c - 运行 ntpclient 时出错，阻塞在 recvfrom() 函数和 settimeofday() 返回 -1

Question

我正在使用此代码在我的 ubuntu 系统中运行 ntp 客户端。

/* 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);

}

我得到这个输出

套接字:成功
发送数据..
发送到:成功
接收数据

我的代码在 recvfrom() 函数中阻塞。这可能是什么问题？

编辑

我能够运行这个程序。问题出在公司的火井上。

现在我想用它来设置我的系统时间。我正在使用 settimeofday() 函数，但 settimeofday() 函数返回 -1。

如何解决？

Answer 1

这些是您可以遵循的调试步骤。

1. 由于 NTP 在端口号 123 上运行。检查此端口的防火墙。请询问您的系统管理员。

2. 由于您正在设置系统时间，因此您应该使用 root 权限运行此程序。如

须藤./ntpProgram.o