# :mod:posix --- The most common POSIX system calls

This module provides access to operating system functionality that is standardized by the C Standard and the POSIX standard (a thinly disguised Unix interface).

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: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.

## Large File Support

Several operating systems (including AIX, HP-UX, Irix and Solaris) provide support for files that are larger than 2 GiB from a C programming model where :c:type:int and :c:type: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:type:long and the :c:type:long long type is available and 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, it is enabled by default with recent versions of Irix, but 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 :mod:os module documentation, :mod:posix defines the following data item: