man/systemd.dnssd.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   5
   6 <refentry id="systemd.dnssd"
   7           xmlns:xi="http://www.w3.org/2001/XInclude"
   8           conditional='ENABLE_RESOLVE'>
   9
  10   <refentryinfo>
  11     <title>systemd.dnssd</title>
  12     <productname>systemd</productname>
  13   </refentryinfo>
  14
  15   <refmeta>
  16     <refentrytitle>systemd.dnssd</refentrytitle>
  17     <manvolnum>5</manvolnum>
  18   </refmeta>
  19
  20   <refnamediv>
  21     <refname>systemd.dnssd</refname>
  22     <refpurpose>DNS-SD configuration</refpurpose>
  23   </refnamediv>
  24
  25   <refsynopsisdiv>
  26     <para><filename><replaceable>network_service</replaceable>.dnssd</filename></para>
  27   </refsynopsisdiv>
  28
  29   <refsect1>
  30     <title>Description</title>
  31
  32     <para>DNS-SD setup is performed by
  33     <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
  34     </para>
  35
  36     <para>The main network service file must have the extension <filename>.dnssd</filename>; other
  37     extensions are ignored.</para>
  38
  39     <para>The <filename>.dnssd</filename> files are read from the files located in the system network
  40     directories <filename>/usr/lib/systemd/dnssd</filename> and
  41     <filename>/usr/local/lib/systemd/dnssd</filename>, the volatile runtime network directory
  42     <filename>/run/systemd/dnssd</filename> and the local administration network directory
  43     <filename>/etc/systemd/dnssd</filename>. All configuration files are collectively sorted and processed in
  44     lexical order, regardless of the directories in which they live. However, files with identical filenames
  45     replace each other. Files in <filename>/etc</filename> have the highest priority, files in
  46     <filename>/run</filename> take precedence over files with the same name in
  47     <filename>/usr/lib</filename>. This can be used to override a system-supplied configuration file with a
  48     local file if needed.</para>
  49
  50     <para>Along with the network service file <filename>foo.dnssd</filename>, a "drop-in" directory
  51     <filename>foo.dnssd.d/</filename> may exist. All files with the suffix
  52     <literal>.conf</literal> from this directory will be parsed after the file itself is
  53     parsed. This is useful to alter or add configuration settings, without having to modify the main
  54     configuration file. Each drop-in file must have appropriate section headers.</para>
  55
  56     <para>In addition to <filename>/etc/systemd/dnssd</filename>, drop-in <literal>.d</literal> directories
  57     can be placed in <filename>/usr/lib/systemd/dnssd</filename> or <filename>/run/systemd/dnssd</filename>
  58     directories. Drop-in files in <filename>/etc</filename> take precedence over those in
  59     <filename>/run</filename> which in turn take precedence over those in <filename>/usr/lib</filename> or
  60     <filename>/usr/local/lib</filename>. Drop-in files under any of these directories take precedence over
  61     the main network service file wherever located.</para>
  62   </refsect1>
  63
  64   <refsect1>
  65     <title>[Service] Section Options</title>
  66
  67       <para>The network service file contains a [Service]
  68       section, which specifies a discoverable network service announced in a
  69       local network with Multicast DNS broadcasts.</para>
  70
  71       <variablelist class='network-directives'>
  72         <varlistentry>
  73           <term><varname>Name=</varname></term>
  74           <listitem>
  75             <para>An instance name of the network service as defined in the section 4.1.1 of <ulink
  76             url="https://tools.ietf.org/html/rfc6763">RFC 6763</ulink>, e.g. <literal>webserver</literal>.</para>
  77             <para>The option supports simple specifier expansion. The following expansions are understood:</para>
  78             <table class='specifiers'>
  79               <title>Specifiers available</title>
  80               <tgroup cols='3' align='left' colsep='1' rowsep='1'>
  81                 <colspec colname="spec" />
  82                 <colspec colname="mean" />
  83                 <colspec colname="detail" />
  84                 <thead>
  85                   <row>
  86                     <entry>Specifier</entry>
  87                     <entry>Meaning</entry>
  88                     <entry>Details</entry>
  89                   </row>
  90                 </thead>
  91                 <tbody>
  92                   <xi:include href="standard-specifiers.xml" xpointer="a"/>
  93                   <xi:include href="standard-specifiers.xml" xpointer="b"/>
  94                   <xi:include href="standard-specifiers.xml" xpointer="B"/>
  95                   <xi:include href="standard-specifiers.xml" xpointer="H"/>
  96                   <xi:include href="standard-specifiers.xml" xpointer="m"/>
  97                   <xi:include href="standard-specifiers.xml" xpointer="o"/>
  98                   <xi:include href="standard-specifiers.xml" xpointer="v"/>
  99                   <xi:include href="standard-specifiers.xml" xpointer="w"/>
 100                   <xi:include href="standard-specifiers.xml" xpointer="W"/>
 101                   <xi:include href="standard-specifiers.xml" xpointer="percent"/>
 102                 </tbody>
 103               </tgroup>
 104             </table>
 105           </listitem>
 106         </varlistentry>
 107         <varlistentry>
 108           <term><varname>Type=</varname></term>
 109           <listitem>
 110             <para>A type of the network service as defined in the section 4.1.2 of <ulink
 111             url="https://tools.ietf.org/html/rfc6763">RFC 6763</ulink>, e.g. <literal>_http._tcp</literal>.
