man/systemd.dnssd.xml

   1 <?xml version='1.0'?>
   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" conditional='ENABLE_RESOLVE'>
   7
   8   <refentryinfo>
   9     <title>systemd.dnssd</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>systemd.dnssd</refentrytitle>
  15     <manvolnum>5</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>systemd.dnssd</refname>
  20     <refpurpose>DNS-SD configuration</refpurpose>
  21   </refnamediv>
  22
  23   <refsynopsisdiv>
  24     <para><filename><replaceable>network_service</replaceable>.dnssd</filename></para>
  25   </refsynopsisdiv>
  26
  27   <refsect1>
  28     <title>Description</title>
  29
  30     <para>DNS-SD setup is performed by
  31     <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
  32     </para>
  33
  34     <para>The main network service file must have the extension <filename>.dnssd</filename>; other
  35     extensions are ignored.</para>
  36
  37     <para>The <filename>.dnssd</filename> files are read from the files located in the system network
  38     directories <filename>/usr/lib/systemd/dnssd</filename> and
  39     <filename>/usr/local/lib/systemd/dnssd</filename>, the volatile runtime network directory
  40     <filename>/run/systemd/dnssd</filename> and the local administration network directory
  41     <filename>/etc/systemd/dnssd</filename>. All configuration files are collectively sorted and processed in
  42     lexical order, regardless of the directories in which they live. However, files with identical filenames
  43     replace each other. Files in <filename>/etc</filename> have the highest priority, files in
  44     <filename>/run</filename> take precedence over files with the same name in
  45     <filename>/usr/lib</filename>. This can be used to override a system-supplied configuration file with a
  46     local file if needed.</para>
  47
  48     <para>Along with the network service file <filename>foo.dnssd</filename>, a "drop-in" directory
  49     <filename>foo.dnssd.d/</filename> may exist. All files with the suffix
  50     <literal>.conf</literal> from this directory will be parsed after the file itself is
  51     parsed. This is useful to alter or add configuration settings, without having to modify the main
  52     configuration file. Each drop-in file must have appropriate section headers.</para>
  53
  54     <para>In addition to <filename>/etc/systemd/dnssd</filename>, drop-in <literal>.d</literal> directories
  55     can be placed in <filename>/usr/lib/systemd/dnssd</filename> or <filename>/run/systemd/dnssd</filename>
  56     directories. Drop-in files in <filename>/etc</filename> take precedence over those in
  57     <filename>/run</filename> which in turn take precedence over those in <filename>/usr/lib</filename> or
  58     <filename>/usr/local/lib</filename>. Drop-in files under any of these directories take precedence over
  59     the main network service file wherever located.</para>
  60   </refsect1>
  61
  62   <refsect1>
  63     <title>[Service] Section Options</title>
  64
  65       <para>The network service file contains a <literal>[Service]</literal>
  66       section, which specifies a discoverable network service announced in a
  67       local network with Multicast DNS broadcasts.</para>
  68
  69       <variablelist class='network-directives'>
  70         <varlistentry>
  71           <term><varname>Name=</varname></term>
  72           <listitem>
  73             <para>An instance name of the network service as defined in the section 4.1.1 of <ulink
  74             url="https://tools.ietf.org/html/rfc6763">RFC 6763</ulink>, e.g. <literal>webserver</literal>.</para>
  75             <para>The option supports simple specifier expansion. The following expansions are understood:</para>
  76             <table>
  77               <title>Specifiers available</title>
  78               <tgroup cols='3' align='left' colsep='1' rowsep='1'>
  79                 <colspec colname="spec" />
  80                 <colspec colname="mean" />
  81                 <colspec colname="detail" />
  82                 <thead>
  83                   <row>
  84                     <entry>Specifier</entry>
  85                     <entry>Meaning</entry>
  86                     <entry>Details</entry>
  87                   </row>
  88                 </thead>
  89                 <tbody>
  90                   <row>
  91                     <entry><literal>%m</literal></entry>
  92                     <entry>Machine ID</entry>
  93                     <entry>The machine ID of the running system, formatted as string. See <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry> for more information.</entry>
  94                   </row>
  95                   <row>
  96                     <entry><literal>%b</literal></entry>
  97                     <entry>Boot ID</entry>
  98                     <entry>The boot ID of the running system, formatted as string. See <citerefentry><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry> for more information.</entry>
  99                   </row>
 100                   <row>
 101                     <entry><literal>%H</literal></entry>
 102                     <entry>Host name</entry>
 103                     <entry>The hostname of the running system.</entry>
 104                   </row>
 105                   <row>
 106                     <entry><literal>%v</literal></entry>
 107                     <entry>Kernel release</entry>
 108                     <entry>Identical to <command>uname -r</command> output.</entry>
 109                   </row>
 110                 </tbody>
 111               </tgroup>
 112             </table>
 113           </listitem>
 114         </varlistentry>
 115         <varlistentry>
 116           <term><varname>Type=</varname></term>
 117           <listitem>
 118             <para>A type of the network service as defined in the section 4.1.2 of <ulink
 119             url="https://tools.ietf.org/html/rfc6763">RFC 6763</ulink>, e.g. <literal>_http._tcp</literal>.
