1 | <?xml version="1.0" encoding="ISO-8859-1"?>
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2 | <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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3 | "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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4 | <!ENTITY % general-entities SYSTEM "../general.ent">
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5 | %general-entities;
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6 | ]>
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7 |
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8 | <sect1 id="ch-scripts-network">
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9 | <?dbhtml filename="network.html"?>
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10 |
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11 | <title>Configuring the network Script</title>
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12 |
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13 | <indexterm zone="ch-scripts-network">
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14 | <primary sortas="d-network">network</primary>
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15 | <secondary>configuring</secondary></indexterm>
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16 |
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17 | <para>This section only applies if a network card is to be
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18 | configured.</para>
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19 |
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20 | <para>If a network card will not be used, there is likely no need to
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21 | create any configuration files relating to network cards. If that is
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22 | the case, remove the <filename class="symlink">network</filename>
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23 | symlinks from all run-level directories (<filename
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24 | class="directory">/etc/rc.d/rc*.d</filename>).</para>
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25 |
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26 | <sect2>
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27 | <title>Creating stable names for network interfaces</title>
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28 |
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29 | <para>With Udev and modular network drivers, the network interface numbering
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30 | is not persistent across reboots by default, because the drivers are loaded
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31 | in parallel and, thus, in random order. For example, on a computer having
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32 | two network cards made by Intel and Realtek, the network card manufactured
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33 | by Intel may become <filename class="devicefile">eth0</filename> and the
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34 | Realtek card becomes <filename class="devicefile">eth1</filename>. In some
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35 | cases, after a reboot the cards get renumbered the other way around. To
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36 | avoid this, Udev comes with a script and some rules to assign stable names
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37 | to network cards based on their MAC address.</para>
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38 |
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39 | <para>Pre-generate the rules to ensure the same names get assigned to the
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40 | same devices at every boot, including the first:</para>
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41 |
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42 | <screen><userinput>for NIC in /sys/class/net/* ; do
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43 | INTERFACE=${NIC##*/} udevadm test --action=add --subsystem=net $NIC
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44 | done</userinput></screen>
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45 |
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46 | <para>Now, inspect the <filename>/etc/udev/rules.d/70-persistent-net.rules</filename>
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47 | file, to find out which name was assigned to which network device:</para>
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48 |
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49 | <screen><userinput>cat /etc/udev/rules.d/70-persistent-net.rules</userinput></screen>
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50 |
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51 | <para>The file begins with a comment block followed by two lines for each
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52 | NIC. The first line for each NIC is a commented description showing its
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53 | hardware IDs (e.g. its PCI vendor and device IDs, if it's a PCI card),
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54 | along with its driver in parentheses, if the driver can be found. Neither
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55 | the hardware ID nor the driver is used to determine which name to give an
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56 | interface; this information is only for reference. The second line is the
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57 | Udev rule that matches this NIC and actually assigns it a name.</para>
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58 |
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59 | <para>All Udev rules are made up of several keys, separated by commas and
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60 | optional whitespace. This rule's keys and an explanation of each of them
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61 | are as follows:</para>
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62 |
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63 | <itemizedlist>
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64 | <listitem>
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65 | <para><literal>SUBSYSTEM=="net"</literal> - This tells Udev to ignore
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66 | devices that are not network cards.</para>
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67 | </listitem>
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68 | <listitem>
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69 | <para><literal>ACTION=="add"</literal> - This tells Udev to ignore this
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70 | rule for a uevent that isn't an add ("remove" and "change" uevents also
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71 | happen, but don't need to rename network interfaces).</para>
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72 | </listitem>
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73 | <listitem>
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74 | <para><literal>DRIVERS=="?*"</literal> - This exists so that Udev will
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75 | ignore VLAN or bridge sub-interfaces (because these sub-interfaces do
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76 | not have drivers). These sub-interfaces are skipped because the name
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77 | that would be assigned would collide with their parent devices.</para>
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78 | </listitem>
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79 | <listitem>
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80 | <para><literal>ATTR{address}</literal> - The value of this key is the
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81 | NIC's MAC address.</para>
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82 | </listitem>
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83 | <listitem>
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84 | <para><literal>ATTR{type}=="1"</literal> - This ensures the rule only
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85 | matches the primary interface in the case of certain wireless drivers,
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86 | which create multiple virtual interfaces. The secondary interfaces are
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87 | skipped for the same reason that VLAN and bridge sub-interfaces are
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88 | skipped: there would be a name collision otherwise.</para>
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89 | </listitem>
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90 | <listitem>
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91 | <para><literal>KERNEL=="eth*"</literal> - This key was added to the
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92 | Udev rule generator to handle machines that have multiple network
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93 | interfaces, all with the same MAC address (the PS3 is one such
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94 | machine). If the independent interfaces have different basenames,
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95 | this key will allow Udev to tell them apart. This is generally not
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96 | necessary for most Linux From Scratch users, but does not hurt.</para>
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97 | </listitem>
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98 | <listitem>
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99 | <para><literal>NAME</literal> - The value of this key is the name that
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100 | Udev will assign to this interface.</para>
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101 | </listitem>
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102 | </itemizedlist>
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103 |
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104 | <para>The value of <literal>NAME</literal> is the important part. Make sure
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105 | you know which name has been assigned to each of your network cards before
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106 | proceeding, and be sure to use that <literal>NAME</literal> value when
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107 | creating your configuration files below.</para>
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108 |
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109 | </sect2>
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110 |
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111 | <sect2>
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112 | <title>Creating Network Interface Configuration Files</title>
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113 |
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114 | <para>Which interfaces are brought up and down by the network script
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115 | depends on the files and directories in the <filename
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116 | class="directory">/etc/sysconfig/network-devices</filename> hierarchy.
