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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: 2006-10-18 15:01:57 +0200 (wo, 18 okt 2006) $</date>">
17 <!-- SECTION should be 1-8, maybe w/ subsection other parameters are
18 allowed: see man(7), man(1). -->
19 <!ENTITY dhsection "<manvolnum>5</manvolnum>">
20 <!ENTITY dhemail "<email>wouter@debian.org</email>">
21 <!ENTITY dhusername "Wouter Verhelst">
22 <!ENTITY dhucpackage "<refentrytitle>NBD-SERVER</refentrytitle>">
23 <!ENTITY dhpackage "$sysconfdir/nbd-server/config">
25 <!ENTITY debian "<productname>Debian GNU/Linux</productname>">
26 <!ENTITY gnu "<acronym>GNU</acronym>">
40 <holder>&dhusername;</holder>
50 <refname>&dhpackage;</refname>
52 <refpurpose>configuration file for nbd-server</refpurpose>
56 <command>&dhpackage; </command>
61 <title>DESCRIPTION</title>
63 <para>This file allows to configure the nbd-server.</para>
66 <filename>$sysconfdir/nbd-server/config</filename> is the default
67 configuration file, this can be varied with the <option>-C</option>
68 option to <command>nbd-server</command>(1).
71 The configuration file consists of section header lines, comment
72 lines, and option lines.
75 A section header is a unique name that
76 is enclosed in square brackets ("[" and "]"). A section header
77 denotes the beginning of a section; a section continues until
78 the next section or the end of the file, whichever is first. The
79 first section in the configuration file must be called
80 <option>generic</option>, and is used for global options that
81 apply to more than one export. This section must always be
82 present, even if it holds no options. Every other section
83 defines one export; the names of these sections are not
84 important, except that you should take care to make sure that
85 each section name is unique. The section name is used as the name
86 for the export in case the client connects with a name rather than
87 a port to specify an export, and must therefore be unique.
90 A comment line is a line that starts with optional whitespace,
91 followed by a pound sign ("#"), and continues until the end of
92 the line. Comments may <emphasis>not</emphasis> be used on
93 option lines or section header lines.
96 An option line is a line that starts with an option name,
97 followed by an equals sign ("="), followed by the option
98 value. An option can be of type string, of type integer, or of
99 type boolean. The value of a boolean option can be denoted with
100 either true or false (so not yes, no, on, off, 1, or 0). All
101 booleans default to false unless specified otherwise. No value
102 may be quoted; always enter it directly. For a string option,
103 leading whitespace is stripped (but trailing whitespace is not).
108 <title>OPTIONS FOR SECTION [generic]</title>
110 <!-- These are in alphabetical order, please keep it that way -->
113 <term><option>group</option></term>
119 The name of the group this server must run as. If this
120 parameter is not specified, then nbd-server will not
121 attempt to change its GID (so the GID it runs as will be
122 the primary group of the user who starts nbd-server). If
123 it is specified, then nbd-server will change its GID after
124 opening ports, but before accepting connections or opening
130 <term><option>user</option></term>
136 The name of the user this server must run as. If this
137 parameter is not specified, then nbd-server will not
138 attempt to change its UID (so the UID it runs as will be
139 the user who starts nbd-server). If it is specified, then
140 nbd-server will change its UID after opening ports, but
141 before accepting connections or opening files.
146 <term><option>oldstyle</option></term>
152 If this option is set to true, nbd-server will export all
153 exports on a separate port with the old (pre-2.9.17)
154 handshake protocol. In that case, the 'port' option for
155 individual exports is mandatory.
158 If the option is set to false, the 'port' option for
159 individual exports is optional (and will be ignored if
160 specified). The server will only export devices on the
164 For upgrades from pre-2.9.17 versions of nbd, it may be
165 appropriate to enable the oldstyle parameter until all
166 clients have been converted to using name-based exports.
169 Note that exports specified on the command line will
170 always use the old handshake protocol and will not allow
174 Also note that even if this parameter is set to true, all
175 exports will also be made available using the new handshake
176 protocol; it is not possible to switch that off. The reason
177 for this is that the old style protocol will eventually be
178 deprecated, and this option is only available to allow for
184 <term><option>listenaddr</option></term>
189 <para>If this option is set, it should contain the local IP
190 address on which we should listen to
191 <command>nbd-client</command>(8) connections. If it is not
192 set, <command>nbd-server</command> will listen to all
193 local IPv4 and IPv6 addresses. To limit to IPv6, specify the
194 address as "::". To limit to IPv4, specify as "0.0.0.0". It
195 is not possible to specify more than one IP address
202 <title>OPTIONS FOR EXPORT SECTIONS</title>
204 <!-- These are in alphabetical order, please keep it that way -->
207 <term><option>authfile</option></term>
210 Optional; string; default
211 <filename>$sysconfdir/nbd-server/allow</filename>.
