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235 lines
10 KiB
XML
235 lines
10 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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-->
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<refentry id="systemd.dnssd" conditional='ENABLE_RESOLVE'>
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<refentryinfo>
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<title>systemd.dnssd</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd.dnssd</refentrytitle>
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<manvolnum>5</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd.dnssd</refname>
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<refpurpose>DNS-SD configuration</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename><replaceable>network_service</replaceable>.dnssd</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>DNS-SD setup is performed by
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<citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
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</para>
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<para>The main network service file must have the extension <filename>.dnssd</filename>; other
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extensions are ignored.</para>
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<para>The <filename>.dnssd</filename> files are read from the files located in the system
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network directory <filename>/usr/lib/systemd/dnssd</filename>, the volatile runtime network
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directory <filename>/run/systemd/dnssd</filename> and the local administration network
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directory <filename>/etc/systemd/dnssd</filename>. All configuration files are collectively
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sorted and processed in lexical order, regardless of the directories in which they live.
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However, files with identical filenames replace each other. Files in <filename>/etc</filename>
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have the highest priority, files in <filename>/run</filename> take precedence over files with
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the same name in <filename>/usr/lib</filename>. This can be used to override a system-supplied
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configuration file with a local file if needed.</para>
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<para>Along with the network service file <filename>foo.dnssd</filename>, a "drop-in" directory
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<filename>foo.dnssd.d/</filename> may exist. All files with the suffix
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<literal>.conf</literal> from this directory will be parsed after the file itself is
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parsed. This is useful to alter or add configuration settings, without having to modify the main
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configuration file. Each drop-in file must have appropriate section headers.</para>
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<para>In addition to <filename>/etc/systemd/dnssd</filename>, drop-in <literal>.d</literal>
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directories can be placed in <filename>/usr/lib/systemd/dnssd</filename> or
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<filename>/run/systemd/dnssd</filename> directories. Drop-in files in
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<filename>/etc</filename> take precedence over those in <filename>/run</filename> which in turn
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take precedence over those in <filename>/usr/lib</filename>. Drop-in files under any of these
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directories take precedence over the main network service file wherever located. (Of course, since
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<filename>/run</filename> is temporary and <filename>/usr/lib</filename> is for vendors, it is
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unlikely drop-ins should be used in either of those places.)</para>
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</refsect1>
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<refsect1>
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<title>[Service] Section Options</title>
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<para>The network service file contains a <literal>[Service]</literal>
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section, which specifies a discoverable network service announced in a
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local network with Multicast DNS broadcasts.</para>
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<variablelist class='network-directives'>
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<varlistentry>
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<term><varname>Name=</varname></term>
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<listitem>
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<para>An instance name of the network service as defined in the section 4.1.1 of <ulink
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url="https://tools.ietf.org/html/rfc6763">RFC 6763</ulink>, e.g. <literal>webserver</literal>.</para>
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<para>The option supports simple specifier expansion. The following expansions are understood:</para>
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<table>
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<title>Specifiers available</title>
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<tgroup cols='3' align='left' colsep='1' rowsep='1'>
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<colspec colname="spec" />
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<colspec colname="mean" />
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<colspec colname="detail" />
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<thead>
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<row>
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<entry>Specifier</entry>
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<entry>Meaning</entry>
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<entry>Details</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><literal>%m</literal></entry>
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<entry>Machine ID</entry>
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<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>
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</row>
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<row>
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<entry><literal>%b</literal></entry>
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<entry>Boot ID</entry>
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<entry>The boot ID of the running system, formatted as string. See <citerefentry><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry> for more information.</entry>
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</row>
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<row>
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<entry><literal>%H</literal></entry>
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<entry>Host name</entry>
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<entry>The hostname of the running system.</entry>
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</row>
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<row>
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<entry><literal>%v</literal></entry>
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<entry>Kernel release</entry>
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<entry>Identical to <command>uname -r</command> output.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>Type=</varname></term>
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<listitem>
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<para>A type of the network service as defined in the section 4.1.2 of <ulink
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url="https://tools.ietf.org/html/rfc6763">RFC 6763</ulink>, e.g. <literal>_http._tcp</literal>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>Port=</varname></term>
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<listitem>
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<para>An IP port number of the network service.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>Priority=</varname></term>
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<listitem>
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<para>A priority number set in SRV resource records corresponding to the network service.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>Weight=</varname></term>
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<listitem>
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<para>A weight number set in SRV resource records corresponding to the network service.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>TxtText=</varname></term>
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<listitem>
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<para>A whitespace-separated list of arbitrary key/value pairs
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conveying additional information about the named service in the corresponding TXT resource record,
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e.g. <literal>path=/portal/index.html</literal>. Keys and values can contain C-style escape
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sequences which get translated upon reading configuration files.
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</para>
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<para>This option together with <varname>TxtData=</varname> may be specified more than once, in which
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case multiple TXT resource records will be created for the service. If the empty string is assigned to
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this option, the list is reset and all prior assignments will have no effect.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>TxtData=</varname></term>
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<listitem>
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<para>A whitespace-separated list of arbitrary key/value pairs
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conveying additional information about the named service in the corresponding TXT resource record
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where values are base64-encoded string representing any binary data,
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e.g. <literal>data=YW55IGJpbmFyeSBkYXRhCg==</literal>. Keys can contain C-style escape
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sequences which get translated upon reading configuration files.
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</para>
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<para>This option together with <varname>TxtText=</varname> may be specified more than once, in which
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case multiple TXT resource records will be created for the service. If the empty string is assigned to
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this option, the list is reset and all prior assignments will have no effect.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Examples</title>
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<example>
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<title>HTTP service</title>
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<programlisting># /etc/systemd/dnssd/http.dnssd
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[Service]
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Name=%H
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Type=_http._tcp
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Port=80
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TxtText=path=/stats/index.html t=temperature_sensor</programlisting>
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<para>This makes the http server running on the host discoverable in the local network
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given MulticastDNS is enabled on the network interface.</para>
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<para>Now the utility <literal>resolvectl</literal> should be able to resolve the
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service to the host's name:</para>
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<programlisting>$ resolvectl service meteo._http._tcp.local
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meteo._http._tcp.local: meteo.local:80 [priority=0, weight=0]
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169.254.208.106%senp0s21f0u2u4
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fe80::213:3bff:fe49:8aa%senp0s21f0u2u4
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path=/stats/index.html
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t=temperature_sensor
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(meteo/_http._tcp/local)
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-- Information acquired via protocol mDNS/IPv6 in 4.0ms.
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-- Data is authenticated: yes</programlisting>
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<para><literal>Avahi</literal> running on a different host in the same local network should see the service as well:</para>
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<programlisting>$ avahi-browse -a -r
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+ enp3s0 IPv6 meteo Web Site local
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+ enp3s0 IPv4 meteo Web Site local
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= enp3s0 IPv6 meteo Web Site local
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hostname = [meteo.local]
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address = [fe80::213:3bff:fe49:8aa]
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port = [80]
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txt = ["path=/stats/index.html" "t=temperature_sensor"]
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= enp3s0 IPv4 meteo Web Site local
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hostname = [meteo.local]
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address = [169.254.208.106]
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port = [80]
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txt = ["path=/stats/index.html" "t=temperature_sensor"]</programlisting>
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</example>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>resolvectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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