Dockerfile CMD vs ENTRYPOINT

I had difficulty in understanding the difference between CMD and ENTRYPOINT in Dockerfile before I did the below experiment. Hope this will help someone like me who cannot understand the difference from the documentation or stackoverflow.

Consider the below docker file

[[email protected] 01.BusyboxWithCMD]$ cat Dockerfile
FROM busybox:latest
CMD ["cat", "/etc/passwd"]

Let's build an image and call it busy_cmd_image

[[email protected] 01.BusyboxWithCMD]$ docker build -t busy_cmd_image .
Sending build context to Docker daemon 2.048 kB
Step 1 : FROM busybox:latest
 ---> 2b8fd9751c4c
Step 2 : CMD cat /etc/passwd
 ---> Using cache
 ---> e4df0d0c0d67
Successfully built e4df0d0c0d67

Now, we ...

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