








			 趨ά׼ȷĵʱ

		       : Ron Bean, rbean@execpc.com

		   : Da-Wei Chiang, dawei@sinica.edu.tw

		   v, December 1996 : 2-16 July 1998



				   Abstract

     趨ά׼ȷĵʱ.



1.  

˵(춰Ĺվ)ʹõ real-time-clock
Ƭ׼ȷ֪.  Ȼ Linux
ҵϵͳṩһ򵥵ķУ׼ȷĵʱ,
ʹõʱӾǲУʱԴҲԴﵽ *൱* ׼ȷĵز.
ƺ˶֪, ԭ:

  1.   һ ``趨 linux ҵϵͳ'' ļвδ,
      ڰװҵϵͳʱԶ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
      ʽԱУʱԴ, ·Уʱŷߵʱź, ȡͬ.

λԱĵͽ׵ʱ趨߶ȵȤ,
ǿҽλЩʱҳ<URL:http://www.eecis.udel.edu/~ntp/> ,
ҳȤ,й xntpd ѶԼ  NIST  USNO
վ̨ĳ.  (ڱҲ xntpd Щļ.)

      ע
	    ͬһ̨ܶҵϵͳ, Ӧֻһ趨
	    CMOS ʱ, ǡ໥Ӱ».
	    ʹƽͬһ̨ Linux  Windows ҵϵͳ,
	    ҪѰһЩУʱʽʱԺ Windows ҵϵͳĲ
	    (οǰ˵ҳĳ).


2.  ʹ``clock''ʽ

Ҫ֪ݶ clock(8) ˵, Ľλ趨.


趨ά׼ȷĵʱ						      1





趨ά׼ȷĵʱ						      2



      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 , õֻһп:

     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,
ʱƫʽɵõ .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򶼻ӿִеִ,
ȻֻҪͿԴﵽ׼ȷʱĿ.

עϵͳʱһγһʱ, Щϵͳ clock
ʽܻ޷ִ.  ⷽ, ʹ xntpd  ntpdate ʽ
𲽵ʱ.

2.3  ʵ










趨ά׼ȷĵʱ						      3



2.3.1  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'') ִеĽ¼.

2.3.2  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,
ʱĻϵʱǼ.  ʹü̴漸:

     date -s hh:mm:00


з벿趨־Ŀǰʱ *֮* һ,
һֱȵٵһ enter  (ڿԹϵ绰).   hh
Ĳʹûصʱּ.  趨 ``ϵͳʱ''.  Ȼִ:

     clock -w


µ (У) ϵͳʱд CMOS ʱ.  Ȼִ:

     date +%j


(ִ ``date +%s'' )








趨ά׼ȷĵʱ						      4



 (Уڼһȷʱ) Կʼƫ.

2.3.3  У

ĳһִ ``date'' ʽʱ, ıʱǿ?  ǿ,
뽫֮ȥһЩԷȷʱ, Ӧдһƫֵ.
,뽫֮һЩԷȷʱ,
Ӧдһƫֵ.

ڽУ.  ֮ǰʹõ ``date +%j'',
ֵΪһĵڼ (1-365,  1-366 ).
Դһ趨ʱӵھ1 1 㻹ҪڶУڼ 365 (
366) ֮ǰʹõ ``date +%s'' ֵĵλΪ, 뽫֮ 86400
Աȡ.

ĵ /etc/adjtime ѾУ, 뽫ǰУǽ,
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-- һǵϵͳػʹõصάּʱܵ
``real time clock'' (Ҳν ``CMOS ʱ'', ``Ӳʱ'',  ``RTC'')
һ ``kernel clock'' (ʱΪ ``ʱ''  ``ϵͳʱ'')
ϵͳʱӵԼʱжźΪ׼ڿʱCMOS ʱӴʼֵ.
ʱвͬʱƫ, Զʱϵʱ𽥵زƫ, Ҳ
``''ʱƫ.

 xntpd ļ ``the clock'' ָ ``kernel clock''.	ִ xntpd
 timed ʽʱ (ʹõ adjtimex ϵͳеĳʽ) linux
ҵϵͳٶϵͳʱӱ CMOS ʱ׼ȷ, һڿÿ 11 趨һ
CMOS ʱ (һֱؿΪֹ).  ζ ``clock'' ʽ֪һ趨
CMOS ʱӵȷʱ, 㲻ʹõ /etc/adjtime еУ.
ڿִеʹ ntpdate ʽ Աڳִ xntpd
ʽ֮ǰУʱŷʱ.  ڿʱһֱ޷׼ȷУʱԴ,
ܻٵһЩ-- ʵ xntpd Ǳ֮ʹõ.

Xntpd ߵʱӵʽ, ҲԱ趨һڲ绰
NIST ĵ绰ӵУʱ
(趨õ绰ӵ֮ȼһµ绰ʵĻ).








趨ά׼ȷĵʱ						      5



УʱԴʧȥһʱ֮ʽҲṩϵͳʱһУ.

󲿷ֵߵʱӴԼҪ $3-4K, Բýϱ˵ ``gadget box'' 
(ʵһ 300 baud ݻ) ĵһ̨̲ߵ֮
Ƶ Canada  CHU Уʱߵ̨ (μַ
<URL:ftp://ftp.udel.edu/pub/ntp/gadget.tar.Z>).  Heathkit WWV 
(``׼ȷʱ'') Ȼĵ (һ׼), ԼҪ $4-500.  ĿǰGPS
ѶȻУʱѶ, Ҳֵ GPS ԽϵԵĴв.
δܻΪͼλĽ.

, һ˿Լдʽʹ NIST ĵ绰ӵУʱԱԶ 
CMOS ʱϵͳʱӵƫ.  ȻҲ֪ǷеĳʽܹﵽĿ,
Ǵ󲿷ֵĳʽӦÿԽ xntpd ʽ.

















































趨ά׼ȷĵʱ						      6





































































				   CONTENTS



1.  ..................................................................... 1

2. ʹ``clock''ʽ ........................................................ 1
   2.1 ҵϵͳ ..................................................... 2
   2.2 ʱӵƫ ..................................................... 2
   2.3 ʵ ................................................................. 2

3. xntpd  ............................................................... 4












































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