"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
+ SPDX-License-Identifier: LGPL-2.1+
+
This file is part of systemd.
Copyright 2014 Tom Gundersen
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
-<refentry id="systemd-resolved.service" conditional='ENABLE_RESOLVED'>
+<refentry id="systemd-resolved.service" conditional='ENABLE_RESOLVE'>
<refentryinfo>
<title>systemd-resolved.service</title>
<itemizedlist>
<listitem><para>The native, fully-featured API <command>systemd-resolved</command> exposes on the bus. See the
- <ulink url="http://www.freedesktop.org/wiki/Software/systemd/resolved">API Documentation</ulink> for
+ <ulink url="https://www.freedesktop.org/wiki/Software/systemd/resolved">API Documentation</ulink> for
details. Usage of this API is generally recommended to clients as it is asynchronous and fully featured (for
example, properly returns DNSSEC validation status and interface scope for addresses as necessary for supporting
link-local networking).</para></listitem>
<listitem><para>The glibc
- <citerefentry><refentrytitle>getaddrinfo</refentrytitle><manvolnum>3</manvolnum></citerefentry> API as defined
+ <citerefentry project='man-pages'><refentrytitle>getaddrinfo</refentrytitle><manvolnum>3</manvolnum></citerefentry> API as defined
by <ulink url="https://tools.ietf.org/html/rfc3493">RFC3493</ulink> and its related resolver functions,
- including <citerefentry><refentrytitle>gethostbyname</refentrytitle><manvolnum>3</manvolnum></citerefentry>. This
+ including <citerefentry project='man-pages'><refentrytitle>gethostbyname</refentrytitle><manvolnum>3</manvolnum></citerefentry>. This
API is widely supported, including beyond the Linux platform. In its current form it does not expose DNSSEC
validation status information however, and is synchronous only. This API is backed by the glibc Name Service
- Switch (<citerefentry><refentrytitle>nss</refentrytitle><manvolnum>5</manvolnum></citerefentry>). Usage of the
+ Switch (<citerefentry project='man-pages'><refentrytitle>nss</refentrytitle><manvolnum>5</manvolnum></citerefentry>). Usage of the
glibc NSS module <citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</manvolnum></citerefentry>
is required in order to allow glibc's NSS resolver functions to resolve host names via
<command>systemd-resolved</command>.</para></listitem>
<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry> for details
about systemd's own configuration files for DNS servers. 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 below).</para>
+ not a symlink to <filename>/run/systemd/resolve/stub-resolv.conf</filename> or
+ <filename>/run/systemd/resolve/resolv.conf</filename> (see below).</para>
<para><command>systemd-resolved</command> synthesizes DNS resource records (RRs) for the following cases:</para>
ending in <literal>.localhost</literal> or <literal>.localhost.localdomain</literal>)
are resolved to the IP addresses 127.0.0.1 and ::1.</para></listitem>
- <listitem><para>The hostname <literal>gateway</literal> is
+ <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>
+ <listitem><para>The mappings defined in <filename>/etc/hosts</filename> are resolved
+ to their configured addresses and back, but they will not affect lookups for
+ non-address types (like MX).</para></listitem>
</itemizedlist>
<para>Lookup requests are routed to the available DNS servers
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
+ <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
+ interfaces that have a DNS server 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>
per-interface domains are exclusively routed to the matching
interfaces.</para>
- <para>See the <ulink url="http://www.freedesktop.org/wiki/Software/systemd/resolved"> resolved D-Bus API
+ <para>See the <ulink url="https://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><filename>/etc/resolv.conf</filename></title>
- <para>Three modes of handling <filename>/etc/resolv.conf</filename> (see
- <citerefentry><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>) are
+ <para>Four modes of handling <filename>/etc/resolv.conf</filename> (see
+ <citerefentry project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>) are
supported:</para>
<itemizedlist>
+ <listitem><para><command>systemd-resolved</command> maintains the
+ <filename>/run/systemd/resolve/stub-resolv.conf</filename> file for compatibility with traditional Linux
+ programs. This file may be symlinked from <filename>/etc/resolv.conf</filename>. This file lists the 127.0.0.53
+ DNS stub (see above) as the only DNS server. It also contains a list of search domains that are in use by
+ systemd-resolved. The list of search domains is always kept up-to-date. Note that
+ <filename>/run/systemd/resolve/stub-resolv.conf</filename> should not be used directly by applications, but only
+ through a symlink from <filename>/etc/resolv.conf</filename>. This file may be symlinked from
+ <filename>/etc/resolv.conf</filename> in order to connect all local clients that bypass local DNS APIs to
+ <command>systemd-resolved</command> with correct search domains settings. This mode of operation is
+ recommended.</para></listitem>
+
<listitem><para>A static file <filename>/usr/lib/systemd/resolv.conf</filename> is provided that lists
the 127.0.0.53 DNS stub (see above) as only DNS server. This file may be symlinked from
<filename>/etc/resolv.conf</filename> in order to connect all local clients that bypass local DNS APIs to
- <command>systemd-resolved</command>. This mode of operation is recommended.</para></listitem>
+ <command>systemd-resolved</command>. This file does not contain any search domains.</para></listitem>
<listitem><para><command>systemd-resolved</command> maintains the
<filename>/run/systemd/resolve/resolv.conf</filename> file for compatibility with traditional Linux
<varlistentry>
<term><constant>SIGUSR1</constant></term>
- <listitem><para>Upon reception of the SIGUSR1 process signal <command>systemd-resolved</command> will dump the
- contents of all DNS resource record caches it maintains into the system logs.</para></listitem>
+ <listitem><para>Upon reception of the <constant>SIGUSR1</constant> process signal
+ <command>systemd-resolved</command> will dump the contents of all DNS resource record caches it maintains, as
+ well as all feature level information it learnt about configured DNS servers into the system
+ logs.</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>SIGUSR2</constant></term>
- <listitem><para>Upon reception of the SIGUSR2 process signal <command>systemd-resolved</command> will flush all
- caches it maintains. Note that it should normally not be necessary to request this explicitly – except for
- debugging purposes – as <command>systemd-resolved</command> flushes the caches automatically anyway any time
- the host's network configuration changes.</para></listitem>
+ <listitem><para>Upon reception of the <constant>SIGUSR2</constant> process signal
+ <command>systemd-resolved</command> will flush all caches it maintains. Note that it should normally not be
+ necessary to request this explicitly – except for debugging purposes – as <command>systemd-resolved</command>
+ flushes the caches automatically anyway any time the host's network configuration changes. Sending this signal
+ to <command>systemd-resolved</command> is equivalent to the <command>systemd-resolve --flush-caches</command>
+ command, however the latter is recommended since it operates in a synchronous way.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><constant>SIGRTMIN+1</constant></term>
+
+ <listitem><para>Upon reception of the <constant>SIGRTMIN+1</constant> process signal
+ <command>systemd-resolved</command> will forget everything it learnt about the configured DNS
+ servers. Specifically any information about server feature support is flushed out, and the server feature
+ probing logic is restarted on the next request, starting with the most fully featured level. Note that it
+ should normally not be necessary to request this explicitly – except for debugging purposes – as
+ <command>systemd-resolved</command> automatically forgets learnt information any time the DNS server
+ configuration changes. Sending this signal to <command>systemd-resolved</command> is equivalent to the
+ <command>systemd-resolve --reset-server-features</command> command, however the latter is recommended since it
+ operates in a synchronous way.</para></listitem>
</varlistentry>
</variablelist>
+
</refsect1>
<refsect1>
projects / thirdparty / systemd.git / blobdiff