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This specifes two new optional fields for /etc/os-release: IMAGE_VERSION= and IMAGE_ID= that are supposed to identify the image of the current booted system by name and version. This is inspired by the versioning stuff in https://github.com/systemd/mkosi/pull/683. In environments where pre-built images are installed and updated as a whole the existing os-release version/distro identifier are not sufficient to describe the system's version, as they describe only the distro an image is built from, but not the image itself, even if that image is deployed many times on many systems, and even if that image contains more resources than just the RPMs/DEBs. In particular, "mkosi" is a tool for building disk images based on distro RPMs with additional resources dropped in. The combination of all of these together with their versions should also carry an identifier and version, and that's what IMAGE_VERSION= and IMAGE_ID= is supposed to be.
226 lines
10 KiB
XML
226 lines
10 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="systemd.dnssd"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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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 network
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directories <filename>/usr/lib/systemd/dnssd</filename> and
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<filename>/usr/local/lib/systemd/dnssd</filename>, the volatile runtime network directory
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<filename>/run/systemd/dnssd</filename> and the local administration network directory
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<filename>/etc/systemd/dnssd</filename>. All configuration files are collectively sorted and processed in
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lexical order, regardless of the directories in which they live. However, files with identical filenames
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replace each other. Files in <filename>/etc/</filename> have the highest priority, files in
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<filename>/run/</filename> take precedence over files with the same name in
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<filename>/usr/lib/</filename>. This can be used to override a system-supplied configuration file with a
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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> directories
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can be placed in <filename>/usr/lib/systemd/dnssd</filename> or <filename>/run/systemd/dnssd</filename>
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directories. Drop-in files in <filename>/etc/</filename> take precedence over those in
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<filename>/run/</filename> which in turn take precedence over those in <filename>/usr/lib/</filename> or
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<filename>/usr/local/lib</filename>. Drop-in files under any of these directories take precedence over
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the main network service file wherever located.</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 [Service]
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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 class='specifiers'>
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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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<xi:include href="standard-specifiers.xml" xpointer="a"/>
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<xi:include href="standard-specifiers.xml" xpointer="A"/>
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<xi:include href="standard-specifiers.xml" xpointer="b"/>
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<xi:include href="standard-specifiers.xml" xpointer="B"/>
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<xi:include href="standard-specifiers.xml" xpointer="H"/>
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<xi:include href="standard-specifiers.xml" xpointer="m"/>
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<xi:include href="standard-specifiers.xml" xpointer="M"/>
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<xi:include href="standard-specifiers.xml" xpointer="o"/>
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<xi:include href="standard-specifiers.xml" xpointer="v"/>
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<xi:include href="standard-specifiers.xml" xpointer="w"/>
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<xi:include href="standard-specifiers.xml" xpointer="W"/>
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<xi:include href="standard-specifiers.xml" xpointer="percent"/>
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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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