docker container run --rm -it <imageName> bash # or sh
# --rm = remove the container right after finishing it
# -i = --interactive
# -t = --tty
# sometimes the entrypoint doesn't allow you to run a shell.
# then you'll need to overwrite the entrypoint
docker container run --rm -it --entrypoint /bin/sh <imageName>
docker container run -it <imageName> bash
# -i = --interactive
# -t = --tty
Remember: the bash right after the <imageName> is the command that replaces the one define in the CMD part of the image's Dockerfile.
In the images created for the famous Linux distributions, the CMD is usually calling a shell. In such cases you don't need to specify it in command line.
Example:
docker container run -it ubuntu # it'll run bash interactively
docker container exec -it <containerName> bash
Note: the exec runs an additional process in the running container. So if you exit the shell launched this way, the container will still be running in background.
Note: This only works when the Dockerfile used to create the image has a CMD calling a shell, which is most common in the images created for Linux distros.
docker container start -ai <containerName>
# -a = --attach
# -i = --interactive
What that command actually do is launch the container and attach its stdin/stdout to the terminal. If the CMD is a shell, then you'll have a shell inside the container, otherwise you'll only be able to interactive with whatever is being called in the CMD.