title: Get Unique System ID using php
body: <p>I want client system's unique id for registering my app. </p>
  
  <p>My Method (or idea):</p>
  
  <ol>
  <li><p>I give a key (<code>key1</code>) to my client when he purchase my application</p></li>
  <li><p>After he installs my application on his local server, I want to verify that installation.so he want to submit a form</p></li>
  <li><p>after receiving that information, I want to store that information and update his local database.</p>
  
  <ol>
  <li><p>my server database 'installations' table structure : name(empty) , email(empty) , address(empty) , key1 , key2 , unique_id(empty) , status(0)</p>
  
  <p><code>if key1 currect and status == 0</code>, his informations with unique_id save in installations table &amp; status set to 1 &amp; his local database will update with key1 and key2.</p>
  
  <p><code>if key1 currect and status == 1</code> (re-installing time), then his local machine unique_id and installations table unique_id will check. if equal, his local database will update with key1 and key2. </p>
  
  <p><code>if not currect</code>, his local database will update with key1('key not valid') and key2('key not valid'). </p></li>
  </ol></li>
  <li><p>if local database verification table values (key1 and key2) not 'key not valid' then application will work.</p></li>
  </ol>
  
  <p>Client form:</p>
  
  <pre><code>&lt;?php
  $unique_id = "i want unique system id here";
  ?&gt;
  &lt;form action="http://www.example.com/verifiy.php" method="post"&gt;
      &lt;p&gt;
          &lt;label&gt;Name&lt;/label&gt;
          &lt;input type="text" name="name" /&gt;
      &lt;/p&gt;
      &lt;p&gt;
          &lt;label&gt;Email&lt;/label&gt;
          &lt;input type="text" name="email" /&gt;
      &lt;/p&gt;
      &lt;p&gt;
          &lt;label&gt;Phone&lt;/label&gt;
          &lt;input type="text" name="phone" /&gt;
      &lt;/p&gt;
      &lt;p&gt;
          &lt;label&gt;Activation key&lt;/label&gt;
          &lt;input type="text" name="name" /&gt;
      &lt;/p&gt;
      &lt;p class="hidden"&gt;
          &lt;input type="text" name="unique_id" value="&lt;?php echo $unique_id; ?&gt;" /&gt;
      &lt;/p&gt;
      &lt;input type="submit" /&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>When client submit this form, i want save all informations with system unique id on my server and i will give him to a key.</p>
  
  <p>please help me, how can i get client system's unique id? sorry for my bad english. Thanks.</p>