The hostname can be set by kernel-level autoconfiguration or in
an initrd. This requires a network resource such as DHCP to supply
the hostname, but there is another alternative: if a node reaches
rc.preinit without having a hostname set, the MAC_ADDR
directives are consulted. This is often necessary
for bringing up stand-alone nodes (ie: the main DHCP server).
Note: The MAC_ADDR directive are only used when no
hostname is set. They do not override a previously set hostname.