title: Can't log into system user postgres
body: <p>I installed postgresql on mac using brew. I wasn't asked about for the password for postgresql during the installation. Now I need to create a user and can't:</p>
  
  <pre><code>Alexs-MacBook-Air:mydir alex$ su - postgres
  Password:
  su: Sorry
  </code></pre>
  
  <p>Whatever password (including empty) I use, it is wrong. What's the easiest way to reset it?</p>