Commands and Arguments

CMD

Command that will start the container process:

FROM ubuntu
CMD echo "Hello World"

FROM ubuntu
CMD ["/usr/bin/wc","--help"]

Similar to CMD but higher priority

FROM ubuntu
ENTRYPOINT ["executable", "param1", "param2"]

If ENTRYPOINT and CMD are used together then the ENTRYPOINT will run first.

Usually when used together the ENTRYPOINT would be the command and CMD the argument, Example:

FROM ubuntu
ENTRYPOINT[echo]
CMD["hi"]

Kubernetes Example

vim commands.yaml

apiVersion: v1
kind: Pod
metadata:
  name: command-demo
  labels:
    purpose: demonstrate-command
spec:
  containers:

  - name: command-demo-container
    image: debian
    command: ["printenv"]
    args: ["HOSTNAME", "KUBERNETES_PORT"]

  - name: echo-demo
    image: debian
    env:
      - name: MESSAGE
        value: "hello world"
    command: ["/bin/echo"]
    args: ["$(MESSAGE)"]

  restartPolicy: OnFailure

Note:
You can only use one command and args per container.
To try both examples, comment/uncomment the relevant lines or create two containers in the pod. 2 containers running is not recomended in production unless its side-container or container that will start another container.

env: - name: MESSAGE value: "hello world" command: ["/bin/echo"] args: ["$(MESSAGE)"]

start pod

kubectl apply -f commands.yaml
kubectl get pod

# wait for status: Completed

kubectl logs command-demo

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