What does the 'docker exec' command allow you to do?

The 'docker exec' command is a powerful feature in Docker that allows you to run a specified command in an already running container. This means that if you have a container that is currently active and performing its tasks, you can use 'docker exec' to execute additional commands inside that container's environment without needing to stop it or create a new instance.

This is particularly useful for various administrative tasks, such as troubleshooting, running interactive sessions, or monitoring processes. For example, you might want to access a shell within your running container to check logs, modify files, or install new packages without interrupting the main process the container is executing.

The other choices pertain to actions that are not served by the 'docker exec' command. Starting a new container, stopping a running container, and creating an image from a container are functions associated with different Docker commands, such as 'docker run', 'docker stop', and 'docker commit', respectively. By focusing on the functionality of executing commands within an existing container, it becomes clear why 'docker exec' is defined by its ability to run commands directly inside a running environment.