ENTRYPOINT vs CMD difference in Docker - Quick Revision & Key Differences

Recall & Review

beginner

What is the purpose of the CMD instruction in a Dockerfile?

CMD sets the default command and arguments for a container. It can be overridden when running the container.

beginner

What does the ENTRYPOINT instruction do in a Dockerfile?

ENTRYPOINT sets the main command that always runs when the container starts. It is not easily overridden.

intermediate

How do ENTRYPOINT and CMD work together in a Dockerfile?

ENTRYPOINT defines the command to run, and CMD provides default arguments to that command. CMD arguments can be overridden at runtime.

intermediate

If a Dockerfile has both ENTRYPOINT and CMD, and you run the container with extra arguments, what happens?

The extra arguments replace CMD arguments but are passed to ENTRYPOINT command. ENTRYPOINT command always runs.

beginner

Which instruction is easier to override when running a Docker container: ENTRYPOINT or CMD?

CMD is easier to override by providing new arguments when running the container. ENTRYPOINT is harder to override.

What happens if you specify both ENTRYPOINT and CMD in a Dockerfile?

A Docker throws an error

B CMD runs as the command, ENTRYPOINT is ignored

C Both ENTRYPOINT and CMD run simultaneously

D ENTRYPOINT runs as the command, CMD provides default arguments

ENTRYPOINT sets the main command, and CMD provides default arguments to it.

Which Dockerfile instruction can be overridden by passing arguments to 'docker run'?

A Neither ENTRYPOINT nor CMD

B CMD

C Both ENTRYPOINT and CMD

D ENTRYPOINT

CMD arguments can be replaced by arguments passed to 'docker run'. ENTRYPOINT is not replaced.

If ENTRYPOINT is set to '/bin/bash' and CMD is set to '-c "echo Hello"', what command runs by default?

A /bin/bash -c "echo Hello"

B Only /bin/bash

C Only echo Hello

D Docker will fail to run

ENTRYPOINT is the command, CMD provides default arguments.

How can you override ENTRYPOINT when running a container?

A Use the --entrypoint flag with 'docker run'

B Pass new arguments after the image name

C Modify CMD in the Dockerfile

D You cannot override ENTRYPOINT

The --entrypoint flag lets you override ENTRYPOINT at runtime.

Which instruction is best to use if you want your container to always run a specific command?

A CMD

B RUN

C ENTRYPOINT

D ENV

ENTRYPOINT ensures the command always runs when the container starts.

Explain the difference between ENTRYPOINT and CMD in Dockerfiles.

Think about which one is the main command and which one provides default options.

Describe how ENTRYPOINT and CMD work together when both are used in a Dockerfile.

Consider how the container runs the command with arguments.