I want to understand how CMD and ENTRYPOINT works. So, I just created a very simple Dockerfile
FROM scratch
CMD echo "Hello First"
ENTRYPOINT echo "Hello second"
Then I build image of this :
docker build -t my_image .
The logs are as below:
Step 1/3 : FROM scratch ---> Step 2/3 : CMD echo "Hello First" ---> Using cache ---> 9f2b6a00982f Step 3/3 : ENTRYPOINT echo "Hello second" ---> Using cache ---> 1bbe520f9526 Successfully built 1bbe520f9526 Successfully tagged my_image:latest SECURITY WARNING: You are building a Docker image from Windows against a non-Windows Docker host. All files and directories added to build context w ill have '-rwxr-xr-x' permissions. It is recommended to double check and reset permissions for sensitive files and directories.
When I create a container of this image it returns:
docker run my_image
Error is:
docker: Error response from daemon: OCI runtime create failed: container_linux.go:344: starting container process caused "exec: \"/bin/sh\": stat /b in/sh: no such file or directory": unknown.
Can someone please help me about error?
There are two things happening here.
A Dockerfile that starts FROM scratch starts from a base image that has absolutely nothing at all in it. It is totally empty. There is not a set of base tools or libraries or anything else, beyond a couple of device files Docker pushes in for you.
The ENTRYPOINT echo ... command gets rewritten by Docker into ENTRYPOINT ["/bin/sh", "-c", "echo ..."], and causes the CMD to be totally ignored. Unless overridden with docker run --entrypoint, this becomes the main process the container runs.
Since it is a FROM scratch image and contains absolutely nothing at all, it doesn't contain a shell, hence the "/bin/sh: no such file or directory" error.
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