title: How to view available postgres users, without having a user to log in?
body: <p>I am using postgres, facing the error:</p>
  
  <pre><code>$ psql -U postgres
  psql: FATAL: role "postgres" does not exist
  </code></pre>
  
  <p>I get a similar error when attempting to connect using my username, and do not know what user I can use to connect. Running <code>$ psql -l</code>, attempting to list users, also fails with the same error since I do not have a user to connect and run the command.</p>
  
  <p><strong>Is there any way to view the available users, when I don't know of a user name that can connect to run <code>$ psql -l</code>?</strong></p>
  
  <p>Is there perhaps a default role that I can use to create my 'postgres' and username roles? Or could I maybe use sudo to look into <code>/var/db/postgresql</code> (my postgres data directory) for the postgres user names?</p>
  
  <p>I am running NixOS 17.03.</p>