title: Which are the source of java to fill system properties
body: <p>Through <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/System.html#getProperty(java.lang.String)" rel="nofollow">System.getProperty(String key)</a> you can get the value of some java system properties, however my question is about how java fill these values, more exactly where is the source of this information. I'm looking in some places like <a href="http://docs.oracle.com/javase/tutorial/essential/environment/sysprop.html" rel="nofollow">here</a> but I didn't found an answer. </p>
  
  <p>My problem is that I'm trying to test some behaviours of my code, and I want to change the system property for <code>os.name</code> value outside of java (I know that I can set the value with <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/System.html#setProperty(java.lang.String,%20java.lang.String)" rel="nofollow"><code>System.setProperty(String key, String value)</code></a> however I want to do it outside), so anybody knows what I've to change in order to get the new value through <code>System.getProperty('os.name')</code>?</p>
  
  <p>Thanks!</p>