# 16.1 `posix` -- The most common POSIX system calls

Availability: Unix.

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 `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.

The descriptions below are very terse; refer to the corresponding Unix manual (or POSIX documentation) entry for more information. Arguments called path refer to a pathname given as a string.

Errors are reported as exceptions; the usual exceptions are given for type errors, while errors reported by the system calls raise `error` (a synonym for the standard exception `OSError`), described below.