man/nss-resolve.xml

   1 <?xml version='1.0'?>
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   5
   6 <refentry id="nss-resolve" conditional='ENABLE_NSS_RESOLVE'>
   7
   8   <refentryinfo>
   9     <title>nss-resolve</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>nss-resolve</refentrytitle>
  15     <manvolnum>8</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>nss-resolve</refname>
  20     <refname>libnss_resolve.so.2</refname>
  21     <refpurpose>Provide hostname resolution via <filename>systemd-resolved.service</filename></refpurpose>
  22   </refnamediv>
  23
  24   <refsynopsisdiv>
  25     <para><filename>libnss_resolve.so.2</filename></para>
  26   </refsynopsisdiv>
  27
  28   <refsect1>
  29     <title>Description</title>
  30
  31     <para><command>nss-resolve</command> is a plug-in module for the GNU Name Service Switch (NSS) functionality of the
  32     GNU C Library (<command>glibc</command>) enabling it to resolve host names via the
  33     <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry> local network
  34     name resolution service. It replaces the <command>nss-dns</command> plug-in module that traditionally resolves
  35     hostnames via DNS.</para>
  36
  37     <para>To activate the NSS module, add <literal>resolve</literal> to the line starting with
  38     <literal>hosts:</literal> in <filename>/etc/nsswitch.conf</filename>. Specifically, it is recommended to place
  39     <literal>resolve</literal> early in <filename>/etc/nsswitch.conf</filename>'s <literal>hosts:</literal> line (but
  40     after the <literal>files</literal> or <literal>mymachines</literal> entries), right before the
  41     <literal>dns</literal> entry if it exists, followed by <literal>[!UNAVAIL=return]</literal>, to ensure DNS queries
  42     are always routed via
  43     <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry> if it is
  44     running, but are routed to <command>nss-dns</command> if this service is not available.</para>
  45
  46     <para>Note that <command>systemd-resolved</command> will synthesize DNS resource
  47     records in a few cases, for example for <literal>localhost</literal> and the
  48     current hostname, see
  49     <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  50     for the full list. This duplicates the functionality of
  51     <citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
  52     but it is still recommended (see examples below) to keep
  53     <command>nss-myhostname</command> configured in
  54     <filename>/etc/nsswitch.conf</filename>, to keep those names resolveable if
  55     <command>systemd-resolved</command> is not running.</para>
  56   </refsect1>
  57
  58   <refsect1>
  59     <title>Example</title>
  60
  61     <para>Here is an example <filename>/etc/nsswitch.conf</filename> file that enables <command>nss-resolve</command>
  62     correctly:</para>
  63
  64     <!-- synchronize with other nss-* man pages and factory/etc/nsswitch.conf -->
  65 <programlisting>passwd:         compat mymachines systemd
  66 group:          compat mymachines systemd
  67 shadow:         compat
  68
  69 hosts:          files mymachines <command>resolve [!UNAVAIL=return]</command> dns myhostname
  70 networks:       files
  71
  72 protocols:      db files
  73 services:       db files
  74 ethers:         db files
  75 rpc:            db files
  76
  77 netgroup:       nis</programlisting>
  78   </refsect1>
  79
  80   <refsect1>
  81     <title>See Also</title>
  82     <para>
  83       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  84       <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
  85       <citerefentry><refentrytitle>nss-systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
  86       <citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
  87       <citerefentry><refentrytitle>nss-mymachines</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
  88       <citerefentry project='man-pages'><refentrytitle>nsswitch.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  89     </para>
  90   </refsect1>
  91
  92 </refentry>