Addition/NTP
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| - | the row " | + | 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 == | ||
Current revision as of 17:40, 26 April 2011
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
Contents |
current time
if you want to know the current time on your server just type in
| Terminal: |
# date |
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
| Terminal: |
# apt-get install ntp |
on CentOS install the package using
| Terminal: |
# yum install ntp |
configuration
afterwards you need to check the config-file for multiple lines starting with
| File: /etc/ntp.conf |
... server HOSTNAME-OF-NTP-SERVER ... ... |
extend these lines to read like that
| File: /etc/ntp.conf |
... server HOSTNAME-OF-NTP-SERVER .... minpoll 4 maxpoll 10 ... |
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
| Terminal: |
# /etc/init.d/ntp restart |
CentOS
| Terminal: |
# /etc/init.d/ntpd restart |
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.
| Terminal: |
# ntpq -n -p
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
|
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
remember to add ntp to default runlevels
on debian this is done automaticaly
for CenOS type
| Terminal: |
# chkconfig --level 345 ntpd on |
want to know more
http://en.wikipedia.org/wiki/Network_Time_Protocol
http://wiki1.dovecot.org/TimeMovedBackwards
http://wiki2.dovecot.org/TimeMovedBackwards