 120             </para>
 121           </listitem>
 122         </varlistentry>
 123         <varlistentry>
 124           <term><varname>Port=</varname></term>
 125           <listitem>
 126             <para>An IP port number of the network service.</para>
 127           </listitem>
 128         </varlistentry>
 129         <varlistentry>
 130           <term><varname>Priority=</varname></term>
 131           <listitem>
 132             <para>A priority number set in SRV resource records corresponding to the network service.</para>
 133           </listitem>
 134         </varlistentry>
 135         <varlistentry>
 136           <term><varname>Weight=</varname></term>
 137           <listitem>
 138             <para>A weight number set in SRV resource records corresponding to the network service.</para>
 139           </listitem>
 140         </varlistentry>
 141         <varlistentry>
 142           <term><varname>TxtText=</varname></term>
 143           <listitem>
 144             <para>A whitespace-separated list of arbitrary key/value pairs
 145             conveying additional information about the named service in the corresponding TXT resource record,
 146             e.g. <literal>path=/portal/index.html</literal>. Keys and values can contain C-style escape
 147             sequences which get translated upon reading configuration files.
 148             </para>
 149             <para>This option together with <varname>TxtData=</varname> may be specified more than once, in which
 150             case multiple TXT resource records will be created for the service. If the empty string is assigned to
 151             this option, the list is reset and all prior assignments will have no effect.
 152             </para>
 153           </listitem>
 154         </varlistentry>
 155         <varlistentry>
 156           <term><varname>TxtData=</varname></term>
 157           <listitem>
 158             <para>A whitespace-separated list of arbitrary key/value pairs
 159             conveying additional information about the named service in the corresponding TXT resource record
 160             where values are base64-encoded string representing any binary data,
 161             e.g. <literal>data=YW55IGJpbmFyeSBkYXRhCg==</literal>. Keys can contain C-style escape
 162             sequences which get translated upon reading configuration files.
 163             </para>
 164             <para>This option together with <varname>TxtText=</varname> may be specified more than once, in which
 165             case multiple TXT resource records will be created for the service. If the empty string is assigned to
 166             this option, the list is reset and all prior assignments will have no effect.
 167             </para>
 168           </listitem>
 169         </varlistentry>
 170       </variablelist>
 171
 172   </refsect1>
 173
 174   <refsect1>
 175     <title>Examples</title>
 176     <example>
 177       <title>HTTP service</title>
 178
 179       <programlisting># /etc/systemd/dnssd/http.dnssd
 180 [Service]
 181 Name=%H
 182 Type=_http._tcp
 183 Port=80
 184 TxtText=path=/stats/index.html t=temperature_sensor</programlisting>
 185
 186       <para>This makes the http server running on the host discoverable in the local network
 187       given MulticastDNS is enabled on the network interface.</para>
 188
 189       <para>Now the utility <literal>resolvectl</literal> should be able to resolve the
 190       service to the host's name:</para>
 191
 192       <programlisting>$ resolvectl service meteo._http._tcp.local
 193 meteo._http._tcp.local: meteo.local:80 [priority=0, weight=0]
 194                         169.254.208.106%senp0s21f0u2u4
 195                         fe80::213:3bff:fe49:8aa%senp0s21f0u2u4
 196                         path=/stats/index.html
 197                         t=temperature_sensor
 198                         (meteo/_http._tcp/local)
 199
 200 -- Information acquired via protocol mDNS/IPv6 in 4.0ms.
 201 -- Data is authenticated: yes</programlisting>
 202
 203       <para><literal>Avahi</literal> running on a different host in the same local network should see the service as well:</para>
 204
 205       <programlisting>$ avahi-browse -a -r
 206 + enp3s0 IPv6 meteo                                         Web Site             local
 207 + enp3s0 IPv4 meteo                                         Web Site             local
 208 = enp3s0 IPv6 meteo                                         Web Site             local
 209    hostname = [meteo.local]
 210    address = [fe80::213:3bff:fe49:8aa]
 211    port = [80]
 212    txt = ["path=/stats/index.html" "t=temperature_sensor"]
 213 = enp3s0 IPv4 meteo                                         Web Site             local
 214    hostname = [meteo.local]
 215    address = [169.254.208.106]
 216    port = [80]
 217    txt = ["path=/stats/index.html" "t=temperature_sensor"]</programlisting>
 218
 219     </example>
 220   </refsect1>
 221
 222   <refsect1>
 223     <title>See Also</title>
 224     <para>
 225       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 226       <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 227       <citerefentry><refentrytitle>resolvectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 228     </para>
 229   </refsect1>
 230
 231 </refentry>