source: chapter07/network.xml@ c729bc9

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Last change on this file since c729bc9 was c729bc9, checked in by Bruce Dubbs <bdubbs@…>, 8 years ago

Add section on systemd customization

git-svn-id: 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

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1<?xml version="1.0" encoding="ISO-8859-1"?>
2<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
3 "" [
4 <!ENTITY % general-entities SYSTEM "../general.ent">
5 %general-entities;
8<sect1 id="ch-scripts-network">
9 <?dbhtml filename="network.html"?>
11 <title>General Network Configuration</title>
13 <indexterm zone="ch-scripts-network">
14 <primary sortas="d-network">network</primary>
15 <secondary>configuring</secondary></indexterm>
17 <para>This section only applies if a network card is to be
18 configured.</para>
20 <para>If a network card will not be used, there is likely no need to create
21 any configuration files relating to network cards. If that is the case, you
22 will need to remove the <filename class="symlink">network</filename> symlinks
23 from all run-level directories (<filename
24 class="directory">/etc/rc.d/rc*.d</filename>) after the bootscripts are
25 installed in <xref linkend="ch-scripts-bootscripts"/>.</para>
27 <sect2 id='stable-net-names'>
28 <title>Creating stable names for network interfaces</title>
30 <para>If there is only one network interface in the system to be
31 configured, this section is optional, although it will never be wrong to do
32 it. In many cases (e.g. a laptop with a wireless and a wired interface),
33 accomplishing the configuration in this section is necessary.</para>
35 <para>With Udev and modular network drivers, the network interface numbering
36 is not persistent across reboots by default, because the drivers are loaded
37 in parallel and, thus, in random order. For example, on a computer having
38 two network cards made by Intel and Realtek, the network card manufactured
39 by Intel may become <filename class="devicefile">eth0</filename> and the
40 Realtek card becomes <filename class="devicefile">eth1</filename>. In some
41 cases, after a reboot the cards get renumbered the other way around. To
42 avoid this, Udev comes with a script and some rules to assign stable names
43 to network cards based on their MAC address.</para>
45 <para>If using the traditional network interface names such as eth0 is desired,
46 generate a custom Udev rule:</para>
48<screen><userinput>bash /lib/udev/</userinput></screen>
50 <para> Now, inspect the
51 <filename>/etc/udev/rules.d/70-persistent-net.rules</filename> file, to
52 find out which name was assigned to which network device:</para>
54<screen role="nodump"><userinput>cat /etc/udev/rules.d/70-persistent-net.rules</userinput></screen>
56 <note><para>In some cases such as when MAC addresess have been assigned to
57 a network card manually or in a virtual environment such as Xen,
58 the network rules file may not have been generated because addresses
59 are not consistently assigned. In these cases, just continue to
60 the next section.</para></note>
62 <para>The file begins with a comment block followed by two lines for each
63 NIC. The first line for each NIC is a commented description showing its
64 hardware IDs (e.g. its PCI vendor and device IDs, if it's a PCI card),
65 along with its driver in parentheses, if the driver can be found. Neither
66 the hardware ID nor the driver is used to determine which name to give an
67 interface; this information is only for reference. The second line is the
68 Udev rule that matches this NIC and actually assigns it a name.</para>
70 <para>All Udev rules are made up of several keys, separated by commas and
71 optional whitespace. This rule's keys and an explanation of each of them
72 are as follows:</para>
74 <itemizedlist>
75 <listitem>
76 <para><literal>SUBSYSTEM=="net"</literal> - This tells Udev to ignore
77 devices that are not network cards.</para>
78 </listitem>
79 <listitem>
80 <para><literal>ACTION=="add"</literal> - This tells Udev to ignore this
81 rule for a uevent that isn't an add ("remove" and "change" uevents also
82 happen, but don't need to rename network interfaces).</para>
83 </listitem>
84 <listitem>
85 <para><literal>DRIVERS=="?*"</literal> - This exists so that Udev will
86 ignore VLAN or bridge sub-interfaces (because these sub-interfaces do
87 not have drivers). These sub-interfaces are skipped because the name
88 that would be assigned would collide with their parent devices.</para>
89 </listitem>
90 <listitem>
91 <para><literal>ATTR{address}</literal> - The value of this key is the
92 NIC's MAC address.</para>
93 </listitem>
94 <listitem>
95 <para><literal>ATTR{type}=="1"</literal> - This ensures the rule only
96 matches the primary interface in the case of certain wireless drivers,
97 which create multiple virtual interfaces. The secondary interfaces are
98 skipped for the same reason that VLAN and bridge sub-interfaces are
99 skipped: there would be a name collision otherwise.</para>
100 </listitem>
101 <listitem>
102 <para><literal>KERNEL=="eth*"</literal> - This key was added to the
103 Udev rule generator to handle machines that have multiple network
104 interfaces, all with the same MAC address (the PS3 is one such
105 machine). If the independent interfaces have different basenames,
106 this key will allow Udev to tell them apart. This is generally not
107 necessary for most Linux From Scratch users, but does not hurt.</para>
108 </listitem>
109 <listitem>
110 <para><literal>NAME</literal> - The value of this key is the name that
111 Udev will assign to this interface.</para>
112 </listitem>
113 </itemizedlist>
115 <para>The value of <literal>NAME</literal> is the important part. Make sure
116 you know which name has been assigned to each of your network cards before
117 proceeding, and be sure to use that <literal>NAME</literal> value when
118 creating your configuration files below.</para>
120 </sect2>
122 <sect2>
123 <title>Creating Network Interface Configuration Files</title>
125 <para>Which interfaces are brought up and down by the network script
