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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. If used in conjunction with
268 the <option>temporary</option>, this specifies a template
269 for the temporary file concerned, and thus can be used
270 to control the directory it is created in. If the file
271 does not exist, but <option>filesize</option> is set, then
272 the file will be created.
275 Note that <command>nbd-server</command> will only try to
276 find and open the exported file when a client actually
277 connects; as a result, <command>nbd-server</command> must
278 be able to open and read this file
279 <emphasis>after</emphasis> changing to the user and group
280 that have been specified by use of the
281 <option>user</option> and <option>group</option> options;
282 also, <command>nbd-server</command> will only detect
283 errors in this option upon connection of a client.
285 <para>When specified on the command line, this should be the
291 <term><option>filesize</option></term>
293 <para>Optional; integer; default autodetected.</para>
295 Disable autodetection of file or block device size, and
296 forcibly specify a size. Sizes must be specified in
297 bytes. If the <option>multifile</option> option is in
298 effect, this option specifies the size of the
299 <emphasis>entire</emphasis> export, not of individual
300 files. If the file is not present, a single file is
301 created of this size.
303 <para>When specified on the command line, this should be the
309 <term><option>temporary</option></term>
311 <para>Optional; boolean.</para>
313 Create a temporary export with a name based on exportname
314 (this can be used to set the directory). A unique filename
315 is created, which is unlinked as soon as it is created,
316 and therefore the export will not persist between
317 invocations of <command>nbd-server</command>. Set the
318 size of the file using the <command>filesize</command>
319 option. This option is incompatible with the
320 <option>multifile</option> option.
322 <para>When specified on the command line, this should be the
328 <term><option>flush</option></term>
330 <para>Optional; boolean.</para>
331 <para>When this option is enabled,
332 <command>nbd-server</command> will inform the client that it
333 supports and desires to be sent flush requests when the
334 elevator layer receives them. Receipt of a flush request
335 will cause an fdatasync() (or, if the sync option is set,
336 an fsync()) on the backend storage. This increases
337 reliability in the case of an unclean shutdown at
338 the expense of a degradation of performance. This option
339 will have no effect unless supported by the client.
344 <term><option>fua</option></term>
346 <para>Optional; boolean.</para>
347 <para>When this option is enabled,
348 <command>nbd-server</command> will inform the client that it
349 supports and desires to be sent fua (force unit access) commands
350 when the elevator layer receives them. Receipt of a force unit
351 access command will cause the specified command to be synced
352 to backend storage using sync_file_range() if supported, or
353 fdatasync() otherwise. This increases
354 reliability in the case of an unclean shutdown at
355 the expense of a degradation of performance. This option
356 will have no effect unless supported by the client.
361 <term>listenaddr</term>
367 If the 'oldstyle' global parameter is specified, works
368 similarly to the global listenaddr parameter, but for the
369 individual port of this particular export. If the 'oldstyle'
370 parameter is not set, this parameter is ignored.
375 <term><option>maxconnections</option></term>
377 <para>Optional; integer</para>
379 If specified, then it limits the number of opened connections for
385 <term><option>multifile</option></term>
387 <para>Optional; boolean.</para>
389 If this option is set to true, then
390 <command>nbd-server</command> will search for files of the
392 <replaceable>exportname</replaceable>.<replaceable>integer</replaceable>,
393 with <replaceable>exportname</replaceable> being the
394 filename that would otherwise have been used (after name
395 transformation for virtualization, if any, has been
396 performed) and <replaceable>integer</replaceable> an
397 integer number, starting with 0 and ending when no more
401 The size of the individual files will be autodetected,
402 <emphasis>even</emphasis> if the <option>filesize</option>
403 option has been specified.
406 Corresponds to the <option>-m</option> option on the
412 <term><option>port</option></term>
414 <para>Required if 'oldstyle' global parameter is set; integer.</para>
416 The port on which this export is to be served using the
417 old-style handshake protocol.
420 This parameter only makes sense when the 'oldstyle'
421 parameter is set to true in the 'generic' section. If that
422 parameter is not set, but this parameter is found in an
423 export section, then nbd-server will issue a warning upon
424 startup but should otherwise continue to function correctly.
427 It is not possible to combine multiple exports on the same
428 port using the old style handshake. Please use the new style
429 handshake for that purpose.
432 When specified on the command line, this should be the
438 <term><option>postrun</option></term>
440 <para>Optional; string</para>
442 If specified, then it is assumed to be a command
443 that will be ran when a client has
444 disconnected. This can be useful to clean up
445 whatever <option>prerun</option> has set up, to log
446 something, or similar.
449 If the literal string '%s' is present in the
450 command, it will be replaced by the file name that
451 has just been closed.
