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<refentry id="systemd-resolved.service" conditional='ENABLE_RESOLVED'>

<refentryinfo>

<title>systemd-resolved.service</title>

<productname>systemd</productname>

<authorgroup>

<author>

<contrib>Developer</contrib>

<firstname>Tom</firstname>

<surname>Gundersen</surname>

<email>teg@jklm.no</email>

</author>

</authorgroup>

</refentryinfo>

<refmeta>

<refentrytitle>systemd-resolved.service</refentrytitle>

<manvolnum>8</manvolnum>

</refmeta>

<refnamediv>

<refname>systemd-resolved.service</refname>

<refname>systemd-resolved</refname>

<refpurpose>Network Name Resolution manager</refpurpose>

</refnamediv>

<refsynopsisdiv>

<para><filename>systemd-resolved.service</filename></para>

<para><filename>/usr/lib/systemd/systemd-resolved</filename></para>

</refsynopsisdiv>

<refsect1>

<title>Description</title>

<para><command>systemd-resolved</command> is a system service that provides network name resolution to local

applications. It implements a caching and validating DNS/DNSSEC stub resolver, as well as an LLMNR resolver and

responder. In addition it maintains the <filename>/run/systemd/resolve/resolv.conf</filename> file for

compatibility with traditional Linux programs. This file may be symlinked from

<filename>/etc/resolv.conf</filename>.</para>

<para>The glibc NSS module

<citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</manvolnum></citerefentry> is required to

permit glibc's NSS resolver functions to resolve host names via <command>systemd-resolved</command>.</para>

<para>The DNS servers contacted are determined from the global

settings in <filename>/etc/systemd/resolved.conf</filename>, the

per-link static settings in <filename>/etc/systemd/network/*.network</filename> files,

and the per-link dynamic settings received over DHCP. See

<citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>

and

<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>

for details. To improve compatibility,

<filename>/etc/resolv.conf</filename> is read in order to discover

configured system DNS servers, but only if it is not a symlink

to <filename>/run/systemd/resolve/resolv.conf</filename> (see above).</para>

<para><command>systemd-resolved</command> synthesizes DNS RRs for the following cases:</para>

<itemizedlist>

<listitem><para>The local, configured hostname is resolved to

all locally configured IP addresses ordered by their scope, or

— if none are configured — the IPv4 address 127.0.0.2 (which

is on the local loopback) and the IPv6 address ::1 (which is the

local host).</para></listitem>

<listitem><para>The hostname <literal>localhost</literal> (as well as any hostname ending in

<literal>.localhost</literal>, <literal>.localdomain</literal> or equal to <literal>localdomain</literal>) is

resolved to the IP addresses 127.0.0.1 and ::1.</para></listitem>

<listitem><para>The hostname <literal>gateway</literal> is

resolved to all current default routing gateway addresses,

ordered by their metric. This assigns a stable hostname to the

current gateway, useful for referencing it independently of the

current network configuration state.</para></listitem>

<listitem><para>The mappings defined in <filename>/etc/hosts</filename> are resolved to their configured

addresses and back.</para></listitem>

</itemizedlist>

<para>Lookup requests are routed to the available DNS servers

and LLMNR interfaces according to the following rules:</para>

<itemizedlist>

<listitem><para>Lookups for the special hostname

<literal>localhost</literal> are never routed to the

network. (A few other, special domains are handled the same way.)</para></listitem>

<listitem><para>Single-label names are routed to all local

interfaces capable of IP multicasting, using the LLMNR

protocol. Lookups for IPv4 addresses are only sent via LLMNR on

IPv4, and lookups for IPv6 addresses are only sent via LLMNR on

IPv6. Lookups for the locally configured host name and the

<literal>gateway</literal> host name are never routed to

LLMNR.</para></listitem>

<listitem><para>Multi-label names are routed to all local

interfaces that have a DNS sever configured, plus the globally

configured DNS server if there is one. Address lookups from the

link-local address range are never routed to

DNS.</para></listitem>

</itemizedlist>

<para>If lookups are routed to multiple interfaces, the first

successful response is returned (thus effectively merging the

lookup zones on all matching interfaces). If the lookup failed on

all interfaces, the last failing response is returned.</para>

<para>Routing of lookups may be influenced by configuring

per-interface domain names. See

<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>

for details. Lookups for a hostname ending in one of the

per-interface domains are exclusively routed to the matching

interfaces.</para>

<para>Note that <filename>/run/systemd/resolve/resolv.conf</filename> should not be used directly by applications,

but only through a symlink from <filename>/etc/resolv.conf</filename>.</para>

<para>See the <ulink url="http://www.freedesktop.org/wiki/Software/systemd/resolved"> resolved D-Bus API

Documentation</ulink> for information about the APIs <filename>systemd-resolved</filename> provides.</para>

</refsect1>

<refsect1>

<title>See Also</title>

<para>

<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,

<citerefentry><refentrytitle>dnssec-trust-anchors.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,

<citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</manvolnum></citerefentry>,

<citerefentry><refentrytitle>systemd-resolve</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,

<citerefentry project='man-pages'><refentrytitle>hosts</refentrytitle><manvolnum>5</manvolnum></citerefentry>,

<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>,

<citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>

</para>

</refsect1>

</refentry>