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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. This option
424 will have no effect unless supported by the client.
429 <term><option>fua</option></term>
431 <para>Optional; boolean.</para>
432 <para>When this option is enabled,
433 <command>nbd-server</command> will inform the client that it
434 supports and desires to be sent fua (force unit access) commands
435 when the elevator layer receives them. Receipt of a force unit
436 access command will cause the specified command to be synced
437 to backend storage using sync_file_range() if supported, or
438 fdatasync() otherwise. This increases
439 reliability in the case of an unclean shutdown at
440 the expense of a degradation of performance. This option
441 will have no effect unless supported by the client.
446 <term><option>rotational</option></term>
448 <para>Optional; boolean.</para>
449 <para>When this option is enabled,
450 <command>nbd-server</command> will inform the client that
451 it would prefer it to send requests in elevator order, perhaps
452 because it has a backing store and no local elevator. By
453 default, the client uses QUEUE_FLAG_NONROT, which effectively
454 restricts the function of the elevator to block merges. By
455 specifying this flag on the server, the client will not use
456 QUEUE_FLAG_NONROT, meaning the client elevator will perform
457 normal elevator ordering of I/O requests. Note that even when
458 the backing store is on rotating media, it is not normally
459 necessary to specify this flag, as the server's elevator
460 algorithm will be used. This flag is only required where
461 the server will not be using an elevator algorithm or where
462 the elevator algorithm is effectively neutered (e.g. with
463 the sync option set). This option will have no effect unless
464 supported by the client.
469 <term><option>sparse_cow</option></term>
471 <para>Optional; boolean.</para>
473 When this option is enabled, <command>nbd-server</command>
474 will use sparse files to implement the copy-on-write
475 option; such files take up less space then they appear to,
476 which allows <command>nbd-server</command> to handle the
477 file as if it was just as large as the block device it's
481 If this option is disabled, <command>nbd-server</command>
482 will map every newly written block to the end of the
483 copy-on-write file, which means that
484 <command>nbd-server</command> will have to lseek(2) to the
485 right position after every 4096-byte block.
488 Using this option may be faster when much is being written
494 <term><option>timeout</option></term>
496 <para>Optional; integer; default 0</para>
498 How many seconds a connection may be idle for this
499 export. When a connection is idle for a longer time,
500 <command>nbd-server</command> will forcibly disconnect the
501 connection. If you specify 0 (the default), then a
502 connection may be idle forever.
505 Corresponds to the <option>-a</option> option on the
511 <term><option>virtstyle</option></term>
513 <para>Optional; string; default "ipliteral"</para>
515 Defines the style of virtualization. Virtualization allows
516 one to create one export that will serve a different file
517 depending on the IP address that is connecting. When
518 virtualization is active, the
519 <replaceable>exportname</replaceable> parameter needs to
520 contain the string '%s'; this will then be replaced by the
521 IP address of the client connecting, in accordance with the
522 option selected here. The result of this transformation is
523 then used as the filename to be opened.
526 There are four types of virtualization that
527 <command>nbd-server</command> supports:
531 <term><option>none</option></term>
534 No virtualization. Will attempt to open the filename
535 as it was written, even if it contains '%s' in the
541 <term><option>ipliteral</option></term>
544 The %s is replaced by the IP address of the connecting
545 host is used as-is. For IPv4, this is done in
546 dotted-quad notation; for IPv6, in hexadecimal form
547 with leading zeros omitted.
550 As an example, if a client connects from 192.168.1.100
551 and <option>exportname</option> is specified as
552 <filename>/export/%s</filename>, then nbd-server will
554 <filename>/export/192.168.1.100</filename>. For IPv6,
555 with a client connecting from 2001:6f8:32f::39, the
557 <filename>/export/2001:6f8:32f:0:0:0:0:39</filename>
562 <term><option>iphash</option></term>
565 Same as above, except that
566 <command>nbd-server</command> will replace the dots
567 in the IP address by forward slashes ('/'); in the
568 same example, <command>nbd-server</command> would
569 open <filename>/export/192/168/1/100</filename>
573 Since there are no dots in most IPv6 addresses, the
574 effect of using this option when IPv6 is in use is
575 indistinguishable from the ipliteral option. It was
576 thought that having to create an eight-deep directory
577 structure would not be as useful.
