title: postgresql application server could not be contacted in ubuntu
body: <p>I'm try to use pgAdmin4 in ubuntu 16.04. But I find this error: &quot;postgresql application server could not be contacted&quot;. I don't find a solutions for ubuntu. Only for Windows platform.
  <a href="https://i.stack.imgur.com/nobJq.png" rel="nofollow noreferrer">enter image description here</a></p>
  <p>Install procedure:</p>
  <pre><code>sudo apt-get install curl ca-certificates 
  
  curl postgresql.org/media/keys/ACCC4CF8.asc | sudo apt-key add - 
  
  sudo sh -c 'echo &quot;deb apt.postgresql.org/pub/repos/apt $(lsb_release -cs)-pgdg main&quot; &gt; /etc/apt/sources.list.d/pgdg.list' 
  
  sudo apt-get update 
  
  sudo apt-get install pgadmin4
  
  pgadmin4
  </code></pre>