Clock delay

[Robin Laing]

Juan L. Pastor wrote:
> On Sat, 2004-09-25 at 02:53, Stewart Nelson wrote:
> 
> 
>>As one of the final shutdown steps, it sets the hardware clock from
>>the system clock.  So even if the BIOS clock was not correct when you
>>started, it should be when you are done.
>>
>>Is NTP running?  If so, does the system have the correct time after it
>>comes up?  After it has been running for a while?  If you forcibly
>>kill the system, e.g. with the reset button, is the BIOS clock
>>still wrong?  How much is the error?
> 
> 
> To answer your questions:
> 
> - ntpd is not running, I don't have permanent connection to the
> internet:
> 
> [root at kalimotxo root]# chkconfig --list | grep ntp
> ntpd            0:off   1:off   2:off   3:off   4:off   5:off   6:off
> 
> - When I boot, the system has the correct time if I had set it just
> before shutting it down.
> 
> - The clock has delays just with 2.6.8-1.521 kernel (not with Win2000 or
> another kernel). The biggest delay it has is around 10 minutes, and it
> takes this delay progressively during the first two hours. Afterward, no
> more delay.
> 
> 
>>If you won't be using NTP, check the BIOS time before booting,
>>the system time right after it starts up, the system time just
>>before shutdown, and the BIOS time after shutdown.  That should
>>show whether the time is being lost at startup, during operation,
>>or at shutdown.
> 
> 
> Right after it starts up, the system time matches the BIOS time. Just
> before shutdown, it has a delay, as I said like 10 min. as maximum, just
> the same as the BIOS time, so the time is lost during operation, which
> is logical as it doesn't happen with Win2000.
> 
> Juan
> 

Now I am going to creep into the older parts of my brain to the 
pre-DSL days.

If I remember correctly, that there is a variable that is set that 
will automatically adjust the time to be more accurate.  This is 
calculated every time that the clock is reset.

from 'man hwclock'
  --adjust
               Add or subtract time from the Hardware Clock to account
               for systematic drift since the last time the clock was
               set or adjusted.
               See discussion below.

The Adjust Function
        The  Hardware Clock is usually not very accurate.  However,
        much of its inaccuracy is completely predictable -  it  gains
        or  loses  the  same amount  of time every day.  This is called
        systematic drift.  hwclock’s "adjust" function lets you make
        systematic corrections to  correct  the systematic drift.

        It works like this: hwclock keeps a file, /etc/adjtime, that
        keeps some historical information.  This is called the adjtime
        file.


It could be as simple as the adjtime may be so far out of sync the the 
system cannot keep accurate time.

I also seem to remember if the time difference is to far, it will not 
correct update the adjtime file properly.


-- 
Robin Laing