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154 lines
6.5 KiB
XML
154 lines
6.5 KiB
XML
<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
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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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This file is part of systemd.
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Copyright 2014 Tom Gundersen
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="systemd-resolved.service" conditional='ENABLE_RESOLVED'>
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<refentryinfo>
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<title>systemd-resolved.service</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Tom</firstname>
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<surname>Gundersen</surname>
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<email>teg@jklm.no</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd-resolved.service</refentrytitle>
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<manvolnum>8</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd-resolved.service</refname>
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<refname>systemd-resolved</refname>
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<refpurpose>Network Name Resolution manager</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>systemd-resolved.service</filename></para>
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<para><filename>/usr/lib/systemd/systemd-resolved</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><command>systemd-resolved</command> is a system service that
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manages network name resolution. It implements a caching DNS stub
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resolver and an LLMNR resolver and responder. It also generates
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<filename>/run/systemd/resolve/resolv.conf</filename> for
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compatibility which may be symlinked from
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<filename>/etc/resolv.conf</filename>. The glibc NSS module
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<citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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is necessary to allow libc's NSS resolver functions to resolve
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host names via <command>systemd-resolved</command>.</para>
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<para>The DNS servers contacted are determined from the global
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settings in <filename>/etc/systemd/resolved.conf</filename>, the
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per-link static settings in <filename>/etc/systemd/network/*.network</filename> files,
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and the per-link dynamic settings received over DHCP. See
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<citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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and
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<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details. To improve compatibility
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<filename>/etc/resolv.conf</filename> is read in order to discover
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configured system DNS servers, however only if it is not a symlink
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to <filename>/run/systemd/resolve/resolv.conf</filename> (see above).</para>
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<para><command>systemd-resolved</command> synthesizes DNS RRs for the following cases:</para>
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<itemizedlist>
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<listitem><para>The local, configured hostname is resolved to
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all locally configured IP addresses ordered by their scope, or
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— if none are configured — the IPv4 address 127.0.0.2 (which
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is on the local loopback) and the IPv6 address ::1 (which is the
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local host).</para></listitem>
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<listitem><para>The hostname <literal>localhost</literal> is
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resolved to the IP addresses 127.0.0.1 and
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::1.</para></listitem>
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<listitem><para>The hostname <literal>gateway</literal> is
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resolved to all current default routing gateway addresses,
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ordered by their metric. This assigns a stable hostname to the
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current gateway, useful for referencing it independently of the
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current network configuration state.</para></listitem>
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</itemizedlist>
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<para>Lookup requests are routed to the available DNS servers
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and LLMNR interfaces according to the following rules:</para>
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<itemizedlist>
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<listitem><para>Lookups for the special hostname
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<literal>localhost</literal> are never routed to the
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network.</para></listitem>
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<listitem><para>Single-label names are routed to all local
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interfaces capable of IP multicasting, using the LLMNR
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protocol. Lookups for IPv4 addresses are only sent via LLMNR on
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IPv4, and lookups for IPv6 addresses are only sent via LLMNR on
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IPv6. Lookups for the locally configured host name and the
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<literal>gateway</literal> host name are never routed to
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LLMNR.</para></listitem>
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<listitem><para>Multi-label names are routed to all local
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interfaces that have a DNS sever configured, plus the globally
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configured DNS server if there is one. Address lookups from the
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link-local addres range are never routed to
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DNS.</para></listitem>
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</itemizedlist>
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<para>If lookups are routed to multiple interfaces, the first
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successful response is returned (thus effectively merging the
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lookup zones on all matching interfaces). If the lookup failed on
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all interfaces the last failing response is returned.</para>
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<para>Routing of lookups may be influenced by configuring
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per-interface domain names, see
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<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details. Lookups for a hostname ending in one of the
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per-interface domains are exclusively routed to the matching
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interfaces.</para>
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<para>Note that
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<filename>/run/systemd/resolve/resolv.conf</filename> should not
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be used directly, but only through a symlink from
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<filename>/etc/resolv.conf</filename>.</para>
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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>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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