
  The Clock Mini-HOWTO
  Ron Bean, rbean@execpc.com
  Dec. 1996

  How to set and keep your computer clock on time.
-----------------

  :    sanghoon_rhee@geocities.com
  2000 1

  ǻ ð踦   ̸  Ȯϰ  ΰ.
-----------------

  1.  Ұ

    ο ǻ  忡 ޷ ִ ǽð ð (Real-time Clock, RTC)
   Ȯ ϱ  ѵ, ̰  ũ̶̼ ؼ ܰ
  ƴմϴ.  ̷ Ȳ,  Ư ϵ
  ܺο ִ Ÿ     ǻ ð踦 *ſ* Ȯϰ
    ִ Ʈ  մϴ. κ   
   𸣰 ִµ ̰ Ƹ    ̶ մϴ:

  1.      ִ `` ġ ''    
     ʰ, ġ     Ȯ ð ߴ  Ʊ ̴. (
     ̳ Ʈũ ī ޷ ִٸ  Ұ   ƴմϴ)

  2. ``man clock''  Է   clock(3) شϴ 
     µ, ̰ clock Ŀǵ忡   ƴϴ. (``man 8 clock''
     ̶ ؾ clock Ŀǵ忡   ɴϴ)

  3. 밳  Ȯ ð ״ Ű澲 ʴ´.

  4. Ϻ ű⿡ Ű澲  louie.udel.edu  xntpd Ű
     ͼ Ʈũ Ÿ  (ǥ  ú    ִ) 
     ð ϵ ̿ؼ ð .

   mini-HOWTO      ϴ Դϴ.
  ̷ ڽ ϴ  ƴ϶ ϴ е
  <http://www.eecis.udel.edu/~ntp/>  湮ؼ Ⱦ ʽÿ. 
  Ʈ xntpd    NIST(1)  USNO(2)  ũ 
  ̷ο ڷḦ ϰ ֽϴ. (   xntpd   ణ
     ξϴ).

     
        ϳ̻ ü ϴ 迡,  ü
        ΰ θ ȥŰ   ϳ ü ð
        ߾ մϴ.  迡    Ͽ
        ϴ      ð ȭ
        α׷      ֽϴ. (  URL )

  2.  ``clock'' α׷ 

     ʿ  clock(8) Ŵ   ϰ ,
  ⼭  ü   ڽϴ.

     
        ``clock'' α׷̳ Ÿ Ŀνð質 CMOSð迡  
        α׷ ݵ Ʈ ؾ ȿ ֽϴ.

  2.1.  ġ¸ Ȯ

    ý õ ũƮ ϵ  ``clock -a''  ``clock -ua'' 
   ϴ  ִ Ȯմϴ. ýۿ ġ ǿ  
   /etc/rc.local  ֱ⵵ ϰ /etc/rc.d/rc.sysinit  ٸ
   Ͽ   ֽϴ.

      ϵ鿡 ``clock -s''  ``clock -us''   ִٸ
  ``s'' ``a''  ϰ /etc/adjtime ̶  ִ Ȯմϴ.
    뷫    ٿ   Դϴ:

       0.000000 842214901 0.000000

     ڸ  ڸ, ù° ڴ `' (Ϸ翡  ʾ
  ð谡 Ʋ °), ι° ڴ  ð豳   (1970
  1 1 0  귯 ʸ ϴ), ° ڴ  ð豳
  ʴ   󸶳  ߴ° ϴ Դϴ.  /etc/adjtime
  ̷  ٸ Ʈ α        0  ǰ
  ؼ  ݴϴ:

       0.0 0 0.0

      ``clock -a''  ``clock -ua''    Էϸ 
  2° ڰ ˴ϴ. ý ð谡 ǥؽ (UTC Ȥ GMT)
  Ѵٸ ``u'' ְ ׷  ׳ ``a'' ɼ ݴϴ.


  2.2.  ý ð  (drift rate) Ѵ.

