title: Lua cannot find installed luarocks on Ubuntu
body: <p>I install luarocks:</p>
  
  <pre><code>$ sudo apt-get install luarocks
  </code></pre>
  
  <p>I install lua-cjson by luarocks:</p>
  
  <pre><code>$sudo luarocks install lua-cjson
  </code></pre>
  
  <p>show packages:</p>
  
  <pre><code>$luarocks list
  
  Installed rocks:
  ----------------
  lua-cjson
     2.1.0-1 (installed) - /usr/local/lib/luarocks/rocks
  </code></pre>
  
  <p>So, I see package:</p>
  
  <pre><code>$luarocks show lua-cjson
  
  License:    MIT
  Homepage:   http://www.kyne.com.au/~mark/software/lua-cjson.php
  Installed in:   /usr/local
  . . . 
  Modules:
      cjson
      lua2json
      json2lua
      cjson.util
  
  
      lua-cjson
            2.1.0-1 (installed) - /usr/local/lib/luarocks/rocks
  </code></pre>
  
  <p>But, Lua can't see the module:</p>
  
  <pre><code>$lua
  Lua 5.2.3  Copyright (C) 1994-2013 Lua.org, PUC-Rio
  &gt; require "cjson"
  stdin:1: module 'cjson' not found:
  ....
  
  
  $locate cjson.so
   /usr/local/lib/lua/5.1/cjson.so
  </code></pre>
  
  <p>What it is the error??</p>