Crate a new, read-only user in postgres

Reference taken from this Article !

Script to Create Read-Only user:

CREATE ROLE Read_Only_User WITH LOGIN PASSWORD 'Test1234' 
NOSUPERUSER INHERIT NOCREATEDB NOCREATEROLE NOREPLICATION VALID UNTIL 'infinity';

Assign permission to this read only user:

GRANT CONNECT ON DATABASE YourDatabaseName TO Read_Only_User;
GRANT USAGE ON SCHEMA public TO Read_Only_User;
GRANT SELECT ON ALL TABLES IN SCHEMA public TO Read_Only_User;
GRANT SELECT ON ALL SEQUENCES IN SCHEMA public TO Read_Only_User;

No need to create a new user in the operating system. Just issue:

CREATE USER newusername

in psql (or pgadmin, or whatever tool you prefer) and you will have a new user. What access this user has depends on what your tables are set up for. But default, it will not have permissions on any tables, so you will have to GRANT this. If you have already GRANTed permissions to the public group, the user will have thos permissions from the start.