World D2: Recipes

CMD vs ENTRYPOINT

You will learn: which part of a start command you can swap, and which part stays.

Checked with Docker Engine 29 on 31 Oct 2026

The problem

The image say:1.0 has CMD ["echo", "Selamat datang!"]. You type docker run --rm say:1.0 echo Hai. What prints?

Watch

~ $ cat sayer/DockerfileFROM alpine:3.22CMD ["echo", "Selamat datang!"]~ $ docker run --rm say:1.0Selamat datang!~ $ docker run --rm say:1.0 echo HaiHai

Your laptop`~`

No open hatches

Lunchboxes (containers)

No containers yet

Frozen packs (images)

alpine:3.221 layers · 12.9MB
greet:1.01 layers · 12.8MB
say:1.01 layers · 12.8MB

CMD is the default order, like “the usual, please”. Say something else after the image name, and your order replaces it.

Try it

greet:1.0 uses : a fixed first part. Run it. Then run it again with a place name at the end.

Your laptop`~`

No open hatches

Lunchboxes (containers)

No containers yet

Frozen packs (images)

alpine:3.221 layers · 12.9MB
greet:1.01 layers · 12.8MB
say:1.01 layers · 12.8MB

Hint

Put your words after greet:1.0, like Pasar Seni.

Predict

greet:1.0 has ENTRYPOINT ["echo", "Selamat datang ke"]. You type docker run --rm greet:1.0 Aina. What prints?

Check

Which instruction does each job?

Drag a card into a box. Or tap the card, then tap the box.

Check

~ $ cat shouter/DockerfileFROM alpine:3.22CMD echo "Selamat datang!"~ $ docker build -t shout:1.0 shouter[+] Building 0.1s (5/5) FINISHED                                  docker:default => [internal] load build definition from Dockerfile                        0.0s => => transferring dockerfile: 81B                                         0.0s => WARN: JSONArgsRecommended: JSON arguments recommended for CMD to prevent unintended behavior related to OS signals (line 2) => [internal] load metadata for docker.io/library/alpine:3.22              0.0s => [internal] load .dockerignore                                           0.0s => => transferring context: 2B                                             0.0s => [1/1] FROM docker.io/library/alpine:3.22@sha256:2e0b81d60597f449baa56d  0.0s => => resolve docker.io/library/alpine:3.22@sha256:2e0b81d60597f449baa56d  0.0s => exporting to image                                                      0.1s => => exporting layers                                                     0.0s => => exporting manifest sha256:17c0813739eb06d2466dedac6df84e320b2c6b8d1  0.0s => => exporting config sha256:26dd70318a6701e122d7ae0bb53c3b179a2872d50c4  0.0s => => exporting attestation manifest sha256:88593f1d74734ee8c332c73cc2347  0.0s => => exporting manifest list sha256:2541b0b4862ea3361151f41a258c4c86a23b  0.0s => => naming to docker.io/library/shout:1.0                                0.0s => => unpacking to docker.io/library/shout:1.0                             0.0s 1 warning found (use docker --debug to expand): - JSONArgsRecommended: JSON arguments recommended for CMD to prevent unintended behavior related to OS signals (line 2)

Your laptop`~`

No open hatches

Lunchboxes (containers)

No containers yet

Frozen packs (images)

alpine:3.221 layers · 12.9MB
greet:1.01 layers · 12.8MB
say:1.01 layers · 12.8MB

Real warning: JSONArgsRecommended. Plain words: write CMD as a list in brackets. Without brackets, a shell runs your app. A stop signal may not reach it.

You did it!

You can now choose between CMD and ENTRYPOINT.

Go deeper (optional)

docker run --entrypoint whoami greet:1.0 swaps the fixed part for one run. The bracket form is called exec form. It runs your app as process 1, so docker stop reaches it quickly.

Real mission

Write a Dockerfile with an ENTRYPOINT echo and a CMD default, like greet.
Build it.
docker build -t greet:1.0 .
Run it with and without your own words.
docker run --rm greet:1.0 Pasar Seni

0 of 3 steps done · Your ticks are saved.

CMD vs ENTRYPOINT

Your laptop~

Lunchboxes (containers)

Frozen packs (images)

Your laptop~

Lunchboxes (containers)

Frozen packs (images)

Your laptop~

Lunchboxes (containers)

Frozen packs (images)

Your laptop`~`

Your laptop`~`

Your laptop`~`