Shell Form

  • RUN | CMD | ENTRYPOINT <command> <params>
  • under the hood it calls /bin/sh -c <command> <params>

  • handles variable substitution, e.g.

      ENV name world
  CMD echo "Hello, ${name}!"

Exec Form

  • RUN | CMD | ENTRYPOINT ["<executable>", "<param>", "<param>", ...]
  • preferred over shell form for CMD and ENTRYPOINT
    • calls executable directly
    • no shell processing
    • no variable substitution

  • explicit variable substitution

      ENV name world!
  CMD ["/bin/bash", "-c", "echo", "Hello, ${world}!"]

RUN

  • executes commands in a new layer and creates a new image

CMD

  • sets default command
  • default command is executed when running container without specifying a command
    • e.g.: $ docker run -it --rm busybox runs CMD ["command", "param1", "param2"]
  • can be overwritten from command line when docker container runs
    • default command in this case is ignored
    • e.g.: $ docker run -it --rm busybox /bin/sh
  • sets default parameters when used with ENTRYPOINT
    • e.g.: CMD ["param1", "param2"]

ENTRYPOINT

  • configures a container that will run as an executable
  • use to always execute a command
  • additionaly use CMD to define such extra default arguments, which can be overwritten from command line

  • ENTRYPOINT commands are always used, regardless of how the container is run, e.g.:

      ENTRYPOINT ["/bin/echo", "Hello, "]
  CMD ["world"]

  $ docker run --rm test-container
  > Hello, world

  $ docker run --rem test-container John
  > Hello, John
  • in exec form CMD params and docker run command line arguments are added
  • in shell form both are ignored

Source

http://goinbigdata.com/docker-run-vs-cmd-vs-entrypoint/