title: how to start postgresql server on Ubuntu 12.04
body: <p>I had just installed a PostgreSQL 9.1 on the Ubuntu 12.04 server (hosted by Amazon EWS).When I tried to launch the <strong>psql</strong> command, the following error message shows up. </p>
  
  <blockquote>
    <p>psql: could not connect to server: No such file or directory  Is the
    server running locally and accepting  connections on Unix domain
    socket "/var/run/postgresql/.s.PGSQL.5432"?</p>
  </blockquote>
  
  <p>After searching on the web, I found I have to start the Server before using it. By following this <strong><a href="http://www.postgresql.org/docs/9.1/static/creating-cluster.html">initdb</a></strong> link, I still cannot use the postgresql database. Are there any further work (like configuration) should I do to start the server ?  </p>
  
  <p>I tried to start the service : <strong>service postgresql start</strong>
  Another error message shows : </p>
  
  <blockquote>
    <p>No PostgreSQL clusters exist; see "man pg_createcluster"</p>
  </blockquote>