source: BOOK/network/common/hosts.xml@ 0561245

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
  <!ENTITY % general-entities SYSTEM "../../general.ent">
  %general-entities;
]>

<sect1 id="ch-network-hosts">
  <?dbhtml filename="hosts.html"?>

  <title>Customizing the /etc/hosts File</title>

  <indexterm zone="ch-network-hosts">
    <primary sortas="e-/etc/hosts">/etc/hosts</primary>
  </indexterm>

  <indexterm zone="ch-network-hosts">
    <primary sortas="d-localnet">localnet</primary>
  <secondary>/etc/hosts</secondary></indexterm>

  <indexterm zone="ch-network-hosts">
    <primary sortas="d-network">network</primary>
  <secondary>/etc/hosts</secondary></indexterm>

  <para>If a network card is to be configured, decide on the IP address,
  fully-qualified domain name (FQDN), and possible aliases for use in the
  <filename>/etc/hosts</filename> file. The syntax is:</para>

<screen>&lt;IP address&gt; myhost.example.org aliases</screen>

  <para>Unless the computer is to be visible to the Internet (i.e.,
  there is a registered domain and a valid block of assigned IP
  addresses&mdash;most users do not have this), make sure that the IP
  address is in the private network IP address range. Valid ranges
  are:</para>

<screen><literal>Private Network Address Range       Normal Prefix
10.0.0.1 - 10.255.255.254           8
172.x.0.1 - 172.x.255.254           16
192.168.y.1 - 192.168.y.254         24</literal></screen>

  <para>x can be any number in the range 16-31. y can be any number in the
  range 0-255.</para>

  <para>A valid IP address could be 192.168.1.1. A valid FQDN for this
  IP could be <uri>www.clfs.org</uri> (not recommended
  because this is a valid registered domain address and could cause
  domain name server issues).</para>

  <para>Even if not using a network card, a valid FQDN is still required.
  This is necessary for certain programs to operate correctly.</para>

  <para>Create the <filename>/etc/hosts</filename> file by running:</para>

<screen role="nodump"><userinput>cat &gt; /etc/hosts &lt;&lt; "EOF"
<literal># Begin /etc/hosts (network card version)

127.0.0.1 localhost
::1       localhost
<replaceable>[192.168.1.1]</replaceable> <replaceable>[&lt;HOSTNAME&gt;.example.org]</replaceable> <replaceable>[HOSTNAME]</replaceable> <replaceable>[alias ...]</replaceable>

# End /etc/hosts (network card version)</literal>
EOF</userinput></screen>

  <para>The <replaceable>[192.168.1.1]</replaceable> and
  <replaceable>[&lt;HOSTNAME&gt;.example.org]</replaceable>
  values need to be changed for specific users or requirements (if
  assigned an IP address by a network/system administrator and the
  machine will be connected to an existing network). The optional
  alias name(s) can be omitted.</para>

  <para>If a network card is not going to be configured, create the
  <filename>/etc/hosts</filename> file by running:</para>

<screen role="nodump"><userinput>cat &gt; /etc/hosts &lt;&lt; "EOF"
<literal># Begin /etc/hosts (no network card version)

127.0.0.1 <replaceable>[&lt;HOSTNAME&gt;.example.org]</replaceable> <replaceable>[HOSTNAME]</replaceable> localhost
::1       localhost

# End /etc/hosts (no network card version)</literal>
EOF</userinput></screen>

<para>The ::1 entry is the IPv6 counterpart of 127.0.0.1 and represents the
      IPv6 loopback interface.</para>

</sect1>