dovecot - May 2007 - Return error instead of dying on time back skip?

Hello everybody!

Currently, dovecot just kills itself if it detects that time has moved 
backwards more than a hardcoded number of seconds. I accept the 
reasons, but I do not like to restart dovecot manually after waiting 
for time to move forward again. A cron job would not help, because 
time might still be wrong when it restarts dovecot.

All our systems run ntpd, but they might be offline for a while before 
they get contact to a time server, e.g. because of DSL problems. When 
they do get contact and time is too far off, ntpd sets the new time 
directly (yes, it could gradually do that, but it might take ages).

Now I wonder if Dovecot could return errors to the users instead of 
dying until time is fine again, e.g. "System time has moved 
backwards, please come back in n seconds". If the time skip is just a 
few seconds, it can of course delay and then go on as it does now. 

With this change, no admin would be needed to carefully restart 
Dovecot at the right time. I have not looked into Dovecot code myself 
yet, but could try a patch if necessary.

Amon Ott
-- 
Amon Ott - m-privacy GmbH
Am K?llnischen Park 1, 10179 Berlin
Tel: +49 30 24342334
Fax: +49 30 24342336
Web: http://www.m-privacy.de
Handelsregister:
 Amtsgericht Charlottenburg HRB 84946
Gesch?ftsf?hrer:
 Dipl.-Kfm. Holger Maczkowsky,
 Roman Maczkowsky
GnuPG-Key-ID: EA898571

Amon Ott wrote:
> All our systems run ntpd, but they might be offline for a while before 
> they get contact to a time server, e.g. because of DSL problems. When 
> they do get contact and time is too far off, ntpd sets the new time 
> directly (yes, it could gradually do that, but it might take ages).
You might want to consider using clockspeed:

	http://cr.yp.to/clockspeed.html

instad of ntpd, since clockspeed handles the underlying clock skew in a 
more robust fashion.  This software needs only a couple of connections 
to figure out how bad the underlying hardware clock skews and 
automatically adjusts it in a smooth fashion.

If you haven't used Dan Bernstein's software before, you will probably 
want to use clockspeed-conf:

	http://foo42.de/devel/sysutils/clockspeed-conf/

to manage the daemons.

John

-- 
John Peacock
Director of Information Research and Technology
Rowman & Littlefield Publishing Group
4501 Forbes Boulevard
Suite H
Lanham, MD  20706
301-459-3366 x.5010
fax 301-429-5748

Hello Amon,

Amon Ott, 02.05.2007 (d.m.y):
> All our systems run ntpd, but they might be offline for a while before 
> they get contact to a time server, e.g. because of DSL problems. 
Define one of your "internal" systems as "master time
server" that
connects to other NTP servers outside your networks and make your
other systems synchronize their system time with this machine.

Gruss/Regards,
Christian Schmidt

-- 
Writing is easy; all you do is sit staring at the blank sheet of paper until
drops of blood form on your forehead.
		-- Gene Fowler

On Friday 04 May 2007 10:07, Christian Schmidt wrote:
> Hello Amon,
>
> Amon Ott, 02.05.2007 (d.m.y):
> > All our systems run ntpd, but they might be offline for a while
> > before they get contact to a time server, e.g. because of DSL
> > problems.
>
> Define one of your "internal" systems as "master time
server" that
> connects to other NTP servers outside your networks and make your
> other systems synchronize their system time with this machine.
Thanks for the tip, but these are customer systems. Most of them only 
buy one server system from us and have Windows clients behind. So 
there is no other system available, which could be master. Instead, 
our server is supposed to be time master. :)

From customer point of view, the mail server does not work without 
reason. An error message would help to understand the problem and the 
proposed behaviour would keep dovecot running. Now some of them just 
reboot the system (Windows users...), this is not the desired 
solution.

Amon Ott
-- 
Amon Ott - m-privacy GmbH
Am K?llnischen Park 1, 10179 Berlin
Tel: +49 30 24342334
Fax: +49 30 24342336
Web: http://www.m-privacy.de
Handelsregister:
 Amtsgericht Charlottenburg HRB 84946
Gesch?ftsf?hrer:
 Dipl.-Kfm. Holger Maczkowsky,
 Roman Maczkowsky
GnuPG-Key-ID: EA898571

On Wed, 2007-05-02 at 10:52 +0200, Amon Ott wrote:
> Now I wonder if Dovecot could return errors to the users instead of 
> dying until time is fine again, e.g. "System time has moved 
> backwards, please come back in n seconds". If the time skip is just a 
> few seconds, it can of course delay and then go on as it does now. 
> 
> With this change, no admin would be needed to carefully restart 
> Dovecot at the right time. I have not looked into Dovecot code myself 
> yet, but could try a patch if necessary. 
I think this is just way too much trouble for handling a situation that
really shouldn't be happening in the first place.. The code already
allows the clock to move backwards by 5 seconds without dying, so how
horrible are the clocks in those computers? :)

It's anyway easy to increase that time by modifying the sources.
src/lib/ioloop.c IOLOOP_MAX_TIME_BACKWARDS_SLEEP

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On 11/05/07, Timo Sirainen <tss at iki.fi> wrote:
>
> On Wed, 2007-05-02 at 10:52 +0200, Amon Ott wrote:
>
> > Now I wonder if Dovecot could return errors to the users instead of
> > dying until time is fine again, e.g. "System time has moved
> > backwards, please come back in n seconds". If the time skip is
just a
> > few seconds, it can of course delay and then go on as it does now.
> >
> > With this change, no admin would be needed to carefully restart
> > Dovecot at the right time. I have not looked into Dovecot code myself
> > yet, but could try a patch if necessary.
>
> I think this is just way too much trouble for handling a situation that
> really shouldn't be happening in the first place.. The code already
> allows the clock to move backwards by 5 seconds without dying, so how
> horrible are the clocks in those computers? :)
>
> It's anyway easy to increase that time by modifying the sources.
> src/lib/ioloop.c IOLOOP_MAX_TIME_BACKWARDS_SLEEP
>
>
Just to add that I've also been bitten by this upon updating from rc18 to
1.0.0. My current kludge is to restart Dovecot in a cron till I try
recompiling/fixing it.

I'm running under a Virtuozzo VPS and there is no way to run ntp. The
underlying server is ntp sync'd anyway and that gets passed up to the VPSs.
So this shouldn't really be happening. It usually kills itself after about
40-50 minutes of running (although the time varies) so Dovecot is
'seeing'
over 5 secs of slippage in an hour, which is unlikely.
FWIW, I run a couple of servers with Virtuozzo and no other software has
registered a problem.

cheers
jalal