Network Interface Guide

servent - Service Names

An Internet family service resides at a specific, well-known port and uses a particular protocol. A service-name-to-port-number mapping is described by the servent structure:

struct servent {
   char     *s_name;         /* official service name */
   char     **s_aliases;     /* alias list */
   int      s_port;          /* port number, network byte order */
   char     *s_proto;        /* protocol to use */
getservbyname(3SOCKET) maps service names and, optionally, a qualifying protocol to a servent structure. The call:
sp = getservbyname("telnet", (char *) 0);
returns the service specification of a telnet server using any protocol. The call:
sp = getservbyname("telnet", "tcp");

returns the telnet server that uses the TCP protocol. getservbyport(3SOCKET) and getservent(3SOCKET) are also provided. getservbyport(3SOCKET) has an interface similar to that of getservbyname(3SOCKET); an optional protocol name can be specified to qualify lookups.