Ubuntu 18.04 LTS Time Drift Breaks Kerberos and TLS

📖 ~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

Authentication and HTTPS sessions fail due to large system clock offsets.

Environment & Reproduction

Occurs on isolated or virtualized Ubuntu 18.04 hosts with unstable NTP synchronization.

Root Cause Analysis

Drift accumulates when NTP services are misconfigured, blocked, or competing for time source control.

Quick Triage

Check timedatectl, compare time against trusted source, and inspect active NTP daemon state.

Step-by-Step Diagnosis

Review chrony or systemd-timesync logs, verify UDP 123 reachability, and measure offset trends.

Solution – Primary Fix

Configure reliable NTP servers, ensure one time daemon is active, and force synchronization if offset is severe.

Solution – Alternative Approaches

Use internal stratum servers or hypervisor-provided time sync as backup.

Verification & Acceptance Criteria

Clock offset remains within policy and Kerberos/TLS operations succeed consistently.

Rollback Plan

Restore prior NTP configuration files and restart time service if new settings fail.

Prevention & Hardening

Monitor offset metrics and alert on time skew before authentication starts failing.

Related Errors & Cross-Refs

Related issues include certificate not yet valid errors and AD login rejections.

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

See chrony docs, Ubuntu time synchronization guidance, and Kerberos clock skew limits.