News
Abstract
This article contains:
* How to troubleshoot chrony issues.
* NTP techniques for accurate and reliable time synchronization.
* How to verify that Chrony clients are synchronizing correctly with NTP servers.
Content
Note: IBM recommends that servers configure at least four time sources.
- Chrony is a pair of programs that are used to maintain the accuracy of the system clock on a computer.
-
Chrony consists of:
* chronyd, a daemon that runs in user space, and
*- chronyc, a command line program for making adjustments to chronyd. -
Some useful commands are:
# chronyc activity
# chronyc ntpdata
# chronyc -n sources -v
# chronyc -n sourcestats -v
# chronyc -n tracking
# systemctl status chronyd
# timedatectl
- Here are some output examples:
# chronyc activity
200 OK
4 sources online
0 sources offline
0 sources doing burst (return to online)
0 sources doing burst (return to offline)
0 sources with unknown address
# chronyc -n 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
|| Reachability register (octal) -. | xxxx = adjusted offset,
|| Log2(Polling interval) --. | | yyyy = measured offset,
|| \ | | zzzz = estimated error.
|| | | \
MS Name/IP address Stratum Poll Reach LastRx Last sample
===============================================================================
^+ 200.160.0.8 2 6 377 60 -7418us[-6893us] +/- 21ms
^+ 201.73.152.122 2 6 377 58 -9712us[-9187us] +/- 169ms
^+ 200.189.40.8 2 6 377 60 +36ms[ +37ms] +/- 83ms
^* 200.160.7.186 1 6 377 56 -6725us[-6200us] +/- 176ms
Note 1: The second character on the server lines should always be a '-', '+', or '*' after running for a while, otherwise the server is having trouble.
Note 2: If Reach is not 377 (octal) and Chrony has been running for a while then access to that server is having connection issues.
Note 3: If LastRx is higher than Poll time (2^X seconds) then the server is having connection issues and it should be reflected in Reach as well.
# chronyc -n 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
==============================================================================
200.160.0.8 15 7 718 2.197 10.669 -7221us 2248us
201.73.152.122 13 7 721 -0.203 2.476 -10ms 463us
200.189.40.8 15 8 718 0.729 9.211 +36ms 2088us
200.160.7.186 8 6 522 -1.902 7.489 -6332us 606us
# chronyc -n tracking
Reference ID : 200.160.7.186 (200.160.7.186)
Stratum : 2
Ref time (UTC) : Wed Nov 5 18:45:23 2014
System time : 0.000799330 seconds fast of NTP time
Last offset : 0.000525316 seconds
RMS offset : 0.015844775 seconds
Frequency : 0.971 ppm fast
Residual freq : -0.002 ppm
Skew : 2.283 ppm
Root delay : 0.349031 seconds
Root dispersion : 0.000644 seconds
Update interval : 65.6 seconds
Leap status : Normal
# systemctl status -l chronyd
chronyd.service - NTP client/server
Loaded: loaded (/usr/lib/systemd/system/chronyd.service; enabled)
Active: active (running) since Wed 2014-11-05 13:34:24 EST; 12min ago
Process: 1921 ExecStartPost=/usr/libexec/chrony-helper add-dhclient-servers (code=exited, status=0/SUCCESS)
Process: 1918 ExecStart=/usr/sbin/chronyd -u chrony $OPTIONS (code=exited, status=0/SUCCESS)
Main PID: 1920 (chronyd)
CGroup: /system.slice/chronyd.service
└─1920 /usr/sbin/chronyd -u chrony
Nov 05 13:34:24 chrony-cli.example.lab chronyd[1920]: chronyd version 1.29.1 starting
Nov 05 13:34:24 chrony-cli.example.lab chronyd[1920]: Linux kernel major=3 minor=10 patch=0
Nov 05 13:34:24 chrony-cli.example.lab chronyd[1920]: hz=100 shift_hz=7 freq_scale=1.00000000 nominal_tick=10000 slew_delta_tick=833 max_tick_bias=1000 shift_pll=2
Nov 05 13:34:24 chrony-cli.example.lab chronyd[1920]: Frequency 0.266 +/- 0.248 ppm read from /var/lib/chrony/drift
Nov 05 13:34:24 chrony-cli.example.lab systemd[1]: Started NTP client/server.
Nov 05 13:34:30 chrony-cli.example.lab chronyd[1920]: Selected source 200.160.7.186
# timedatectl
Local time: Wed 2014-11-05 13:48:16 EST
Universal time: Wed 2014-11-05 18:48:16 UTC
RTC time: Wed 2014-11-05 18:48:15
Timezone: America/New_York (EST, -0500)
NTP enabled: yes
NTP synchronized: no
RTC in local TZ: no
DST active: no
Last DST change: DST ended at
Sun 2014-11-02 01:59:59 EDT
Sun 2014-11-02 01:00:00 EST
Next DST change: DST begins (the clock jumps one hour forward) at
Sun 2015-03-08 01:59:59 EST
Sun 2015-03-08 03:00:00 EDT
If chronyd is unable to see any servers, the following may be helpful.
The resulting chronyd.output and chronyd.strace files may reveal the reason it can't communicate.
# systemctl stop chronyd
# strace -fttTvyys 4096 -o chronyd.strace chronyd -d -d -q > chronyd.output 2>&1
# systemctl start chronyd
- Additional References:
* NTP deployment strategies for resilient time synchronization
* /usr/share/doc/chrony*
[{"Type":"MASTER","Line of Business":{"code":"LOB66","label":"Technology Lifecycle Services"},"Business Unit":{"code":"BU070","label":"IBM Infrastructure"},"Product":{"code":"SSSEWFV","label":"Storage Fusion Data Foundation"},"ARM Category":[{"code":"a8m3p000000UoIPAA0","label":"Support Reference Guide"}],"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"All Versions"}]
Was this topic helpful?
Document Information
Modified date:
27 August 2025
UID
ibm17171543