126 depends on the files in <filename
127 class="directory">/etc/sysconfig/</filename>. This directory should
128 contain a file for each interface to be configured, such as
129 <filename></filename>, where <quote>xyz</quote> is required to
130 be a Network Card Interface name (e.g. eth0). Inside this file are
131 attributes to this interface, such as its IP address(es), subnet masks, and
132 so forth. It is necessary that the stem of the filename be
133 <emphasis>ifconfig</emphasis>.</para>
135 <note><para>If the procedure in the previous section was not used, Udev
136 will assign network card interface names based on system physical
137 characteristics such as enp2s1. If you are not sure what your interface
138 name is, you can always run <command>ip link</command> after you have
139 booted your system. Again, it is important that is named
140 after correct network card interface name (e.g. ifconfig.enp2s1 or
141 ifconfig.eth0) or your network interface will not be initialized during
142 the boot process.</para></note>
144 <para>The following command creates a sample file for the
145 <emphasis>eth0</emphasis> device with a static IP address:</para>
147<screen><userinput>cd /etc/sysconfig/
148cat &gt; ifconfig.eth0 &lt;&lt; "EOF"
158 <para>The values of these variables must be changed in every file to match
159 the proper setup.</para>
161 <para>If the <envar>ONBOOT</envar> variable is set to <quote>yes</quote> the
162 System V network script will bring up the Network Interface Card (NIC) during
163 booting of the system. If set to anything but <quote>yes</quote> the NIC
164 will be ignored by the network script and not be automatically brought up.
165 The interface can be manually started or stopped with the
166 <command>ifup</command> and <command>ifdown</command> commands.</para>
168 <para>The <envar>IFACE</envar> variable defines the interface name,
169 for example, eth0. It is required for all network device configuration
170 files. </para>
172 <para>The <envar>SERVICE</envar> variable defines the method used for
173 obtaining the IP address. The LFS-Bootscripts package has a modular IP
174 assignment format, and creating additional files in the <filename
175 class="directory">/lib/services/</filename> directory allows other IP
176 assignment methods. This is commonly used for Dynamic Host Configuration
177 Protocol (DHCP), which is addressed in the BLFS book.</para>
179 <para>The <envar>GATEWAY</envar> variable should contain the default
180 gateway IP address, if one is present. If not, then comment out the
181 variable entirely.</para>
183 <para>The <envar>PREFIX</envar> variable contains the number of
184 bits used in the subnet. Each octet in an IP address is 8 bits. If the
185 subnet's netmask is, then it is using the first three octets
186 (24 bits) to specify the network number. If the netmask is,
187 it would be using the first 28 bits. Prefixes longer than 24 bits are
188 commonly used by DSL and cable-based Internet Service Providers (ISPs).
189 In this example (PREFIX=24), the netmask is Adjust the
190 <envar>PREFIX</envar> variable according to your specific subnet.
191 If omitted, the PREFIX defaults to 24.</para>
193 <para>For more information see the <command>ifup</command> man page.</para>
195 </sect2>
197 <sect2 id="systemd-net-enable">
198 <title>Configuring the Network Interface Card at boot (systemd)</title>
200 <para>Enabling of the network interface card configuration
201 in systemd is done per interface. To enable network interface card
202 configuration at boot, run:</para>
204<screen><userinput>systemctl enable ifupdown@eth0</userinput></screen>
206 <para>To disable a previously enabled network interface
207 card configuration at boot, run:</para>
209<screen role="nodump"><userinput>systemctl disable ifupdown@eth0</userinput></screen>
211 <para>To manually start the network interface card configuration,
212 run:</para>
214<screen role="nodump"><userinput>systemctl start ifupdown@eth0</userinput></screen>
216 <para>Replace eth0 with the correct network interface card
217 name as described on the beginning of this page.</para>
219 <note><para>The network card can also be started or stopped
220 with the traditional <command>ifup &lt;device&gt;</command> or
221 <command>ifdown &lt;device&gt;</command> commands.</para></note>
223 </sect2>
225 <sect2 id="resolv.conf">
226 <title>Creating the /etc/resolv.conf File</title>
228 <indexterm zone="resolv.conf">
229 <primary sortas="e-/etc/resolv.conf">/etc/resolv.conf</primary>
230 </indexterm>
232 <para>If the system is going to be connected to the Internet, it will
233 need some means of Domain Name Service (DNS) name resolution to
234 resolve Internet domain names to IP addresses, and vice versa. This is
235 best achieved by placing the IP address of the DNS server, available
236 from the ISP or network administrator, into
237 <filename>/etc/resolv.conf</filename>. Create the file by running the
238 following:</para>
240<screen><userinput>cat &gt; /etc/resolv.conf &lt;&lt; "EOF"
241<literal># Begin /etc/resolv.conf
243domain <replaceable>&lt;Your Domain Name&gt;</replaceable>
244nameserver <replaceable>&lt;IP address of your primary nameserver&gt;</replaceable>
245nameserver <replaceable>&lt;IP address of your secondary nameserver&gt;</replaceable>
247# End /etc/resolv.conf</literal>
250 <para>The <varname>domain</varname> statement can be omitted
251 or replaced with a <varname>search</varname> statement. See the man page for
252 resolv.conf for more details.</para>
254 <para>Replace <replaceable>&lt;IP address of the nameserver&gt;</replaceable>
255 with the IP address of the DNS most appropriate for the setup. There will
256 often be more than one entry (requirements demand secondary servers for
257 fallback capability). If you only need or want one DNS server, remove the
258 second <emphasis>nameserver</emphasis> line from the file. The IP address
259 may also be a router on the local network.</para>
261 <note><para>The Google Public IPv4 DNS addresses are and</para></note>
263 </sect2>
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