 112             </para>
 113           </listitem>
 114         </varlistentry>
 115         <varlistentry>
 116           <term><varname>Port=</varname></term>
 117           <listitem>
 118             <para>An IP port number of the network service.</para>
 119           </listitem>
 120         </varlistentry>
 121         <varlistentry>
 122           <term><varname>Priority=</varname></term>
 123           <listitem>
 124             <para>A priority number set in SRV resource records corresponding to the network service.</para>
 125           </listitem>
 126         </varlistentry>
 127         <varlistentry>
 128           <term><varname>Weight=</varname></term>
 129           <listitem>
 130             <para>A weight number set in SRV resource records corresponding to the network service.</para>
 131           </listitem>
 132         </varlistentry>
 133         <varlistentry>
 134           <term><varname>TxtText=</varname></term>
 135           <listitem>
 136             <para>A whitespace-separated list of arbitrary key/value pairs
 137             conveying additional information about the named service in the corresponding TXT resource record,
 138             e.g. <literal>path=/portal/index.html</literal>. Keys and values can contain C-style escape
 139             sequences which get translated upon reading configuration files.
 140             </para>
 141             <para>This option together with <varname>TxtData=</varname> may be specified more than once, in which
 142             case multiple TXT resource records will be created for the service. If the empty string is assigned to
 143             this option, the list is reset and all prior assignments will have no effect.
 144             </para>
 145           </listitem>
 146         </varlistentry>
 147         <varlistentry>
 148           <term><varname>TxtData=</varname></term>
 149           <listitem>
 150             <para>A whitespace-separated list of arbitrary key/value pairs
 151             conveying additional information about the named service in the corresponding TXT resource record
 152             where values are base64-encoded string representing any binary data,
 153             e.g. <literal>data=YW55IGJpbmFyeSBkYXRhCg==</literal>. Keys can contain C-style escape
 154             sequences which get translated upon reading configuration files.
 155             </para>
 156             <para>This option together with <varname>TxtText=</varname> may be specified more than once, in which
 157             case multiple TXT resource records will be created for the service. If the empty string is assigned to
 158             this option, the list is reset and all prior assignments will have no effect.
 159             </para>
 160           </listitem>
 161         </varlistentry>
 162       </variablelist>
 163
 164   </refsect1>
 165
 166   <refsect1>
 167     <title>Examples</title>
 168     <example>
 169       <title>HTTP service</title>
 170
 171       <programlisting># /etc/systemd/dnssd/http.dnssd
 172 [Service]
 173 Name=%H
 174 Type=_http._tcp
 175 Port=80
 176 TxtText=path=/stats/index.html t=temperature_sensor</programlisting>
 177
 178       <para>This makes the http server running on the host discoverable in the local network
 179       given MulticastDNS is enabled on the network interface.</para>
 180
 181       <para>Now the utility <literal>resolvectl</literal> should be able to resolve the
 182       service to the host's name:</para>
 183
 184       <programlisting>$ resolvectl service meteo._http._tcp.local
 185 meteo._http._tcp.local: meteo.local:80 [priority=0, weight=0]
 186                         169.254.208.106%senp0s21f0u2u4
 187                         fe80::213:3bff:fe49:8aa%senp0s21f0u2u4
 188                         path=/stats/index.html
 189                         t=temperature_sensor
 190                         (meteo/_http._tcp/local)
 191
 192 -- Information acquired via protocol mDNS/IPv6 in 4.0ms.
 193 -- Data is authenticated: yes</programlisting>
 194
 195       <para><literal>Avahi</literal> running on a different host in the same local network should see the service as well:</para>
 196
 197       <programlisting>$ avahi-browse -a -r
 198 + enp3s0 IPv6 meteo                                         Web Site             local
 199 + enp3s0 IPv4 meteo                                         Web Site             local
 200 = enp3s0 IPv6 meteo                                         Web Site             local
 201    hostname = [meteo.local]
 202    address = [fe80::213:3bff:fe49:8aa]
 203    port = [80]
 204    txt = ["path=/stats/index.html" "t=temperature_sensor"]
 205 = enp3s0 IPv4 meteo                                         Web Site             local
 206    hostname = [meteo.local]
 207    address = [169.254.208.106]
 208    port = [80]
 209    txt = ["path=/stats/index.html" "t=temperature_sensor"]</programlisting>
 210
 211     </example>
 212   </refsect1>
 213
 214   <refsect1>
 215     <title>See Also</title>
 216     <para>
 217       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 218       <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 219       <citerefentry><refentrytitle>resolvectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 220     </para>
 221   </refsect1>
 222
 223 </refentry>