Fatal error: Call to undefined function session_id() when installing
<p>I've installed <em>opencart</em> version 2.2.0.0 in a FreeBSD server 10.3-RELEASE-p3.  Followed the installation instructions for Linux of the <code>install.txt</code> file.</p>

<p>In step 5, <em>Visit the store homepage e.g. <a href="http://www.example.com" rel="nofollow">http://www.example.com</a> or <a href="http://www.example.com/store/" rel="nofollow">http://www.example.com/store/</a></em>, what I get in response is a Fatal error:</p>

<pre><code>Fatal error: Call to undefined function session_id() in /usr/local/www/opencart/system/library/session.php on line 23
</code></pre>

<p>This happens when installing both from the FreeBSD package and also from source.
Any ideas?</p>