I cannot connect to the newly installed postgres instance.
This is by design, you have take a few actions before it functions.
Switch to user postgres by the command: "su postgres". Now you can create a user and a database for use. After this action you can connect with psql by using the normal useraccount.
About the Author
Wim Peeters is electronics engineer with an additional master in IT and over 30 years of experience including time spent in support, development, consulting, training and database administration. Wim has worked with SQL Server since version 6.5. He has developed in C/C++, Java and C# on Windows and Linux in different European countries and different European languages. He writes knowledge base articles to solve IT problems and publishes them on the Lubby Knowledge Platform where he is one of the most important contributors and the main developer.