DX Application Performance Management

I have a requirement to create a read only user in APMDB which is PostgreSQL database in our environment. when I am trying to create readonly only I am getting following ERRORS

cemdb=> CREATE USER mcnealj;
ERROR:  permission denied to create role
cemdb=> \q
[wahabak@sp-sec-stgapmdb ~]$ psql postgres admin
Password for user admin:
psql (8.4.20, server 9.2.9)
WARNING: psql version 8.4, server version 9.2.
         Some psql features might not work.
Type "help" for help.

postgres=> CREATE USER mcnealj;
ERROR:  permission denied to create role
postgres=>

postgres=> \du
            List of roles
 Role name | Attributes  | Member of
-----------+-------------+-----------
 admin     |             | {}
 postgres  | Superuser   | {}
           : Create role
           : Create DB

I try to create read only user in both ways. using postgres user and cemdb but  unsuccessful. Does any one try this before can help me ? 

You need to connect as an administrator, so you should be connected as 'postgres' or whatever you chose when you installed the database server.

You may find it easier to use pgAdmin to do this instead of psql.

How do you create a read-only user in PostgreSQL? - Stack Overflow 

It's also important to set the 'valid until' for the user account:

PostgreSQL: Script to Create a Read-Only Database User 

Here's my blog about this:

Changing passwords for PostgreSQL