214 The name of the authorization file for this export. This
215 file should contain one line per IP-address, or per
216 network (which must be specified in CIDR-style
217 <option><replaceable>network</replaceable>/<replaceable>masklen</replaceable></option>)
218 and must not contain empty lines. If the file
219 does not exist, everyone is allowed to connect. If the
220 file exists but is empty, nobody is allowed to
221 connect. Otherwise, <command>nbd-server</command> will
222 only allow clients to connect whose IP-adres is listed in
225 <para>Corresponds to the <option>-l</option> option on the
230 <term><option>copyonwrite</option></term>
236 Whether this is a copy-on-write export. If it is, then any
237 writes to this export will not be written to the master
238 file, but to a separate file which will be removed upon
239 disconnect. The result of using this option is that
240 nbd-server will be somewhat slower, and that any writes will
241 be lost upon disconnect.
243 <para>Corresponds to the <option>-c</option> option on the
248 <term><option>exportname</option></term>
250 <para>Required; string.</para>
252 The name of the file (or block device) that will be
253 exported. This must be a fully-qualified path and filename;
254 relative paths are not allowed.
257 Note that <command>nbd-server</command> will only try to
258 find and open the exported file when a client actually
259 connects; as a result, <command>nbd-server</command> must
260 be able to open and read this file
261 <emphasis>after</emphasis> changing to the user and group
262 that have been specified by use of the
263 <option>user</option> and <option>group</option> options;
264 also, <command>nbd-server</command> will only detect
265 errors in this option upon connection of a client.
267 <para>When specified on the command line, this should be the
273 <term><option>filesize</option></term>
275 <para>Optional; integer; default autodetected.</para>
277 Disable autodetection of file or block device size, and
278 forcibly specify a size. Sizes must be specified in
279 bytes. If the <option>multifile</option> option is in
280 effect, this option specifies the size of the
281 <emphasis>entire</emphasis> export, not of individual
284 <para>When specified on the command line, this should be the
290 <term>listenaddr</term>
296 If the 'oldstyle' global parameter is specified, works
297 similarly to the global listenaddr parameter, but for the
298 individual port of this particular export. If the 'oldstyle'
299 parameter is not set, this parameter is ignored.
304 <term><option>multifile</option></term>
306 <para>Optional; boolean.</para>
308 If this option is set to true, then
309 <command>nbd-server</command> will search for files of the
311 <replaceable>exportname</replaceable>.<replaceable>integer</replaceable>,
312 with <replaceable>exportname</replaceable> being the
313 filename that would otherwise have been used (after name
314 transformation for virtualization, if any, has been
315 performed) and <replaceable>integer</replaceable> an
316 integer number, starting with 0 and ending when no more
320 The size of the individual files will be autodetected,
321 <emphasis>even</emphasis> if the <option>filesize</option>
322 option has been specified.
325 Corresponds to the <option>-m</option> option on the
331 <term><option>port</option></term>
333 <para>Required if 'oldstyle' global parameter is set; integer.</para>
335 The port on which this export is to be served using the
336 old-style handshake protocol.
339 This parameter only makes sense when the 'oldstyle'
340 parameter is set to true in the 'generic' section. If that
341 parameter is not set, but this parameter is found in an
342 export section, then nbd-server will issue a warning upon
343 startup but should otherwise continue to function correctly.
346 It is not possible to combine multiple exports on the same
347 port using the old style handshake. Please use the new style
348 handshake for that purpose.
351 When specified on the command line, this should be the
357 <term><option>readonly</option></term>
359 <para>Optional; boolean.</para>
361 Disallow writes to the device. If this option is
362 specified, <command>nbd-server</command> will issue an
363 error to any client that tries to write to the device.
366 Use of this option in conjunction with
367 <option>copyonwrite</option> is possible, but silly.
369 <para>Corresponds to the <option>-r</option> option on the
374 <term><option>sdp</option></term>
376 <para>Optional; boolean.</para>
378 When this option is enabled, <command>nbd-server</command>
379 will use the Socket Direct Protocol (SDP) to serve the
380 export, rather than just IP. This is faster, but requires
381 special hardware (usually something like InfiniBand) and
382 support in the kernel.
385 Additionally, support for this option must be enabled at
386 compile time, using the <option>--enable-sdp</option> option
387 to the <command>configure</command> script. If this option
388 is found in a configuration file and
389 <command>nbd-server</command> does not have support for SDP,
390 then <command>nbd-server</command> will exit with an error
396 <term><option>sync</option></term>
398 <para>Optional; boolean.</para>
399 <para>When this option is enabled,
400 <command>nbd-server</command> will call an fsync() after every
401 write to the backend storage. Calling fsync() increases
402 reliability in case of an unclean shutdown of nbd-server; but,
403 depending on the file system used on the nbd-server side, may
404 degrade performance. The use of this option isn't always
405 necessary; e.g., on ext3 filesystems, it is recommended that
406 it is <emphasis>not</emphasis> enabled, since it seriously
407 reduces performance on ext3 filesystems while not
408 importantly impacting reliability.