    , ð ؼ    ʿ䰡 ְ :-) ? 츮 
  ľϰ ִ  ð Ȯ  ְ Ȯ   ֽϴ.
  ڴ (303)499-7111  ȭ ؼ WWV (3)   ȳ
  ̿ϴ  մϴ ( ȣ Ÿ ȭԴϴ). Ʈũ
  Ÿ    ִٸ xntpd Ű ԵǾ ִ ntpdate
  α׷ ϸ մϴ. (ntpdate   -b ɼ
    Ŀ CMOS ð踦 ߸ ǵ帱  ֽϴ).
  ƴϸ ``date -s hh:mm:ss''   Էؼ Ŀ ð踦  
  ִµ ̷ ϰ  ``clock -w''  ָ Ŀ ð踦 
  CMOS ð踦 ߰ ˴ϴ.  ð ٲ  
    ξ ϴ ٲٰ  ٷ ð Ȯؼ  Ӵϴ.
  ntpdate   ``date +%s''  ؼ  ڸ
   Ӵϴ. (  1970 1 1 0  귯 Դϴ)

    ׷   ̳  ֵ ذ ٰ ٽ ƿͼ ð
  󸶳 Ʋ Ȯմϴ. ntpdate  ʰ ۾
  ð ٸ ּ 2  ̻   Ȯϴ 
  ϴ.    0.1  ݿø ؼ ϴ.
       Ѵٸ  0.01  Ȯϰ
    ֽϴ. (  ̰ͺ    ŷ 
  ִٰ մϴٸ, ణ  ϴ  ).
  ntpdate ϴ  ׷  ٸ ʿ , 
   ߰   ð ڿ ѹ  ð ϴ 
   ʿմϴ.

    cron ̿ϸ ``clock -a'' ֱ ؼ Ŀ ð踦
  CMOSð迡 ġ Ű   ֽϴ.   
  õ ũƮ 򰡿  ֱ    ý    
  ˴ϴ.    Ѵٸ װ ε CMOS ð
  Ŀ ð踦    ġ Ű ȿ   ֽϴ.
  (  ϴ  ?)

     α׷ Ŀ ð谡 ѹ 1 ̻ ǰų Ŀ ð谡
  ڷ   ޽ ⵵ մϴ. ̷    xntpd
  ntpdateα׷ ؼ, Ŀνð谡   CMOS ð
  ġ ǰ    ֽϴ.

  2.3.  

  2.3.1.  ð ߱

    , Ʈ α մϴ. (303)499-7111 (3) ȭ ɾ ú
  ȳ ϴ. ׸   Էϰ (Ű̸ ġ  ä)
  ٸϴ:

       date -s hh:mm:ss

    úȳ ''Ҹ  Ű̸ ϴ. (⼭
  ``date'' ƴ϶ ``ntpdate'' ϴ  ȭɰ '' Ҹ
  ٸ ϴ     ʿ䰡 ϴ).
    ̷ ϸ ``Ŀ ð'' ο  ˴ϴ.  
    Էմϴ;

  clock -w

    ̷ ϸ CMOS ð踦 Ŀ ð迡 ϴ.   
   Էմϴ:

       date +%j

    ׸ µǴ ڸ   ؼ   Ӵϴ.
  ( ``date'' ``ntpdate'' ߴ ̶ ``date +%s''
  մϴ)

  2.3.2.  ð ʱȭ ϰ ð  (drift rate)  ȮѴ.

       ¥ Ȯմϴ.   Ʈ α ؼ
    Էմϴ:

       clock -a

  ȭ ɾ ú ȳ 鼭,   ԷѴ:
    ̷ ϸ Ŀνð踦  CMOS ð迡 ϴ.
  (303)499-7111 (3)  ȭ ɾ ú ȳ 鼭, 
   Էմϴ ( Ű̸  ʽϴ):

       date

    `' Ҹ ٸ  ú  ˷ִ ð 
   Ӵϴ. ׸ `' Ҹ  ͸ Ĩϴ. ,  ȭ
   ȵ˴ϴ. ̷ ؼ ð (ú `' Ҹ  )
  Ŀ ð (date   µ ð) 󸶳 ̰ 
  Ȯ   ֽϴ.
  ,    Էմϴ:

       date hh:mm:00

        ú   ִ ں 1  
     ʽÿ.  ٲ  `' Ҹ  Ű
  Ĩϴ. (  ȭ  ˴ϴ). hhκп ø
  ϴ.   ``Ŀ ð'' ߴ Դϴ.  
    Էմϴ:

       clock -w

    ̷ ϸ ο ( Ȯ) Ŀ ð谪 CMOS ð踦
  ϴ.  

       date +%j

     Էմϴ. (  ``date +%s''  ٸ ⼭
     ϴ).

    ̷ ϸ  (drift rate) ϱ  ʿ 3 ġ
  ( ¥ 2  ʴ )  Ȯ  ˴ϴ.

  2.3.3.    (correction factor)  Ѵ.

    ``date'' ؼ ð  , ý ð ?
  ƴϸ  ? ð ٸ    󸶰  ־
  ϹǷ   ˴ϴ. ð  ִٸ   
  󸶰   ־ ϹǷ   ˴ϴ.

