man/nss-resolve.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
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   8
   9 <refentry id="nss-resolve" conditional='ENABLE_NSS_RESOLVE'>
  10
  11   <refentryinfo>
  12     <title>nss-resolve</title>
  13     <productname>systemd</productname>
  14   </refentryinfo>
  15
  16   <refmeta>
  17     <refentrytitle>nss-resolve</refentrytitle>
  18     <manvolnum>8</manvolnum>
  19   </refmeta>
  20
  21   <refnamediv>
  22     <refname>nss-resolve</refname>
  23     <refname>libnss_resolve.so.2</refname>
  24     <refpurpose>Provide hostname resolution via <filename>systemd-resolved.service</filename></refpurpose>
  25   </refnamediv>
  26
  27   <refsynopsisdiv>
  28     <para><filename>libnss_resolve.so.2</filename></para>
  29   </refsynopsisdiv>
  30
  31   <refsect1>
  32     <title>Description</title>
  33
  34     <para><command>nss-resolve</command> is a plug-in module for the GNU Name Service Switch (NSS) functionality of the
  35     GNU C Library (<command>glibc</command>) enabling it to resolve host names via the
  36     <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry> local network
  37     name resolution service. It replaces the <command>nss-dns</command> plug-in module that traditionally resolves
  38     hostnames via DNS.</para>
  39
  40     <para>To activate the NSS module, add <literal>resolve</literal> to the line starting with
  41     <literal>hosts:</literal> in <filename>/etc/nsswitch.conf</filename>. Specifically, it is recommended to place
  42     <literal>resolve</literal> early in <filename>/etc/nsswitch.conf</filename>'s <literal>hosts:</literal> line (but
  43     after the <literal>files</literal> or <literal>mymachines</literal> entries), right before the
  44     <literal>dns</literal> entry if it exists, followed by <literal>[!UNAVAIL=return]</literal>, to ensure DNS queries
  45     are always routed via
  46     <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry> if it is
  47     running, but are routed to <command>nss-dns</command> if this service is not available.</para>
  48
  49     <para>Note that <command>systemd-resolved</command> will synthesize DNS resource
  50     records in a few cases, for example for <literal>localhost</literal> and the
  51     current hostname, see
  52     <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  53     for the full list. This duplicates the functionality of
  54     <citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
  55     but it is still recommended (see examples below) to keep
  56     <command>nss-myhostname</command> configured in
  57     <filename>/etc/nsswitch.conf</filename>, to keep those names resolveable if
  58     <command>systemd-resolved</command> is not running.</para>
  59   </refsect1>
  60
  61   <refsect1>
  62     <title>Example</title>
  63
  64     <para>Here is an example <filename>/etc/nsswitch.conf</filename> file that enables <command>nss-resolve</command>
  65     correctly:</para>
  66
  67 <programlisting>passwd:         compat mymachines systemd
  68 group:          compat mymachines systemd
  69 shadow:         compat
  70
  71 hosts:          files mymachines <command>resolve [!UNAVAIL=return]</command> dns myhostname
  72 networks:       files
  73
  74 protocols:      db files
  75 services:       db files
  76 ethers:         db files
  77 rpc:            db files
  78
  79 netgroup:       nis</programlisting>
  80   </refsect1>
  81
  82   <refsect1>
  83     <title>See Also</title>
  84     <para>
  85       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  86       <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
  87       <citerefentry><refentrytitle>nss-systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
  88       <citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
  89       <citerefentry><refentrytitle>nss-mymachines</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
  90       <citerefentry project='man-pages'><refentrytitle>nsswitch.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  91     </para>
  92   </refsect1>
  93
  94 </refentry>