Move OSError docs to exceptions doc, remove obsolete descriptions
from os docs, rework posix docs.
diff --git a/Doc/library/exceptions.rst b/Doc/library/exceptions.rst
index 6122d44..1d85ddf 100644
--- a/Doc/library/exceptions.rst
+++ b/Doc/library/exceptions.rst
@@ -233,11 +233,24 @@
.. exception:: OSError
- This class is derived from :exc:`EnvironmentError` and is used primarily as the
- :mod:`os` module's ``os.error`` exception. See :exc:`EnvironmentError` above for
- a description of the possible associated values.
+ and is used primarily as
+ the :mod:`os` module's :exc:`os.error` exception. See :exc:`EnvironmentError`
+ above for a description of the possible associated values.
.. versionadded:: 1.5.2
+ .. index:: module: errno
+
+ This exception is derived from :exc:`EnvironmentError`. It is raised when a
+ function returns a system-related error (not for illegal argument types or
+ other incidental errors). The :attr:`errno` attribute is a numeric error
+ code from :cdata:`errno`, and the :attr:`strerror` attribute is the
+ corresponding string, as would be printed by the C function :cfunc:`perror`.
+ See the module :mod:`errno`, which contains names for the error codes defined
+ by the underlying operating system.
+
+ For exceptions that involve a file system path (such as :func:`chdir` or
+ :func:`unlink`), the exception instance will contain a third attribute,
+ :attr:`filename`, which is the file name passed to the function.
.. exception:: OverflowError