/etc/netplan에 01-netcfg.yaml 내용을 아래와 같이 수정합니다​ 

없을 경우 새로 만듭니다

network:
  version: 2
  wifis:
    wlan0:
      dhcp4: no
      addresses:
        - 192.168.0.14/24
      gateway4: 192.168.0.1
      nameservers:
        addresses: [8.8.8.8, 8.8.4.4]
      access-points:
        "wifi_name":
          password: "passwd"

위의 wifi_name에 wifi ssid를 적어 주시고(따옴표는 지우시지 마시고) 

passwd에 wifi 비밀번호 적어 주시면 됩니다 

혹시 wifi가 wlan0으로 잡히지 않았다면 잡힌 번호로 적어주시면 됩니다 

그후 아래 명령으로 적용해 주시면 됩니다

sudo netplan apply