File: //usr/share/doc/python3-dev/html/library/posix.html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" /><meta name="generator" content="Docutils 0.17.1: http://docutils.sourceforge.net/" />
<title>posix — The most common POSIX system calls — Python 3.10.12 documentation</title><meta name="viewport" content="width=device-width, initial-scale=1.0">
<link rel="stylesheet" type="text/css" href="../_static/pygments.css" />
<link rel="stylesheet" type="text/css" href="../_static/pydoctheme.css?2022.1" />
<script data-url_root="../" id="documentation_options" src="../_static/documentation_options.js"></script>
<script src="../_static/jquery.js"></script>
<script src="../_static/underscore.js"></script>
<script src="../_static/doctools.js"></script>
<script src="../_static/sidebar.js"></script>
<link rel="search" type="application/opensearchdescription+xml"
title="Search within Python 3.10.12 documentation"
href="../_static/opensearch.xml"/>
<link rel="author" title="About these documents" href="../about.html" />
<link rel="index" title="Index" href="../genindex.html" />
<link rel="search" title="Search" href="../search.html" />
<link rel="copyright" title="Copyright" href="../copyright.html" />
<link rel="next" title="pwd — The password database" href="pwd.html" />
<link rel="prev" title="Unix Specific Services" href="unix.html" />
<link rel="canonical" href="file:///usr/share/doc/python3.10/html/library/posix.html" />
<style>
@media only screen {
table.full-width-table {
width: 100%;
}
}
</style>
<link rel="shortcut icon" type="image/png" href="../_static/py.svg" />
<script type="text/javascript" src="../_static/copybutton.js"></script>
<script type="text/javascript" src="../_static/menu.js"></script>
</head>
<body>
<div class="mobile-nav">
<input type="checkbox" id="menuToggler" class="toggler__input" aria-controls="navigation"
aria-pressed="false" aria-expanded="false" role="button" aria-label="Menu" />
<label for="menuToggler" class="toggler__label">
<span></span>
</label>
<nav class="nav-content" role="navigation">
<a href="https://www.python.org/" class="nav-logo">
<img src="../_static/py.svg" alt="Logo"/>
</a>
<div class="version_switcher_placeholder"></div>
<form role="search" class="search" action="../search.html" method="get">
<svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 24 24" class="search-icon">
<path fill-rule="nonzero"
d="M15.5 14h-.79l-.28-.27a6.5 6.5 0 001.48-5.34c-.47-2.78-2.79-5-5.59-5.34a6.505 6.505 0 00-7.27 7.27c.34 2.8 2.56 5.12 5.34 5.59a6.5 6.5 0 005.34-1.48l.27.28v.79l4.25 4.25c.41.41 1.08.41 1.49 0 .41-.41.41-1.08 0-1.49L15.5 14zm-6 0C7.01 14 5 11.99 5 9.5S7.01 5 9.5 5 14 7.01 14 9.5 11.99 14 9.5 14z" fill="#444"></path>
</svg>
<input type="text" name="q" aria-label="Quick search"/>
<input type="submit" value="Go"/>
</form>
</nav>
<div class="menu-wrapper">
<nav class="menu" role="navigation" aria-label="main navigation">
<div class="language_switcher_placeholder"></div>
<h3><a href="../contents.html">Table of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">posix</span></code> — The most common POSIX system calls</a><ul>
<li><a class="reference internal" href="#large-file-support">Large File Support</a></li>
<li><a class="reference internal" href="#notable-module-contents">Notable Module Contents</a></li>
</ul>
</li>
</ul>
<h4>Previous topic</h4>
<p class="topless"><a href="unix.html"
title="previous chapter">Unix Specific Services</a></p>
<h4>Next topic</h4>
<p class="topless"><a href="pwd.html"
title="next chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">pwd</span></code> — The password database</a></p>
<div role="note" aria-label="source link">
<h3>This Page</h3>
<ul class="this-page-menu">
<li><a href="../bugs.html">Report a Bug</a></li>
<li>
<a href="https://github.com/python/cpython/blob/3.10/Doc/library/posix.rst"
rel="nofollow">Show Source
</a>
</li>
</ul>
</div>
</nav>
</div>
</div>
<div class="related" role="navigation" aria-label="related navigation">
<h3>Navigation</h3>
<ul>
<li class="right" style="margin-right: 10px">
<a href="../genindex.html" title="General Index"
accesskey="I">index</a></li>
<li class="right" >
<a href="../py-modindex.html" title="Python Module Index"
>modules</a> |</li>
<li class="right" >
<a href="pwd.html" title="pwd — The password database"
accesskey="N">next</a> |</li>
<li class="right" >
<a href="unix.html" title="Unix Specific Services"
accesskey="P">previous</a> |</li>
<li><img src="../_static/py.svg" alt="python logo" style="vertical-align: middle; margin-top: -1px"/></li>
<li><a href="https://www.python.org/">Python</a> »</li>
<li class="switchers">
<div class="language_switcher_placeholder"></div>
<div class="version_switcher_placeholder"></div>
</li>
<li>
</li>
