Dockerfile is used to create docker image
Docker Hub: Online cloud repository
docker container is the instance of the docker image
1. If you stop the docker, this problem shows up
you can run this command to restart
systemctl start docker
2. If you get permission denied issue, you can
sudo chmod 666 /var/run/docker.sock
https://stackoverflow.com/questions/48957195/how-to-fix-docker-got-permission-denied-issue