CentOS Stream 10 – Common Problem 190 – Diagnosis and Fix

📖 ~1 min read

Table of contents

1. Symptom & Impact
2. Environment & Reproduction
3. Root Cause Analysis
4. Quick Triage
5. Step-by-Step Diagnosis
6. Solution – Primary Fix
7. Solution – Alternative Approaches
8. Verification & Acceptance Criteria
9. Rollback Plan
10. Prevention & Hardening
11. Related Errors & Cross-Refs
12. References & Further Reading

Symptom & Impact

chronyc tracking shows large offset or ‘Not synchronised’.

Environment & Reproduction

Restrictive firewalls or wrong upstream pools in /etc/chrony.conf.

rpm -q chrony
chronyc tracking

Root Cause Analysis

Outbound NTP (UDP 123) blocked or all sources unreachable.

Quick Triage

Check source reachability and selection.

chronyc sources -v
ss -uan | grep ':123'

Step-by-Step Diagnosis

Confirm firewall rules and DNS for pool members.

firewall-cmd --list-all
getent hosts 2.centos.pool.ntp.org

Solution – Primary Fix

Adjust upstream sources and reload chrony.

sed -i 's/^server .*/server 0.centos.pool.ntp.org iburst/' /etc/chrony.conf
systemctl restart chronyd
chronyc makestep

Solution – Alternative Approaches

Use internal NTP server if outbound is filtered.

echo 'server ntp.internal iburst' >> /etc/chrony.conf
systemctl restart chronyd

Verification & Acceptance Criteria

chronyc tracking reports a small offset and ‘Normal’.

chronyc tracking
chronyc sources -v

Rollback Plan

Restore prior chrony.conf.

cp /etc/chrony.conf.bak /etc/chrony.conf && systemctl restart chronyd

Prevention & Hardening

Document NTP egress in the firewall change record.

firewall-cmd --permanent --add-service=ntp && firewall-cmd --reload

Related Errors & Cross-Refs

Clock drift, kerberos clock skew, TLS cert validation errors.

Related tutorial: View the step-by-step tutorial for centos-stream-10.

View all centos-stream-10 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

chrony docs, time keeping best practice.