static hostname； transient hostname； pretty hostname

The static host name is the traditional hostname, which can be chosen by the user, and is stored in the /etc/hostname file

The “transient” hostname is a dynamic host name maintained by the kernel. It is initialized to the static host name by default, whose value defaults to “localhost”.It can be changed by DHCP or mDNS at runtime.

The pretty hostname is a free-form UTF8 host name for presentation to the user.