Ubuntu 18.04 LTS – cron jobs do not run at scheduled times

📖 ~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

Scheduled maintenance tasks are skipped, causing backups or reports to fail.

Environment & Reproduction

Common when cron environment assumptions differ from interactive shell behavior.

Root Cause Analysis

Cron command paths, permissions, or timing definitions prevent execution.

Quick Triage

Verify cron daemon status and inspect syslog entries for schedule triggers.

Step-by-Step Diagnosis

Test command with cron environment and review user crontab syntax.

Solution – Primary Fix

Use absolute paths, correct permissions, and explicit shell/environment settings.

Solution – Alternative Approaches

Migrate critical schedules to systemd timers with richer dependency controls.

Verification & Acceptance Criteria

Scheduled jobs execute on time and produce expected output artifacts.

Rollback Plan

Restore previous crontab definitions if new schedule introduces regressions.

Prevention & Hardening

Add heartbeat checks and alerting for missed task windows.

Related Errors & Cross-Refs

CRON entries without output and command not found in scheduled context.

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

Cron behavior, environment handling, and systemd timer migration guidance.