systemd-hostnamed.service, systemd-hostnamed — Hostname bus mechanism
systemd-hostnamed.service
/usr/lib/systemd/systemd-hostnamed
systemd-hostnamed is a system
                service that may be used as mechanism to change the
                system hostname. systemd-hostnamed is
                automatically activated on request and terminates
                itself when it is unused.
The tool hostnamectl(1) is a command line client to this service.
See the 
                developer documentation for information about
                the APIs systemd-hostnamed
                provides.