413 <term><option>flush</option></term>
415 <para>Optional; boolean.</para>
416 <para>When this option is enabled,
417 <command>nbd-server</command> will inform the client that it
418 supports and desires to be sent flush requests when the
419 elevator layer receives them. Receipt of a flush request
420 will cause an fdatasync() (or, if the sync option is set,
421 an fsync()) on the backend storage. This increases
422 reliability in the case of an unclean shutdown at
423 the expense of a degradation of performance. The default
424 state is disabled. This option will have no effect unless
425 supported by the client.
430 <term><option>fua</option></term>
432 <para>Optional; boolean.</para>
433 <para>When this option is enabled,
434 <command>nbd-server</command> will inform the client that it
435 supports and desires to be sent fua (force unit access) commands
436 when the elevator layer receives them. Receipt of a force unit
437 access command will cause the specified command to be synced
438 to backend storage using sync_file_range() if supported, or
439 fdatasync() otherwise. This increases
440 reliability in the case of an unclean shutdown at
441 the expense of a degradation of performance. The default
442 state is disabled. This option will have no effect unless
443 supported by the client.
448 <term><option>rotational</option></term>
450 <para>Optional; boolean.</para>
451 <para>When this option is enabled,
452 <command>nbd-server</command> will inform the client that it
453 it would prefer it to send requests in elevator order, perhaps
454 because it has a backing store and no local elevator. By
455 default, the client uses QUEUE_FLAG_NONROT, which effectively
456 restricts the function of the elevator to block merges. By
457 specifying this flag on the server, the client will not use
458 QUEUE_FLAG_NONROT, meaning the client elevator will perform
459 normal elevator ordering of I/O requests. Note that even when
460 the backing store is on rotating media, it is not normally
461 necessary to specify this flag, as the server's elevator
462 algorithm will be used. This flag is only required where
463 the server will not be using an elevator algorithm or where
464 the elevator algorithm is effectively neutered (e.g. with
465 the sync option set). This option will have no effect unless
466 supported by the client.
471 <term><option>sparse_cow</option></term>
473 <para>Optional; boolean.</para>
475 When this option is enabled, <command>nbd-server</command>
476 will use sparse files to implement the copy-on-write
477 option; such files take up less space then they appear to,
478 which allows <command>nbd-server</command> to handle the
479 file as if it was just as large as the block device it's
483 If this option is disabled, <command>nbd-server</command>
484 will map every newly written block to the end of the
485 copy-on-write file, which means that
486 <command>nbd-server</command> will have to lseek(2) to the
487 right position after every 4096-byte block.
490 Using this option may be faster when much is being written
496 <term><option>timeout</option></term>
498 <para>Optional; integer; default 0</para>
500 How many seconds a connection may be idle for this
501 export. When a connection is idle for a longer time,
502 <command>nbd-server</command> will forcibly disconnect the
503 connection. If you specify 0 (the default), then a
504 connection may be idle forever.
507 Corresponds to the <option>-a</option> option on the
513 <term><option>virtstyle</option></term>
515 <para>Optional; string; default "ipliteral"</para>
517 Defines the style of virtualization. Virtualization allows
518 one to create one export that will serve a different file
519 depending on the IP address that is connecting. When
520 virtualization is active, the
521 <replaceable>exportname</replaceable> parameter needs to
522 contain the string '%s'; this will then be replaced by the
523 IP address of the client connecting, in accordance with the
524 option selected here. The result of this transformation is
525 then used as the filename to be opened.
528 There are four types of virtualization that
529 <command>nbd-server</command> supports:
533 <term><option>none</option></term>
536 No virtualization. Will attempt to open the filename
537 as it was written, even if it contains '%s' in the
543 <term><option>ipliteral</option></term>
546 The %s is replaced by the IP address of the connecting
547 host is used as-is. For IPv4, this is done in
548 dotted-quad notation; for IPv6, in hexadecimal form
549 with leading zeros omitted.
552 As an example, if a client connects from 192.168.1.100
553 and <option>exportname</option> is specified as
554 <filename>/export/%s</filename>, then nbd-server will
556 <filename>/export/192.168.1.100</filename>. For IPv6,
557 with a client connecting from 2001:6f8:32f::39, the
559 <filename>/export/2001:6f8:32f:0:0:0:0:39</filename>
564 <term><option>iphash</option></term>
567 Same as above, except that
568 <command>nbd-server</command> will replace the dots
569 in the IP address by forward slashes ('/'); in the
570 same example, <command>nbd-server</command> would
571 open <filename>/export/192/168/1/100</filename>
575 Since there are no dots in most IPv6 addresses, the
576 effect of using this option when IPv6 is in use is
577 indistinguishable from the ipliteral option. It was
578 thought that having to create an eight-deep directory
579 structure would not be as useful.
