
                         趨ά׼ȷĵʱ
                                       
: Ron Bean, [1]rbean@execpc.com
: Da-Wei Chiang, [2]dawei@sinica.edu.tw

   v, December 1996 : 2-16 July 1998
     _________________________________________________________________
   
   趨ά׼ȷĵʱ.
     _________________________________________________________________
   
1. 

2. ʹ``clock''ʽ

     * 2.1 ҵϵͳ
     * 2.2 ʱӵƫ
     * 2.3 ʵ
       
3. xntpd 
     _________________________________________________________________
   
1. 

   ˵(춰Ĺվ)ʹõ real-time-clock Ƭ׼
   ȷ֪. Ȼ Linux ҵϵͳṩһ򵥵ķУ
   ׼ȷĵʱ, ʹõʱӾǲУʱԴҲԴﵽ *൱*
   ׼ȷĵز. ƺ˶֪, ԭ:
   
    1. һ ``趨 linux ҵϵͳ'' ļвδ, 
       װҵϵͳʱԶ趨 (ϲǲܵ, 
       һ̨ݻĻ).
    2. ʹ``man clock''鿴趨ʱӵ˵ʱ, ܻȡ÷Ԥڵ
       clock(3) ˵. (ʹ``man 8 clock'').
    3. ƺ˲ڵȷʱǶ.
    4. Щ louie.udel.edu ṩ xntpd ʽԱ
       УʱԴ, ·Уʱŷߵʱź, ȡͬ.
       
   λԱĵͽ׵ʱ趨߶ȵȤ, ǿҽ
   λЩʱҳ [3]http://www.eecis.udel.edu/~ntp/ , ҳ
   Ȥ,й xntpd ѶԼ NIST  USNO վ
   ̨ĳ. (ڱҲ xntpd Щļ.)
   
   ע
          ͬһ̨ܶҵϵͳ, Ӧֻһ趨
          CMOS ʱ, ǡ໥Ӱ». ʹƽͬһ̨
           Linux  Windows ҵϵͳ, ҪѰһЩУ
          ʱʽʱԺ Windows ҵϵͳĲ (οǰ˵ҳĳ
          ).
          
2. ʹ``clock''ʽ

   Ҫ֪ݶ clock(8) ˵, Ľλ
   .
   
   ע
          Ҫִ``clock''Ӱ쵽ϵͳʱ CMOS ʱӵĳʽ, 
          ӵ root Ȩ.
          
2.1 ҵϵͳ

   ҵϵͳĿִеǷ``clock -a'' ``clock -ua''
   . ܷ /etc/rc.local , /etc/rc.d/rc.sysinit , 
   Ƶĵط, Ҫ㰲װһ Linux ҵϵͳ.
   
   ҵ ``clock -s''  ``clock -us'' , 뽫 ``s'' ĳ
   ``a'' , 鿴Ƿ /etc/adjtime , õֻһ
   :
   
0.000000 842214901 0.000000

   ЩУ (ÿƫ), һУʱӵʱ ( Jan
   1, 1970 ʼ), һУ۳. Ҳ,
    root ݲ˵, ֻһп (ȫ):
   
0.0 0 0.0

   Ȼ͸ shell ִֶ ``clock -a''  ``clock -ua'' Աµڶ
    (ʱӱ趨ЭʱǱʱ ʹ ``u''
   ).
   
2.2 ʱӵƫ

   ֪ڵǼ :-). ıʱǲ׼ȷ. 
   ϲķǲ绰 WWV  (303)499-7111 绰ʱ̨ (Ǹѵ绰).
   ܹ·Уʱŷ, Ҳʹ xntpd ʽṩ
   ntpdate ʽУʱ (ʹ -b ѡԱϵͳŪ CMOS ʱ). ʹ
   ``date -s hh:mm:ss'' ֶʽ趨ϵͳʱ, һַᶼʹ
   ``clock -w'' ϵͳʱд CMOS ʱ. ǵһ趨ʱӵ
   , ýдڲʧĵط. ʹõ ntpdate 
   ʽ, ִ ``date +%s'' ȻдԴ Jan 1,1970 𵽸óʽִе.
   
   Ȼȴ򼸸֮ٻʱӵƫ˶ʱ. 
   ֶķʽ趨ʱ, ٵõȴ֮, ʱƫʽ
   õ .1 sec/day Ľ. ֮ƫӦû .01 sec/day (
   ЩӦø׼ȷ, Ҹ˳ֱ̬). ʹ ntpdate ʽ
   趨ʱܲصȴ̫õʱ, Ȼʹַʽ֮ᶼЩ΢
   Ĺ.
   
   ʹ cron һʱִ ``clock -a'' Աϵͳʱܹ
   (У) CMOSʱάһ. ʵÿοʱ򶼻ӿִе
   ִ, ȻֻҪͿԴﵽ׼ȷʱĿ
   .
   
   עϵͳʱһγһʱ, Щϵͳ clock 
   ʽܻ޷ִ. ⷽ, ʹ xntpd  ntpdate 
   ʽ 𲽵ʱ.
   
