docker: Got permission denied while trying to connect to the Docker daemon socket 오류발생

$ sudo usermod -a -G docker $USER

$ sudo service docker restart

 

출처: http://www.kwangsiklee.com/2017/05/%ED%95%B4%EA%B2%B0%EB%B0%A9%EB%B2%95-solving-docker-permission-denied-while-trying-to-connect-to-the-docker-daemon-socket/