So I freshly installed kali linux and logged into the root user to create a user called gyrgamfor personal use. The first command I typed was createuser gyrgam, which gave me this output 
createuser: error: could not connect to database postgres: could not connect to server: No such file or directory
    Is the server running locally and accepting
    connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?
I searched for a solution to this here on stack, but I only managed to find how to start the postgresql service with systemctl start postgresql.service. Now after trying createuser gyrgam again, it now gives me this error:
createuser: error: could not connect to database postgres: FATAL:  role "root" does not exist
I even did reinstall whole linux, to solve this. Before the reinstall, I of course had the same problem and I tried solutions like here or here but they either didn't work for me or gave me other errors.
My goal is to create an user called gyrgam. But as explained, I get some postgres database error.
 
    