    տ  2 ¥  մϴ. ``date +%j''  
     ׳ 1   ° ̾° ϴ  ˷ ݴϴ.
  (  1 ~ 365      1 ~ 366  
  ɴϴ).  ð    1 1 ̾ٸ  °
  ¥ ( ¥) 365 366 ؼ  ؾմϴ.
  ``date +%s''    1970  ؼ  
  Ƿ ׳       86400  ָ  
   ̿ 귯 ¥ ڿ ɴϴ.

    /etc/adjtime ̹   ִ    
     մϴ.  ( ġ) ʹ Ǵٸ 
          ȣ ٸ Դϴ.
  ׷ ʴٸ  ȣ ǰ.     
  ϰ,   ʴ    մϴ. (  ȣ 
   ʽÿ. ȣ  ٸ      ۾ մϴ.
  ׷ ʴٸ     ū  )

    ̷  ' '    ο 
  ɴϴ.   /etc/adjtime ڱ ڸ  ֽϴ. ο ¥
  () (   )  ξ   մϴ.


   ý /etc/adjtime   ϴ:

       -9.600000 845082716 -0.250655

  (Ϸ翡 9.6ʶ  Ѵ̸  5  ǹմϴ!)

  3.  xntpd ؼ

    ǻͿ δ 2 ð谡 ֽϴ. ϳ  Ǵ
  ``ǽð ð(real time clock)'' ̶ ε ý   
   ư鼭 ð ϰ ֽϴ. (ٸ δ ``CMOS ð'',
  ``ϵ ð'', ``RTC''  մϴ) ι° ``Ŀ ð'' ε
  ̰ ó  ÿ CMOS ð迡 ؼ    Ÿ̸ ͷƮ
  ؼ ŵ˴ϴ. (̰ ``Ʈ ð'' Ǵ ``ý ð''
   մϴ).      ݾ,  ٸ  Ʋ
   ð     Ȯ ð ̰ Ŀ  Ӹ ƴ϶
        ̰ Ŀ ˴ϴ.

    xntp  ``ð (the clock)'' ̶    ``Ŀ ð''
  ǹϰ ֽϴ. xntp timed (Ǵ adjtimex() ý  ϴ
  ٸ α׷)  ϴ , Ŀ ð谡 CMOS ð   Ȯϴٰ
  ϰ  11  CMOS ð踦 ٽ ϴ. (ý  ϱ
    ˴ϴ). ٽ ؼ ``clock''    CMOS ð谡
    Ǿ   , /etc/adjtime    
     ȴٴ Դϴ.

    Xntpd  ϵ ` ð (radio clock)' ġ 
  ϹǷ, ֱ NIST  ϴ ú 񽺿 ȭ Ͽ
  ð   ְ Ǿ ֽϴ. (ȭ Ŵ ð  
   ȭ ݿ Ű ʽÿ.) ̰ (xntpd)   ð
  ̻ (NIST ) ܺ ú     Ȳ 
    ̿ؼ Ŀ ð踦    ְ Ǿ ֽϴ.

    밳 ` ð' ġ 3000~4000 ޷  , 
  ``ġ (gadget box)'' (δ 300 baud )  ý۰
  ĳ CHU ú ̾     ؼ
     ֽϴ. (<ftp://ftp.udel.edu/pub/ntp/gadget.tar.Z>
   Ͻʽÿ). Heathkit WWV ű (`` Ȯ ð''  
  ϴ ǰ)    ִµ ̰  400~500 ޷  մϴ.
  GPS ȣ ð  ϰ հ  GPS ű ǻ 
  Ʈ   ְ Ǿ ֽϴ.  巡 ̷ GPS ű⸦
   ݿ   ְ   𸨴ϴ.


    ̷д ڸ, NIST ȭ ú 񽺿 ڵ ؼ 
  ڵ ϰ CMOS ð Ŀ ð踦 ڵ   ִ α׷
   ͵ մϴ.  ̷   α׷ 
  ,   Ѵٸ xntpd ҽ  ص κ 
      Դϴ.

1) NIST : National Institutes of Standards and Technology, ̱
              ǥر
2) USNO : U.S. Naval Observatory  ر 
3) WWV : NBS (̱ ǥر) ϴ, ǥ ú ۱ ȭ 
             ú ȳ 񽺵 ϰ ֽ. ѱ  116
             ȭɸ ú ȳ ɴϴ.

--̻--

