Ubuntu Networking

From almost any Linux system you can use "ip" or the ifconfig/route commands to set up the network.

# Bring up the CPU network interface
ifconfig eth0 up

# Or if you're on a baseboard with a second ethernet port, you can use that as:
ifconfig eth1 up

# Set an ip address (assumes 255.255.255.0 subnet mask)
ifconfig eth0 192.168.0.50

# Set a specific subnet
ifconfig eth0 192.168.0.50 netmask 255.255.0.0

# Configure your route.  This is the server that provides your internet connection.
route add default gw 192.168.0.1

# Edit /etc/resolv.conf for your DNS server
echo "nameserver 192.168.0.1" > /etc/resolv.conf

Most networks will offer DHCP which can be set up with one command:

# To setup the default CPU ethernet port
dhclient eth0
# Or if you're on a baseboard with a second ethernet port, you can use that as:
dhclient eth1
# You can configure all ethernet ports for a dhcp response with
dhclient

To make DHCP run on startup systemd's networking will need to be configured.

In /etc/systemd/network/eth.network

[Match]
Name=eth*

[Network]
DHCP=yes

Then, if you intend to use DHCP to configure your DNS, start and enable the network name resolver service:

systemctl start systemd-resolved.service 
systemctl enable systemd-resolved.service
ln -s /run/systemd/resolve/resolv.conf /etc/resolv.conf

For a static configuration create a config file for that specific interface. /etc/systemd/network/eth0.network

[Match]
Name=eth0

[Network]
Address=192.168.0.50/24
Gateway=192.168.0.1
DNS=192.168.0.1

For more information on networking, see Ubuntu and systemd's documentation:

• Systemd Networking Documentation
• Ubuntu Documentation