diff options
Diffstat (limited to 'src/grp-resolve/systemd-resolved/systemd-resolved.service.xml')
| -rw-r--r-- | src/grp-resolve/systemd-resolved/systemd-resolved.service.xml | 234 |
1 files changed, 234 insertions, 0 deletions
diff --git a/src/grp-resolve/systemd-resolved/systemd-resolved.service.xml b/src/grp-resolve/systemd-resolved/systemd-resolved.service.xml new file mode 100644 index 0000000000..56f67960ce --- /dev/null +++ b/src/grp-resolve/systemd-resolved/systemd-resolved.service.xml @@ -0,0 +1,234 @@ +<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*--> +<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> + +<!-- + This file is part of systemd. + + Copyright 2014 Tom Gundersen + + systemd is free software; you can redistribute it and/or modify it + under the terms of the GNU Lesser General Public License as published by + the Free Software Foundation; either version 2.1 of the License, or + (at your option) any later version. + + systemd is distributed in the hope that it will be useful, but + WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public License + along with systemd; If not, see <http://www.gnu.org/licenses/>. +--> + +<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. Local applications may submit network name resolution requests via three interfaces:</para> + + <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 + 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 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 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 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> + + <listitem><para>Additionally, <command>systemd-resolved</command> provides a local DNS stub listener on IP + address 127.0.0.53 on the local loopback interface. Programs issuing DNS requests directly, bypassing any local + API may be directed to this stub, in order to connect them to <command>systemd-resolved</command>. Note however + that it is strongly recommended that local programs use the glibc NSS or bus APIs instead (as described above), + as various network resolution concepts (such as link-local addressing, or LLMNR Unicode domains) cannot be mapped + to the unicast DNS protocol.</para></listitem> + </itemizedlist> + + <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, the per-link dynamic settings received over DHCP and any + DNS server information made available by other system services. See + <citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> and + <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> + + <para><command>systemd-resolved</command> synthesizes DNS resource records (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 hostnames <literal>localhost</literal> and + <literal>localhost.localdomain</literal> (as well as any hostname + 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 + 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>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><filename>/etc/resolv.conf</filename></title> + + <para>Three 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>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> + + <listitem><para><command>systemd-resolved</command> 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> and is always kept up-to-date, + containing information about all known DNS servers. Note the file format's limitations: it does not know a + concept of per-interface DNS servers and hence only contains system-wide DNS server definitions. 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>. If this mode of operation is used local clients + that bypass any local DNS API will also bypass <command>systemd-resolved</command> and will talk directly to the + known DNS servers.</para> </listitem> + + <listitem><para>Alternatively, <filename>/etc/resolv.conf</filename> may be managed by other packages, in which + case <command>systemd-resolved</command> will read it for DNS configuration data. In this mode of operation + <command>systemd-resolved</command> is consumer rather than provider of this configuration + file. </para></listitem> + </itemizedlist> + + <para>Note that the selected mode of operation for this file is detected fully automatically, depending on whether + <filename>/etc/resolv.conf</filename> is a symlink to <filename>/run/systemd/resolve/resolv.conf</filename> or + lists 127.0.0.53 as DNS server.</para> + </refsect1> + + <refsect1> + <title>Signals</title> + + <variablelist> + <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> + </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> + </varlistentry> + </variablelist> + </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> |