由于實際要求，需要讓 Linux 系統的時間和局域網的其他設備保持同步。為了實現上述目標，本文使用 NTP 協議進行時間同步。

由于是局域網環境，不適合直接從互聯網上獲取當前時間進行時間同步。為此本文采用了在局域網內搭建 NTP 服務器，所有的 Linux 設備都通過向該服務器同步時間，從而保證局域網內的設備時間保持同步。

本文使用 Windows Server 2012 搭建 NTP 服務器， Windows 配置 NTP 服務器可以使用以下方法：

• 通過配置注冊表實現，但是操作太麻煩；
• 安裝 SNTP Service 軟件，安裝該軟件后默認開啟 SNTP 服務，然后就可以使用 NTP 客戶端進行時間同步了。

本文采用第二種方法，簡單方便。下面是搭建步驟：

1. 下載 SNTP Service 軟件 進入 SNTP Service 軟件官網下載該軟件。

2. 點擊安裝 SNTP Service 軟件

3. 點擊 next

4. 選擇安裝目錄，并點擊 next

5. 自定義安裝組件，并點擊 next

6. 并點擊 install 進入安裝

7. 等待安裝完成

8. 安裝完成

經過上述步驟后， SNTP 服務就開啟了，可以使用 NTP 客戶端進行時間同步了。

本文使用 Python 腳本編寫 NTP 客戶端腳本 ntpclient.py ，使用該腳本訪問搭建好的 NTP 服務器獲取當前時間。該腳本是基于 ntplib 庫， 其源碼如下所示：