<li id="cpython-language-and-version">
<a href="../index.html">3.10.12 Documentation</a> »
</li>
<li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li>
<li class="nav-item nav-item-2"><a href="unix.html" accesskey="U">Unix Specific Services</a> »</li>
<li class="nav-item nav-item-this"><a href=""><code class="xref py py-mod docutils literal notranslate"><span class="pre">posix</span></code> — The most common POSIX system calls</a></li>
<li class="right">
<div class="inline-search" role="search">
<form class="inline-search" action="../search.html" method="get">
<input placeholder="Quick search" aria-label="Quick search" type="text" name="q" />
<input type="submit" value="Go" />
<input type="hidden" name="check_keywords" value="yes" />
<input type="hidden" name="area" value="default" />
</form>
</div>
|
</li>
</ul>
</div>
<div class="document">
<div class="documentwrapper">
<div class="bodywrapper">
<div class="body" role="main">
<section id="module-posix">
<span id="posix-the-most-common-posix-system-calls"></span><h1><a class="reference internal" href="#module-posix" title="posix: The most common POSIX system calls (normally used via module os). (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">posix</span></code></a> — The most common POSIX system calls<a class="headerlink" href="#module-posix" title="Permalink to this headline">¶</a></h1>
<hr class="docutils" />
<p>This module provides access to operating system functionality that is
standardized by the C Standard and the POSIX standard (a thinly disguised Unix
interface).</p>
<p id="index-0"><strong>Do not import this module directly.</strong> Instead, import the module <a class="reference internal" href="os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a>,
which provides a <em>portable</em> version of this interface. On Unix, the <a class="reference internal" href="os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a>
module provides a superset of the <a class="reference internal" href="#module-posix" title="posix: The most common POSIX system calls (normally used via module os). (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">posix</span></code></a> interface. On non-Unix operating
systems the <a class="reference internal" href="#module-posix" title="posix: The most common POSIX system calls (normally used via module os). (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">posix</span></code></a> module is not available, but a subset is always
available through the <a class="reference internal" href="os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a> interface. Once <a class="reference internal" href="os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a> is imported, there is
<em>no</em> performance penalty in using it instead of <a class="reference internal" href="#module-posix" title="posix: The most common POSIX system calls (normally used via module os). (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">posix</span></code></a>. In addition,
<a class="reference internal" href="os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a> provides some additional functionality, such as automatically calling
<a class="reference internal" href="os.html#os.putenv" title="os.putenv"><code class="xref py py-func docutils literal notranslate"><span class="pre">putenv()</span></code></a> when an entry in <code class="docutils literal notranslate"><span class="pre">os.environ</span></code> is changed.</p>
<p>Errors are reported as exceptions; the usual exceptions are given for type
errors, while errors reported by the system calls raise <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OSError</span></code></a>.</p>
<section id="large-file-support">
<span id="posix-large-files"></span><h2>Large File Support<a class="headerlink" href="#large-file-support" title="Permalink to this headline">¶</a></h2>
<p id="index-1">Several operating systems (including AIX and Solaris) provide
support for files that are larger than 2 GiB from a C programming model where
<span class="c-expr sig sig-inline c"><span class="kt">int</span></span> and <span class="c-expr sig sig-inline c"><span class="kt">long</span></span> 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 <em class="dfn">large files</em>.</p>
<p>Large file support is enabled in Python when the size of an <code class="xref c c-type docutils literal notranslate"><span class="pre">off_t</span></code> is
larger than a <span class="c-expr sig sig-inline c"><span class="kt">long</span></span> and the <span class="c-expr sig sig-inline c"><span class="kt">long</span><span class="w"> </span><span class="kt">long</span></span> is at least as large
as an <code class="xref c c-type docutils literal notranslate"><span class="pre">off_t</span></code>.
