title: What is SOL_SOCKET used for?
body: <p>As it is stated in the Linux <code>man</code> page </p>
  
  <blockquote>
    <p>Use this constant as the level argument to <code>getsockopt</code> or <code>setsockopt</code> to manipulate the socket-level options described in this section</p>
  </blockquote>
  
  <p>But I don't get this explanation. What is the purpose of <code>SOL_SOCKET</code>? What does it do? </p>