Getting a shell prompt in an existing, running Docker container
So, you have a container thats running, merrily sitting over there on your Docker server doing ... something.
And you want command prompt access to it.
Well, luckily, its fairly easy - you can run commands in existing and running containers by using:
$ sudo docker exec -i -t <ID> /bin/bash
Just remember that changes made to the container are not persistent - if you recreate the container from an image, any changes you made that weren't part of a connected volume will be reverted to whatever the image consisted of.