[Dovecot] Time just moved backwards

[Bill Cole]

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.


Absolutely.

>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 
sites.

-- 
Bill Cole                                  
bill at scconsult.com