#-*- coding:utf-8 -*-################################################################################ ntplib - Python NTP library.# Copyright (C) 2009 Charles-Francois Natali <cf.natali@Gmail.com>## ntplib is free software; you can redistribute it and/or modify it under the# terms of the GNU Lesser General Public License as published by the Free# Software Foundation; either version 2 of the License, or (at your option) any# later version.## This PRogram is distributed in the hope that it will be useful, but WITHOUT# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS# FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more# details.## You should have received a copy of the GNU Lesser General Public License# along with this program; if not, write to the Free Software Foundation, 51# Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA###############################################################################"""Python NTP library.Implementation of client-side NTP (RFC-1305), and useful NTP-relatedfunctions."""import osimport sysimport datetimeimport socketimport structimport timefrom optparse import OptionParserclass NTPException(Exception):    """Exception raised by this module."""    passclass NTP:    """Helper class defining constants."""    _SYSTEM_EPOCH = datetime.date(*time.gmtime(0)[0:3])    """system epoch"""    _NTP_EPOCH = datetime.date(1900, 1, 1)    """NTP epoch"""    NTP_DELTA = (_SYSTEM_EPOCH - _NTP_EPOCH).days * 24 * 3600    """delta between system and NTP time"""    REF_ID_TABLE = {        "GOES":  "Geostationary Orbit Environment Satellite",        "GPS/0": "Global Position System",        "GAL/0": "Galileo Positioning System",        "PPS/0": "Generic pulse-per-second",        "IRIG":  "Inter-Range Instrumentation Group",        "WWVB":  "LF Radio WWVB Ft. Collins, CO 60 kHz",        "DCF/0": "LF Radio DCF77 Mainflingen, DE 77.5 kHz",        "HBG/0": "LF Radio HBG Prangins, HB 75 kHz",        "MSF/0": "LF Radio MSF Anthorn, UK 60 kHz",        "JJY/0": "LF Radio JJY Fukushima, JP 40 kHz, Saga, JP 60 kHz",        "LORC":  "MF Radio LORAN C station, 100 kHz",        "TDF/0": "MF Radio Allouis, FR 162 kHz",        "CHU/0": "HF Radio CHU Ottawa, Ontario",        "WWV/0": "HF Radio WWV Ft. Collins, CO",        "WWVH":  "HF Radio WWVH Kauai, HI",        "NIST":  "NIST telephone modem",        "ACTS":  "NIST telephone modem",        "USNO":  "USNO telephone modem",        "PTB/0": "European telephone modem",        "LOCL":  "uncalibrated local clock",        "CESM":  "calibrated Cesium clock",        "RBDM":  "calibrated Rubidium clock",        "OMEG":  "OMEGA radionavigation system",        "DCN/0": "DCN routing protocol",        "TSP/0": "TSP time protocol",        "DTS/0": "Digital Time Service",        "ATOM":  "Atomic clock (calibrated)",        "VLF/0": "VLF radio (OMEGA,, etc.)",        "1PPS":  "External 1 PPS input",        "FREE":  "(Internal clock)",        "INIT":  "(Initialization)",        "/0/0/0/0":   "NULL",    }    """reference identifier table"""    STRATUM_TABLE = {        0: "unspecified or invalid",        1: "primary reference (%s)",    }    """stratum table"""    MODE_TABLE = {        0: "reserved",        1: "symmetric active",        2: "symmetric passive",        3: "client",        4: "server",        5: "broadcast",        6: "reserved for NTP control messages",        7: "reserved for private use",    }    """mode table"""    LEAP_TABLE = {        0: "no warning",        1: "last minute of the day has 61 seconds",        2: "last minute of the day has 59 seconds",        3: "unknown (clock unsynchronized)",    }    """leap indicator table"""class NTPPacket:    """NTP packet class.    This represents an NTP packet.    """    _PACKET_FORMAT = "!B B B b 11I"    """packet format to pack/unpack"""    def __init__(self, version=2, mode=3, tx_timestamp=0):        """Constructor.        Parameters:        version      -- NTP version        mode         -- packet mode (client, server)        tx_timestamp -- packet transmit timestamp        """        self.leap = 0        """leap second indicator"""        self.version = version        """version"""        self.mode = mode        """mode"""        self.stratum = 0        """stratum"""        self.poll = 0        """poll interval"""        self.precision = 0        """precision"""        self.root_delay = 0        """root delay"""        self.root_dispersion = 0        """root dispersion"""        self.ref_id = 0        """reference clock identifier"""        self.ref_timestamp = 0        """reference timestamp"""        self.orig_timestamp = 0        """originate timestamp"""        self.recv_timestamp = 0        """receive timestamp"""        self.tx_timestamp = tx_timestamp        """tansmit timestamp"""    def to_data(self):        """Convert this NTPPacket to a buffer that can be sent over a socket.        Returns:        buffer representing this packet        Raises:        NTPException -- in case of invalid field        """        try:            packed = struct.pack(NTPPacket._PACKET_FORMAT,                (self.leap << 6 | self.version << 3 | self.mode),                self.stratum,                self.poll,                self.precision,                _to_int(self.root_delay) << 16 | _to_frac(self.root_delay, 16),                _to_int(self.root_dispersion) << 16 |                _to_frac(self.root_dispersion, 16),                self.ref_id,                _to_int(self.ref_timestamp),                _to_frac(self.ref_timestamp),                _to_int(self.orig_timestamp),                _to_frac(self.orig_timestamp),                _to_int(self.recv_timestamp),                _to_frac(self.recv_timestamp),                _to_int(self.tx_timestamp),                _to_frac(self.tx_timestamp))        except struct.error:            raise NTPException("Invalid NTP packet fields.")        return packed    def from_data(self, data):        """Populate this instance from a NTP packet payload received from        the network.        Parameters:        data -- buffer payload        Raises:        NTPException -- in case of invalid packet format        """        try:            unpacked = struct.unpack(NTPPacket._PACKET_FORMAT,                    data[0:struct.calcsize(NTPPacket._PACKET_FORMAT)])        except struct.error:            raise NTPException("Invalid NTP packet.")        self.leap = unpacked[0] >> 6 & 0x3        self.version = unpacked[0] >> 3 & 0x7        self.mode = unpacked[0] & 0x7        self.stratum = unpacked[1]        self.poll = unpacked[2]        self.precision = unpacked[3]        self.root_delay = float(unpacked[4])/2**16        self.root_dispersion = float(unpacked[5])/2**16        self.ref_id = unpacked[6]        self.ref_timestamp = _to_time(unpacked[7], unpacked[8])        self.orig_timestamp = _to_time(unpacked[9], unpacked[10])        self.recv_timestamp = _to_time(unpacked[11], unpacked[12])        self.tx_timestamp = _to_time(unpacked[13], unpacked[14])class NTPStats(NTPPacket):    """NTP statistics.    