Docker nsenter

https://blog.docker.com/tag/nsenter/

Introducing nsenter

nsenter is a small tool allowing to enter into namespaces. Technically, it can enter existingnamespaces, or spawn a process into a new set of namespaces. “What are those namespaces you’re blabbering about?” They are one of the essential constituants of containers. The short version is: with nsenter, you can get a shell into an existing container, even if that container doesn’t run SSH or any kind of special-purpose daemon.

Where do I get nsenter?

Check jpetazzo/nsenter on GitHub. The short version is that if you run:

docker run -v /usr/local/bin:/target jpetazzo/nsenter

This will install nsenter in /usr/local/bin and you will be able to use it immediately. nsenter might also be available in your distro (in the util-linux package).

How do I use it?

First, figure out the PID of the container you want to enter:

PID=$(docker inspect --format {{.State.Pid}} )

Then enter the container:

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

You will get a shell inside the container. That’s it. If you want to run a specific script or program in an automated manner, add it as argument tonsenter. It works a bit like chroot, except that it works with containers instead of plain directories.



Reference:

Backup data, check logs, restart service ... use volume
https://docs.docker.com/userguide/dockervolumes/