Added section about setting up cron

documentation/installation_guide.html

@@ -48,6 +48,7 @@
   <li><a href="#9._WIRIS_mathematical_formulas">Mathematical formulas with WIRIS</a></li>
   <li><a href="#10._Xapian_fulltext_indexing">Full-text indexation with Xapian</a></li>
   <li><a href="#11._Chamilo_rapid_ppt_conversion">Chamilo Rapid - PPT conversion system</a></li>
+  <li><a href="#12._Setting_cron_up">Setting chronological tasks</a></li>
 </ol>
 
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@@ -742,6 +743,27 @@ Then go to your administration page -&gt; <i>Chamilo Rapid</i> and set the host
 <em>Note</em>: Sometimes, this doesn't work out so easily. You can probably ask for the assistance of any system administrator around with a bit of Java and PHP experience, or you can always ask one of the Chamilo's Official Providers for assistance (ask for a guaranteed commercial contract).
 </p>
 
+<hr style="width: 100%; height: 2px;" />
+<h2><a name="12._Setting_cron_up"></a>Setting chronological tasks</h2>
+<p>
+Since Chamilo 1.8.8, a few tasks need to be executed regularly in order to get 
+the best out of your server resources. One of such tasks (and the only one 
+around at the time of Chamilo 1.8.8) is the sending of internal messaging 
+notifications by e-mail, i.e. when you receive an e-mail from another person or
+from a group inside the internal messaging system of Chamilo, if all e-mails are
+sent immediately, then you might not have the chance to receive them at your 
+pace, once a day or even once a week. For cases like this you, as a Chamilo 
+administrator, should setup a cron process on the server to check the queue of
+e-mails and send is timely.</p>
+<p>
+Setting up a cron task is easy and there are several ways to do it. We recommend
+you have a look at the <a href="http://drupal.org/cron">Drupal documentation 
+for setting up cron</a> and define your own cron process as:
+<pre>
+35 * * * * wget -O - -q -t 1 http://campus.example.com/main/cron/notification.php
+</pre> 
+</p>
+
 <hr style="width: 100%; height: 2px;" />
 <p>
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