Docker Images and Containers

Overview

An image is a read-only template that contains everything needed to run an application: code, runtime, libraries, and settings. A container is a running (or stopped) instance created from an image. You can start many containers from a single image, and each one has its own isolated writable layer on top of the shared image layers.

Syntax / Usage

Images and containers are managed with separate sets of commands. Images are listed and removed with docker image (or docker images), while containers use docker ps and docker rm.

# List local images
docker images

# List all containers, including stopped ones
docker ps -a

# Create a container from an image
docker run --name app node:20

# Inspect and view logs
docker inspect app
docker logs app

# Remove a container, then its image
docker rm app
docker rmi node:20

Examples

Start a container, execute a command inside a running one, then stop it:

docker run -d --name redis redis
docker exec -it redis redis-cli ping
docker stop redis

Remove all stopped containers and dangling images to reclaim space:

docker container prune
docker image prune

Common Mistakes

• Trying to docker rmi an image while a container still uses it
• Confusing docker ps (running only) with docker ps -a (all containers)
• Expecting changes made inside a container to update the underlying image
• Naming collisions from reusing --name without removing the old container
• Accumulating dangling images from repeated builds and never pruning

See Also

docker-introduction docker-dockerfile docker-volumes