Docker Entrypoint vs CMD

Docker has a default entrypoint which is /bin/sh -c but does not have a default command. ENTRYPOINT and --entrypoint were introduced to allow to override /bin/sh -c.

CMD specify a default command that executes when the container is starting.

Taking docker run -i -t ubuntu bash as example, with the entrypoint /bin/sh -c, the command is the actual thing that gets executed: docker run -i -t ubuntu <cmd>. C

If we run docker run -i -t ubuntu, it will start bash shell and that’s because the Ubuntu Dockerfile has CMD ["bash"]