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:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">CFLAGS</span><span class="o">=</span><span class="s2">"`getconf LFS_CFLAGS`"</span> <span class="n">OPT</span><span class="o">=</span><span class="s2">"-g -O2 $CFLAGS"</span> \
<span class="o">./</span><span class="n">configure</span>
</pre></div>
</div>
<p>On large-file-capable Linux systems, this might work:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">CFLAGS</span><span class="o">=</span><span class="s1">'-D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64'</span> <span class="n">OPT</span><span class="o">=</span><span class="s2">"-g -O2 $CFLAGS"</span> \
<span class="o">./</span><span class="n">configure</span>
</pre></div>
</div>
</section>
<section id="notable-module-contents">
<span id="posix-contents"></span><h2>Notable Module Contents<a class="headerlink" href="#notable-module-contents" title="Permalink to this headline">¶</a></h2>
<p>In addition to many functions described in the <a class="reference internal" href="os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a> module documentation,
<a class="reference internal" href="#module-posix" title="posix: The most common POSIX system calls (normally used via module os). (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">posix</span></code></a> defines the following data item:</p>
<dl class="py data">
<dt class="sig sig-object py" id="posix.environ">
<span class="sig-prename descclassname"><span class="pre">posix.</span></span><span class="sig-name descname"><span class="pre">environ</span></span><a class="headerlink" href="#posix.environ" title="Permalink to this definition">¶</a></dt>
<dd><p>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, <code class="docutils literal notranslate"><span class="pre">environ[b'HOME']</span></code> (<code class="docutils literal notranslate"><span class="pre">environ['HOME']</span></code> on Windows) is the
pathname of your home directory, equivalent to <code class="docutils literal notranslate"><span class="pre">getenv("HOME")</span></code> in C.</p>
<p>Modifying this dictionary does not affect the string environment passed on by
<a class="reference internal" href="os.html#os.execv" title="os.execv"><code class="xref py py-func docutils literal notranslate"><span class="pre">execv()</span></code></a>, <a class="reference internal" href="os.html#os.popen" title="os.popen"><code class="xref py py-func docutils literal notranslate"><span class="pre">popen()</span></code></a> or <a class="reference internal" href="os.html#os.system" title="os.system"><code class="xref py py-func docutils literal notranslate"><span class="pre">system()</span></code></a>; if you need to
change the environment, pass <code class="docutils literal notranslate"><span class="pre">environ</span></code> to <a class="reference internal" href="os.html#os.execve" title="os.execve"><code class="xref py py-func docutils literal notranslate"><span class="pre">execve()</span></code></a> or add
variable assignments and export statements to the command string for
<a class="reference internal" href="os.html#os.system" title="os.system"><code class="xref py py-func docutils literal notranslate"><span class="pre">system()</span></code></a> or <a class="reference internal" href="os.html#os.popen" title="os.popen"><code class="xref py py-func docutils literal notranslate"><span class="pre">popen()</span></code></a>.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.2: </span>On Unix, keys and values are bytes.</p>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The <a class="reference internal" href="os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a> module provides an alternate implementation of <code class="docutils literal notranslate"><span class="pre">environ</span></code>
which updates the environment on modification. Note also that updating
