man/nss-resolve.xml

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   8   This file is part of systemd.
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  10   Copyright 2011 Lennart Poettering
  11   Copyright 2013 Tom Gundersen
  12
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  26
  27 <refentry id="nss-resolve" conditional='ENABLE_RESOLVE'>
  28
  29   <refentryinfo>
  30     <title>nss-resolve</title>
  31     <productname>systemd</productname>
  32
  33     <authorgroup>
  34       <author>
  35         <contrib>Developer</contrib>
  36         <firstname>Lennart</firstname>
  37         <surname>Poettering</surname>
  38         <email>lennart@poettering.net</email>
  39       </author>
  40     </authorgroup>
  41   </refentryinfo>
  42
  43   <refmeta>
  44     <refentrytitle>nss-resolve</refentrytitle>
  45     <manvolnum>8</manvolnum>
  46   </refmeta>
  47
  48   <refnamediv>
  49     <refname>nss-resolve</refname>
  50     <refname>libnss_resolve.so.2</refname>
  51     <refpurpose>Provide hostname resolution via <filename>systemd-resolved.service</filename></refpurpose>
  52   </refnamediv>
  53
  54   <refsynopsisdiv>
  55     <para><filename>libnss_resolve.so.2</filename></para>
  56   </refsynopsisdiv>
  57
  58   <refsect1>
  59     <title>Description</title>
  60
  61     <para><command>nss-resolve</command> is a plug-in module for the GNU Name Service Switch (NSS) functionality of the
  62     GNU C Library (<command>glibc</command>) enabling it to resolve host names via the
  63     <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry> local network
  64     name resolution service. It replaces the <command>nss-dns</command> plug-in module that traditionally resolves
  65     hostnames via DNS.</para>
  66
  67     <para>To activate the NSS module, add <literal>resolve</literal> to the line starting with
  68     <literal>hosts:</literal> in <filename>/etc/nsswitch.conf</filename>. Specifically, it is recommended to place
  69     <literal>resolve</literal> early in <filename>/etc/nsswitch.conf</filename>'s <literal>hosts:</literal> line (but
  70     after the <literal>files</literal> or <literal>mymachines</literal> entries), right before the
  71     <literal>dns</literal> entry if it exists, followed by <literal>[!UNAVAIL=return]</literal>, to ensure DNS queries
  72     are always routed via
  73     <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry> if it is
  74     running, but are routed to <command>nss-dns</command> if this service is not available.</para>
  75
  76     <para>Note that <command>systemd-resolved</command> will synthesize DNS resource
  77     records in a few cases, for example for <literal>localhost</literal> and the
  78     current hostname, see
  79     <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  80     for the full list. This duplicates the functionality of
  81     <citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
  82     but it is still recommended (see examples below) to keep
  83     <command>nss-myhostname</command> configured in
  84     <filename>/etc/nsswitch.conf</filename>, to keep those names resolveable if
  85     <command>systemd-resolved</command> is not running.</para>
  86   </refsect1>
  87
  88   <refsect1>
  89     <title>Example</title>
  90
  91     <para>Here is an example <filename>/etc/nsswitch.conf</filename> file that enables <command>nss-resolve</command>
  92     correctly:</para>
  93
  94 <programlisting>passwd:         compat mymachines systemd
  95 group:          compat mymachines systemd
  96 shadow:         compat
  97
  98 hosts:          files mymachines <command>resolve [!UNAVAIL=return]</command> dns myhostname
  99 networks:       files
 100
 101 protocols:      db files
 102 services:       db files
 103 ethers:         db files
 104 rpc:            db files
 105
 106 netgroup:       nis</programlisting>
 107   </refsect1>
 108
 109   <refsect1>
 110     <title>See Also</title>
 111     <para>
 112       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 113       <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 114       <citerefentry><refentrytitle>nss-systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 115       <citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 116       <citerefentry><refentrytitle>nss-mymachines</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 117       <citerefentry project='man-pages'><refentrytitle>nsswitch.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 118     </para>
 119   </refsect1>
 120
 121 </refentry>