582 <term><option>cidrhash</option></term>
585 This option requires one to add a space and a number
586 after it. <command>nbd-server</command> will use the
587 number as a network mask in CIDR style, and use that
588 as a hash cutoff point. In the above example, if
589 <option>virtstyle</option> has been specified as
590 <constant>cidrhash 16</constant>, then
591 <command>nbd-server</command> will try to open
592 <filename>/export/192.168.0.0/192.168.1.100</filename>;
593 if <option>virtstyle</option> were specified as
594 <constant>cidrhash 26</constant>, then
595 <command>nbd-server</command> will try to open
596 <filename>/export/192.168.1.64/192.168.1.100</filename>.
598 <para>For IPv6, in the above example, with
599 <constant>cidrhash 42</constant>, the filename would
601 <filename>/export/2001:32f:6c0:0:0:0:0:0/2001:32f:6f8:0:0:0:0:39</filename>.</para>
608 <term><option>prerun</option></term>
610 <para>Optional; string</para>
612 If specified, then this command will be ran after a
613 client has connected to the server (and has been
614 accepted), but before the server starts serving. If
615 the command contains the literal string '%s', then
616 this string will be replaced by the filename of the
617 file which nbd-server wants to export.
620 This is useful to create export files on the fly, or
621 to verify that a file can be used for export, to
622 write something to a log file, or similar.
625 If the command runs with a non-zero exit status,
626 then nbd-server will assume the export will fail,
627 and refuse to serve it.
632 <term><option>postrun</option></term>
634 <para>Optional; string</para>
636 If specified, then it is assumed to be a command
637 that will be ran when a client has
638 disconnected. This can be useful to clean up
639 whatever <option>prerun</option> has set up, to log
640 something, or similar.
643 If the literal string '%s' is present in the
644 command, it will be replaced by the file name that
645 has just been closed.
648 In contrast to the <option>prerun</option> option,
649 the exit state of <option>postrun</option> is
650 <emphasis>ignored</emphasis>.
655 <term><option>maxconnections</option></term>
657 <para>Optional; integer</para>
659 If specified, then it limits the number of opened connections for
665 <term><option>transactionlog</option></term>
667 <para>Optional; string</para>
669 If specified, then this pathname is used to generate a transaction
670 log. A transaction log is a binary file consisting of the requests
671 sent to and the replies received by the server, but excluding any
672 data (so, for a write command, it records the offset and length
673 of the write but not the data written). It is therefore relatively
674 safe to distribute to a third party. Note that the transaction log
675 does not include the negotiation sequence. Transaction logs are
676 mainly useful for debugging. The program
677 <emphasis>nbd-tester-client</emphasis> distributed with the source
678 to this program can reply a transaction log against a server and
679 perform a data integrity test. Note that the transaction log is
680 written to for every client opened. If it is necessary to maintain
681 separate transaction logs for each client, the
682 <emphasis>prerun</emphasis> script should rename the transaction log
683 (which will just have been opened in order to avoid transaction logs
684 overwriting eachother. This action should be race-free.
692 <title>SEE ALSO</title>
694 <para>nbd-server (1), nbd-client (8)</para>
699 <title>AUTHOR</title>
700 <para>The NBD kernel module and the NBD tools were originally
701 written by Pavel Machek (pavel@ucw.cz)</para>
703 <para>The Linux kernel module is now maintained by Paul Clements
704 (Paul.Clements@steeleye.com), while the userland tools are
705 maintained by &dhusername; (&dhemail;)</para>
707 <para>On The Hurd there is a regular translator available to perform the
708 client side of the protocol, and the use of
709 <command>nbd-client</command> is not required. Please see the
710 relevant documentation for more information.</para>
712 <para>This manual page was written by &dhusername; (&dhemail;) for
713 the &debian; system (but may be used by others). Permission is
714 granted to copy, distribute and/or modify this document under
715 the terms of the <acronym>GNU</acronym> General Public License,
716 version 2, as published by the Free Software Foundation.</para>
720 <title>EXAMPLES</title>
721 <para>A simple <command>nbd-server</command> configuration file
722 would look like this:</para>
726 exportname = /export/blkdev
729 <para>For increased security, one might want to create an
730 authorization file, and set the UID and GID to run as:</para>
736 exportname = /export/blkdev
738 authfile = $sysconfdir/nbd-server/allow
740 <para>With $sysconfdir/nbd-server/allow containing the following:</para>
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