454 In contrast to the <option>prerun</option> option,
455 the exit state of <option>postrun</option> is
456 <emphasis>ignored</emphasis>.
461 <term><option>prerun</option></term>
463 <para>Optional; string</para>
465 If specified, then this command will be ran after a
466 client has connected to the server (and has been
467 accepted), but before the server starts serving. If
468 the command contains the literal string '%s', then
469 this string will be replaced by the filename of the
470 file which nbd-server wants to export.
473 This is useful to create export files on the fly, or
474 to verify that a file can be used for export, to
475 write something to a log file, or similar.
478 If the command runs with a non-zero exit status,
479 then nbd-server will assume the export will fail,
480 and refuse to serve it.
485 <term><option>readonly</option></term>
487 <para>Optional; boolean.</para>
489 Disallow writes to the device. If this option is
490 specified, <command>nbd-server</command> will issue an
491 error to any client that tries to write to the device.
494 Use of this option in conjunction with
495 <option>copyonwrite</option> is possible, but silly.
497 <para>Corresponds to the <option>-r</option> option on the
502 <term><option>rotational</option></term>
504 <para>Optional; boolean.</para>
505 <para>When this option is enabled,
506 <command>nbd-server</command> will inform the client that
507 it would prefer it to send requests in elevator (i.e., optimized) order, perhaps
508 because it has a backing store and no local elevator. By
509 default, the client uses QUEUE_FLAG_NONROT, which effectively
510 restricts the function of the elevator to block merges. By
511 specifying this flag on the server, the client will not use
512 QUEUE_FLAG_NONROT, meaning the client elevator will perform
513 normal elevator ordering of I/O requests. Note that even when
514 the backing store is on rotating media, it is not normally
515 necessary to specify this flag, as the server's elevator
516 algorithm will be used. This flag is only required where
517 the server will not be using an elevator algorithm or where
518 the elevator algorithm is effectively neutered (e.g. with
519 the sync option set). This option will have no effect unless
520 supported by the client.
525 <term><option>sdp</option></term>
527 <para>Optional; boolean.</para>
529 When this option is enabled, <command>nbd-server</command>
530 will use the Socket Direct Protocol (SDP) to serve the
531 export, rather than just IP. This is faster, but requires
532 special hardware (usually something like InfiniBand) and
533 support in the kernel.
536 Additionally, support for this option must be enabled at
537 compile time, using the <option>--enable-sdp</option> option
538 to the <command>configure</command> script. If this option
539 is found in a configuration file and
540 <command>nbd-server</command> does not have support for SDP,
541 then <command>nbd-server</command> will exit with an error
547 <term><option>sparse_cow</option></term>
549 <para>Optional; boolean.</para>
551 When this option is enabled, <command>nbd-server</command>
552 will use sparse files to implement the copy-on-write
553 option; such files take up less space then they appear to,
554 which allows <command>nbd-server</command> to handle the
555 file as if it was just as large as the block device it's
559 If this option is disabled, <command>nbd-server</command>
560 will map every newly written block to the end of the
561 copy-on-write file, which means that
562 <command>nbd-server</command> will have to lseek(2) to the
563 right position after every 4096-byte block.
566 Using this option may be faster when much is being written
572 <term><option>sync</option></term>
574 <para>Optional; boolean.</para>
575 <para>When this option is enabled,
576 <command>nbd-server</command> will call an fsync() after every
577 write to the backend storage. Calling fsync() increases
578 reliability in case of an unclean shutdown of nbd-server; but,
579 depending on the file system used on the nbd-server side, may
580 degrade performance. The use of this option isn't always
581 necessary; e.g., on ext3 filesystems, it is recommended that
582 it is <emphasis>not</emphasis> enabled, since it seriously
583 reduces performance on ext3 filesystems while not
584 importantly impacting reliability.
589 <term><option>timeout</option></term>
591 <para>Optional; integer; default 0</para>
593 How many seconds a connection may be idle for this
594 export. When a connection is idle for a longer time,
595 <command>nbd-server</command> will forcibly disconnect the
596 connection. If you specify 0 (the default), then a
597 connection may be idle forever.
600 Corresponds to the <option>-a</option> option on the
606 <term><option>transactionlog</option></term>
608 <para>Optional; string</para>
610 If specified, then this pathname is used to generate a transaction
611 log. A transaction log is a binary file consisting of the requests
612 sent to and the replies received by the server, but excluding any
613 data (so, for a write command, it records the offset and length
614 of the write but not the data written). It is therefore relatively
615 safe to distribute to a third party. Note that the transaction log
616 does not include the negotiation sequence. Transaction logs are
617 mainly useful for debugging. The program
618 <emphasis>nbd-tester-client</emphasis> distributed with the source
619 to this program can reply a transaction log against a server and
620 perform a data integrity test. Note that the transaction log is
621 written to for every client opened. If it is necessary to maintain
622 separate transaction logs for each client, the
623 <emphasis>prerun</emphasis> script should rename the transaction log
624 (which will just have been opened in order to avoid transaction logs
625 overwriting eachother. This action should be race-free.
