"posix" — The most common POSIX system calls
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This module provides access to operating system functionality that is
standardized by the C Standard and the POSIX standard (a thinly
disguised Unix interface).

Availability: Unix.

**Do not import this module directly.**  Instead, import the module
"os", which provides a *portable* version of this interface.  On Unix,
the "os" module provides a superset of the "posix" interface.  On non-
Unix operating systems the "posix" module is not available, but a
subset is always available through the "os" interface.  Once "os" is
imported, there is *no* performance penalty in using it instead of
"posix".  In addition, "os" provides some additional functionality,
such as automatically calling "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
"OSError".


Large File Support
==================

Several operating systems (including AIX and Solaris) provide support
for files that are larger than 2 GiB from a C programming model where
int and 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 *large files*.

Large file support is enabled in Python when the size of an "off_t" is
larger than a long and the long long is at least as large as an
"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


Notable Module Contents
=======================

In addition to many functions described in the "os" module
documentation, "posix" defines the following data item:

posix.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 "execv()", "popen()" or "system()"; if you need to
   change the environment, pass "environ" to "execve()" or add
   variable assignments and export statements to the command string
   for "system()" or "popen()".

   Changed in version 3.2: On Unix, keys and values are bytes.

   Note:

     The "os" module provides an alternate implementation of "environ"
     which updates the environment on modification. Note also that
     updating "os.environ" will render this dictionary obsolete. Use
     of the "os" module version of this is recommended over direct
     access to the "posix" module.
