After I install PostgreSQL in Mac OS, I have to produce a user named "postgres' to be able to install the DB. I believe exactly the same factor is applicable for a lot of other DBs in Unix. What exactly 's the reason that people require a new user for installation?

Since it is wise decision to operate various things as different customers to ensure that if somebody breaks in via a security hole in a single program they're limited with what they are able to do in order to things that the consumer for your particular service can perform.

PostgreSQL does not require special account. It may be any, as lengthy as it is not root. You are able to run Postgres instance by yourself user, or other.

Most installations do create or require some "postgres" user due to security - running because the same user as webserver could be rather bad idea.

Because within the traditional *nix security model, exactly what a program is permitted to complete is determined through the user that program is running as.

You will find also security subsystems (e.g: Selinux, SMACK, RSBAC ...), where exactly what a program is permitted to complete is usually based on explicit rules controlled through the Security Administrator.