How to edit a file dynamically in a running docker container

Background

I had build a npm server(sinopia) docker image(https://github.com/feuyeux/docker-atue/blob/master/docker-images/feuyeux_sinopia.md), and in the CMD line, it will run the start.sh every time when the container is generated.

CMD ["/opt/sinopia/start.sh"]

This shell will create a yaml file dynamically.

sed -e 's/\#listen\: localhost/listen\: 0.0.0.0/' -e 's/allow_publish\: admin/allow_publish\: all/' /tmp/config.yaml > /opt/sinopia/config.yaml

Question

I wish I could edit this config.yaml when the container is running, because I hope the content should be changed on demand.

see the snapshot photo

As shown above, the first line runs a sinopia container, and in this container, there's /opt/sinopia/config.yaml. But I don't know how to obtain this running container and edit and check this file. If I did as the line of sinopia-ls, there's a new container runs instead of the before running one.

Thanks guys!

Answer(details please see below what I accepted)

sudo nsenter --target $PID --mount --uts --ipc --net --pid

root@58075317e47d:/# ls /opt/sinopia/
config.yaml  config_gen.js  start.sh  storage
root@58075317e47d:/# cat /opt/sinopia/config.yaml

With docker 1.3, there is a new command docker exec. This allows you to enter a running docker:

docker exec -it <container-id> bash