title: JSON module is probably installed but json_encode() doesn't exist
body: <p>I've installed LAMP on Ubuntu 14.04 and then php5-json module. It seems to be installed because it's situated on list of modules on phpinfo() page. <img src="https://i.stack.imgur.com/D21k3.jpg" alt="phpinfo()"></p>
  
  <p>But <code>function_exists("json_encode")</code> returns <code>false</code></p>
  
  <p>UPDATE:
  <br>
  I solved this problem by editing file which path is marked below:
  <img src="https://i.stack.imgur.com/fqZcs.jpg" alt="enter image description here"></p>