Wrapper for NTPPacket, offering additional statistics like offset and    delay, and timestamps converted to system time.    """    def __init__(self):        """Constructor."""        NTPPacket.__init__(self)        self.dest_timestamp = 0        """destination timestamp"""    @property    def offset(self):        """offset"""        return ((self.recv_timestamp - self.orig_timestamp) +                (self.tx_timestamp - self.dest_timestamp))/2    @property    def delay(self):        """round-trip delay"""        return ((self.dest_timestamp - self.orig_timestamp) -                (self.tx_timestamp - self.recv_timestamp))    @property    def tx_time(self):        """Transmit timestamp in system time."""        return ntp_to_system_time(self.tx_timestamp)    @property    def recv_time(self):        """Receive timestamp in system time."""        return ntp_to_system_time(self.recv_timestamp)    @property    def orig_time(self):        """Originate timestamp in system time."""        return ntp_to_system_time(self.orig_timestamp)    @property    def ref_time(self):        """Reference timestamp in system time."""        return ntp_to_system_time(self.ref_timestamp)    @property    def dest_time(self):        """Destination timestamp in system time."""        return ntp_to_system_time(self.dest_timestamp)class NTPClient:    """NTP client session."""    def __init__(self):        """Constructor."""        pass    def request(self, host, version=2, port='ntp', timeout=5):        """Query a NTP server.        Parameters:        host    -- server name/address        version -- NTP version to use        port    -- server port        timeout -- timeout on socket Operations        Returns:        NTPStats object        """        # lookup server address        addrinfo = socket.getaddrinfo(host, port)[0]        family, sockaddr = addrinfo[0], addrinfo[4]        # create the socket        s = socket.socket(family, socket.SOCK_DGRAM)        try:            s.settimeout(timeout)            # create the request packet - mode 3 is client            query_packet = NTPPacket(mode=3, version=version,                                tx_timestamp=system_to_ntp_time(time.time()))            # send the request            s.sendto(query_packet.to_data(), sockaddr)            # wait for the response - check the source address            src_addr = None,            while src_addr[0] != sockaddr[0]:                response_packet, src_addr = s.recvfrom(256)            # build the destination timestamp            dest_timestamp = system_to_ntp_time(time.time())        except socket.timeout:            raise NTPException("No response received from %s." % host)        finally:            s.close()        # construct corresponding statistics        stats = NTPStats()        stats.from_data(response_packet)        stats.dest_timestamp = dest_timestamp        return statsdef _to_int(timestamp):    """Return the integral part of a timestamp.    Parameters:    timestamp -- NTP timestamp    Retuns:    integral part    """    return int(timestamp)def _to_frac(timestamp, n=32):    """Return the fractional part of a timestamp.    Parameters:    timestamp -- NTP timestamp    n         -- number of bits of the fractional part    Retuns:    fractional part    """    return int(abs(timestamp - _to_int(timestamp)) * 2**n)def _to_time(integ, frac, n=32):    """Return a timestamp from an integral and fractional part.    Parameters:    integ -- integral part    frac  -- fractional part    n     -- number of bits of the fractional part    Retuns:    timestamp    """    return integ + float(frac)/2**ndef ntp_to_system_time(timestamp):    """Convert a NTP time to system time.    Parameters:    timestamp -- timestamp in NTP time    Returns:    corresponding system time    """    return timestamp - NTP.NTP_DELTAdef system_to_ntp_time(timestamp):    """Convert a system time to a NTP time.    Parameters:    timestamp -- timestamp in system time    Returns:    corresponding NTP time    """    return timestamp + NTP.NTP_DELTAdef leap_to_text(leap):    """Convert a leap indicator to text.    Parameters:    leap -- leap indicator value    Returns:    corresponding message    Raises:    NTPException -- in case of invalid leap indicator    """    if leap in NTP.LEAP_TABLE:        return NTP.LEAP_TABLE[leap]    else:        raise NTPException("Invalid leap indicator.")def mode_to_text(mode):    """Convert a NTP mode value to text.    Parameters:    mode -- NTP mode    Returns:    corresponding message    Raises:    NTPException -- in case of invalid mode    """    if mode in NTP.MODE_TABLE:        return NTP.MODE_TABLE[mode]    else:        raise NTPException("Invalid mode.")def stratum_to_text(stratum):    """Convert a stratum value to text.    Parameters:    stratum -- NTP stratum    Returns:    corresponding message    Raises:    NTPException -- in case of invalid stratum    """    if stratum in NTP.STRATUM_TABLE:        return NTP.STRATUM_TABLE[stratum] % (stratum)    elif 1 < stratum < 16:        return "secondary reference (%s)" % (stratum)    elif stratum == 16:        return "unsynchronized (%s)" % (stratum)    else:        raise NTPException("Invalid stratum or reserved.")def ref_id_to_text(ref_id, stratum=2):    """Convert a reference clock identifier to text according to its stratum.    Parameters:    ref_id  -- reference clock indentifier    stratum -- NTP stratum    Returns:    corresponding message    Raises:    NTPException -- in case of invalid stratum    """    fields = (ref_id >> 24 & 0xff, ref_id >> 16 & 0xff,              ref_id >> 8 & 0xff, ref_id & 0xff)    # return the result as a string or dot-formatted IP address    if 0 <= stratum <= 1:        text = '%c%c%c%c' % fields        if text in NTP.REF_ID_TABLE:            return NTP.REF_ID_TABLE[text]        else:            return "Unidentified reference source '%s'" % (text)    elif 2 <= stratum < 255:        return '%d.%d.%d.%d' % fields    else:        raise NTPException("Invalid stratum.")if __name__ == '__main__':'''if len(sys.argv) <= 1:print "error, parameters is invalid!"exit(1)'''# 解析用戶輸入的參數parser = OptionParser(version="%prog 0.1") # 獲取參數的選項parser.add_option("-u", "--url", action="store",type="string", dest="url",help="the url of ntp server.")(options, args) = parser.parse_args()if options.url == None:print "error, url is invalid!"exit(1)# 建立NTP客戶端client = NTPClient()response = client.request(options.url, version=3)# 從NTP服務器獲得當前時間cur = time.ctime(response.tx_time)# 打印當前時間print "%s" %cur

上述客戶端腳本只是從 NTP 服務器獲取當前時間，而不能設置 Linux 當前時間。為實現該功能，本文創建 Shell 腳本 time_demo.sh 來更新 Linux 的時間。其源碼如下所示：

#!/bin/bash # 將本文件和 ntpclient.py 放在同一目錄下time=`python ./ntpclient.py -u 172.16.177.212`date -s "$time" > /dev/null

[root@00:B3:42:01:02:23 bin]# dateMon Aug  9 00:00:03 CST 2010[root@00:B3:42:01:02:23 bin]# ./time_demo.sh [root@00:B3:42:01:02:23 bin]# dateFri Nov 21 17:04:09 CST 2014