How can you run a command inside a running Docker container?

Running a command inside a running Docker container is accomplished using the docker exec command. This command allows you to execute specific commands within an already running container's context. It can start a new process in the container without needing to stop or restart it, which provides flexibility for managing and interacting with the containerized environment.

For instance, you might want to open a shell session inside the container or run certain scripts or binaries related to the application that’s executing inside the container. The docker exec command is particularly useful for debugging or modifying the state of a running container without interrupting its primary functionality.

The other options refer to different actions related to Docker containers. The docker run command is used to create and start a new container from an image, which is not applicable when trying to interact with an already running instance. The docker start command is intended for restarting a stopped container, rather than executing commands within it. Lastly, the docker attach command connects your terminal to a running container’s standard input/output streams, but it does not allow you to execute new commands independently, as it relies on the existing processes within the container.