[Dovecot] Time just moved backwards

Bill Cole dovecot-20061108 at billmail.scconsult.com
Sun Apr 8 21:00:29 EEST 2007

At 7:25 PM +0200 4/8/07, Chaos Engine wrote:
>Hi there,
>I got a daily cron (rdate to local time server) job wich adjusts time and
>which constantly gives me headache.
>Every day my dovecot suicides with:
>"dovecot: Time just moved backwards by 11 seconds. This might cause a lot of
>problems, so I'll just kill myself now."
>Of course my onboard clock is constantly off by more than 5 secs.

How "of course?"

The last time I had a machine's NTP synch stop working, it diverged 
less than 2 seconds from reality in a week. Looking at a few machines 
where the LOM cards have RTC's independent of the motherboard RTC's, 
I see divergence of 0-4 seconds  over the past 2 months.

>I don't want
>to abandon time synchronization and I want to use dovecot. Maybe a
>-HUP signal would do? What do you propose?

3 options

1. Repair your hardware. Gaining 5 seconds per day is not normal, and 
really should not be tolerated in a system that has to converse with 
other machines.
2. Set up something that will do the adjustment for you on a more 
continuous basis. Xntpd will track your drift and keep you more in 
sync on a continuous basis by slewing the clock rather than stepping 
it back daily.
3. Make that cron job smarter but stopping Dovecot (and anything else 
that might care about time moving backwards) ahead of the change, and 
then waiting until your clock is back ahead of that to restart them.

There are technical strategies (e.g. Maildir naming) which rely on 
the assumption of the clock never repeating the same second twice.
Bill Cole                                  
bill at scconsult.com

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