Ubuntu 22.04 LTS Cron Jobs Not Running After Timezone and DST Adjustments

📖 ~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

Expected cron tasks are skipped or run at unexpected times following timezone changes. Backups, billing, and maintenance tasks miss critical execution windows.

Environment & Reproduction

Ubuntu 22.04 LTS with cron and mixed timezone assumptions across system and application scripts. Reproduce around DST change or manual timedatectl timezone adjustments.

Root Cause Analysis

Cron interprets schedules based on system timezone unless job-level overrides exist. DST transitions can duplicate or skip wall-clock times, causing apparent job loss.

Quick Triage

Confirm current timezone and inspect cron daemon status and logs for missed invocation records around transition period.

Step-by-Step Diagnosis

Review crontab entries, environment variables, and script-level timezone handling to detect mismatches between expected and actual execution context.

Solution – Primary Fix

Set server timezone policy explicitly (often UTC), adjust cron expressions accordingly, restart cron, and log timestamped execution markers for validation.

Solution – Alternative Approaches

Move critical schedules to systemd timers with persistent mode, use application schedulers aware of business timezone, or add CRON_TZ per job where needed.

Verification & Acceptance Criteria

Jobs run at expected UTC times, no skips across restart, and audit logs confirm consistent trigger cadence through timezone boundaries.

Rollback Plan

Revert timezone setting and previous crontab backup, restart cron, and notify stakeholders of temporary schedule shift until permanent fix is approved.

Prevention & Hardening

Standardize infrastructure on UTC, document timezone-sensitive jobs, and test schedules during DST simulations in pre-production environments.

Related Errors & Cross-Refs

Related to anacron delays, incorrect script shebang environment, and system clock drift causing scheduler confusion near boundary times.

Related tutorial: View the step-by-step tutorial for Ubuntu 22.04 LTS.

View all Ubuntu 22.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

See cron(8), crontab(5), systemd.timer(5), and Ubuntu time management guidance for deterministic scheduling practices.