1:mod:`!posix` --- The most common POSIX system calls 2==================================================== 3 4.. module:: posix 5 :platform: Unix 6 :synopsis: The most common POSIX system calls (normally used via module os). 7 8-------------- 9 10This module provides access to operating system functionality that is 11standardized by the C Standard and the POSIX standard (a thinly disguised Unix 12interface). 13 14.. availability:: Unix. 15 16.. index:: pair: module; os 17 18**Do not import this module directly.** Instead, import the module :mod:`os`, 19which provides a *portable* version of this interface. On Unix, the :mod:`os` 20module provides a superset of the :mod:`posix` interface. On non-Unix operating 21systems the :mod:`posix` module is not available, but a subset is always 22available through the :mod:`os` interface. Once :mod:`os` is imported, there is 23*no* performance penalty in using it instead of :mod:`posix`. In addition, 24:mod:`os` provides some additional functionality, such as automatically calling 25:func:`~os.putenv` when an entry in ``os.environ`` is changed. 26 27Errors are reported as exceptions; the usual exceptions are given for type 28errors, while errors reported by the system calls raise :exc:`OSError`. 29 30 31.. _posix-large-files: 32 33Large File Support 34------------------ 35 36.. index:: 37 single: large files 38 single: file; large files 39 40.. sectionauthor:: Steve Clift <clift@mail.anacapa.net> 41 42Several operating systems (including AIX and Solaris) provide 43support for files that are larger than 2 GiB from a C programming model where 44:c:expr:`int` and :c:expr:`long` are 32-bit values. This is typically accomplished 45by defining the relevant size and offset types as 64-bit values. Such files are 46sometimes referred to as :dfn:`large files`. 47 48Large file support is enabled in Python when the size of an :c:type:`off_t` is 49larger than a :c:expr:`long` and the :c:expr:`long long` is at least as large 50as an :c:type:`off_t`. 51It may be necessary to configure and compile Python with certain compiler flags 52to enable this mode. For example, with Solaris 2.6 and 2.7 you need to do 53something like:: 54 55 CFLAGS="`getconf LFS_CFLAGS`" OPT="-g -O2 $CFLAGS" \ 56 ./configure 57 58On large-file-capable Linux systems, this might work:: 59 60 CFLAGS='-D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64' OPT="-g -O2 $CFLAGS" \ 61 ./configure 62 63 64.. _posix-contents: 65 66Notable Module Contents 67----------------------- 68 69In addition to many functions described in the :mod:`os` module documentation, 70:mod:`posix` defines the following data item: 71 72.. data:: environ 73 74 A dictionary representing the string environment at the time the interpreter 75 was started. Keys and values are bytes on Unix and str on Windows. For 76 example, ``environ[b'HOME']`` (``environ['HOME']`` on Windows) is the 77 pathname of your home directory, equivalent to ``getenv("HOME")`` in C. 78 79 Modifying this dictionary does not affect the string environment passed on by 80 :func:`~os.execv`, :func:`~os.popen` or :func:`~os.system`; if you need to 81 change the environment, pass ``environ`` to :func:`~os.execve` or add 82 variable assignments and export statements to the command string for 83 :func:`~os.system` or :func:`~os.popen`. 84 85 .. versionchanged:: 3.2 86 On Unix, keys and values are bytes. 87 88 .. note:: 89 90 The :mod:`os` module provides an alternate implementation of ``environ`` 91 which updates the environment on modification. Note also that updating 92 :data:`os.environ` will render this dictionary obsolete. Use of the 93 :mod:`os` module version of this is recommended over direct access to the 94 :mod:`posix` module. 95