7.2. General Network Configuration

7.2.1. Network Interface Configuration Files

Starting with version 209, systemd ships a network configuration daemon called systemd-networkd which can be used for basic network configuration.

Configuration files for systemd-networkd can be placed in /usr/lib/systemd/network or /etc/systemd/network. Note that files in /etc/systemd/network have higher priority than the ones in /usr/lib/systemd/network.

There are three types of configuration files: .link, .netdev and .network files. For detailed explanation about contents of the mentioned configuration files, consult systemd-link(5), systemd-netdev(5) and systemd-network(5) manual pages.

Note

Udev may 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 ip link after you have booted your system.

cat > /etc/systemd/network/10-static-eth0.network << "EOF"
[Match]
Name=eth0

[Network]
Address=192.168.0.2/24
Gateway=192.168.0.1
DNS=192.168.0.1
EOF

cat > /etc/systemd/network/10-dhcp-eth0.network << "EOF"
[Match]
Name=eth0

[Network]
DHCP=yes
EOF

7.2.2. 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.

If static /etc/resolv.conf is desired, create it by running the following command:

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
EOF

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.

Note

The Google Public IPv4 DNS addresses are 8.8.8.8 and 8.8.4.4.

When using systemd-networkd for network configuration, another daemon, systemd-resolved, is responsible for creating the /etc/resolv.conf file. It is, however, placed in a non-standard location which is writable since early boot, so it is necessary to create a symlink to it by running the following command:

ln -sfv /run/systemd/resolve/resolv.conf /etc/resolv.conf

This is required if you are specifying DNS entries in .network files or using the built in DHCP client to obtain DNS addresses.

7.2.3. Configuring the system hostname

During the boot process, the file /etc/hostname is used for establishing the system's hostname.

Create the /etc/hostname file and enter a hostname by running:

echo "<lfs>" > /etc/hostname

<lfs> 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 /etc/hosts file.

7.2.4. Customizing the /etc/hosts File

Decide on the IP address, fully-qualified domain name (FQDN), and possible aliases for use in the /etc/hosts file. The syntax is:

IP_address myhost.example.org aliases

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—most users do not have this), make sure that the IP address is in the private network IP address range. Valid ranges are:

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

x can be any number in the range 16-31. y can be any number in the range 0-255.

A valid private IP address could be 192.168.1.1. A valid FQDN for this IP could be lfs.example.org.

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

Create the /etc/hosts file by running:

cat > /etc/hosts << "EOF"
# Begin /etc/hosts (network card version)

127.0.0.1 localhost
::1       localhost
<192.168.0.2> <HOSTNAME.example.org> [alias1] [alias2] ...

# End /etc/hosts (network card version)
EOF

The <192.168.0.2> and <HOSTNAME.example.org> 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.

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

cat > /etc/hosts << "EOF"
# Begin /etc/hosts (no network card version)

127.0.0.1 <HOSTNAME.example.org> <HOSTNAME> localhost
::1       localhost

# End /etc/hosts (no network card version)
EOF

The ::1 entry is the IPv6 counterpart of 127.0.0.1 and represents the IPv6 loopback interface.