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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>listenaddr</option></term>
135 <para>If this option is set, it should contain the local IP
136 address on which we should listen to
137 <command>nbd-client</command>(8) connections. If it is not
138 set, <command>nbd-server</command> will listen to all
139 local IPv4 and IPv6 addresses. To limit to IPv6, specify the
140 address as "::". To limit to IPv4, specify as "0.0.0.0". It
141 is not possible to specify more than one IP address
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>port</option></term>
190 The port on which to listen for new-style nbd-client
191 connections. If not specified, the IANA-assigned port of
197 <term><option>user</option></term>
203 The name of the user this server must run as. If this
204 parameter is not specified, then nbd-server will not
205 attempt to change its UID (so the UID it runs as will be
206 the user who starts nbd-server). If it is specified, then
207 nbd-server will change its UID after opening ports, but
208 before accepting connections or opening files.
215 <title>OPTIONS FOR EXPORT SECTIONS</title>
217 <!-- These are in alphabetical order, please keep it that way -->
220 <term><option>authfile</option></term>
223 Optional; string; default
224 <filename>$sysconfdir/nbd-server/allow</filename>.
227 The name of the authorization file for this export. This
228 file should contain one line per IP-address, or per
229 network (which must be specified in CIDR-style
230 <option><replaceable>network</replaceable>/<replaceable>masklen</replaceable></option>)
231 and must not contain empty lines. If the file
232 does not exist, everyone is allowed to connect. If the
233 file exists but is empty, nobody is allowed to
234 connect. Otherwise, <command>nbd-server</command> will
235 only allow clients to connect whose IP-adres is listed in
238 <para>Corresponds to the <option>-l</option> option on the
243 <term><option>copyonwrite</option></term>
249 Whether this is a copy-on-write export. If it is, then any
250 writes to this export will not be written to the master
251 file, but to a separate file which will be removed upon
252 disconnect. The result of using this option is that
253 nbd-server will be somewhat slower, and that any writes will
254 be lost upon disconnect.
256 <para>Corresponds to the <option>-c</option> option on the
261 <term><option>exportname</option></term>
263 <para>Required; string.</para>
265 The name of the file (or block device) that will be
266 exported. This must be a fully-qualified path and filename;
267 relative paths are not allowed.
270 Note that <command>nbd-server</command> will only try to
271 find and open the exported file when a client actually
272 connects; as a result, <command>nbd-server</command> must
273 be able to open and read this file
274 <emphasis>after</emphasis> changing to the user and group
275 that have been specified by use of the
276 <option>user</option> and <option>group</option> options;
277 also, <command>nbd-server</command> will only detect
278 errors in this option upon connection of a client.
280 <para>When specified on the command line, this should be the
286 <term><option>filesize</option></term>
288 <para>Optional; integer; default autodetected.</para>
290 Disable autodetection of file or block device size, and
291 forcibly specify a size. Sizes must be specified in
292 bytes. If the <option>multifile</option> option is in
293 effect, this option specifies the size of the
294 <emphasis>entire</emphasis> export, not of individual
297 <para>When specified on the command line, this should be the
303 <term><option>flush</option></term>
305 <para>Optional; boolean.</para>
306 <para>When this option is enabled,
307 <command>nbd-server</command> will inform the client that it
308 supports and desires to be sent flush requests when the
309 elevator layer receives them. Receipt of a flush request
310 will cause an fdatasync() (or, if the sync option is set,
311 an fsync()) on the backend storage. This increases
312 reliability in the case of an unclean shutdown at
313 the expense of a degradation of performance. This option
314 will have no effect unless supported by the client.
319 <term><option>fua</option></term>
321 <para>Optional; boolean.</para>
322 <para>When this option is enabled,
323 <command>nbd-server</command> will inform the client that it
324 supports and desires to be sent fua (force unit access) commands
325 when the elevator layer receives them. Receipt of a force unit
326 access command will cause the specified command to be synced
327 to backend storage using sync_file_range() if supported, or
328 fdatasync() otherwise. This increases
329 reliability in the case of an unclean shutdown at
330 the expense of a degradation of performance. This option
331 will have no effect unless supported by the client.
336 <term>listenaddr</term>
342 If the 'oldstyle' global parameter is specified, works
343 similarly to the global listenaddr parameter, but for the
344 individual port of this particular export. If the 'oldstyle'
345 parameter is not set, this parameter is ignored.
350 <term><option>maxconnections</option></term>
352 <para>Optional; integer</para>
354 If specified, then it limits the number of opened connections for
360 <term><option>multifile</option></term>
362 <para>Optional; boolean.</para>
364 If this option is set to true, then
365 <command>nbd-server</command> will search for files of the
367 <replaceable>exportname</replaceable>.<replaceable>integer</replaceable>,
368 with <replaceable>exportname</replaceable> being the
369 filename that would otherwise have been used (after name
370 transformation for virtualization, if any, has been
371 performed) and <replaceable>integer</replaceable> an
372 integer number, starting with 0 and ending when no more
376 The size of the individual files will be autodetected,
377 <emphasis>even</emphasis> if the <option>filesize</option>
378 option has been specified.