<a class="reference internal" href="os.html#os.environ" title="os.environ"><code class="xref py py-data docutils literal notranslate"><span class="pre">os.environ</span></code></a> will render this dictionary obsolete. Use of the
<a class="reference internal" href="os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a> module version of this is recommended over direct access to the
<a class="reference internal" href="#module-posix" title="posix: The most common POSIX system calls (normally used via module os). (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">posix</span></code></a> module.</p>
</div>
</dd></dl>
</section>
</section>
<div class="clearer"></div>
</div>
</div>
</div>
<div class="sphinxsidebar" role="navigation" aria-label="main navigation">
<div class="sphinxsidebarwrapper">
<h3><a href="../contents.html">Table of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">posix</span></code> — The most common POSIX system calls</a><ul>
<li><a class="reference internal" href="#large-file-support">Large File Support</a></li>
<li><a class="reference internal" href="#notable-module-contents">Notable Module Contents</a></li>
</ul>
</li>
</ul>
<h4>Previous topic</h4>
<p class="topless"><a href="unix.html"
title="previous chapter">Unix Specific Services</a></p>
<h4>Next topic</h4>
<p class="topless"><a href="pwd.html"
title="next chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">pwd</span></code> — The password database</a></p>
<div role="note" aria-label="source link">
<h3>This Page</h3>
<ul class="this-page-menu">
<li><a href="../bugs.html">Report a Bug</a></li>
<li>
<a href="https://github.com/python/cpython/blob/3.10/Doc/library/posix.rst"
rel="nofollow">Show Source
</a>
</li>
</ul>
</div>
</div>
</div>
<div class="clearer"></div>
</div>
<div class="related" role="navigation" aria-label="related navigation">
<h3>Navigation</h3>
<ul>
<li class="right" style="margin-right: 10px">
<a href="../genindex.html" title="General Index"
>index</a></li>
<li class="right" >
<a href="../py-modindex.html" title="Python Module Index"
>modules</a> |</li>
<li class="right" >
<a href="pwd.html" title="pwd — The password database"
>next</a> |</li>
<li class="right" >
<a href="unix.html" title="Unix Specific Services"
>previous</a> |</li>
<li><img src="../_static/py.svg" alt="python logo" style="vertical-align: middle; margin-top: -1px"/></li>
<li><a href="https://www.python.org/">Python</a> »</li>
<li class="switchers">
<div class="language_switcher_placeholder"></div>
<div class="version_switcher_placeholder"></div>
</li>
<li>
</li>
<li id="cpython-language-and-version">
<a href="../index.html">3.10.12 Documentation</a> »
</li>
<li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li>
<li class="nav-item nav-item-2"><a href="unix.html" >Unix Specific Services</a> »</li>
<li class="nav-item nav-item-this"><a href=""><code class="xref py py-mod docutils literal notranslate"><span class="pre">posix</span></code> — The most common POSIX system calls</a></li>
<li class="right">
<div class="inline-search" role="search">
<form class="inline-search" action="../search.html" method="get">
<input placeholder="Quick search" aria-label="Quick search" type="text" name="q" />
<input type="submit" value="Go" />
<input type="hidden" name="check_keywords" value="yes" />
<input type="hidden" name="area" value="default" />
</form>
</div>
|
</li>
</ul>
</div>
<div class="footer">
© <a href="../copyright.html">Copyright</a> 2001-2025, Python Software Foundation.
<br />
This page is licensed under the Python Software Foundation License Version 2.
<br />
Examples, recipes, and other code in the documentation are additionally licensed under the Zero Clause BSD License.
<br />
See <a href="/license.html">History and License</a> for more information.<br />
<br />
The Python Software Foundation is a non-profit corporation.
<a href="https://www.python.org/psf/donations/">Please donate.</a>
<br />
<br />
Last updated on August 15, 2025.
<a href="/bugs.html">Found a bug</a>?
<br />
Created using <a href="https://www.sphinx-doc.org/">Sphinx</a> 4.3.2.
</div>
</body>
</html>