title: How do I find the current system timezone?
body: <p>On Linux, I need to find the currently configured timezone as an Olson location. I want my (C or C++) code to be portable to as many Linux systems as possible.</p>
  
  <p>For example. I live in London, so my current Olson location is "Europe/London". I'm <strong>not</strong> interested in timezone IDs like "BST", "EST" or whatever.</p>
  
  <p>Debian and Ubuntu have a file <code>/etc/timezone</code> that contains this information, but I don't think I can rely on that file always being there, can I? Gnome has a function <code>oobs_time_config_get_timezone()</code> which also returns the right string, but I want my code to work on systems without Gnome.</p>
  
  <p>So, what's the best general way to get the currently configured timezone as an Olson location, on Linux?</p>