381 Corresponds to the <option>-m</option> option on the
387 <term><option>port</option></term>
389 <para>Required if 'oldstyle' global parameter is set; integer.</para>
391 The port on which this export is to be served using the
392 old-style handshake protocol.
395 This parameter only makes sense when the 'oldstyle'
396 parameter is set to true in the 'generic' section. If that
397 parameter is not set, but this parameter is found in an
398 export section, then nbd-server will issue a warning upon
399 startup but should otherwise continue to function correctly.
402 It is not possible to combine multiple exports on the same
403 port using the old style handshake. Please use the new style
404 handshake for that purpose.
407 When specified on the command line, this should be the
413 <term><option>postrun</option></term>
415 <para>Optional; string</para>
417 If specified, then it is assumed to be a command
418 that will be ran when a client has
419 disconnected. This can be useful to clean up
420 whatever <option>prerun</option> has set up, to log
421 something, or similar.
424 If the literal string '%s' is present in the
425 command, it will be replaced by the file name that
426 has just been closed.
429 In contrast to the <option>prerun</option> option,
430 the exit state of <option>postrun</option> is
431 <emphasis>ignored</emphasis>.
436 <term><option>prerun</option></term>
438 <para>Optional; string</para>
440 If specified, then this command will be ran after a
441 client has connected to the server (and has been
442 accepted), but before the server starts serving. If
443 the command contains the literal string '%s', then
444 this string will be replaced by the filename of the
445 file which nbd-server wants to export.
448 This is useful to create export files on the fly, or
449 to verify that a file can be used for export, to
450 write something to a log file, or similar.
453 If the command runs with a non-zero exit status,
454 then nbd-server will assume the export will fail,
455 and refuse to serve it.
460 <term><option>readonly</option></term>
462 <para>Optional; boolean.</para>
464 Disallow writes to the device. If this option is
465 specified, <command>nbd-server</command> will issue an
466 error to any client that tries to write to the device.
469 Use of this option in conjunction with
470 <option>copyonwrite</option> is possible, but silly.
472 <para>Corresponds to the <option>-r</option> option on the
477 <term><option>rotational</option></term>
479 <para>Optional; boolean.</para>
480 <para>When this option is enabled,
481 <command>nbd-server</command> will inform the client that
482 it would prefer it to send requests in elevator (i.e., optimized) order, perhaps
483 because it has a backing store and no local elevator. By
484 default, the client uses QUEUE_FLAG_NONROT, which effectively
485 restricts the function of the elevator to block merges. By
486 specifying this flag on the server, the client will not use
487 QUEUE_FLAG_NONROT, meaning the client elevator will perform
488 normal elevator ordering of I/O requests. Note that even when
489 the backing store is on rotating media, it is not normally
490 necessary to specify this flag, as the server's elevator
491 algorithm will be used. This flag is only required where
492 the server will not be using an elevator algorithm or where
493 the elevator algorithm is effectively neutered (e.g. with
494 the sync option set). This option will have no effect unless
495 supported by the client.
500 <term><option>sdp</option></term>
502 <para>Optional; boolean.</para>
504 When this option is enabled, <command>nbd-server</command>
505 will use the Socket Direct Protocol (SDP) to serve the
506 export, rather than just IP. This is faster, but requires
507 special hardware (usually something like InfiniBand) and
508 support in the kernel.
511 Additionally, support for this option must be enabled at
512 compile time, using the <option>--enable-sdp</option> option
513 to the <command>configure</command> script. If this option
514 is found in a configuration file and
515 <command>nbd-server</command> does not have support for SDP,
516 then <command>nbd-server</command> will exit with an error
522 <term><option>sparse_cow</option></term>
524 <para>Optional; boolean.</para>
526 When this option is enabled, <command>nbd-server</command>
527 will use sparse files to implement the copy-on-write
528 option; such files take up less space then they appear to,
529 which allows <command>nbd-server</command> to handle the
530 file as if it was just as large as the block device it's
534 If this option is disabled, <command>nbd-server</command>
535 will map every newly written block to the end of the
536 copy-on-write file, which means that
537 <command>nbd-server</command> will have to lseek(2) to the
538 right position after every 4096-byte block.
541 Using this option may be faster when much is being written
547 <term><option>sync</option></term>
549 <para>Optional; boolean.</para>
550 <para>When this option is enabled,
551 <command>nbd-server</command> will call an fsync() after every
552 write to the backend storage. Calling fsync() increases
553 reliability in case of an unclean shutdown of nbd-server; but,
554 depending on the file system used on the nbd-server side, may
555 degrade performance. The use of this option isn't always
556 necessary; e.g., on ext3 filesystems, it is recommended that
557 it is <emphasis>not</emphasis> enabled, since it seriously
558 reduces performance on ext3 filesystems while not
559 importantly impacting reliability.
564 <term><option>timeout</option></term>
566 <para>Optional; integer; default 0</para>
568 How many seconds a connection may be idle for this
569 export. When a connection is idle for a longer time,
570 <command>nbd-server</command> will forcibly disconnect the
571 connection. If you specify 0 (the default), then a
572 connection may be idle forever.