630 <term><option>virtstyle</option></term>
632 <para>Optional; string; default "ipliteral"</para>
634 Defines the style of virtualization. Virtualization allows
635 one to create one export that will serve a different file
636 depending on the IP address that is connecting. When
637 virtualization is active, the
638 <replaceable>exportname</replaceable> parameter needs to
639 contain the string '%s'; this will then be replaced by the
640 IP address of the client connecting, in accordance with the
641 option selected here. The result of this transformation is
642 then used as the filename to be opened.
645 There are four types of virtualization that
646 <command>nbd-server</command> supports:
650 <term><option>none</option></term>
653 No virtualization. Will attempt to open the filename
654 as it was written, even if it contains '%s' in the
660 <term><option>ipliteral</option></term>
663 The %s is replaced by the IP address of the connecting
664 host is used as-is. For IPv4, this is done in
665 dotted-quad notation; for IPv6, in hexadecimal form
666 with leading zeros omitted.
669 As an example, if a client connects from 192.168.1.100
670 and <option>exportname</option> is specified as
671 <filename>/export/%s</filename>, then nbd-server will
673 <filename>/export/192.168.1.100</filename>. For IPv6,
674 with a client connecting from 2001:6f8:32f::39, the
676 <filename>/export/2001:6f8:32f:0:0:0:0:39</filename>
681 <term><option>iphash</option></term>
684 Same as above, except that
685 <command>nbd-server</command> will replace the dots
686 in the IP address by forward slashes ('/'); in the
687 same example, <command>nbd-server</command> would
688 open <filename>/export/192/168/1/100</filename>
692 Since there are no dots in most IPv6 addresses, the
693 effect of using this option when IPv6 is in use is
694 indistinguishable from the ipliteral option. It was
695 thought that having to create an eight-deep directory
696 structure would not be as useful.
701 <term><option>cidrhash</option></term>
704 This option requires one to add a space and a number
705 after it. <command>nbd-server</command> will use the
706 number as a network mask in CIDR style, and use that
707 as a hash cutoff point. In the above example, if
708 <option>virtstyle</option> has been specified as
709 <constant>cidrhash 16</constant>, then
710 <command>nbd-server</command> will try to open
711 <filename>/export/192.168.0.0/192.168.1.100</filename>;
712 if <option>virtstyle</option> were specified as
713 <constant>cidrhash 26</constant>, then
714 <command>nbd-server</command> will try to open
715 <filename>/export/192.168.1.64/192.168.1.100</filename>.
717 <para>For IPv6, in the above example, with
718 <constant>cidrhash 42</constant>, the filename would
720 <filename>/export/2001:32f:6c0:0:0:0:0:0/2001:32f:6f8:0:0:0:0:39</filename>.</para>
730 <title>SEE ALSO</title>
732 <para>nbd-server (1), nbd-client (8), nbd-trdump (8)</para>
737 <title>AUTHOR</title>
738 <para>The NBD kernel module and the NBD tools were originally
739 written by Pavel Machek (pavel@ucw.cz)</para>
741 <para>The Linux kernel module is now maintained by Paul Clements
742 (Paul.Clements@steeleye.com), while the userland tools are
743 maintained by &dhusername; (&dhemail;)</para>
745 <para>On The Hurd there is a regular translator available to perform the
746 client side of the protocol, and the use of
747 <command>nbd-client</command> is not required. Please see the
748 relevant documentation for more information.</para>
750 <para>This manual page was written by &dhusername; (&dhemail;) for
751 the &debian; system (but may be used by others). Permission is
752 granted to copy, distribute and/or modify this document under
753 the terms of the <acronym>GNU</acronym> General Public License,
754 version 2, as published by the Free Software Foundation.</para>
758 <title>EXAMPLES</title>
759 <para>A simple <command>nbd-server</command> configuration file
760 would look like this:</para>
764 exportname = /export/blkdev
767 <para>For increased security, one might want to create an
768 authorization file, and set the UID and GID to run as:</para>
774 exportname = /export/blkdev
776 authfile = $sysconfdir/nbd-server/allow
778 <para>With $sysconfdir/nbd-server/allow containing the following:</para>
787 <!-- Keep this comment at the end of the file
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