diskimage-builder/diskimage_builder/elements/dib-python
Nir Magnezi ee46e2f9b7 Add version-less RHEL element for RHEL7 and RHEL8
Make a version-less RHEL element to handle both '7' and '8' DIB_RELEASE.
The element usage should align with other elements which operate in the
same way such as the Fedora element.

Additionally, this patch adds support for RHEL8 that operates with
Python 3.
As of now, users of diskimage-builder will still be able to use the
'rhel7' element, or migrate to 'rhel' and specify their respective
DIB_RELEASE value.

* mount the xfs file-system for extraction as read-only.  vaguely
  based on explaination in [1] and the fact we only read the image
  data into a tar, so can ignore this.

    XFS (dm-1): Superblock has unknown read-only compatible features (0x4) enabled.

* Use the redhat system python as the dib-python version.  dib was
  ahead of it's time making an abstracted python interpreter for
  system work ;) the system python should work for running the various
  dib element scripts.

[1] https://unix.stackexchange.com/questions/247550/unmountable-xfs-filesystem

Redhat-Bug: https://bugzilla.redhat.com/show_bug.cgi?id=1700253
Co-Authored-By: Ian Wienand <iwienand@redhat.com>
Change-Id: I90540675c70bb475d9db2ae24f81c648a31f3f95
2019-05-29 11:28:53 +03:00
..
cleanup.d Clean up dib-python symlink 2017-04-12 14:33:57 +10:00
environment.d Add version-less RHEL element for RHEL7 and RHEL8 2019-05-29 11:28:53 +03:00
pre-install.d Add version-less RHEL element for RHEL7 and RHEL8 2019-05-29 11:28:53 +03:00
README.rst Clean up dib-python symlink 2017-04-12 14:33:57 +10:00

==========
dib-python
==========

Adds a symlink to ``/usr/local/bin/dib-python`` which points at either a
``python2`` or ``python3`` executable as appropriate.

In-chroot scripts should use this as their interpreter
(``#!/usr/local/bin/dib-python``) to make scripts that are compatible
with both ``python2`` and ``python3``.  We can not assume
``/usr/bin/python`` exists, as some platforms have started shipping with
only Python 3.

``DIB_PYTHON`` will be exported as the python interpreter.  You should
use this instead of ``python script.py`` (e.g. ``${DIB_PYTHON}
script.py``).  Note you can also call ``/usr/local/bin/dib-python
script.py`` but in some circumstances, such as creating a ``virtualenv``,
it can create somewhat confusing references to ``dib-python`` that
remain in the built image.

This does not install a python if one does not exist, and instead fails.

This also exports a variable ``DIB_PYTHON_VERSION`` which will either be
'2' or '3' depending on the python version which dib-python points to.


.. note::

  The ``dib-python`` interpreter will be removed in ``cleanup.d``.  It
  is only intended for build scripts.