ifconfig | grep -i "^en"

# ifconfig not found 발생 시 아래 명령어로 패키지 설치
sudo apt-get install -y net-tools

sudo su
vim /etc/netplan/01-network-manager-all.yaml

network:
  ethernetes:
    ens3:
      dhcp4: true
  version: 2
  renderer: NetworkManager

network:
  ethernets:
    ens3:
      addresses:
        - "192.168.219.5/24"
      nameservers:
        addresses: [8.8.8.8, 8.8.4.4]
      routes:
        - to: default
          via: 192.168.219.1
  version: 2
  renderer: NetworkManager

sudo netplan apply

$ ip addr

or

$ ifconfig

$ find / -name "interfaces" -type f 2>/dev/null -exec sh -c "vi {}" \;

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet dhcp

# The primary network interface
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet static
address 192.168.121.129
netmask 255.255.255.0
gateway 192.168.121.
dns-nameservers 8.8.8.8

$ service networking restart

or 

$ systemctl restart networking