ProtoentDefines the protocol Name-to-Number mapping. The protocol entry is represented by ($name, $aliases, $proto).
hostentDefines the Internet host Name-to-Address mapping. The host entry is represented by ($name, $aliases, $addrtype, $length, @addrs) where @addrs is a list of raw addresses.
netentDefines the Network Name-to-Network Number mapping. The net entry is represented by ($name, $aliases, $addrtype, $net).
serventMaps service names to port numbers. The service entry is represented by ($name, $%aliases, $port, $proto).