Difference between Running and Starting a Docker container

In practice to start a container I do:

docker run a8asd8f9asdf0

If thats the case, what does:

docker start

do?

In the manual it says

Start one or more stopped containers

This is a very important question and the answer is very simple, but fundamental:

1. Run: create a new container of an image, and execute the container. You can create N clones of the same image. The command is: docker run IMAGE_ID and not docker run CONTAINER_ID

2. Start: Launch a container previously stopped. For example, if you had stopped a database with the command docker stop CONTAINER_ID, you can relaunch the same container with the command docker start CONTAINER_ID, and the data and settings will be the same.

• run runs an image
• start starts a container.

The docker run doc does mention:

The docker run command first creates a writeable container layer over the specified image, and then starts it using the specified command.

That is, docker run is equivalent to the API /containers/create then /containers/(id)/start.

You do not run an existing container, you docker exec to it (since docker 1.3).
You can restart an exited container.