[Dovecot] dovecot and ntp: Fatal: Time just moved backwards

[Juergen Daubert]

On Wed, Jun 10, 2009 at 01:01:28AM +0400, Eugene wrote:
> Hello
>
> From: "Timo Sirainen" <tss at iki.fi>
>>> But really, all this leads is that admin has to detect the dovecot  
>>> termination and simply go and restart it manually -- after some bad  
>>> thoughts.
>> Or the admin actually permanently fixes the time.
>
> In most cases we talk about, it can't be fixed permanently because this  
> happens after (cold or warm) system restart, when ntpd can take up to 15  
> minutes (and in most cases about 3-5 minutes) to actually resync the 
> time.

With chrony it can be fixed, almost. 

What chrony does, besides acting as an NTP client when online, is to 
compare the hw clock to the system clock (kept in time via ntp) and 
determine the offset and rate of the hardware clock. 

When you start up your computer with chrony's -r -s options, it reads 
the file, and corrects the time read from the harware clock according 
to the offset and rate error of the hardware clock. 

The hardware clock rate changes by ppm so this is not perfect, e.g. 
if the computer is off for a week, it may well be out by a second, 
but of course if you did not do the rate correction it could be out 
by 10-100 sec.
 

regards
Juergen

-- 
Juergen Daubert  |  mailto:jue at jue.li  
Korb, Germany    |  http://jue.li/crux