Addition/NTP - Revision history

Mike.f: /* date still stays seconds/minutes wrong */ it's offset :)

Mike.f — Tue, 26 Apr 2011 17:40:40 GMT

date still stays seconds/minutes wrong: it's offset :)

← Older revision		Revision as of 17:40, 26 April 2011
Line 64:		Line 64:

	</pre>}}		</pre>}}
-	the row "~~delay~~" gives you the difference that needs to be catched up. Just leave it and recheck after a cup of coffee :)	+	the row "offset" gives you the difference that needs to be catched up. Just leave it and recheck after a cup of coffee :)

	== add to default runlevels ==		== add to default runlevels ==

Mike.f: /* date still stays seconds/minutes wrong */ screen-output

Mike.f — Tue, 26 Apr 2011 17:39:02 GMT

date still stays seconds/minutes wrong: screen-output

← Older revision		Revision as of 17:39, 26 April 2011
Line 52:		Line 52:
	== date still stays seconds/minutes wrong ==		== date still stays seconds/minutes wrong ==
	don't worry - this is a feature to keep applications like dovecot alive. The time will be synced in the background and "slowly" adjusted.		don't worry - this is a feature to keep applications like dovecot alive. The time will be synced in the background and "slowly" adjusted.
-	{{cmd\|<pre># ntpq -n -p~~</pre>}}~~	+	{{cmd\|<pre># ntpq -n -p
-	~~the row "delay" gives you the difference that needs to be catched up. Just leave it and recheck after a cup of coffee :)~~	+

		+
		+	remote refid st t when poll reach delay offset jitter
		+	==============================================================================
		+	+XX.XX.XX.XX .ATOM. 1 u 2 64 377 27.695 -0.217 0.518
		+	*XXX.XXX.XXX.XXX .ATOM. 1 u 44 64 377 27.985 0.117 0.381
		+	+X.X.X.X .ATOM. 1 u 32 64 377 27.346 0.046 0.273
		+
		+
		+
		+	</pre>}}
		+	the row "delay" gives you the difference that needs to be catched up. Just leave it and recheck after a cup of coffee :)

	== add to default runlevels ==		== add to default runlevels ==

Mike.f: initial

Mike.f — Tue, 26 Apr 2011 17:27:02 GMT

initial

New page

Dovecot and OpenLDAP may react very ugly when your computer-time is not correct.

OpenLDAP needs correct time-values if you want to implement replication.
And dovecot simply stops with an Error "time moved backwards"

This problem may be seen especially on virtualized Hosts (like ESX/ESXi/Xen/KVM/...).
But also "real server" may benefit of correct time-settings

== current time ==
if you want to know the current time on your server just type in

{{cmd|<pre># date</pre>}}
compare the result with your own watch :)

== installation ==
The NTP-daemon is not installed by default on every system.

on debian you can install it using
{{cmd|<pre># apt-get install ntp</pre>}}
on CentOS install the package using
{{cmd|<pre># yum install ntp</pre>}}

== configuration ==

afterwards you need to check the config-file for multiple lines starting with
{{cfg|/etc/ntp.conf|<pre>
...
server HOSTNAME-OF-NTP-SERVER ...
...
</pre>}}
extend these lines to read like that
{{cfg|/etc/ntp.conf|<pre>
...
server HOSTNAME-OF-NTP-SERVER .... minpoll 4 maxpoll 10
...
</pre>}}
the "maxpoll" interval is quite important: it tells ntp how often to talk to the ntp-server

the last number '''10''' (= every 1024 sec) is quite reasonable on real hardware 
maybe you want to set it to 8 in virtual environments 
please '''do not''' set it below 6 (= every 64 sec) as this might be seen as abusive 
if you really want to have a very good time sync just use more server as reference

== start/restart the service ==

afterwards remember to restart your ntp-daemon
debian {{cmd|<pre># /etc/init.d/ntp restart</pre>}}
CentOS {{cmd|<pre># /etc/init.d/ntpd restart</pre>}}

== date still stays seconds/minutes wrong ==
don't worry - this is a feature to keep applications like dovecot alive. The time will be synced in the background and "slowly" adjusted.
{{cmd|<pre># ntpq -n -p</pre>}}
the row "delay" gives you the difference that needs to be catched up. Just leave it and recheck after a cup of coffee :)

== add to default runlevels ==

remember to add ntp to default runlevels

on debian this is done automaticaly 
for CenOS type {{cmd|<pre># chkconfig --level 345 ntpd on</pre>}}

== want to know more ==

http://en.wikipedia.org/wiki/Network_Time_Protocol 
http://wiki1.dovecot.org/TimeMovedBackwards 
http://wiki2.dovecot.org/TimeMovedBackwards