title: "Role" does not exists in Postgresql
body: <p>I have been reading <a href="http://workshop.pgrouting.org/chapters/installation.html#add-pgrouting-functions-to-database" rel="nofollow noreferrer">this tutorial</a>. There is the below command to login as a user: </p>
  
  <pre><code># login as user "user"
  psql -U user
  </code></pre>
  
  <p>when I execute the above command, I get an error saying the following: </p>
  
  <pre><code>psql: FATAL:  role "user" does not exist
  </code></pre>
  
  <p>The only help I saw online was <a href="https://help.ubuntu.com/community/PostgreSQL#FATAL:__role_.22myusername.22_does_not_exist" rel="nofollow noreferrer">here</a>, the have said the following: </p>
  
  <blockquote>
    <p><strong>FATAL: role "myusername" does not exist</strong></p>
    
    <p>By default PostgreSQL connects to the PostgreSQL user with the same
    name as the current unix user. You have not created a PostgreSQL user
    by that name in your database.</p>
    
    <p>Create a suitable user, or specify a different username to connect
    with. In the command line tools the -U flag does this.</p>
  </blockquote>
  
  <p>But I still don't quite understand why I am getting this error.</p>