pychroot 0.10.4

a python library and cli tool that simplify chroot handling

pychroot

pychroot is a python library and cli tool that simplify chroot handling. Specifically, the library provides a Chroot context manager that enables more pythonic methods for running code in chroots while the pychroot utility works much like an extended chroot command in the terminal.

Usage

In its simplest form, the library can be used similar to the following:

from pychroot import Chroot

with Chroot('/path/to/chroot'):
    code that will be run
    inside the chroot

By default, this will bind mount the host’s /dev, /proc, and /sys filesystems into the chroot as well as the /etc/resolv.conf file (so DNS resolution works as expected in the chroot).

A simple chroot equivalent is also installed as pychroot. It can be used in a similar fashion to chroot; however, it also performs the bind mounts previously mentioned so the environment is usable. In addition, pychroot supports specifying custom bind mounts, for example:

pychroot -R /home/user ~/chroot

will recursively bind mount the user’s home directory at the same location inside the chroot directory in addition to the standard bind mounts. See pychroot’s help output for more options.

When running on a system with a recent kernel (Linux 3.8 and on) and user namespaces enabled pychroot can be run by a regular user. Currently pychroot just maps the current user to root in the chroot environment. This means that recursively chown-ing the chroot directory to the user running pychroot should essentially allow that user to act as root in the pychroot environment.

Implementation details

Namespaces are used by the context manager to isolate the chroot instance from the host system and to simplify the teardown phase for the environments. By default, new mount, UTS, IPC, and pid namespaces are used. In addition, if running as non-root, both user and network namespaces will be enabled as well so that the chrooting and mounting process will work without elevated permissions.

One quirk of note is that currently local variables are not propagated back from the chroot context to the main context due to the usage of separate processes running the contexts. This means that something similar to the following won’t work:

from pychroot import Chroot

with Chroot('/path/to/chroot'):
    answer = 42
print(answer)

In this case, a NameError exception will be raised unless the variable answer was previously defined. This will probably be fixed to some extent in a future release.

Requirements

pychroot is quite Linux specific due to the use of namespaces via the snakeoil library which also require proper kernel support. Specifically, the following kernel config options are required to be enabled for full namespace support:

CONFIG_NAMESPACES=y
CONFIG_UTS_NS=y
CONFIG_IPC_NS=y
CONFIG_USER_NS=y
CONFIG_PID_NS=y
CONFIG_NET_NS=y

Installing

Installing latest pypi release:

pip install pychroot

Installing from git:

pip install https://github.com/pkgcore/pychroot/archive/master.tar.gz

Installing from a tarball:

python setup.py install

Tests

A standalone test runner is integrated in setup.py; to run, just execute:

python setup.py test

In addition, a tox config is provided so the testsuite can be run in a virtualenv setup against all supported python versions. To run tests for all environments just execute tox in the root directory of a repo or unpacked tarball. Otherwise, for a specific python version execute something similar to the following:

tox -e py39