specified, is
197 <filename>$sysconfdir/nbd-server/config</filename>.</para>
198 <para>Note that the configuration file is always parsed and
199 the entries in the file used, even if an extra server is
200 specified on the command line. To disable the configuration
201 file entirely, either move it away or use the -C option to
202 point <command>nbd-server</command>(1) to a non-existing or
203 empty configuration file.</para>
204 <para>Also note that if an empty, incomplete, or invalid
205 configuration file is specified, nbd-server will produce a
206 warning about failure to parse the config file. If the
207 command line contains a fully specified configuration, this
208 warning is harmless and may be ignored.</para>
212 <term><option>-M</option></term>
214 <para>Specify the maximum number of opened connections. If this
215 parameter is not specified, no limit is set.</para>
219 <term><option>host list filename</option></term>
221 <para>This argument should contain a list of IP-addresses
222 for hosts that may connect to the server. Wildcards are
223 <emphasis>not</emphasis> allowed. If the file does not
224 exist, it is ignored (and any host can connect); If the file
225 does exist, but is empty, no host can connect. By default,
226 the name 'nbd_server.allow' is used, and looked for in the
227 current directory, unless nbd-server is compiled as a
228 daemon, in which case it is looked for in the
229 root-directory.</para>
233 <term><option>section name</option></term>
235 <para>If the <option>-o</option> argument is given on the
236 command line, then &dhpackage; will output a configuration
237 file section with this as the header that is functionally
238 equivalent to the other options specified on the command line,
239 and exit. This is useful for migrating pre-2.9 nbd-server
240 initscript configuration files to the new format.</para>
247 <title>EXAMPLES</title>
248 <para>Some examples of nbd-server usage:</para>
249 <itemizedlist mark="none">
251 <para>To export a file /export/nbd/exp-bl-dev on port 2000:</para>
252 <para><command>nbd-server 2000 /export/nbd/exp-bl-dev</command></para>
255 <para>To export a the same file read-only:</para>
256 <para><command>nbd-server 2000 /export/nbd/exp-bl-dev -r</command></para>
259 <para>To export the same file read-write, but make sure
260 changes are lost after restarting the client or the
262 <para><command>nbd-server 2000 /export/nbd/exp-bl-dev
268 <title>SEE ALSO</title>
270 <para>nbd-client (8), nbd-server (5)</para>
274 <title>AUTHOR</title>
275 <para>The NBD kernel module and the NBD tools were originally
276 written by Pavel Machek (pavel@ucw.cz)</para>
278 <para>The Linux kernel module is now maintained by Paul Clements
279 (Paul.Clements@steeleye.com), while the userland tools are
280 maintained by &dhusername; (&dhemail;)</para>
282 <para>On The Hurd there is a regular translator available to perform the
283 client side of the protocol, and the use of
284 <command>nbd-client</command> is not required. Please see the
285 relevant documentation for more information.</para>
287 <para>This manual page was written by &dhusername; (&dhemail;) for
288 the &debian; system (but may be used by others). Permission is
289 granted to copy, distribute and/or modify this document under
290 the terms of the <acronym>GNU</acronym> General Public License,
291 version 2, as published by the Free Software Foundation.</para>