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117 | This directory should contain a sub-directory for each interface to be
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118 | configured, such as <filename>ifconfig.xyz</filename>, where
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119 | <quote>xyz</quote> is a network interface name. Inside this directory
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120 | would be files defining the attributes to this interface, such as its IP
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121 | address(es), subnet masks, and so forth.</para>
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122 |
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123 | <para>The following command creates a sample <filename>ipv4</filename>
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124 | file for the <emphasis>eth0</emphasis> device:</para>
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125 |
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126 | <screen><userinput>cd /etc/sysconfig/network-devices
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127 | mkdir -v ifconfig.eth0
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128 | cat > ifconfig.eth0/ipv4 << "EOF"
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129 | <literal>ONBOOT=yes
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130 | SERVICE=ipv4-static
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131 | IP=192.168.1.1
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132 | GATEWAY=192.168.1.2
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133 | PREFIX=24
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134 | BROADCAST=192.168.1.255</literal>
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135 | EOF</userinput></screen>
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136 |
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137 | <para>The values of these variables must be changed in every file to match
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138 | the proper setup. If the <envar>ONBOOT</envar> variable is set to
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139 | <quote>yes</quote> the network script will bring up the Network Interface
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140 | Card (NIC) during booting of the system. If set to anything but
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141 | <quote>yes</quote> the NIC will be ignored by the network script and not
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142 | be brought up.</para>
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143 |
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144 | <para>The <envar>SERVICE</envar> variable defines the method used for
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145 | obtaining the IP address. The LFS-Bootscripts package has a modular IP
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146 | assignment format, and creating additional files in the <filename
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147 | class="directory">/etc/sysconfig/network-devices/services</filename>
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148 | directory allows other IP assignment methods. This is commonly used for
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149 | Dynamic Host Configuration Protocol (DHCP), which is addressed in the
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150 | BLFS book.</para>
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151 |
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152 | <para>The <envar>GATEWAY</envar> variable should contain the default
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153 | gateway IP address, if one is present. If not, then comment out the
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154 | variable entirely.</para>
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155 |
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156 | <para>The <envar>PREFIX</envar> variable needs to contain the number of
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157 | bits used in the subnet. Each octet in an IP address is 8 bits. If the
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158 | subnet's netmask is 255.255.255.0, then it is using the first three octets
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159 | (24 bits) to specify the network number. If the netmask is 255.255.255.240,
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160 | it would be using the first 28 bits. Prefixes longer than 24 bits are
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161 | commonly used by DSL and cable-based Internet Service Providers (ISPs).
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162 | In this example (PREFIX=24), the netmask is 255.255.255.0. Adjust the
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163 | <envar>PREFIX</envar> variable according to your specific subnet.</para>
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164 |
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165 | </sect2>
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166 |
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167 | <sect2 id="resolv.conf">
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168 | <title>Creating the /etc/resolv.conf File</title>
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169 |
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170 | <indexterm zone="resolv.conf">
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171 | <primary sortas="e-/etc/resolv.conf">/etc/resolv.conf</primary>
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172 | </indexterm>
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173 |
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174 | <para>If the system is going to be connected to the Internet, it will
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175 | need some means of Domain Name Service (DNS) name resolution to
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176 | resolve Internet domain names to IP addresses, and vice versa. This is
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177 | best achieved by placing the IP address of the DNS server, available
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178 | from the ISP or network administrator, into
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179 | <filename>/etc/resolv.conf</filename>. Create the file by running the
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180 | following:</para>
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181 |
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182 | <screen><userinput>cat > /etc/resolv.conf << "EOF"
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183 | <literal># Begin /etc/resolv.conf
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184 |
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185 | domain <replaceable><Your Domain Name></replaceable>
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186 | nameserver <replaceable><IP address of your primary nameserver></replaceable>
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187 | nameserver <replaceable><IP address of your secondary nameserver></replaceable>
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188 |
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189 | # End /etc/resolv.conf</literal>
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190 | EOF</userinput></screen>
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191 |
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192 | <para>Replace <replaceable><IP address of the nameserver></replaceable>
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193 | with the IP address of the DNS most appropriate for the setup. There will
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194 | often be more than one entry (requirements demand secondary servers for
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195 | fallback capability). If you only need or want one DNS server, remove the
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196 | second <emphasis>nameserver</emphasis> line from the file. The IP address
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197 | may also be a router on the local network.</para>
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198 |
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199 | </sect2>
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200 |
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201 | </sect1>
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