ENTRYPOINT vs CMD difference in Docker - Visual Side-by-Side Comparison

Process Flow - ENTRYPOINT vs CMD difference

Dockerfile Build

↓

Set ENTRYPOINT?

No→Default ENTRYPOINT: none

|Yes↓

Set CMD?

No→Default CMD: none

|Yes↓

Container Run

↓

Run ENTRYPOINT + CMD

↓

Override CMD with args?

Yes→Run ENTRYPOINT + new args

No↓

Container runs with ENTRYPOINT + CMD

Docker builds image setting ENTRYPOINT and CMD. When running container, ENTRYPOINT runs always, CMD provides default arguments. CMD can be overridden at run time.

Execution Sample

Docker

FROM alpine
ENTRYPOINT ["echo"]
CMD ["Hello, World!"]

This Dockerfile sets ENTRYPOINT to 'echo' and CMD to 'Hello, World!'. Running container prints 'Hello, World!'.

Process Table

Step	Action	ENTRYPOINT	CMD	Run Command	Output
1	Build image	echo	Hello, World!	N/A	N/A
2	Run container without args	echo	Hello, World!	echo Hello, World!	Hello, World!
3	Run container with args 'Hi there'	echo	Hello, World!	echo Hi there	Hi there
4	Run container overriding ENTRYPOINT (not typical)	/bin/echo	Hello, World!	/bin/echo Hello, World!	Hello, World!
5	Run container with no ENTRYPOINT or CMD	none	none	none	No command runs

💡 Container stops after running the combined ENTRYPOINT and CMD or overridden command.

Status Tracker

Variable	Start	After Build	After Run No Args	After Run With Args	After ENTRYPOINT Override
ENTRYPOINT	none	echo	echo	echo	/bin/echo
CMD	none	Hello, World!	Hello, World!	Hi there	Hello, World!
Run Command	none	N/A	echo Hello, World!	echo Hi there	/bin/echo Hello, World!

Key Moments - 3 Insights

Why does the container run 'echo Hello, World!' when no arguments are given?

Because ENTRYPOINT is set to 'echo' and CMD provides default arguments 'Hello, World!'. See execution_table row 2.

What happens if you provide arguments when running the container?

The CMD default arguments are replaced by the new arguments, but ENTRYPOINT stays the same. See execution_table row 3.

Can ENTRYPOINT be overridden at runtime like CMD?

Yes, but it is less common and requires special syntax. Overriding ENTRYPOINT changes the main command run. See execution_table row 4.

Visual Quiz - 3 Questions

Look at the execution table, what is the run command at step 3?

A echo Hi there

B /bin/sh Hello, World!

C echo Hello, World!

D none

💡 Hint

Check the 'Run Command' column at step 3 in the execution_table.

At which step does the ENTRYPOINT get overridden?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look at the 'ENTRYPOINT' column changes in variable_tracker and execution_table.

If CMD is not set, but ENTRYPOINT is 'echo', what happens when you run the container with no arguments?

A Container runs default shell

B Container fails to run

C Container runs 'echo' with no arguments and prints nothing

D Container runs 'echo Hello, World!'

💡 Hint

Think about how ENTRYPOINT and CMD combine; CMD provides default args if present.

Concept Snapshot

ENTRYPOINT sets the main command always run.
CMD provides default arguments to ENTRYPOINT.
CMD can be overridden at container run.
ENTRYPOINT can be overridden but less common.
Without ENTRYPOINT, CMD runs as command.
Together they define container start behavior.

Full Transcript

Docker images can define ENTRYPOINT and CMD. ENTRYPOINT is the main command that always runs when the container starts. CMD provides default arguments to ENTRYPOINT or acts as the command if ENTRYPOINT is not set. When running a container, you can override CMD by passing new arguments, but ENTRYPOINT stays unless explicitly overridden. This lets you set a fixed command with flexible arguments. The execution table shows how ENTRYPOINT and CMD combine to form the final run command and output. Overriding ENTRYPOINT changes the main command, which is less common. Understanding this helps control container startup behavior clearly.