man/systemd.dnssd.xml

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   6   Copyright 2017 Dmitry Rozhkov
   7 -->
   8
   9 <refentry id="systemd.dnssd" conditional='ENABLE_RESOLVE'>
  10
  11   <refentryinfo>
  12     <title>systemd.dnssd</title>
  13     <productname>systemd</productname>
  14
  15     <authorgroup>
  16       <author>
  17         <contrib>Developer</contrib>
  18         <firstname>Dmitry</firstname>
  19         <surname>Rozhkov</surname>
  20         <email>dmitry.rozhkov@intel.com</email>
  21       </author>
  22     </authorgroup>
  23   </refentryinfo>
  24
  25   <refmeta>
  26     <refentrytitle>systemd.dnssd</refentrytitle>
  27     <manvolnum>5</manvolnum>
  28   </refmeta>
  29
  30   <refnamediv>
  31     <refname>systemd.dnssd</refname>
  32     <refpurpose>DNS-SD configuration</refpurpose>
  33   </refnamediv>
  34
  35   <refsynopsisdiv>
  36     <para><filename><replaceable>network_service</replaceable>.dnssd</filename></para>
  37   </refsynopsisdiv>
  38
  39   <refsect1>
  40     <title>Description</title>
  41
  42     <para>DNS-SD setup is performed by
  43     <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
  44     </para>
  45
  46     <para>The main network service file must have the extension <filename>.dnssd</filename>; other
  47     extensions are ignored.</para>
  48
  49     <para>The <filename>.dnssd</filename> files are read from the files located in the system
  50     network directory <filename>/usr/lib/systemd/dnssd</filename>, the volatile runtime network
  51     directory <filename>/run/systemd/dnssd</filename> and the local administration network
  52     directory <filename>/etc/systemd/dnssd</filename>. All configuration files are collectively
  53     sorted and processed in lexical order, regardless of the directories in which they live.
  54     However, files with identical filenames replace each other. Files in <filename>/etc</filename>
  55     have the highest priority, files in <filename>/run</filename> take precedence over files with
  56     the same name in <filename>/usr/lib</filename>. This can be used to override a system-supplied
  57     configuration file with a local file if needed.</para>
  58
  59     <para>Along with the network service file <filename>foo.dnssd</filename>, a "drop-in" directory
  60     <filename>foo.dnssd.d/</filename> may exist. All files with the suffix
  61     <literal>.conf</literal> from this directory will be parsed after the file itself is
  62     parsed. This is useful to alter or add configuration settings, without having to modify the main
  63     configuration file. Each drop-in file must have appropriate section headers.</para>
  64
  65     <para>In addition to <filename>/etc/systemd/dnssd</filename>, drop-in <literal>.d</literal>
  66     directories can be placed in <filename>/usr/lib/systemd/dnssd</filename> or
  67     <filename>/run/systemd/dnssd</filename> directories. Drop-in files in
  68     <filename>/etc</filename> take precedence over those in <filename>/run</filename> which in turn
  69     take precedence over those in <filename>/usr/lib</filename>. Drop-in files under any of these
  70     directories take precedence over the main network service file wherever located. (Of course, since
  71     <filename>/run</filename> is temporary and <filename>/usr/lib</filename> is for vendors, it is
  72     unlikely drop-ins should be used in either of those places.)</para>
  73   </refsect1>
  74
  75   <refsect1>
  76     <title>[Service] Section Options</title>
  77
  78       <para>The network service file contains a <literal>[Service]</literal>
  79       section, which specifies a discoverable network service announced in a
  80       local network with Multicast DNS broadcasts.</para>
  81
  82       <variablelist class='network-directives'>
  83         <varlistentry>
  84           <term><varname>Name=</varname></term>
  85           <listitem>
  86             <para>An instance name of the network service as defined in the section 4.1.1 of <ulink
  87             url="https://tools.ietf.org/html/rfc6763">RFC 6763</ulink>, e.g. <literal>webserver</literal>.</para>
  88             <para>The option supports simple specifier expansion. The following expansions are understood:</para>
  89             <table>
  90               <title>Specifiers available</title>
  91               <tgroup cols='3' align='left' colsep='1' rowsep='1'>
  92                 <colspec colname="spec" />
  93                 <colspec colname="mean" />
  94                 <colspec colname="detail" />
  95                 <thead>
  96                   <row>
  97                     <entry>Specifier</entry>
  98                     <entry>Meaning</entry>
  99                     <entry>Details</entry>
 100                   </row>
 101                 </thead>
 102                 <tbody>
 103                   <row>
 104                     <entry><literal>%m</literal></entry>
 105                     <entry>Machine ID</entry>
 106                     <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>
 107                   </row>
 108                   <row>
 109                     <entry><literal>%b</literal></entry>
 110                     <entry>Boot ID</entry>
 111                     <entry>The boot ID of the running system, formatted as string. See <citerefentry><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry> for more information.</entry>
 112                   </row>
 113                   <row>
 114                     <entry><literal>%H</literal></entry>
 115                     <entry>Host name</entry>
 116                     <entry>The hostname of the running system.</entry>
 117                   </row>
 118                   <row>
 119                     <entry><literal>%v</literal></entry>
 120                     <entry>Kernel release</entry>
 121                     <entry>Identical to <command>uname -r</command> output.</entry>
 122                   </row>
 123                 </tbody>
 124               </tgroup>
 125             </table>
 126           </listitem>
 127         </varlistentry>
 128         <varlistentry>
 129           <term><varname>Type=</varname></term>
 130           <listitem>
 131             <para>A type of the network service as defined in the section 4.1.2 of <ulink
 132             url="https://tools.ietf.org/html/rfc6763">RFC 6763</ulink>, e.g. <literal>_http._tcp</literal>.
