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<?xml version='1.0'?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
SPDX-License-Identifier: LGPL-2.1+
-->
<refentry id="nss-resolve" conditional='ENABLE_NSS_RESOLVE'>
<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>Provide 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 host names 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</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 (but
after the <literal>files</literal> or <literal>mymachines</literal> entries), right before the
<literal>dns</literal> entry if it exists, followed by <literal>[!UNAVAIL=return]</literal>, to ensure DNS queries
are always routed via
<citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry> if it is
running, but are routed to <command>nss-dns</command> if this service 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 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>
</refsect1>
<refsect1>
<title>Example</title>
<para>Here is an example <filename>/etc/nsswitch.conf</filename> file that enables <command>nss-resolve</command>
correctly:</para>
<programlisting>passwd: compat mymachines systemd
group: compat mymachines systemd
shadow: compat
hosts: files mymachines <command>resolve [!UNAVAIL=return]</command> dns myhostname
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>
</para>
</refsect1>
</refentry>
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