584 <term><option>cidrhash</option></term>
587 This option requires one to add a space and a number
588 after it. <command>nbd-server</command> will use the
589 number as a network mask in CIDR style, and use that
590 as a hash cutoff point. In the above example, if
591 <option>virtstyle</option> has been specified as
592 <constant>cidrhash 16</constant>, then
593 <command>nbd-server</command> will try to open
594 <filename>/export/192.168.0.0/192.168.1.100</filename>;
595 if <option>virtstyle</option> were specified as
596 <constant>cidrhash 26</constant>, then
597 <command>nbd-server</command> will try to open
598 <filename>/export/192.168.1.64/192.168.1.100</filename>.
600 <para>For IPv6, in the above example, with
601 <constant>cidrhash 42</constant>, the filename would
603 <filename>/export/2001:32f:6c0:0:0:0:0:0/2001:32f:6f8:0:0:0:0:39</filename>.</para>
610 <term><option>prerun</option></term>
612 <para>Optional; string</para>
614 If specified, then this command will be ran after a
615 client has connected to the server (and has been
616 accepted), but before the server starts serving. If
617 the command contains the literal string '%s', then
618 this string will be replaced by the filename of the
619 file which nbd-server wants to export.
622 This is useful to create export files on the fly, or
623 to verify that a file can be used for export, to
624 write something to a log file, or similar.
627 If the command runs with a non-zero exit status,
628 then nbd-server will assume the export will fail,
629 and refuse to serve it.
634 <term><option>postrun</option></term>
636 <para>Optional; string</para>
638 If specified, then it is assumed to be a command
639 that will be ran when a client has
640 disconnected. This can be useful to clean up
641 whatever <option>prerun</option> has set up, to log
642 something, or similar.
645 If the literal string '%s' is present in the
646 command, it will be replaced by the file name that
647 has just been closed.
650 In contrast to the <option>prerun</option> option,
651 the exit state of <option>postrun</option> is
652 <emphasis>ignored</emphasis>.
657 <term><option>maxconnections</option></term>
659 <para>Optional; integer</para>
661 If specified, then it limits the number of opened connections for
667 <term><option>transactionlog</option></term>
669 <para>Optional; string</para>
671 If specified, then this pathname is used to generate a transaction
672 log. A transaction log is a binary file consisting of the requests
673 sent to and the replies received by the server, but excluding any
674 data (so, for a write command, it records the offset and length
675 of the write but not the data written). It is therefore relatively
676 safe to distribute to a third party. Note that the transaction log
677 does not include the negotiation sequence. Transaction logs are
678 mainly useful for debugging. The program
679 <emphasis>nbd-tester-client</emphasis> distributed with the source
680 to this program can reply a transaction log against a server and
681 perform a data integrity test. Note that the transaction log is
682 written to for every client opened. If it is necessary to maintain
683 separate transaction logs for each client, the
684 <emphasis>prerun</emphasis> script should rename the transaction log
685 (which will just have been opened in order to avoid transaction logs
686 overwriting eachother. This action should be race-free.
694 <title>SEE ALSO</title>
696 <para>nbd-server (1), nbd-client (8)</para>
701 <title>AUTHOR</title>
702 <para>The NBD kernel module and the NBD tools were originally
703 written by Pavel Machek (pavel@ucw.cz)</para>
705 <para>The Linux kernel module is now maintained by Paul Clements
706 (Paul.Clements@steeleye.com), while the userland tools are
707 maintained by &dhusername; (&dhemail;)</para>
709 <para>On The Hurd there is a regular translator available to perform the
710 client side of the protocol, and the use of
711 <command>nbd-client</command> is not required. Please see the
712 relevant documentation for more information.</para>
714 <para>This manual page was written by &dhusername; (&dhemail;) for
715 the &debian; system (but may be used by others). Permission is
716 granted to copy, distribute and/or modify this document under
717 the terms of the <acronym>GNU</acronym> General Public License,
718 version 2, as published by the Free Software Foundation.</para>
722 <title>EXAMPLES</title>
723 <para>A simple <command>nbd-server</command> configuration file
724 would look like this:</para>
728 exportname = /export/blkdev
731 <para>For increased security, one might want to create an
732 authorization file, and set the UID and GID to run as:</para>
738 exportname = /export/blkdev
740 authfile = $sysconfdir/nbd-server/allow
742 <para>With $sysconfdir/nbd-server/allow containing the following:</para>
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