 133             </para>
 134           </listitem>
 135         </varlistentry>
 136         <varlistentry>
 137           <term><varname>Port=</varname></term>
 138           <listitem>
 139             <para>An IP port number of the network service.</para>
 140           </listitem>
 141         </varlistentry>
 142         <varlistentry>
 143           <term><varname>Priority=</varname></term>
 144           <listitem>
 145             <para>A priority number set in SRV resource records corresponding to the network service.</para>
 146           </listitem>
 147         </varlistentry>
 148         <varlistentry>
 149           <term><varname>Weight=</varname></term>
 150           <listitem>
 151             <para>A weight number set in SRV resource records corresponding to the network service.</para>
 152           </listitem>
 153         </varlistentry>
 154         <varlistentry>
 155           <term><varname>TxtText=</varname></term>
 156           <listitem>
 157             <para>A whitespace-separated list of arbitrary key/value pairs
 158             conveying additional information about the named service in the corresponding TXT resource record,
 159             e.g. <literal>path=/portal/index.html</literal>. Keys and values can contain C-style escape
 160             sequences which get translated upon reading configuration files.
 161             </para>
 162             <para>This option together with <varname>TxtData=</varname> may be specified more than once, in which
 163             case multiple TXT resource records will be created for the service. If the empty string is assigned to
 164             this option, the list is reset and all prior assignments will have no effect.
 165             </para>
 166           </listitem>
 167         </varlistentry>
 168         <varlistentry>
 169           <term><varname>TxtData=</varname></term>
 170           <listitem>
 171             <para>A whitespace-separated list of arbitrary key/value pairs
 172             conveying additional information about the named service in the corresponding TXT resource record
 173             where values are base64-encoded string representing any binary data,
 174             e.g. <literal>data=YW55IGJpbmFyeSBkYXRhCg==</literal>. Keys can contain C-style escape
 175             sequences which get translated upon reading configuration files.
 176             </para>
 177             <para>This option together with <varname>TxtText=</varname> may be specified more than once, in which
 178             case multiple TXT resource records will be created for the service. If the empty string is assigned to
 179             this option, the list is reset and all prior assignments will have no effect.
 180             </para>
 181           </listitem>
 182         </varlistentry>
 183       </variablelist>
 184
 185   </refsect1>
 186
 187   <refsect1>
 188     <title>Examples</title>
 189     <example>
 190       <title>HTTP service</title>
 191
 192       <programlisting># /etc/systemd/dnssd/http.dnssd
 193 [Service]
 194 Name=%H
 195 Type=_http._tcp
 196 Port=80
 197 TxtText=path=/stats/index.html t=temperature_sensor</programlisting>
 198
 199       <para>This makes the http server running on the host discoverable in the local network
 200       given MulticastDNS is enabled on the network interface.</para>
 201
 202       <para>Now the utility <literal>resolvectl</literal> should be able to resolve the
 203       service to the host's name:</para>
 204
 205       <programlisting>$ resolvectl service meteo._http._tcp.local
 206 meteo._http._tcp.local: meteo.local:80 [priority=0, weight=0]
 207                         169.254.208.106%senp0s21f0u2u4
 208                         fe80::213:3bff:fe49:8aa%senp0s21f0u2u4
 209                         path=/stats/index.html
 210                         t=temperature_sensor
 211                         (meteo/_http._tcp/local)
 212
 213 -- Information acquired via protocol mDNS/IPv6 in 4.0ms.
 214 -- Data is authenticated: yes</programlisting>
 215
 216       <para><literal>Avahi</literal> running on a different host in the same local network should see the service as well:</para>
 217
 218       <programlisting>$ avahi-browse -a -r
 219 + enp3s0 IPv6 meteo                                         Web Site             local
 220 + enp3s0 IPv4 meteo                                         Web Site             local
 221 = enp3s0 IPv6 meteo                                         Web Site             local
 222    hostname = [meteo.local]
 223    address = [fe80::213:3bff:fe49:8aa]
 224    port = [80]
 225    txt = ["path=/stats/index.html" "t=temperature_sensor"]
 226 = enp3s0 IPv4 meteo                                         Web Site             local
 227    hostname = [meteo.local]
 228    address = [169.254.208.106]
 229    port = [80]
 230    txt = ["path=/stats/index.html" "t=temperature_sensor"]</programlisting>
 231
 232     </example>
 233   </refsect1>
 234
 235   <refsect1>
 236     <title>See Also</title>
 237     <para>
 238       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 239       <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 240       <citerefentry><refentrytitle>resolvectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 241     </para>
 242   </refsect1>
 243
 244 </refentry>