575 Corresponds to the <option>-a</option> option on the
581 <term><option>transactionlog</option></term>
583 <para>Optional; string</para>
585 If specified, then this pathname is used to generate a transaction
586 log. A transaction log is a binary file consisting of the requests
587 sent to and the replies received by the server, but excluding any
588 data (so, for a write command, it records the offset and length
589 of the write but not the data written). It is therefore relatively
590 safe to distribute to a third party. Note that the transaction log
591 does not include the negotiation sequence. Transaction logs are
592 mainly useful for debugging. The program
593 <emphasis>nbd-tester-client</emphasis> distributed with the source
594 to this program can reply a transaction log against a server and
595 perform a data integrity test. Note that the transaction log is
596 written to for every client opened. If it is necessary to maintain
597 separate transaction logs for each client, the
598 <emphasis>prerun</emphasis> script should rename the transaction log
599 (which will just have been opened in order to avoid transaction logs
600 overwriting eachother. This action should be race-free.
605 <term><option>virtstyle</option></term>
607 <para>Optional; string; default "ipliteral"</para>
609 Defines the style of virtualization. Virtualization allows
610 one to create one export that will serve a different file
611 depending on the IP address that is connecting. When
612 virtualization is active, the
613 <replaceable>exportname</replaceable> parameter needs to
614 contain the string '%s'; this will then be replaced by the
615 IP address of the client connecting, in accordance with the
616 option selected here. The result of this transformation is
617 then used as the filename to be opened.
620 There are four types of virtualization that
621 <command>nbd-server</command> supports:
625 <term><option>none</option></term>
628 No virtualization. Will attempt to open the filename
629 as it was written, even if it contains '%s' in the
635 <term><option>ipliteral</option></term>
638 The %s is replaced by the IP address of the connecting
639 host is used as-is. For IPv4, this is done in
640 dotted-quad notation; for IPv6, in hexadecimal form
641 with leading zeros omitted.
644 As an example, if a client connects from 192.168.1.100
645 and <option>exportname</option> is specified as
646 <filename>/export/%s</filename>, then nbd-server will
648 <filename>/export/192.168.1.100</filename>. For IPv6,
649 with a client connecting from 2001:6f8:32f::39, the
651 <filename>/export/2001:6f8:32f:0:0:0:0:39</filename>
656 <term><option>iphash</option></term>
659 Same as above, except that
660 <command>nbd-server</command> will replace the dots
661 in the IP address by forward slashes ('/'); in the
662 same example, <command>nbd-server</command> would
663 open <filename>/export/192/168/1/100</filename>
667 Since there are no dots in most IPv6 addresses, the
668 effect of using this option when IPv6 is in use is
669 indistinguishable from the ipliteral option. It was
670 thought that having to create an eight-deep directory
671 structure would not be as useful.
676 <term><option>cidrhash</option></term>
679 This option requires one to add a space and a number
680 after it. <command>nbd-server</command> will use the
681 number as a network mask in CIDR style, and use that
682 as a hash cutoff point. In the above example, if
683 <option>virtstyle</option> has been specified as
684 <constant>cidrhash 16</constant>, then
685 <command>nbd-server</command> will try to open
686 <filename>/export/192.168.0.0/192.168.1.100</filename>;
687 if <option>virtstyle</option> were specified as
688 <constant>cidrhash 26</constant>, then
689 <command>nbd-server</command> will try to open
690 <filename>/export/192.168.1.64/192.168.1.100</filename>.
692 <para>For IPv6, in the above example, with
693 <constant>cidrhash 42</constant>, the filename would
695 <filename>/export/2001:32f:6c0:0:0:0:0:0/2001:32f:6f8:0:0:0:0:39</filename>.</para>
705 <title>SEE ALSO</title>
707 <para>nbd-server (1), nbd-client (8), nbd-trdump (8)</para>
712 <title>AUTHOR</title>
713 <para>The NBD kernel module and the NBD tools were originally
714 written by Pavel Machek (pavel@ucw.cz)</para>
716 <para>The Linux kernel module is now maintained by Paul Clements
717 (Paul.Clements@steeleye.com), while the userland tools are
718 maintained by &dhusername; (&dhemail;)</para>
720 <para>On The Hurd there is a regular translator available to perform the
721 client side of the protocol, and the use of
722 <command>nbd-client</command> is not required. Please see the
723 relevant documentation for more information.</para>
725 <para>This manual page was written by &dhusername; (&dhemail;) for
726 the &debian; system (but may be used by others). Permission is
727 granted to copy, distribute and/or modify this document under
728 the terms of the <acronym>GNU</acronym> General Public License,
729 version 2, as published by the Free Software Foundation.</para>
733 <title>EXAMPLES</title>
734 <para>A simple <command>nbd-server</command> configuration file
735 would look like this:</para>
739 exportname = /export/blkdev
742 <para>For increased security, one might want to create an
743 authorization file, and set the UID and GID to run as:</para>
749 exportname = /export/blkdev
751 authfile = $sysconfdir/nbd-server/allow
753 <para>With $sysconfdir/nbd-server/allow containing the following:</para>
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