It's maybe the most powerful all--around tool when working with Docker images. The exec command allows you to run arbitrary commands inside a running container.

In opposite of the overriding the CMD or ENTRYPOINT, the command started using docker exec will only run while the container's primary process (PID 1) is running.

Also, the syntax of the exec command is different. It's not a part of the Docker run command, it's rather a new separate command, executed after you run your container with the docker run. Consider the following example and run the following in one shell terminal:

docker run -it ubuntu bash --name myUbuntuBash

Then run the next command in the second shell terminal window:

dockerexec -d myUbuntuBash touch /tmp/myFile

In the preceding example, the first command fill starts the interactive bash shell from the Ubuntu container, ok that is nothing new; however...