"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
+ SPDX-License-Identifier: LGPL-2.1+
+
This file is part of systemd.
Copyright 2011 Lennart Poettering
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
-<refentry id="nss-resolve" conditional='ENABLE_RESOLVED'>
+<refentry id="nss-resolve" conditional='ENABLE_RESOLVE'>
<refentryinfo>
<title>nss-resolve</title>
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>.</para>
-
- <para>It is recommended to place <literal>resolve</literal> early in <filename>/etc/nsswitch.conf</filename>'
- <literal>hosts:</literal> line (but after the <literal>files</literal> or <literal>mymachines</literal> entries),
- replacing the <literal>dns</literal> entry if it exists, to ensure DNS queries are always routed via
- <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
-
- <para>Note that <command>nss-resolve</command> will chain-load <command>nss-dns</command> if
- <filename>systemd-resolved.service</filename> is not running, ensuring that basic DNS resolution continues to work
- if the service is down.</para>
+ <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>
<para>Here is an example <filename>/etc/nsswitch.conf</filename> file that enables <command>nss-resolve</command>
correctly:</para>
-<programlisting>passwd: compat mymachines
-group: compat mymachines
+<programlisting>passwd: compat mymachines systemd
+group: compat mymachines systemd
shadow: compat
-hosts: files mymachines <command>resolve</command> myhostname
+hosts: files mymachines <command>resolve [!UNAVAIL=return]</command> dns myhostname
networks: files
protocols: db files
rpc: db files
netgroup: nis</programlisting>
-
</refsect1>
<refsect1>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>nss-mymachines</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>