mirror of https://github.com/python/cpython
93 lines
3.5 KiB
ReStructuredText
93 lines
3.5 KiB
ReStructuredText
:mod:`posix` --- The most common POSIX system calls
|
|
===================================================
|
|
|
|
.. module:: posix
|
|
:platform: Unix
|
|
:synopsis: The most common POSIX system calls (normally used via module os).
|
|
|
|
--------------
|
|
|
|
This module provides access to operating system functionality that is
|
|
standardized by the C Standard and the POSIX standard (a thinly disguised Unix
|
|
interface).
|
|
|
|
.. index:: pair: module; os
|
|
|
|
**Do not import this module directly.** Instead, import the module :mod:`os`,
|
|
which provides a *portable* version of this interface. On Unix, the :mod:`os`
|
|
module provides a superset of the :mod:`posix` interface. On non-Unix operating
|
|
systems the :mod:`posix` module is not available, but a subset is always
|
|
available through the :mod:`os` interface. Once :mod:`os` is imported, there is
|
|
*no* performance penalty in using it instead of :mod:`posix`. In addition,
|
|
:mod:`os` provides some additional functionality, such as automatically calling
|
|
:func:`~os.putenv` when an entry in ``os.environ`` is changed.
|
|
|
|
Errors are reported as exceptions; the usual exceptions are given for type
|
|
errors, while errors reported by the system calls raise :exc:`OSError`.
|
|
|
|
|
|
.. _posix-large-files:
|
|
|
|
Large File Support
|
|
------------------
|
|
|
|
.. index::
|
|
single: large files
|
|
single: file; large files
|
|
|
|
.. sectionauthor:: Steve Clift <clift@mail.anacapa.net>
|
|
|
|
Several operating systems (including AIX and Solaris) provide
|
|
support for files that are larger than 2 GiB from a C programming model where
|
|
:c:expr:`int` and :c:expr:`long` are 32-bit values. This is typically accomplished
|
|
by defining the relevant size and offset types as 64-bit values. Such files are
|
|
sometimes referred to as :dfn:`large files`.
|
|
|
|
Large file support is enabled in Python when the size of an :c:type:`off_t` is
|
|
larger than a :c:expr:`long` and the :c:expr:`long long` is at least as large
|
|
as an :c:type:`off_t`.
|
|
It may be necessary to configure and compile Python with certain compiler flags
|
|
to enable this mode. For example, with Solaris 2.6 and 2.7 you need to do
|
|
something like::
|
|
|
|
CFLAGS="`getconf LFS_CFLAGS`" OPT="-g -O2 $CFLAGS" \
|
|
./configure
|
|
|
|
On large-file-capable Linux systems, this might work::
|
|
|
|
CFLAGS='-D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64' OPT="-g -O2 $CFLAGS" \
|
|
./configure
|
|
|
|
|
|
.. _posix-contents:
|
|
|
|
Notable Module Contents
|
|
-----------------------
|
|
|
|
In addition to many functions described in the :mod:`os` module documentation,
|
|
:mod:`posix` defines the following data item:
|
|
|
|
.. data:: environ
|
|
|
|
A dictionary representing the string environment at the time the interpreter
|
|
was started. Keys and values are bytes on Unix and str on Windows. For
|
|
example, ``environ[b'HOME']`` (``environ['HOME']`` on Windows) is the
|
|
pathname of your home directory, equivalent to ``getenv("HOME")`` in C.
|
|
|
|
Modifying this dictionary does not affect the string environment passed on by
|
|
:func:`~os.execv`, :func:`~os.popen` or :func:`~os.system`; if you need to
|
|
change the environment, pass ``environ`` to :func:`~os.execve` or add
|
|
variable assignments and export statements to the command string for
|
|
:func:`~os.system` or :func:`~os.popen`.
|
|
|
|
.. versionchanged:: 3.2
|
|
On Unix, keys and values are bytes.
|
|
|
|
.. note::
|
|
|
|
The :mod:`os` module provides an alternate implementation of ``environ``
|
|
which updates the environment on modification. Note also that updating
|
|
:data:`os.environ` will render this dictionary obsolete. Use of the
|
|
:mod:`os` module version of this is recommended over direct access to the
|
|
:mod:`posix` module.
|