📖 ~1 min read
Table of contents
Symptom & Impact
Secure connections fail because host time is outside certificate validity windows or token tolerances.
Environment & Reproduction
Common on VMs with paused clocks, misconfigured NTP, or blocked time synchronization endpoints.
Root Cause Analysis
Clock drift invalidates cryptographic trust decisions that depend on accurate not-before and not-after checks.
Quick Triage
Compare system time to trusted source and inspect chrony or systemd-timesyncd service status immediately.
Step-by-Step Diagnosis
Analyze synchronization peers, offset metrics, and firewall routes to NTP servers.
Solution – Primary Fix
Correct timezone and NTP settings, force sync, and verify sustained offset within acceptable limits.
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Solution – Alternative Approaches
Use local NTP hierarchy, hardware clock sync policy, or hypervisor guest time integration tuning.
Verification & Acceptance Criteria
TLS handshakes succeed consistently and measured clock offset remains stable over monitoring period.
Rollback Plan
Reapply prior time daemon configuration if new upstream peers prove unreliable.
Prevention & Hardening
Alert on clock drift thresholds and maintain redundant trusted NTP sources for production hosts.
Related Errors & Cross-Refs
Cross-reference expired cert alerts and auth token failures with linked Ubuntu security tutorial.
Related tutorial: View the step-by-step tutorial for Ubuntu 18.04 LTS.
View all Ubuntu 18.04 LTS tutorials on the Tutorials Hub →
Browse all common problems & solutions on the Tutorials Hub.
References & Further Reading
Consult chrony docs, systemd time sync guidance, and PKI operational best practices.
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