[解決]Dockerエラー'ERROR: Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?'が出た時の対処法

これを解決します

[vagrant@localhost ~]$ sudo docker version
Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?
##方法

$ sudo groupadd docker

$ sudo usermod -aG docker $USER

再度ログイン

$ newgrp docker 

$ sudo docker version

daemonのエラーが出てなければ解決

参考
https://docs.docker.com/engine/install/linux-postinstall/
https://stackoverflow.com/questions/21871479/docker-cant-connect-to-docker-daemon