Windows: The User directive specifies the user account the server runs with. By using a specific user account (other than LocalSystem), you can restrict or enable system features for the server. For example, you can use a user account that can mount files from another machine.
UNIX: The User directive specifies the UNIX user account for the server. If the server is started by the superuser or root user, the server binds to the port you specify and then switches its user ID to the user account specified with the User directive. This directive is ignored if the server isn’t started as root. The user account you specify should have read permission to the server’s root and subdirectories. The user account should have write access to the logs directory and execute permissions to any CGI programs. The user account should not have write access to the configuration files. This ensures that in the unlikely event that someone compromises the server, they won’t be able to change configuration files and gain broader access to your machine. Although you can use the nobody user, it isn’t recommended.
name is the 8-character (or less) login name for the Unix user account.
If there is no User directive, the server runs with the user account it was started with.