man/nss-myhostname.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
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   6   This file is part of systemd.
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   8   Copyright 2011 Lennart Poettering
   9   Copyright 2013 Tom Gundersen
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  24
  25 <refentry id="nss-myhostname" conditional='HAVE_MYHOSTNAME'>
  26
  27         <refentryinfo>
  28                 <title>nss-myhostname</title>
  29                 <productname>systemd</productname>
  30
  31                 <authorgroup>
  32                         <author>
  33                                 <contrib>Developer</contrib>
  34                                 <firstname>Lennart</firstname>
  35                                 <surname>Poettering</surname>
  36                                 <email>lennart@poettering.net</email>
  37                         </author>
  38                 </authorgroup>
  39         </refentryinfo>
  40
  41         <refmeta>
  42                 <refentrytitle>nss-myhostname</refentrytitle>
  43                 <manvolnum>8</manvolnum>
  44         </refmeta>
  45
  46         <refnamediv>
  47                 <refname>nss-myhostname</refname>
  48                 <refpurpose>Provide hostname resolution for the locally
  49                 configured system hostname.</refpurpose>
  50         </refnamediv>
  51
  52         <refsynopsisdiv>
  53                 <para><filename>nss-myhostname.la</filename></para>
  54         </refsynopsisdiv>
  55
  56         <refsect1>
  57                 <title>Description</title>
  58
  59                 <para><command>nss-myhostname</command> is a plugin for the GNU Name Service Switch
  60                 (NSS) functionality of the GNU C Library (<command>glibc</command>)
  61                 providing hostname resolution for the locally configured system
  62                 hostname as returned by
  63                 <citerefentry><refentrytitle>gethostname</refentrytitle><manvolnum>2</manvolnum></citerefentry>.
  64                 Various software relies on an always-resolvable local hostname. When
  65                 using dynamic hostnames, this is usually achieved by patching
  66                 <filename>/etc/hosts</filename> at the same time as changing the host
  67                 name. This however is not ideal since it requires a writable
  68                 <filename>/etc</filename> file system and is fragile because the file
  69                 might be edited by the administrator at the same time. <command>nss-myhostname</command>
  70                 simply returns all locally configured public IP addresses, or, if none
  71                 are configured, the IPv4 address 127.0.0.2 (which is on the local
  72                 loopback) and the IPv6 address ::1 (which is the local host) for
  73                 whatever system hostname is configured locally. Patching
  74                 <filename>/etc/hosts</filename> is thus no longer necessary.</para>
  75
  76                 <para>To activate the NSS modules, <option>myhostname</option>
  77                 has to be added to the line starting with "<varname>hosts:</varname>" in
  78                 <filename>/etc/nsswitch.conf</filename></para>
  79
  80                 <para>It is recommended to put <option>myhostname</option>
  81                 last in the <filename>nsswitch.conf</filename> line to make
  82                 sure that this mapping is only used as fallback, and any DNS
  83                 or <filename>/etc/hosts</filename> based mapping takes precedence.</para>
  84         </refsect1>
  85
  86         <refsect1>
  87                 <title>Example</title>
  88
  89                 <programlisting>
  90 # /etc/nsswitch.conf
  91
  92 passwd:         compat
  93 group:          compat
  94 shadow:         compat
  95
  96 hosts:          files dns <varname>myhostname</varname>
  97 networks:       files
  98
  99 protocols:      db files
 100 services:       db files
 101 ethers:         db files
 102 rpc:            db files
 103
 104 netgroup:       nis
 105                 </programlisting>
 106
 107                 <para>To test, use <command>glibc</command>'s <command>getent</command> tool:</para>
 108
 109                 <programlisting>
 110 $ getent ahosts `hostname`
 111 ::1             STREAM omega
 112 ::1             DGRAM
 113 ::1             RAW
 114 127.0.0.2       STREAM
 115 127.0.0.2       DGRAM
 116 127.0.0.2       RAW
 117                 </programlisting>
 118
 119                 <para>In this case the local hostname is <varname>omega</varname>.</para>
 120
 121         </refsect1>
 122
 123         <refsect1>
 124                 <title>See Also</title>
 125                 <para>
 126                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 127                         <citerefentry><refentrytitle>systemd-logind.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 128                         <citerefentry><refentrytitle>logind.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 129                         <citerefentry><refentrytitle>loginctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 130                         <citerefentry><refentrytitle>pam.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 131                         <citerefentry><refentrytitle>pam.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 132                         <citerefentry><refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 133                         <citerefentry><refentrytitle>pam_loginuid</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 134                 </para>
 135         </refsect1>
 136
 137 </refentry>