Which command can you use to enter a shell inside a running container?

The command that allows you to enter a shell inside a running container is docker exec -it [container_id] /bin/bash. This command is designed for interacting with containers by executing commands directly within their environment in real-time.

The exec part of the command is critical because it creates a new process inside the specified container. The -it flags are used together to enable interactive mode and to allocate a pseudo-TTY. This means you can interact with the shell as if you are on a terminal, allowing for input and output operations just as if you were operating on a local machine. By specifying /bin/bash, you are indicating that you want to start a Bash shell session in the container. This is particularly useful for debugging or performing administrative tasks.

In contrast, commands like docker attach [container_id] attach your terminal to a running process in the container rather than starting a new shell session, which might not be the same as having a full interactive shell environment. The nonexistent commands such as docker shell [container_id] and docker enter [container_id] do not exist in the Docker command set, which further emphasizes the validity of using docker exec for this purpose.