systemd-hostnamed.service
/lib/systemd/systemd-hostnamed
systemd-hostnamed is a system service that may be used as a mechanism to change the system's 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 m[blue]developer documentationm[][1] for information about the APIs systemd-hostnamed provides.
systemd(1), hostname(5), machine-info(5), hostnamectl(1), sethostname(2)