2.3 ʵ

  趨ʱ
  
   ǩϵͳΪ root. 绰 (303)499-7111 (), ʱ.
   Ȼʹü̴漸:
   
date -s hh:mm:ss

   һֱȵٵһ enter . (ڴ˴ʹ ``ntpdate'' ʽ, 
   ʡԲ绰Ķ) 趨 ``ϵͳʱ''. ִ:
   
clock -w

   轫ϵͳʱд CMOS ʱöʱһ. ִ:
   
date +%j

   (ǰʹ ``ntpdate'' ʽִ ``date +%s'') ִеĽ
   ¼.
   
  趨ʱƫ
  
   ҳϴд. ǩϵͳΪ root. Ȼִ:
   
clock -a

   轫 CMOS ʱдϵͳʱöʱһ. 绰 (303)499-7111
   (), ʱ. ʹü̴漸:
   
date

   һֱȵٵһ enter , ǵȴʱ, д±ʱ, 
   һҪϵ绰. ֪ĿǰʱǼ, ʱ
   ĻϵʱǼ. ʹü̴漸:
   
date -s hh:mm:00

   з벿趨־Ŀǰʱ *֮* һ, һֱȵ
   һ enter  (ڿԹϵ绰).  hh Ĳʹû
   ʱּ. 趨 ``ϵͳʱ''. Ȼִ:
   
clock -w

   µ (У) ϵͳʱд CMOS ʱ. Ȼִ:
   
date +%j

   (ִ ``date +%s'' )
   
    (Уڼһȷʱ) Կʼƫ
   .
   
  У
  
   ĳһִ ``date'' ʽʱ, ıʱǿ? 
   ǿ, 뽫֮ȥһЩԷȷʱ, Ӧдһƫ
   ֵ. ,뽫֮һЩԷȷʱ, Ӧд
   һƫֵ.
   
   ڽУ. ֮ǰʹõ ``date +%j'', ֵ
   Ϊһĵڼ (1-365,  1-366 ). Դһ趨ʱ
   ھ1 1 㻹ҪڶУڼ 365 ( 366) ֮ǰʹ
   õ ``date +%s'' ֵĵλΪ, 뽫֮ 86400 Աȡ
   .
   
   ĵ /etc/adjtime ѾУ, 뽫ǰУ
   ǽ, У, УӵŽ⵽ƫֵ
   ; Уͬ. ɵУӳ, Ȼ
   õƫ (ע-- ͬ, 㽫ȡһϴƫֵ,
   ෴, 㽫ȡһСƫֵ).
   
   ƫԱȡµУ, ȻὫ
   /etc/adjtime оɵУӴµ. дµУ (
   Ϊλ) Ա´ʹ.
   
   ҵ /etc/adjtime :
   
-9.600000 845082716 -0.250655

   (עÿ 9.6 һ½ 5 ӵƫ!)
   
3. xntpd 

   ϵͳʵжʱ-- һǵϵͳػʹõصάּʱ
    ``real time clock'' (Ҳν ``CMOS ʱ'', ``Ӳʱ'', 
   ``RTC'') һ ``kernel clock'' (ʱΪ ``ʱ''  ``ϵͳʱ
   '') ϵͳʱӵԼʱжźΪ׼ڿʱCMOS ʱӴ
   ʼֵ. ʱвͬʱƫ, Զʱϵʱ𽥵ز
   ƫ, Ҳ ``''ʱƫ.
   
    xntpd ļ ``the clock'' ָ ``kernel clock''. ִ
   xntpd  timed ʽʱ (ʹõ adjtimex ϵͳеĳʽ) linux 
   ҵϵͳٶϵͳʱӱ CMOS ʱ׼ȷ, һڿÿ 11 
   һ CMOS ʱ (һֱؿΪֹ). ζ ``clock'' ʽ֪
   һ趨 CMOS ʱӵȷʱ, 㲻ʹõ /etc/adjtime 
   У. ڿִеʹ ntpdate ʽ Աڳִ xntpd
   ʽ֮ǰУʱŷʱ. ڿʱһֱ޷׼ȷУʱԴ,
   ܻٵһЩ-- ʵ xntpd Ǳ֮ʹ
   õ.
   
   Xntpd ߵʱӵʽ, ҲԱ趨һڲ
   绰 NIST ĵ绰ӵУʱ (趨õ绰ӵ֮
   һµ绰ʵĻ). УʱԴʧȥһʱ֮ʽҲ
   ṩϵͳʱһУ.
   
   󲿷ֵߵʱӴԼҪ $3-4K, Բýϱ˵ ``gadget
   box''  (ʵһ 300 baud ݻ) ĵһ̨̲
   ߵ֮ Ƶ Canada  CHU Уʱߵ̨ (μַ
   [4]ftp://ftp.udel.edu/pub/ntp/gadget.tar.Z). Heathkit WWV  (``
   ׼ȷʱ'') Ȼĵ (һ׼), ԼҪ $4-500. Ŀ
   ǰGPS ѶȻУʱѶ, Ҳֵ GPS ԽϵԵ
   в. δܻΪͼλĽ.
   
   , һ˿Լдʽʹ NIST ĵ绰ӵУʱԱԶ
    CMOS ʱϵͳʱӵƫ. ȻҲ֪Ƿеĳʽܹﵽ
   Ŀ, Ǵ󲿷ֵĳʽӦÿԽ xntpd ʽ.

References

   1. mailto:rbean@execpc.com
   2. mailto:dawei@sinica.edu.tw
   3. http://www.eecis.udel.edu/~ntp/
   4. ftp://ftp.udel.edu/pub/ntp/gadget.tar.Z
