title: Postgresql does not restart after changing max_connections or shared_buffers
body: <p>I have tested pgtune on my postgres.config so I know what I can change there, but when I try to change max_connections or shared_buffers I can't restart postgres. I just get an error, but there is nothing in the log specifying the error. (Not sure where those logs go, but they are not in regular pg_log dir.)</p>
  
  <p>My settings is:</p>
  
  <pre><code>shared_buffers = 24MB  # (pgtune wizard 2013-04-11 = 120MB)
  max_connections = 120  # (pgtune wizard 2013-04-11 = 200)
  </code></pre>
  
  <p>Im on a 512 linode which only runs postgresql. If I change shared_buffers beyond 24MB or max_connections beyond 120, I can't restart postgres. </p>
  
  <p>I'm running on a Linode xen instance with Ubuntu 12.04.2 LTS:</p>
  
  <pre><code>Ubuntu 12.04.2 LTS (GNU/Linux 3.8.4-x86_64-linode31 x86_64)
  </code></pre>
  
  <p>Anyone know if postgres it self determine that 24MB and 120 connections is max for my system?</p>