The ENTRYPOINT specifies a command that will always be executed when the container starts.

The CMD specifies arguments that will be fed to the ENTRYPOINT.

FROM debian:wheezy
ENTRYPOINT ["/bin/ping"]
CMD ["localhost"]

$ docker run -it img google.com

Ref: https://stackoverflow.com/questions/21553353/what-is-the-difference-between-cmd-and-entrypoint-in-a-dockerfile/34245657#34245657