man/nss-resolve.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7
   8   Copyright © 2013 Tom Gundersen
   9 -->
  10
  11 <refentry id="nss-resolve" conditional='ENABLE_RESOLVE'>
  12
  13   <refentryinfo>
  14     <title>nss-resolve</title>
  15     <productname>systemd</productname>
  16
  17     <authorgroup>
  18       <author>
  19         <contrib>Developer</contrib>
  20         <firstname>Lennart</firstname>
  21         <surname>Poettering</surname>
  22         <email>lennart@poettering.net</email>
  23       </author>
  24     </authorgroup>
  25   </refentryinfo>
  26
  27   <refmeta>
  28     <refentrytitle>nss-resolve</refentrytitle>
  29     <manvolnum>8</manvolnum>
  30   </refmeta>
  31
  32   <refnamediv>
  33     <refname>nss-resolve</refname>
  34     <refname>libnss_resolve.so.2</refname>
  35     <refpurpose>Provide hostname resolution via <filename>systemd-resolved.service</filename></refpurpose>
  36   </refnamediv>
  37
  38   <refsynopsisdiv>
  39     <para><filename>libnss_resolve.so.2</filename></para>
  40   </refsynopsisdiv>
  41
  42   <refsect1>
  43     <title>Description</title>
  44
  45     <para><command>nss-resolve</command> is a plug-in module for the GNU Name Service Switch (NSS) functionality of the
  46     GNU C Library (<command>glibc</command>) enabling it to resolve host names via the
  47     <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry> local network
  48     name resolution service. It replaces the <command>nss-dns</command> plug-in module that traditionally resolves
  49     hostnames via DNS.</para>
  50
  51     <para>To activate the NSS module, add <literal>resolve</literal> to the line starting with
  52     <literal>hosts:</literal> in <filename>/etc/nsswitch.conf</filename>. Specifically, it is recommended to place
  53     <literal>resolve</literal> early in <filename>/etc/nsswitch.conf</filename>'s <literal>hosts:</literal> line (but
  54     after the <literal>files</literal> or <literal>mymachines</literal> entries), right before the
  55     <literal>dns</literal> entry if it exists, followed by <literal>[!UNAVAIL=return]</literal>, to ensure DNS queries
  56     are always routed via
  57     <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry> if it is
  58     running, but are routed to <command>nss-dns</command> if this service is not available.</para>
  59
  60     <para>Note that <command>systemd-resolved</command> will synthesize DNS resource
  61     records in a few cases, for example for <literal>localhost</literal> and the
  62     current hostname, see
  63     <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  64     for the full list. This duplicates the functionality of
  65     <citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
  66     but it is still recommended (see examples below) to keep
  67     <command>nss-myhostname</command> configured in
  68     <filename>/etc/nsswitch.conf</filename>, to keep those names resolveable if
  69     <command>systemd-resolved</command> is not running.</para>
  70   </refsect1>
  71
  72   <refsect1>
  73     <title>Example</title>
  74
  75     <para>Here is an example <filename>/etc/nsswitch.conf</filename> file that enables <command>nss-resolve</command>
  76     correctly:</para>
  77
  78 <programlisting>passwd:         compat mymachines systemd
  79 group:          compat mymachines systemd
  80 shadow:         compat
  81
  82 hosts:          files mymachines <command>resolve [!UNAVAIL=return]</command> dns myhostname
  83 networks:       files
  84
  85 protocols:      db files
  86 services:       db files
  87 ethers:         db files
  88 rpc:            db files
  89
  90 netgroup:       nis</programlisting>
  91   </refsect1>
  92
  93   <refsect1>
  94     <title>See Also</title>
  95     <para>
  96       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  97       <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
  98       <citerefentry><refentrytitle>nss-systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
  99       <citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 100       <citerefentry><refentrytitle>nss-mymachines</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 101       <citerefentry project='man-pages'><refentrytitle>nsswitch.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 102     </para>
 103   </refsect1>
 104
 105 </refentry>