ntp won't set clock [Was clock.redhat.com question]

[Corné Beerse]

Steve Blackwell wrote:
> On 05/13/2004 10:17:37 AM, Corné Beerse wrote:
> 
>> Steve Blackwell wrote:
>>
>>> Last weekend, a lightning stike knocked out a switch which was   
>>> connecting my ntp server. As a result my ntp server's time is off 
>>> by   about 3 days.
>>>
>>> After rebooting the switch and the server, the server will not set  
>>> the  correct time. I'm using the -g option to ntpd.
>>
>>
>>
>> Most systems start with the time found in the bios.
>> Then ntp only updates the time if it is within reasonable limits  
>> (couple of minutes or up to an hour).
> 
> 
> The way I understand it is that if you use the -g option when ntpd is  
> started, asI have done, it does a one time update of the clock  
> regardless of the time difference. But in my case, it seems that the -g  
> flag was ignored. I am curious as to why. Here is the section of the  
> ntpd man page for the -g option:
> 
> -g      Normally, ntpd  exits if the offset exceeds the  sanity  limit,
>        which is 1000 s by default. If the sanity limit is set to 
> zero,                         no sanity checking is performed and any 
> offset  is  acceptable.
>        This  option  overrides the limit and allows the time to be 
> set                                 to any value without restriction; 
> however, this can happen only
>        once.   After  that,  ntpd  will exit if the limit is exceeded.
>        This option can be used with the -q  option.
> 
> The other strange thing is that since I am off by >1000s, why hasn't  
> ntpd exited?


In short, the -g option removes the sanity limit once. Now ntpd tries to correct 
the time even if it is way out of sync. ntpd by default does not set the new 
time but it slows or speeds the clock to get in sync. This is up to a couple of 
miliseconds per second. Hence 1 or 2 minutes per hour.

You should read the last line about the -p option as a hint: That realy sets the 
time.

Most configurations start with an `ntpdate` followed by `ntpd`. Current 
implementations can do so at once with `ntpd -p -g`.


CBee


> 
> Steve.
>                                                                                 
> 
>