NSEnter

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:

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.