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Docker CMD VS ENTRYPOINT

Git RepositoryEdit on Github
2 minutes to read

Definition

  • CMD sets default command and/or parameters, which can be overwritten from command line when docker container runs.
  • ENTRYPOINT configures a container that will run as an executable.

When to use CMD or ENTRYPOINT

  • Prefer ENTRYPOINT to CMD when building executable Docker image and you need a command always to be executed.
  • Choose CMD if you need to provide a default command and/or arguments that can be overwritten from command line when docker container runs.
  • Choose CMD to be be a default parameter of ENTRYPOINT that can be overwritten later.

Example of how to use CMD & ENTRYPOINT together

  • Create a Docker file
FROM alpine
ENTRYPOINT ["echo", "Hello"]
CMD ["World"]
  • Launch a new shell.
  • Build a Docker image.
docker build -t my-custom-image .
  • List images.
docker image ls
  • Launch a container with default arguments.
docker run my-custom-image
// Output
Hello world
  • Launch a container with override arguments.
docker run my-custom-image .NET TH
// Output
Hello .NET TH

Command in a Docker compose file

The Docker Compose command or everything in a docker run invocation after the image name, overrides the Dockerfile CMD.

If the image also has an ENTRYPOINT, the command you provide here is passed as arguments to the entrypoint in the same way the Dockerfile CMD does.

Maintainers

  • KubeOps
  • Yosapol Jitrak
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