Sometimes you want a quick and easy way to look inside a container before it's stopped- to debug it, to see what's going on. One way to change a way the image's container starts:

docker run --rm  --env-file .env --entrypoint="/bin/sleep" <image name> 120


docker run --rm  --env-file .env --entrypoint="/bin/sleep" myimage 120

Also look into nsenter and if you're unlucky with a very old unmaintained system look at jpetazzo/nsenter