Play with TCP socket options related to keep-alive.

tcp_keepalive.c

/* tcp_keepalive.c
 *
 * References:
 * http://tldp.org/HOWTO/TCP-Keepalive-HOWTO/usingkeepalive.html
 * http://www.tldp.org/HOWTO/html_single/TCP-Keepalive-HOWTO/
 */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/tcp.h>

int main()
{
   int s;
   int optval;
   socklen_t optlen = sizeof(optval);

   /* Create the socket */
   if((s = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0) {
      perror("socket()");
      exit(EXIT_FAILURE);
   }

   /*****************************************************************/

   /* Check the status for the keepalive option */
   if(getsockopt(s, SOL_SOCKET, SO_KEEPALIVE, &optval, &optlen) < 0) {
      perror("getsockopt()");
      close(s);
      exit(EXIT_FAILURE);
   }
   printf("SO_KEEPALIVE is %s\n", (optval ? "ON" : "OFF"));

   /* Set the option active */
   optval = 1;
   optlen = sizeof(optval);
   if(setsockopt(s, SOL_SOCKET, SO_KEEPALIVE, &optval, optlen) < 0) {
      perror("setsockopt()");
      close(s);
      exit(EXIT_FAILURE);
   }
   printf("SO_KEEPALIVE is set to ON\n");

   /* Check the status again */
   if(getsockopt(s, SOL_SOCKET, SO_KEEPALIVE, &optval, &optlen) < 0) {
      perror("getsockopt()");
      close(s);
      exit(EXIT_FAILURE);
   }
   printf("SO_KEEPALIVE is %s\n\n", (optval ? "ON" : "OFF"));

   /*****************************************************************/

    /* Check tcp_keepalive_probes */
   if(getsockopt(s, SOL_TCP, TCP_KEEPCNT, &optval, &optlen) < 0) {
      perror("getsockopt()");
      close(s);
      exit(EXIT_FAILURE);
   }
   printf("TCP_KEEPCNT is %d\n", optval);

   optval = 5;
   optlen = sizeof(optval);
   if(setsockopt(s, SOL_TCP, TCP_KEEPCNT, &optval, optlen) < 0) {
      perror("setsockopt()");
      close(s);
      exit(EXIT_FAILURE);
   }
   printf("TCP_KEEPCNT is set to %d\n", optval);

    /* Check tcp_keepalive_time */
   if(getsockopt(s, SOL_TCP, TCP_KEEPCNT, &optval, &optlen) < 0) {
      perror("getsockopt()");
      close(s);
      exit(EXIT_FAILURE);
   }
   printf("TCP_KEEPCNT is %d\n\n", optval);

   /*****************************************************************/

    /* Check tcp_keepalive_time */
   if(getsockopt(s, SOL_TCP, TCP_KEEPIDLE, &optval, &optlen) < 0) {
      perror("getsockopt()");
      close(s);
      exit(EXIT_FAILURE);
   }
   printf("TCP_KEEPIDLE is %d\n", optval);

   optval = 10;
   optlen = sizeof(optval);
   if(setsockopt(s, SOL_TCP, TCP_KEEPIDLE, &optval, optlen) < 0) {
      perror("setsockopt()");
      close(s);
      exit(EXIT_FAILURE);
   }
   printf("TCP_KEEPIDLE is set to %d\n", optval);

    /* Check tcp_keepalive_time */
   if(getsockopt(s, SOL_TCP, TCP_KEEPIDLE, &optval, &optlen) < 0) {
      perror("getsockopt()");
      close(s);
      exit(EXIT_FAILURE);
   }
   printf("TCP_KEEPIDLE is %d\n\n", optval);

   /*****************************************************************/

    /* Check tcp_keepalive_intvl */
   if(getsockopt(s, SOL_TCP, TCP_KEEPINTVL, &optval, &optlen) < 0) {
      perror("getsockopt()");
      close(s);
      exit(EXIT_FAILURE);
   }
   printf("TCP_KEEPINTVL is %d\n", optval);

   optval = 5;
   optlen = sizeof(optval);
   if(setsockopt(s, SOL_TCP, TCP_KEEPINTVL, &optval, optlen) < 0) {
      perror("setsockopt()");
      close(s);
      exit(EXIT_FAILURE);
   }
   printf("TCP_KEEPINTVL is set to %d\n", optval);

    /* Check tcp_keepalive_intvl */
   if(getsockopt(s, SOL_TCP, TCP_KEEPINTVL, &optval, &optlen) < 0) {
      perror("getsockopt()");
      close(s);
      exit(EXIT_FAILURE);
   }
   printf("TCP_KEEPINTVL is %d\n\n", optval);

   /*****************************************************************/

   close(s);

   exit(EXIT_SUCCESS);
}

Hi there, based on your code snippet I completed an article. So I posted it here in case you would be interested. Thanks.