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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-10 20:49:52 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-10 20:49:52 +0000
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Adding upstream version 255.4.upstream/255.4
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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+<?xml version='1.0'?>
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
+
+<refentry id="nss-resolve" conditional='ENABLE_NSS_RESOLVE'
+ xmlns:xi="http://www.w3.org/2001/XInclude">
+
+ <refentryinfo>
+ <title>nss-resolve</title>
+ <productname>systemd</productname>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>nss-resolve</refentrytitle>
+ <manvolnum>8</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>nss-resolve</refname>
+ <refname>libnss_resolve.so.2</refname>
+ <refpurpose>Hostname resolution via <filename>systemd-resolved.service</filename></refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <para><filename>libnss_resolve.so.2</filename></para>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para><command>nss-resolve</command> is a plug-in module for the GNU Name Service Switch (NSS) functionality of the
+ GNU C Library (<command>glibc</command>) enabling it to resolve hostnames via the
+ <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry> local network
+ name resolution service. It replaces the <command>nss-dns</command> plug-in module that traditionally resolves
+ hostnames via DNS.</para>
+
+ <para>To activate the NSS module, add <literal>resolve [!UNAVAIL=return]</literal> to the line starting
+ with <literal>hosts:</literal> in <filename>/etc/nsswitch.conf</filename>. Specifically, it is
+ recommended to place <literal>resolve</literal> early in <filename>/etc/nsswitch.conf</filename>'s
+ <literal>hosts:</literal> line. It should be before the <literal>files</literal> entry, since
+ <filename>systemd-resolved</filename> supports <filename>/etc/hosts</filename> internally, but with
+ caching. To the contrary, it should be after <literal>mymachines</literal>, to give hostnames given to
+ local VMs and containers precedence over names received over DNS. Finally, we recommend placing
+ <literal>dns</literal> somewhere after <literal>resolve</literal>, to fall back to
+ <command>nss-dns</command> if <filename>systemd-resolved.service</filename> is not available.</para>
+
+ <para>Note that <command>systemd-resolved</command> will synthesize DNS resource records in a few cases,
+ for example for <literal>localhost</literal> and the current local hostname, see
+ <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry> for
+ the full list. This duplicates the functionality of
+ <citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>8</manvolnum></citerefentry>, but
+ it is still recommended (see examples below) to keep <command>nss-myhostname</command> configured in
+ <filename>/etc/nsswitch.conf</filename>, to keep those names resolveable if
+ <command>systemd-resolved</command> is not running.</para>
+
+ <para>Please keep in mind that <command>nss-myhostname</command> (and <command>nss-resolve</command>) also resolve
+ in the other direction — from locally attached IP addresses to
+ hostnames. If you rely on that lookup being provided by DNS, you might
+ want to order things differently.
+ </para>
+
+ <para>Communication between <command>nss-resolve</command> and
+ <filename>systemd-resolved.service</filename> takes place via the
+ <filename>/run/systemd/resolve/io.systemd.Resolve</filename> <constant>AF_UNIX</constant> socket.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Environment variables</title>
+
+ <variablelist class='environment-variables'>
+ <varlistentry>
+ <term><varname>$SYSTEMD_NSS_RESOLVE_VALIDATE</varname></term>
+
+ <listitem><para>Takes a boolean argument. When false, cryptographic validation of resource records
+ via DNSSEC will be disabled. This may be useful for testing, or when system time is known to be
+ unreliable.</para>
+
+ <xi:include href="version-info.xml" xpointer="v250"/></listitem>
+ </varlistentry>
+ </variablelist>
+
+ <variablelist class='environment-variables'>
+ <varlistentry>
+ <term><varname>$SYSTEMD_NSS_RESOLVE_SYNTHESIZE</varname></term>
+
+ <listitem><para>Takes a boolean argument. When false, synthetic records, e.g. for the local host
+ name, will not be returned. See section SYNTHETIC RECORDS in
+ <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ for more information. This may be useful to query the "public" resource records, independent of the
+ configuration of the local machine.</para>
+
+ <xi:include href="version-info.xml" xpointer="v250"/></listitem>
+ </varlistentry>
+ </variablelist>
+
+ <variablelist class='environment-variables'>
+ <varlistentry>
+ <term><varname>$SYSTEMD_NSS_RESOLVE_CACHE</varname></term>
+
+ <listitem><para>Takes a boolean argument. When false, the cache of previously queried records will
+ not be used by
+ <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
+ </para>
+
+ <xi:include href="version-info.xml" xpointer="v250"/></listitem>
+ </varlistentry>
+ </variablelist>
+
+ <variablelist class='environment-variables'>
+ <varlistentry>
+ <term><varname>$SYSTEMD_NSS_RESOLVE_ZONE</varname></term>
+
+ <listitem><para>Takes a boolean argument. When false, answers using locally registered public
+ LLMNR/mDNS resource records will not be returned.</para>
+
+ <xi:include href="version-info.xml" xpointer="v250"/></listitem>
+ </varlistentry>
+ </variablelist>
+
+ <variablelist class='environment-variables'>
+ <varlistentry>
+ <term><varname>$SYSTEMD_NSS_RESOLVE_TRUST_ANCHOR</varname></term>
+
+ <listitem><para>Takes a boolean argument. When false, answers using locally configured trust anchors
+ will not be used.</para>
+
+ <xi:include href="version-info.xml" xpointer="v250"/></listitem>
+ </varlistentry>
+ </variablelist>
+
+ <variablelist class='environment-variables'>
+ <varlistentry>
+ <term><varname>$SYSTEMD_NSS_RESOLVE_NETWORK</varname></term>
+
+ <listitem><para>Takes a boolean argument. When false, answers will be returned without using the
+ network, i.e. either from local sources or the cache in
+ <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
+ </para>
+
+ <xi:include href="version-info.xml" xpointer="v250"/></listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+
+ <refsect1>
+ <title>Example</title>
+
+ <para>Here is an example <filename>/etc/nsswitch.conf</filename> file that enables
+ <command>nss-resolve</command> correctly:</para>
+
+ <!-- synchronize with other nss-* man pages and factory/etc/nsswitch.conf -->
+<programlisting>passwd: files systemd
+group: files [SUCCESS=merge] systemd
+shadow: files systemd
+gshadow: files systemd
+
+hosts: mymachines <command>resolve [!UNAVAIL=return]</command> files myhostname dns
+networks: files
+
+protocols: db files
+services: db files
+ethers: db files
+rpc: db files
+
+netgroup: nis</programlisting>
+ </refsect1>
+
+ <refsect1>
+ <title>See Also</title>
+ <para>
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>nss-systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>nss-mymachines</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ <citerefentry project='man-pages'><refentrytitle>nsswitch.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd.syntax</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ </para>
+ </refsect1>
+
+</refentry>