PHP通过NTP服务器获取时间脚本

ntp-client.php

#!/usr/bin/php -q
<?php
echo "PHP Time Protocol Client\n";
echo "-----------------\n";

/* NTP服务器列表 */
$ntp_server_list = array(
	'0.hk.pool.ntp.org',
	'0.asia.pool.ntp.org',
	'1.asia.pool.ntp.org',
	'2.asia.pool.ntp.org',
	'3.asia.pool.ntp.org',
	'time.windows.com',
	'time.nist.gov'
);

/* NTP服务器数量 */
$ntp_server_count = count($ntp_server_list);

/* Flag: 已经获取到时间 */
$have_got_time = false;

/* 设置时区 */
date_default_timezone_set('Asia/Shanghai');

for ($i = 0; $i < $ntp_server_count; $i++) {
	$ntp_server = $ntp_server_list[$i];
	echo "Connect to NTP server {$ntp_server} ... ";

	$fp = @fsockopen($ntp_server, 37, $errno, $errmsg, 10);
	if (!$fp) {
		echo "Failed!\n";
	} else {
		echo "Connected\n";

		$result = null;
		while (!feof($fp))
			$result .= fgets($fp, 1452);
		fclose($fp);

		if (strlen($result) != 4) {
			echo " > NTP Server return a unexpect data\n";
			echo " > Try next server\n";
		} else {
			echo " > Got valied data\n";
			$have_got_time = true;
			break;
		}
	}
}

if ($have_got_time) {
	$NTP_timestamp = ord($result{0}) * pow(256, 3) + ord($result{1}) * pow(256, 2) + ord($result{2}) * 256 + ord($result{3});

	/*
	 * PHP的Timestamp是从1970/1/1开始计算的
	 * Time协议的Timestamp是从1900/1/1开始计算的
	 * 他俩之间差25567天
	 * 所以通过NTP server获取的时间戳减去25567天就是PHP的时间戳
	 */

	$real_timestamp = $NTP_timestamp - 25567*24*60*60;
	$date_string = date('j M Y H:i:s', $real_timestamp);
	echo " > {$date_string}\n";

	$sys_date = exec("date -s \"{$date_string}\"");
	echo " > System date set to {$sys_date}\n";
} else {
	echo "Can not get any valid data from NTP server list\n";
}
?>