Client processes (Internet domain)

While the server side of the remote login service is a passive entity, listening for client connections, the client process is an active entity which initiates a connection when invoked.

As in the server process, the first step taken by the client remote login process is to locate the service definition for a remote login.

   sp = getservbyname("login" "tcp");


   if (sp == NULL) {
           fprintf(stderr, "rlogin: tcp/login: unknown service\n");
           exit(1);
   }

   p = gethostbyname(argv[1]);
   if (hp == NULL) {
           fprintf(stderr, "rlogin: %s: unknown host\n", argv[1]);
           exit(2);
   }

With this accomplished, all that is required is to establish a connection to the server at the requested host and start up the remote login protocol. The address buffer is cleared, then filled in with the Internet address of the foreign host and the port number at which the login process resides.

   memset((char *)&sin, 0, sizeof(sin));
   memcpy (&sin.sin_addr, hp->h_addr, hp->h_length) ;
   sin.sin_family = hp->h_addrtype;
   sin.sin_port = sp->s_port;

   s = socket(hp->h_addrtype, SOCK_STREAM, 0);
   if (s < 0) {
           perror("rlogin: socket");
           exit(3);
   }
   /* ... */
   if (connect(s, (struct sockaddr *) &sin, sizeof (sin)) < 0) {
           perror("rlogin: connect");
           exit(4);
   }