======= NSEnter

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NSEnter is a Python package that enables you to enter Linux kernel namespaces — mount, IPC, net, PID, user and UTS — with a single, simple "setns" syscall. The command line interface is similar to the nsenter_ C program.

Project Origins

When working with Docker_ containers, questions usually arise about how to connect into a running container without starting an explicit SSH daemon (which is considered a bad idea_). One way is to use Linux Kernel namespaces, which Docker uses to restrict the view from within containers.

The util-linux package provides the nsenter command line utility, but Ubuntu 16.04 LTS_ unfortunately does not. Jérôme Petazzoni provides a Docker recipe_ for nsenter on GitHub, or you can compile nsenter from source_. As there is only one simple syscall to enter a namespace, we can do the call directly from within Python using the ctypes module. We bundled this syscall to create NSEnter.

Additional Links

- "Entering Kernel Namespaces from Python," Zalando Tech `blog post`_
- On PyPi_

Requirements
````````````
- Python 2.6 or higher

Installation
````````````
From PyPI::

    sudo pip3 install nsenter

From git source::

    python3 setup.py install

Usage
`````
Example of command line usage::

    docker run -d --name=redis -t redis
    sudo nsenter --all --target=`docker inspect --format '{{ .State.Pid }}' redis` /bin/bash


Example of usage from Python:

.. code:: python

    import subprocess
    from nsenter import Namespace

    with Namespace(mypid, 'net'):
        # output network interfaces as seen from within the mypid's net NS:
        subprocess.check_output(['ip', 'a'])

    # or enter an arbitrary namespace:
    with Namespace('/var/run/netns/foo', 'net'):
        # output network interfaces as seen from within the net NS "foo":
        subprocess.check_output(['ip', 'a'])

Development Status

This project works as-is. There are currently no plans to extend it, but if you have an idea please submit an Issue to the maintainers.

License

See file_.

.. _Docker: https://www.docker.com/ .. _which is considered a bad idea: https://jpetazzo.github.io/2014/06/23/docker-ssh-considered-evil/ .. _Ubuntu 16.04 LTS: https://askubuntu.com/questions/439056/why-there-is-no-nsenter-in-util-linux .. _Docker recipe: https://github.com/jpetazzo/nsenter .. _from source: https://askubuntu.com/questions/439056/why-there-is-no-nsenter-in-util-linux .. _nsenter: http://man7.org/linux/man-pages/man1/nsenter.1.html .. _blog post: http://tech.zalando.com/posts/entering-kernel-namespaces-with-python.html .. _PyPi: https://pypi.python.org/pypi/nsenter .. _file: https://github.com/zalando/python-nsenter/blob/master/LICENSE