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2dc6b11d | 1 | <?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*--> |
091a364c | 2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" |
12b42c76 | 3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
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4 | |
5 | <!-- | |
6 | This file is part of systemd. | |
7 | ||
8 | Copyright 2014 Tom Gundersen | |
9 | ||
10 | systemd is free software; you can redistribute it and/or modify it | |
11 | under the terms of the GNU Lesser General Public License as published by | |
12 | the Free Software Foundation; either version 2.1 of the License, or | |
13 | (at your option) any later version. | |
14 | ||
15 | systemd is distributed in the hope that it will be useful, but | |
16 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
17 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
18 | Lesser General Public License for more details. | |
19 | ||
20 | You should have received a copy of the GNU Lesser General Public License | |
21 | along with systemd; If not, see <http://www.gnu.org/licenses/>. | |
22 | --> | |
23 | ||
24 | <refentry id="systemd-resolved.service" conditional='ENABLE_RESOLVED'> | |
25 | ||
798d3a52 ZJS |
26 | <refentryinfo> |
27 | <title>systemd-resolved.service</title> | |
28 | <productname>systemd</productname> | |
29 | ||
30 | <authorgroup> | |
31 | <author> | |
32 | <contrib>Developer</contrib> | |
33 | <firstname>Tom</firstname> | |
34 | <surname>Gundersen</surname> | |
35 | <email>teg@jklm.no</email> | |
36 | </author> | |
37 | </authorgroup> | |
38 | </refentryinfo> | |
39 | ||
40 | <refmeta> | |
41 | <refentrytitle>systemd-resolved.service</refentrytitle> | |
42 | <manvolnum>8</manvolnum> | |
43 | </refmeta> | |
44 | ||
45 | <refnamediv> | |
46 | <refname>systemd-resolved.service</refname> | |
47 | <refname>systemd-resolved</refname> | |
48 | <refpurpose>Network Name Resolution manager</refpurpose> | |
49 | </refnamediv> | |
50 | ||
51 | <refsynopsisdiv> | |
52 | <para><filename>systemd-resolved.service</filename></para> | |
12b42c76 | 53 | <para><filename>/usr/lib/systemd/systemd-resolved</filename></para> |
798d3a52 ZJS |
54 | </refsynopsisdiv> |
55 | ||
56 | <refsect1> | |
57 | <title>Description</title> | |
58 | ||
59 | <para><command>systemd-resolved</command> is a system service that | |
60 | manages network name resolution. It implements a caching DNS stub | |
61 | resolver and an LLMNR resolver and responder. It also generates | |
62 | <filename>/run/systemd/resolve/resolv.conf</filename> for | |
63 | compatibility which may be symlinked from | |
437293cf LP |
64 | <filename>/etc/resolv.conf</filename>. The glibc NSS module |
65 | <citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</manvolnum></citerefentry> | |
66 | is necessary to allow libc's NSS resolver functions to resolve | |
67 | host names via <command>systemd-resolved</command>.</para> | |
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68 | |
69 | <para>The DNS servers contacted are determined from the global | |
437293cf LP |
70 | settings in <filename>/etc/systemd/resolved.conf</filename>, the |
71 | per-link static settings in <filename>/etc/systemd/network/*.network</filename> files, | |
72 | and the per-link dynamic settings received over DHCP. See | |
73 | <citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
74 | and | |
798d3a52 | 75 | <citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry> |
b938cb90 | 76 | for details. To improve compatibility, |
437293cf | 77 | <filename>/etc/resolv.conf</filename> is read in order to discover |
a8eaaee7 | 78 | configured system DNS servers, but only if it is not a symlink |
437293cf | 79 | to <filename>/run/systemd/resolve/resolv.conf</filename> (see above).</para> |
798d3a52 | 80 | |
2dc6b11d LP |
81 | <para><command>systemd-resolved</command> synthesizes DNS RRs for the following cases:</para> |
82 | ||
83 | <itemizedlist> | |
84 | <listitem><para>The local, configured hostname is resolved to | |
85 | all locally configured IP addresses ordered by their scope, or | |
86 | — if none are configured — the IPv4 address 127.0.0.2 (which | |
87 | is on the local loopback) and the IPv6 address ::1 (which is the | |
88 | local host).</para></listitem> | |
89 | ||
90 | <listitem><para>The hostname <literal>localhost</literal> is | |
91 | resolved to the IP addresses 127.0.0.1 and | |
92 | ::1.</para></listitem> | |
93 | ||
94 | <listitem><para>The hostname <literal>gateway</literal> is | |
95 | resolved to all current default routing gateway addresses, | |
96 | ordered by their metric. This assigns a stable hostname to the | |
97 | current gateway, useful for referencing it independently of the | |
98 | current network configuration state.</para></listitem> | |
99 | </itemizedlist> | |
100 | ||
101 | <para>Lookup requests are routed to the available DNS servers | |
102 | and LLMNR interfaces according to the following rules:</para> | |
103 | ||
104 | <itemizedlist> | |
105 | <listitem><para>Lookups for the special hostname | |
106 | <literal>localhost</literal> are never routed to the | |
107 | network.</para></listitem> | |
108 | ||
109 | <listitem><para>Single-label names are routed to all local | |
110 | interfaces capable of IP multicasting, using the LLMNR | |
111 | protocol. Lookups for IPv4 addresses are only sent via LLMNR on | |
112 | IPv4, and lookups for IPv6 addresses are only sent via LLMNR on | |
113 | IPv6. Lookups for the locally configured host name and the | |
114 | <literal>gateway</literal> host name are never routed to | |
115 | LLMNR.</para></listitem> | |
116 | ||
117 | <listitem><para>Multi-label names are routed to all local | |
118 | interfaces that have a DNS sever configured, plus the globally | |
119 | configured DNS server if there is one. Address lookups from the | |
120 | link-local addres range are never routed to | |
121 | DNS.</para></listitem> | |
122 | </itemizedlist> | |
123 | ||
124 | <para>If lookups are routed to multiple interfaces, the first | |
125 | successful response is returned (thus effectively merging the | |
126 | lookup zones on all matching interfaces). If the lookup failed on | |
b938cb90 | 127 | all interfaces, the last failing response is returned.</para> |
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128 | |
129 | <para>Routing of lookups may be influenced by configuring | |
b938cb90 | 130 | per-interface domain names. See |
2dc6b11d LP |
131 | <citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry> |
132 | for details. Lookups for a hostname ending in one of the | |
133 | per-interface domains are exclusively routed to the matching | |
134 | interfaces.</para> | |
135 | ||
798d3a52 ZJS |
136 | <para>Note that |
137 | <filename>/run/systemd/resolve/resolv.conf</filename> should not | |
138 | be used directly, but only through a symlink from | |
139 | <filename>/etc/resolv.conf</filename>.</para> | |
140 | </refsect1> | |
141 | ||
142 | <refsect1> | |
143 | <title>See Also</title> | |
144 | <para> | |
145 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
146 | <citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
437293cf | 147 | <citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</manvolnum></citerefentry>, |
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148 | <citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>, |
149 | <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> | |
150 | </para> | |
151 | </refsect1> | |
091a364c TG |
152 | |
153 | </refentry> |