As with any server daemon that is accessible to the outside world, it is advisable to run PostgreSQL under a separate user account. This user account should only own the data that is managed by the server, and should not be shared with other daemons. (For example, using the user nobody is a bad idea.) In particular, it is advisable that this user account not own the PostgreSQL executable files, to ensure that a compromised server process could not modify those executables.
Pre-packaged versions of PostgreSQL will typically create a suitable user account automatically during package installation.
To add a Unix user account to your system, look for a command useradd or adduser. The user name postgres is often used, and is assumed throughout this book, but you can use another name if you like.
Read the upstream documentation. For corrections, first check the current version.