lfs-book/chapter07/network.xml

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

  <title>General Network Configuration</title>

  <indexterm zone="ch-scripts-network">
    <primary sortas="d-network">network</primary>
  <secondary>configuring</secondary></indexterm>

  <para>This section only applies if a network card is to be
  configured.</para>

  <para>If a network card will not be used, there is likely no need to create
  any configuration files relating to network cards. If that is the case, you
  will need to remove the <filename class="symlink">network</filename> symlinks
  from all run-level directories (<filename
  class="directory">/etc/rc.d/rc*.d</filename>) after the bootscripts are
  installed in <xref linkend="ch-scripts-bootscripts"/>.</para>

  <sect2>
    <title>Creating Network Interface Configuration Files</title>

    <para>Which interfaces are brought up and down by the network script
    usually depends on the files in <filename
    class="directory">/etc/sysconfig/</filename>.  This directory should
    contain a file for each interface to be configured, such as
    <filename>ifconfig.xyz</filename>, where <quote>xyz</quote> is required to
    be a Network Card Interface name (e.g. eth0).  Inside this file are
    attributes to this interface, such as its IP address(es), subnet masks, and
    so forth.  It is necessary that the stem of the filename be
    <emphasis>ifconfig</emphasis>.</para>

    <note><para>If the procedure in the previous section was not used, Udev
    will assign network card interface names based on system physical
    characteristics such as enp2s1. If you are not sure what your interface
    name is, you can always run <command>ip link</command>  after you have
    booted your system.  Again, it is important that ifconfig.xyz is named
    after correct network card interface name (e.g. ifconfig.enp2s1 or
    ifconfig.eth0) or your network interface will not be initialized during
    the boot process.</para></note>

    <para>The following command creates a sample file for the
    <emphasis>eth0</emphasis> device with a static IP address:</para>

<screen><userinput>cd /etc/sysconfig/
cat &gt; ifconfig.eth0 &lt;&lt; "EOF"
<literal>ONBOOT=yes
IFACE=eth0
SERVICE=ipv4-static
IP=192.168.1.2
GATEWAY=192.168.1.1
PREFIX=24
BROADCAST=192.168.1.255</literal>
EOF</userinput></screen>

    <para>The values of these variables must be changed in every file to match
    the proper setup.</para>

    <para>If the <envar>ONBOOT</envar> variable is set to <quote>yes</quote> the
    System V network script will bring up the Network Interface Card (NIC) during
    booting of the system. If set to anything but <quote>yes</quote> the NIC
    will be ignored by the network script and not be automatically brought up.
    The interface can be manually started or stopped with the
    <command>ifup</command> and <command>ifdown</command> commands.</para>

    <para>The <envar>IFACE</envar> variable defines the interface name,
    for example, eth0.  It is required for all network device configuration
    files. </para>

    <para>The <envar>SERVICE</envar> variable defines the method used for
    obtaining the IP address. The LFS-Bootscripts package has a modular IP
    assignment format, and creating additional files in the <filename
    class="directory">/lib/services/</filename> directory allows other IP
    assignment methods. This is commonly used for Dynamic Host Configuration
    Protocol (DHCP), which is addressed in the BLFS book.</para>

    <para>The <envar>GATEWAY</envar> variable should contain the default
    gateway IP address, if one is present. If not, then comment out the
    variable entirely.</para>

    <para>The <envar>PREFIX</envar> variable contains the number of
    bits used in the subnet. Each octet in an IP address is 8 bits. If the
    subnet's netmask is 255.255.255.0, then it is using the first three octets
    (24 bits) to specify the network number. If the netmask is 255.255.255.240,
    it would be using the first 28 bits.  Prefixes longer than 24 bits are
    commonly used by DSL and cable-based Internet Service Providers (ISPs).
    In this example (PREFIX=24), the netmask is 255.255.255.0. Adjust the
    <envar>PREFIX</envar> variable according to your specific subnet.
    If omitted, the PREFIX defaults to 24.</para>

    <para>For more information see the <command>ifup</command> man page.</para>

  </sect2>

  <sect2 id="systemd-net-enable">
    <title>Configuring the Network Interface Card at boot (systemd)</title>

    <para>Enabling of the network interface card configuration 
    in systemd is done per interface. To enable network interface card
    configuration at boot, run:</para>

<screen><userinput>systemctl enable ifupdown@eth0</userinput></screen>

    <para>To disable a previously enabled network interface
    card configuration at boot, run:</para>

<screen role="nodump"><userinput>systemctl disable ifupdown@eth0</userinput></screen>

    <para>To manually start the network interface card configuration,
    run:</para>

<screen role="nodump"><userinput>systemctl start ifupdown@eth0</userinput></screen>

    <para>Replace eth0 with the correct network interface card
    name as described on the beginning of this page.</para>

    <note><para>These procedures require the configuration files as specified
    in the previous section.</para></note>

    <note><para>The network card can also be started or stopped
    with the traditional <command>ifup &lt;device&gt;</command> or
    <command>ifdown &lt;device&gt;</command> commands.</para></note>

