What is the difference between CMD and ENTRYPOINT in a Dockerfile?

Question

In Dockerfiles there are two commands that look similar to me: CMD and ENTRYPOINT. But I guess that there is a (subtle?) difference between them -

Answer 1

Most people explain it perfectly here, so I won't repeat all the answers. But to get a good feeling I would suggest testing it yourself by looking at the processes in the container.

Create a tiny Dockerfile of the form:

FROM ubuntu:latest
CMD /bin/bash

Build it, run it in with docker run -it theimage and run ps -eo ppid,pid,args in the container. Compare this output to the output you receive from ps when using:

• docker run -it theimage bash
• Rebuilding the image but with ENTRYPOINT /bin/bash and running it in both ways
• Using CMD ["/bin/bash"]
• ...

This way you will easily see the differences between all possible methods for yourself.