hostname — machine names and resolution

Option case matters: -i resolves addresses for the host name, whereas -I enumerates interface addresses without relying on resolution of that name. The -I result excludes loopback and IPv6 link-local addresses; order is not guaranteed. Neither option means “public IP”.

-F reads a name from a file and changes state. A plain hostname operand also sets the current node name. For persistent Ubuntu configuration, use hostnamectl and check local name resolution.