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Tag Archive for 'ntp'

Installing NTP (time synchronisation)

Published on May 19, 2005 in Linux. 0 Comments Tags: , , , .
Set timezone (optional)
create symbolical link from /usr/share/zoneinfo/... to /etc/localtime:
ln -sf /usr/share/zoneinfo/Europe/Brussels /etc/localtime
Set UTC mode (optional)
if your hardware clock runs in UTC (Universal Coordinated Time) mode, add
UTC=true
to the /etc/sysconfig/clock file
Make sure ntpd is not running
Use service ntpd stop to stop it.
Choose the NTP server you will get your time from
it can be an internal server that has the NTP service open for clients, or an public NTP server. To be sure, use 2 servers. To check if you can access it, run ntpdate timeserver.ntp.ch
Edit the /etc/ntp.conf file
Rename the current file to ntp.bak.conf and make a small new one:
restrict default ignore
server timeserver.ntp.ch # Swiss time
server ntp.ucsd.edu # Univ of California, San Diego
restrict timeserver.ntp.ch mask 255.255.255.255 nomodify notrap noquery
restrict ntp.ucsd.edu mask 255.255.255.255 nomodify notrap noquery
server 127.127.1.0 # local clock
fudge 127.127.1.0 stratum 10 #so it only takes over if the rest fails
restrict 127.0.0.1 driftfile /etc/ntp/drift broadcastdelay 0.008 authenticate no
Set your system clock right
Run the following command a couple of times:
ntpdate -u timeserver.ntp.ch # or whatever server you want to use
You will see the initial diffence in time go away afer the 2nd or 3rd time.
Set hardware clock
/sbin/hwclock --systohc
Run the ntpd daemon
service ntpd start
Add ntpd to the services started at boot time
chkconfig ntpd on
Check the NTP results
ntpd -p
will show you what the difference is between your clock and that of the servers you added. You are looking for lines like

remote refid st t when poll reach delay offset jitter
==========================================================================
LOCAL LOCAL 10 l 30 64 377 0.000 0.000 0.004 *
192.168.246.107 192.168.246.88 3 u 41 128 177 0.313 5.598 0.345
and not lines like

remote refid st t when poll reach delay offset jitter
==========================================================================
192.168.246.126 LOCAL 11 u 37 128 375 0.204 6082.02 6069.84
Jitter is too high!