Docker run vs pull

Question

I am a beginner in docker and referring this to install and understand basics but I am little confused about run and pull command.

What is the difference between docker run and docker pull commands for Docker images?

Answer 1

docker run runs an instance of a container. In order to do that it will pull all the required images needed to run the container (i.e. base images) in the background if they are not part of the local cache.

docker pull will fetch/pull an image from the docker registry.

Think of it similar to git fetch and git pull if you have worked with git.
git pull will do git fetch (and git merge)

Answer 2

From the docs:

docker run:

The docker run command first creates a writeable container layer over the specified image, and then starts it using the specified command. A stopped container can be restarted with all its previous changes intact using docker start. See docker ps -a to view a list of all containers.

If the image you are trying to run is not downloaded yet it will be automatically fetched with pull.

docker pull:

Most of your images will be created on top of a base image from the Docker Hub registry.

Docker Hub contains many pre-built images that you can pull and try without needing to define and configure your own.

To download a particular image, or set of images (i.e., a repository), use docker pull.

So docker pull will download or update an image.

Answer 3

Pull will download new versions of images if there are any, while run will only download an image if you don't have a local copy.