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. Additionally, since version 213, DNS name resolution can be handled by systemd-resolved in place of a static /etc/resolv.conf file. Both services are enabled by default.

Configuration files for systemd-networkd (and systemd-resolved) can be placed in /usr/lib/systemd/network or /etc/systemd/network. Files in /etc/systemd/network have a higher priority than the ones in /usr/lib/systemd/network. There are three types of configuration files: .link, .netdev and .network files. For detailed descriptions and example contents of these configuration files, consult the 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-eth0-static.network << "EOF"
[Match]
Name=eth0

[Network]
Address=192.168.0.2/24
Gateway=192.168.0.1
DNS=192.168.0.1
Domains=<Your Domain Name>
EOF

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

[Network]
DHCP=ipv4

[DHCP]
UseDomains=true
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.

7.2.2.1. systemd-resolved Configuration

Note

If using another means to configure your network interfaces (ex: ppp, network-manager, etc.), or if using any type of local resolver (ex: bind, dnsmasq, etc.), or any other software that generates an /etc/resolv.conf (ex: resolvconf), the systemd-resolved service should not be used.

When using systemd-resolved for DNS configuration, it creates the file /run/systemd/resolve/resolv.conf. Create a symlink in /etc to use the generated file:

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

7.2.2.2. Static resolv.conf Configuration

If a 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 for IPv4, and 2001:4860:4860::8888 and 2001:4860:4860::8844 for IPv6.

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 a fully-qualified domain name (FQDN), and possible aliases for use in the /etc/hosts file. If using static addresses, you'll also need to decide on an IP address. The syntax for a hosts file entry 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.

If using DHCP, DHCPv6, IPv6 Autoconfiguration, or if a network card is not going to be configured, create the /etc/hosts file by running the following command:

cat > /etc/hosts << "EOF"
# Begin /etc/hosts

127.0.0.1 localhost
127.0.1.1 <FQDN> <HOSTNAME>
::1       localhost ip6-localhost ip6-loopback
ff02::1   ip6-allnodes
ff02::2   ip6-allrouters

# End /etc/hosts
EOF

The ::1 entry is the IPv6 counterpart of 127.0.0.1 and represents the IPv6 loopback interface. 127.0.1.1 is a loopback entry reserved specifically for the FQDN.

If using a static address, create the /etc/hosts file by running this command instead:

cat > /etc/hosts << "EOF"
# Begin /etc/hosts

127.0.0.1 localhost
127.0.1.1 <FQDN> <HOSTNAME>
<192.168.0.2> <FQDN> <HOSTNAME> [alias1] [alias2] ...
::1       localhost ip6-localhost ip6-loopback
ff02::1   ip6-allnodes
ff02::2   ip6-allrouters

# End /etc/hosts
EOF

The <192.168.0.2>, <FQDN>, and <HOSTNAME> 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.