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diff --git a/man/nss-resolve.xml b/man/nss-resolve.xml new file mode 100644 index 0000000..d633be2 --- /dev/null +++ b/man/nss-resolve.xml @@ -0,0 +1,182 @@ +<?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> |