gcc -ggdb -c pcs.c gcc -ggdb -o pcs pcs.o -lm Undefined first referenced symbol in file recv pcs.o send pcs.o gethostbyname pcs.o socket pcs.o connect pcs.o ld: fatal: Symbol referencing errors. No output written to pcs collect2: ld returned 1 exit status *** Error code 1 make: Fatal error: Command failed for target `pcs' #include <stdio.h> #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <netdb.h> #include <string.h> #define PORT 0x1234 #define HOST "myHost" #define DIRSIZE 8192 int main(int argc, char *argv[]) { char hostname[100]; char dir[DIRSIZE]; int sd; struct sockaddr_in sin; struct sockaddr_in pin; struct hostent *hp; strcpy(hostname,HOST); if (argc>2) { strcpy(hostname,argv[2]); } /* go find out about the desired host machine */ hp = gethostbyname(hostname); /*if ((hp = gethostbyname(hostname)) == 0) { perror("gethostbyname"); exit(1); }*/ /* fill in the socket structure with host information */ memset(&pin, 0, sizeof(pin)); pin.sin_family = AF_INET; pin.sin_addr.s_addr = ((struct in_addr *)(hp->h_addr))->s_addr; pin.sin_port = htons(PORT); /* grab an Internet domain socket */ if ((sd = socket(AF_INET, SOCK_STREAM, 0)) == -1) { perror("socket"); exit(1); } /* connect to PORT on HOST */ connect(sd,(struct sockaddr *) &pin, sizeof(pin)); /* if (connect(sd,(struct sockaddr *) &pin, sizeof(pin)) == -1) { perror("connect"); exit(1); }*/ /* send a message to the server PORT on machine HOST */ send(sd, argv[1], strlen(argv[1]), 0); /*if (send(sd, argv[1], strlen(argv[1]), 0) == -1) { perror("send"); exit(1); }*/ /* wait for a message to come back from the server */ recv(sd, dir, DIRSIZE, 0); /*if (recv(sd, dir, DIRSIZE, 0) == -1) { perror("recv"); exit(1); }*/ printf("%s\n", dir); close(sd); return 0; }

That error means it can't find the recv() and the send() functions. Depending on your platform, it may be as simple as including a link to libsocket.

bingo. THANK YOU!