Looks to me like
/etc/hostname and sends a D-Bus signal.
hostnamectl --static should equal
hostname. According to the manpage,
hostname -f ==
hostname --fqdn ==
The FQDN (Fully Qualified Domain Name) of the system is the name that the resolver(3)
returns for the host name, such as, ursula.example.com. It is usually the hostname
followed by the DNS domain name (the part after the first dot). You can check the
FQDN using hostname --fqdn or the domain name using dnsdomainname.
The recommended method of setting the FQDN is to make the hostname be an alias for
the fully qualified name using /etc/hosts, DNS, or NIS. For example, if the hostname
was "ursula", one might have a line in /etc/hosts which reads
127.0.1.1 ursula.example.com ursula
I guess you want to put a record like that in /etc/hosts?