[Dovecot] Time just moved backwards

Bill Cole dovecot-20061108 at billmail.scconsult.com
Mon Apr 9 00:20:39 EEST 2007

At 12:03 PM -0700 4/8/07, Sean Kamath wrote:


>It's not just dovecot, by the way.  MANY things don't like have time 
>move backward, like Cron, at, etc.


>You should *NEVER* have the clock jump back in time (except during 
>DST changes -- yuk).

DST changes (at least on sane systems) do not change the system clock 
time. Time zones are a cosmetic feature, i.e. how humans are shown a 
description of time.  For example, the following are different ways 
of displaying exactly the same time:

12:03 PM -0700 4/8/07
15:03 PM EDT 4/8/07
14:03 PM EST 4/8/07
19:03 PM -0000 4/8/07
00:03 PM +0500 4/9/07

>The correct way to handle time on Unix systems is to set the clock 
>at boot (rdate, ntpdate, etc), and then *skew* the clock, so time 
>slows down to match the right time.  It can always jump forward, but 
>NTP only jumps by a (settable) maximum amount per time-quantum. 
>This prevents things like make, and NFS caching, and a bunch of 
>other stuff "just work".
>As far as I know, all shipping OSes now have a working NTP client, 
>and it's VERY easy to just add
>server pool.ntp.org
>to the ntpd.conf file, and you're good to go on reboot.

It is important for people to understand how much simpler it is now 
to run  basically functional and non-abusive NTP than it was even 5 
years ago. The work put into making pool.ntp.org usable has 
essentially eliminated the need to think much about NTP for most 

Bill Cole                                  
bill at scconsult.com

More information about the dovecot mailing list