centos TCP连接最大时间，可一定程度上代替心跳机制

static void set_keepalive(int fd)
{
	int keepAlive = config_get_intval("SO_KEEPALIVE",1);
	if (keepAlive == 0)
	{
		return;
	}

	setsockopt(fd,SOL_SOCKET,SO_KEEPALIVE,(void*)&keepAlive,sizeof(keepAlive));

	// 这里default给了65秒，自定义的话到配置文件中修改，一般心跳60秒即可，客户端有延时
	int keepIdle = config_get_intval("TCP_KEEPIDLE",65);
	setsockopt(fd,SOL_TCP,TCP_KEEPIDLE,(void *)&keepIdle,sizeof(keepIdle));

	int keepInterval = config_get_intval("TCP_KEEPINTVL",10);
	setsockopt(fd,TCP_KEEPINTVL,(void *)&keepInterval,sizeof(keepInterval));

	int keepCount = config_get_intval("TCP_KEEPCNT",TCP_KEEPCNT,(void *)&keepCount,sizeof(keepCount));
}

也可以直接修改系统的TCP最大连接时间，但是这个是极不推荐的。因为系统的修改了会影响所有运行在这台计算机上的进程，尤其是有些不活跃的进程。

参考： http://www.cnblogs.com/lidabo/p/3804108.html