7.3. General Network Configuration

This section only applies if a network card is to be configured.

7.3.1. Creating Network Interface Configuration Files

Which interfaces are brought up and down by the network script depends on the files in /etc/sysconfig/. This directory should contain a file for each interface to be configured, such as ifconfig.xyz, where xyz 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 ifconfig.



Udev may assign random Network Card Interface names for some network cards such as enp2s1. If you are not sure what your Network Card Interface name is, you can always run ip l 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 Systemd will fail to bring up your network interface.

The following command creates a sample file for the eth0 device with a static IP address:

cd /etc/sysconfig/
cat > ifconfig.eth0 << "EOF"

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

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

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

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

The PREFIX 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, then it is using the first three octets (24 bits) to specify the network number. If the netmask is, 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 Adjust the PREFIX variable according to your specific subnet. If omitted, the PREFIX defaults to 24.

For more information see the ifup man page.

7.3.2. Configuring the Network Interface Card at boot

Enabling of the Network Interface Card configuration is done per interface. To enable Network Interface Card configuration at boot, run:

systemctl enable ifupdown@eth0

To disable previously enabled Network Interface Card configuration at boot, run:

systemctl disable ifupdown@eth0

To manually start the Network Interface Card configuration, run:

systemctl start ifupdown@eth0

Replace eth0 with the correct Network Interface Card name as described on the beginning of this page.

7.3.3. Creating the /etc/resolv.conf File

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 /etc/resolv.conf. Create the file by running the following:

cat > /etc/resolv.conf << "EOF"
# Begin /etc/resolv.conf

domain <Your Domain Name>
nameserver <IP address of your primary nameserver>
nameserver <IP address of your secondary nameserver>

# End /etc/resolv.conf

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

Replace <IP address of the nameserver> 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 nameserver line from the file. The IP address may also be a router on the local network.



The Google Public IPv4 DNS addresses are and