Docker Default Executable A Default Executable is the command that will run when the container is started. It is defined in the Dockerfile as an ENTRYPOINT or CMD instruction. CMD and ENTRYPOINT instructions both define the startup command for a container. You can enter one or the other, or both in the Dockerfile. This example runs the debian container and starts a shell . The default executable, the shell , is defined in the Dockerfile as a default executable. If a default executable is not specified in the Dockerfile and an argument is not given at the command line, the container will error out when called: The above error can be remedied by entering the starting command at the command line. In this example, the shell, sh , is given as the starting command: Entry Point instruction An ENTRYPOINT allows you to configure a container to behave as