Although you need root privileges to install Calendar Server, it is possible to run the services as a non-root user.
However, if you start the services as root, each process changes the effective UID to the runtime (non-root) user and group once the tasks that need the root privileges have been executed. Doing it this way allows the use of ports below 1024. Instead, when you start services as the non-root runtime user and group, the web server port must be set to a value greater than 1024 in order for the services to start successfully.
The non-root user or group are created automatically at the time of configuration. The defaults are icsuser, and icsgroup.