  </sect2>

  <sect2 id="systemd2-net-enable">
    <title>Configuring the Network Interface Card for systemd-networkd</title>

    <para>An alternative way to configure a NIC when booting with with
    systemd is to create a configuration file recognized by the
    systemd-networkd daemon.  To configure the device create a file similar
    to this:</para>

<screen role="nodump"><userinput>cat &gt; /etc/systemd/network/10-static-eth0.network &lt;&lt; "EOF"
[Match]
Name=eth0

[Network]
Address=192.168.0.2/24
Gateway=192.168.0.1
EOF</userinput></screen>

    <para>You can use multiple .network files if desired.  You can also specify
    DHCP=yes instead of the Address and Gateway settings.  See the man page for
    systemd.network for more details,</para>

    <note><para>If this method is used, be sure to disable ifupdown@eth0 as 
    described in the previous section (if it was enabled).</para></note>

  </sect2>

  <sect2 id="resolv.conf">
    <title>Creating the /etc/resolv.conf File</title>

    <indexterm zone="resolv.conf">
      <primary sortas="e-/etc/resolv.conf">/etc/resolv.conf</primary>
    </indexterm>

    <para>If the system is going to be connected to the Internet, it will
    need some means of Domain Name Service (DNS) name resolution to
    resolve Internet domain names to IP addresses, and vice versa. This is
    best achieved by placing the IP address of the DNS server, available
    from the ISP or network administrator, into
    <filename>/etc/resolv.conf</filename>. Create the file by running the
    following:</para>

<screen><userinput>cat &gt; /etc/resolv.conf &lt;&lt; "EOF"
<literal># Begin /etc/resolv.conf

domain <replaceable>&lt;Your Domain Name&gt;</replaceable>
nameserver <replaceable>&lt;IP address of your primary nameserver&gt;</replaceable>
nameserver <replaceable>&lt;IP address of your secondary nameserver&gt;</replaceable>

# End /etc/resolv.conf</literal>
EOF</userinput></screen>

    <para>The <varname>domain</varname> statement can be omitted
    or replaced with a <varname>search</varname> statement.  See the man page for
    resolv.conf for more details.</para>

    <para>Replace <replaceable>&lt;IP address of the nameserver&gt;</replaceable>
    with the IP address of the DNS most appropriate for the setup. There will
    often be more than one entry (requirements demand secondary servers for
    fallback capability). If you only need or want one DNS server, remove the
    second <emphasis>nameserver</emphasis> line from the file. The IP address
    may also be a router on the local network.</para>

    <note><para>The Google Public IPv4 DNS addresses are 8.8.8.8 and 8.8.4.4.</para></note>

  </sect2>

  <sect2 id="ch-scripts-hostname">
    <title>Configuring the system hostname</title>

    <indexterm zone="ch-scripts-hostname">
      <primary sortas="d-hostname">hostname</primary>
      <secondary>configuring</secondary>
    </indexterm>

     <para>During the boot process, both Systemd and System V use the same file
     for establishing the system's hostname.  This needs to be configured by
     creating <filename>/etc/hostname</filename>.</para>

     <para>Create the <filename>/etc/hostname</filename> file and enter a
     hostname by running:</para>

<screen><userinput>echo "<replaceable>&lt;lfs&gt;</replaceable>" &gt; /etc/hostname</userinput></screen>

     <para><replaceable>&lt;lfs&gt;</replaceable> needs to be replaced with the
     name given to the computer. Do not enter the Fully Qualified Domain Name
     (FQDN) here. That information is put in the
     <filename>/etc/hosts</filename> file.</para>

  </sect2>

  <sect2 id="ch-scripts-hosts">
     <title>Customizing the /etc/hosts File</title>

     <indexterm zone="ch-scripts-hosts">
       <primary sortas="e-/etc/hosts">/etc/hosts</primary>
     </indexterm>
   
     <indexterm zone="ch-scripts-hosts">
       <primary sortas="d-localnet">localnet</primary>
       <secondary>/etc/hosts</secondary>
     </indexterm>
   
     <indexterm zone="ch-scripts-hosts">
       <primary sortas="d-network">network</primary>
       <secondary>/etc/hosts</secondary>
     </indexterm>
   
     <para>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><literal>IP_address myhost.example.org aliases</literal></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 private IP address could be 192.168.1.1. A valid FQDN for
     this IP could be lfs.example.org.</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><userinput>cat &gt; /etc/hosts &lt;&lt; "EOF"
<literal># Begin /etc/hosts (network card version)

127.0.0.1 localhost
<replaceable>&lt;192.168.1.1&gt;</replaceable> <replaceable>&lt;HOSTNAME.example.org&gt;</replaceable> <replaceable>[alias1] [alias2 ...]</replaceable>

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

     <para>The <replaceable>&lt;192.168.1.1&gt;</replaceable> and
     <replaceable>&lt;HOSTNAME.example.org&gt;</replaceable> values need to be
     changed for specific uses 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.example.org&gt;</replaceable> <replaceable>&lt;HOSTNAME&gt;</replaceable> localhost

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

   </sect2>

</sect1>