As you can recall from Chapter 6, Creating Images, when we create a Docker image, we provide the default command or options either using the CMD instruction or default command to execute at runtime using the ENTRYPOINT instruction. But without the possibility to influence the container startup process by providing different commands or parameters, other than the image author provided, it wouldn't be possible to use Docker in many cases. Images would be rather static and sometimes just useless. Luckily, Docker supports overriding those defaults and this feature makes it very flexible tool. As you remember from the previous chapter, there's an important difference between ENTRYPOINT and CMD instructions: the ENTRYPOINT defines the process that runs as PID 1 in the container and the CMD  provides options for it. If the ENTRYPOINT has not been specified in the Dockerfile, but CMDwas, then the shell /bin/sh -c will be the image's entry point. The CMD...