Error in running ntpclient, blocking at recvfrom() function and settimeofday() returnning -1

Question

I am using this code for running ntp client in my ubuntu system.

/* This code will query a ntp server for the local time and display

 * it.  it is intended to show how to use a NTP server as a time
 * source for a simple network connected device.
 * This is the C version.  The orignal was in Perl
 *
 * For better clock management see the offical NTP info at:
 * http://www.eecis.udel.edu/~ntp/
 *
 * written by Tim Hogard (thogard@abnormal.com)
 * Thu Sep 26 13:35:41 EAST 2002
 * Converted to C Fri Feb 21 21:42:49 EAST 2003
 * this code is in the public domain.
 * it can be found here http://www.abnormal.com/~thogard/ntp/
 *
 */
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <time.h>
#include <string.h>

void ntpdate();

int main() {
    ntpdate();
    return 0;
}

void ntpdate() {
char *hostname="200.160.7.193";
int portno=123;     //NTP is port 123
int maxlen=1024;        //check our buffers
int i;          // misc var i
unsigned char msg[48]={010,0,0,0,0,0,0,0,0};    // the packet we send
unsigned long  buf[maxlen]; // the buffer we get back
//struct in_addr ipaddr;        //  
struct protoent *proto;     //
struct sockaddr_in server_addr;
int s;  // socket
int tmit;   // the time -- This is a time_t sort of
struct timeval tv;
//use Socket;
//
//#we use the system call to open a UDP socket
//socket(SOCKET, PF_INET, SOCK_DGRAM, getprotobyname("udp")) or die "socket: $!";
proto=getprotobyname("udp");
s=socket(PF_INET, SOCK_DGRAM, proto->p_proto);
perror("socket");
//
//#convert hostname to ipaddress if needed
//$ipaddr   = inet_aton($HOSTNAME);
memset( &server_addr, 0, sizeof( server_addr ));
server_addr.sin_family=AF_INET;
server_addr.sin_addr.s_addr = inet_addr(hostname);
//argv[1] );
//i   = inet_aton(hostname,&server_addr.sin_addr);
server_addr.sin_port=htons(portno);
//printf("ipaddr (in hex): %x\n",server_addr.sin_addr);

/*
 * build a message.  Our message is all zeros except for a one in the
 * protocol version field
 * msg[] in binary is 00 001 000 00000000 
 * it should be a total of 48 bytes long
*/

// send the data
printf("sending data..\n");
i=sendto(s,msg,sizeof(msg),0,(struct sockaddr *)&server_addr,sizeof(server_addr));
perror("sendto");
// get the data back
struct sockaddr saddr;
socklen_t saddr_l = sizeof (saddr);

printf("receiving data\n");
i=recvfrom(s,buf,48,0,&saddr,&saddr_l);
perror("recvfr:");

//We get 12 long words back in Network order
/*
for(i=0;i<12;i++)
    printf("%d\t%-8x\n",i,ntohl(buf[i]));
*/

/*
 * The high word of transmit time is the 10th word we get back
 * tmit is the time in seconds not accounting for network delays which
 * should be way less than a second if this is a local NTP server
 */

tmit=ntohl((time_t)buf[10]);    //# get transmit time
//printf("tmit=%d\n",tmit);

tmit-= 2208988800U; 

//#compare to system time
printf("Time: %s",ctime(&tmit));
i=time(0);
//printf("%d-%d=%d\n",i,tmit,i-tmit);
printf("System time is %d seconds off\n",i-tmit);


tv.tv_sec = (time_t)tmit;
tv.tv_usec = 0;
i = settimeofday(&tv,NULL);
printf("i is %d\n",i);

}

I am getting this output

socket: Success
sending data..
sendto: Success
receiving data

My code is blocking in recvfrom() function. What might be the problem here ?

EDIT

I was able to run this program. Problem was with firewell of company.

Now I want to set my system time using this. I am using settimeofday() function but settimeofday() function is returning -1.

How to resolve this?

Answer 1

These are the debug steps that you can follow.

1. As NTP runs at port number 123. Check firewall at this port. Ask your system administrator.

2. Since you are setting system time, You should run this program using root permission.like

sudo ./ntpProgram.o