CodeBlanks Logo Icon CodeBlanks
Login Register

docker pull

Learn to pull images from a registry with docker pull.

docker pull

docker pull downloads an image from the registry. The image arrives in layers; layers already present locally aren't downloaded again (Already exists):

$ docker pull python:3.12-slim
3.12-slim: Pulling from library/python
a2318d6c47ec: Already exists
7f9a2c0b1d3e: Pull complete
Digest: sha256:9c4f…
Status: Downloaded newer image for python:3.12-slim

docker run pulls automatically if the image is missing; but it doesn't update an image that exists.

Platform and digest

Images are published for several processor architectures (amd64, arm64). Docker picks the one matching your machine; another architecture can be requested with --platform. Pulling by digest guarantees exactly the same content:

docker pull --platform linux/arm64 nginx:alpine
docker pull nginx@sha256:2d19…
docker run --pull always nginx:alpine     # check for the latest every time

Practice Run with the current image

Write two commands: pull the python:3.12-slim image; then start a container named web in the background, checking the registry for the current nginx:alpine image every time.

Starter code

terminal
# buraya yaz

Sample solution

terminal
docker pull python:3.12-slim
docker run -d --pull always --name web nginx:alpine

Expected output

Status: Downloaded newer image for python:3.12-slim
alpine: Pulling from library/nginx
Status: Image is up to date for nginx:alpine
9d8c7b6a5f4e

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 With an old nginx:alpine locally, what does docker run nginx:alpine do?

  • It uses the old local image Correct answer
  • It always downloads the newest
  • It errors
  • It merges the two

Explanation: To update, docker pull or docker run --pull always is used.

2 Pull an image for the ARM architecture.

Question 
docker pull ____ linux/arm64 nginx:alpine
Answer 
docker pull --platform linux/arm64 nginx:alpine

Explanation: --platform takes os/architecture.

3 Match.

Term Meaning
Already exists Layer exists locally
Pull complete Layer downloaded
--platform Architecture choice
@sha256: Immutable content

All lessons in Beginner

1 What is Docker?

  1. What is Docker?
  2. Containers and virtual machines
  3. Images and containers
  4. Docker architecture
  5. Use cases
  6. Summary - What is Docker

2 Installation and first commands

  1. Installing Docker
  2. docker version
  3. docker info
  4. The hello-world container
  5. Docker Desktop
  6. Summary - Installation

3 First container

  1. docker run basics
  2. Running in the background
  3. docker ps
  4. docker stop and rm
  5. docker logs
  6. Summary - First container

4 Dockerfile basics

  1. What is a Dockerfile?
  2. The FROM instruction
  3. The RUN instruction
  4. COPY and ADD
  5. CMD and ENTRYPOINT
  6. Summary - Dockerfile

5 Build and images

  1. docker build
  2. Tagging images
  3. Build context
  4. Layers and cache
  5. .dockerignore
  6. Summary - Build

6 docker run options

  1. Interactive mode
  2. Naming containers
  3. Restart policy
  4. Working directory
  5. Switching users
  6. Summary - docker run

7 Image management

  1. docker images
  2. docker rmi
  3. docker pull
  4. docker push
  5. docker tag
  6. Summary - Image management

8 Port mapping

  1. The port concept
  2. The -p flag
  3. Multiple ports
  4. Random ports
  5. IP binding
  6. Summary - Port mapping

9 Volumes and data

  1. Data persistence
  2. Named volumes
  3. The -v flag
  4. Bind mounts
  5. Volume management
  6. Summary - Volumes

10 Environment variables

  1. The -e flag
  2. The ENV instruction
  3. The ARG instruction
  4. env-file
  5. The WORKDIR instruction
  6. Summary - Environment

11 Project: docker-compose

  1. Compose design
  2. Service definition
  3. Database service
  4. Volume and network
  5. Putting it together - compose

12 Docker Hub and registry

  1. What is Docker Hub?
  2. docker login
  3. Searching images
  4. Official images
  5. Private registry
  6. Summary - Registry

13 Network basics

  1. Network drivers
  2. docker network ls
  3. Bridge network
  4. Container connectivity
  5. Publishing ports
  6. Summary - Network

14 Beginner final

  1. Challenge - Dockerfile
  2. Challenge - Build and run
  3. Challenge - Volume
  4. Challenge - Compose
  5. Challenge - Beginner project