List of NTP-Servers

If you don’t use NTP service daemon but use a command to sync time at once, use ntpdate like follows.

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# yum -y install ntpdate
# ntpdate 0.at.pool.ntp.org
# systemctl enable ntpdate
# systemctl start ntpdate

The Chrony Package

Install the Chrony service:

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# yum install -y chrony
# systemctl enable chronyd
# systemctl start chronyd

The Chrony configuration is in the /etc/chrony.conf file:

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# chronyc tracking
Reference ID : 94.23.44.157 (merzhin.deuza.net)
Stratum : 3
Ref time (UTC) : Thu Jul 3 22:26:27 2014
System time : 0.000265665 seconds fast of NTP time
Last offset : 0.000599796 seconds
RMS offset : 3619.895751953 seconds
Frequency : 0.070 ppm slow
Residual freq : 0.012 ppm
Skew : 0.164 ppm
Root delay : 0.030609 seconds
Root dispersion : 0.005556 seconds
Update interval : 1026.9 seconds
Leap status : Normal

To get information about the main time reference, type:

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# chronyc sources -v
210 Number of sources = 4

.-- Source mode '^' = server, '=' = peer, '#' = local clock.
/ .- Source state '*' = current synced, '+' = combined , '-' = not combined,
| / '?' = unreachable, 'x' = time may be in error, '~' = time too variable.
|| .- xxxx [ yyyy ] +/- zzzz
|| / xxxx = adjusted offset,
|| Log2(Polling interval) -. | yyyy = measured offset,
|| \ | zzzz = estimated error.
|| | |
MS Name/IP address Stratum Poll Reach LastRx Last sample
===============================================================================
^+ merlin.ensma.fr 2 6 77 61 +295us[+1028us] +/- 69ms
^* lafkor.de 2 6 77 61 -1371us[ -638us] +/- 65ms
^+ kimsuflol.iroqwa.org 3 6 77 61 -240us[ -240us] +/- 92ms
^+ merzhin.deuza.net 2 6 77 61 +52us[ +52us] +/- 48ms

# chronyc sourcestats -v
210 Number of sources = 4
.- Number of sample points in measurement set.
/ .- Number of residual runs with same sign.
| / .- Length of measurement set (time).
| | / .- Est. clock freq error (ppm).
| | | / .- Est. error in freq.
| | | | / .- Est. offset.
| | | | | | On the -.
| | | | | | samples. \
| | | | | | |
Name/IP Address NP NR Span Frequency Freq Skew Offset Std Dev
==============================================================================
merlin.ensma.fr 7 5 200 0.106 6.541 +381us 176us
lafkor.de 7 4 199 0.143 10.145 -916us 290us
kimsuflol.iroqwa.org 7 7 200 -0.298 6.717 +69us 184us
merzhin.deuza.net 7 5 200 0.585 11.293 +675us 314us

To quickly synchronize a server, type:

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# ntpdate pool.ntp.org