네트워크 장치를 나열합니다.

$ ls /sys/class/net
lo wlp2s0

구성 파일을 편집하십시오.

$ vi /etc/netplan/50-cloud-init.yaml
# This file is generated from information provided by the datasource.  Changes
# to it will not persist across an instance reboot.  To disable cloud-init's
# network configuration capabilities, write a file
# /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg with the following:
# network: {config: disabled}
network:
    ethernets:
        eth0:
            dhcp4: true
            optional: true
    version: 2
    wifis:
        wlp3s0:
            optional: true
            access-points:
              "SSID-NAME-HERE":
                password: "PASSWORD-HERE"
            dhcp4: true

관련유틸 설치

wpasupplicant이 방법으로 설치 ...

sudo apt-get update

sudo apt-get install wpasupplicant

sudo apt-get install net-tools (iwconfig 쓸려면 필요함)

reboot

구성을 적용하십시오.

# sudo netplan generate (이건 apply할때 실행되니까 할 필요 없다)

sudo netplan apply

reboot 혹은 

#재부팅 명령어는? sudo systemctl restart system-networkd

재부팅하십시오.