man/systemd.dnssd.xml

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