Ubuntu利用TCP协议来获取服务器时间的方法
<p style='margin: 0px; padding: 5px 0px; outline: none; font-size: 14px; line-height: 30px; font-family: tahoma, arial, "Microsoft YaHei";'>这里使用Unix网络编程里面的一个小程序，该客户端建立一个到服务器的TCP连接，然后读取由服务器以直观可读格式简单地送回的当前时间和日期.</p>
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<span><u>复制代码</u></span>
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代码如下:</p>
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#include "unp.h"<br>
int main(int argc, char **argv)<br>
{<br>
int sockfd, n;<br>
char recvline;<br>
struct sockaddr_in servaddr;<br>
if (argc != 2)<br>
err_quit("usage: a.out <IPaddress>");<br>
if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)<br>
err_sys("socket error");<br>
bzero(&servaddr, sizeof(servaddr));<br>
servaddr.sin_family = AF_INET;<br>
servaddr.sin_port = htons(13); /* daytime server */<br>
if (inet_pton(AF_INET, argv, &servaddr.sin_addr) <= 0)<br>
err_quit("inet_pton error for %s", argv);<br>
if (connect(sockfd, (SA *) &servaddr, sizeof(servaddr)) < 0)<br>
err_sys("connect error");<br>
while ( (n = read(sockfd, recvline, MAXLINE)) > 0) {<br>
recvline = 0; /* null terminate */<br>
if (fputs(recvline, stdout) == EOF)<br>
err_sys("fputs error");<br>
}<br>
if (n < 0)<br>
err_sys("read error");<br>
exit(0);<br>
} </div>
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然后我们运行这个程序若干次，每次以不同的IP地址作为命令行参数.</p>
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首先我们测试本机的时间，你必须要先打开Linux下的daytime服务,方法如下</p>
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<span><u>复制代码</u></span>
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<p>
代码如下:</p>
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sudo apt-get install xinetd<br>
sudo vi /etc/xinetd.d/daytime</div>
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找到这一行,然后把yes改成no </p>
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<span><u>复制代码</u></span>
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<p>
代码如下:</p>
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(disable = yes) -> (disable = no)sudo /etc/init.d/xinetd restart</div>
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测试本机</p>
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<span><u>复制代码</u></span>
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<p>
代码如下:</p>
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root@ubuntu:/home/jiang/UNP_STUDY/unpv13e/intro# ./daytimetcpcli 127.0.0.1</div>
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结果为:</p>
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24 OCT 2014 00:39:36 CST</p>
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那么要想测试互联网上服务器的daytime,首先得找到支持用TCP协议返回时间的服务器.测试了一些可能的主机,发现有一些可以返回，一些超时或者拒绝访问。</p>
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可能的主机列表如下,就是windows下右下角时间同步的那个列表。</p>
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<img style="max-width:100%!important;height:auto!important;"title="Ubuntu利用TCP协议来获取服务器时间的方法" alt="Ubuntu利用TCP协议来获取服务器时间的方法" src="https://zhuji.jb51.net/uploads/img/202305/1096691f5a80080889f5109fc40e3fa2.jpg"></p>
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这里使用dig指令来解析域名</p>
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<span><u>复制代码</u></span>
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<p>
代码如下:</p>
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dig time.windows.com +short<br>
time.microsoft.akadns.net.</div>
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64.4.10.33</p>
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运行程序尝试获取时间</p>
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./daytimetcpcli 64.4.10.33</p>
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第一次</p>
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<span><u>复制代码</u></span>
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<p>
代码如下:</p>
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connect error: Connection timed out</div>
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第二次</p>
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<span><u>复制代码</u></span>
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代码如下:</p>
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connect error: Connection refused</div>
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换个服务器</p>
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dig time.nist.gov<br>
./daytimetcpcli 128.138.141.172</p>
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结果</p>
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56953 14-10-23 16:46:39 11 0 0 0.0 UTC(NIST) *<br>
可以看直观的看出来，当地的时间为下午4点钟. </p>
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