(Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Get http://%2Fvar%2Frun%2Fdocker.sock/v1.30/info: dial unix /var/run/docker.sock: connect: permission denied). Using system default: https://index.docker.io/v1/
The error message tells you that your current user can’t access the docker engine, because you’re lacking permissions to access the unix socket to communicate with the engine.
As a temporary solution, you can use sudo to run the failed command as root.
However it is recommended to fix the issue by adding the current user to the docker group:
Run this command in your favourite shell and then completely log out of your account and log back in (if in doubt, reboot!):
After doing that, you should be able to run the command without any issues. Run docker run hello-world as a normal user in order to check if it works. Reboot if the issue still persists.
Logging out and logging back in is required because the group change will not have an effect unless your session is closed.