Ubuntu 20.04 LTS – Common Problem 021 – 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

Scheduled jobs do not run, causing missed backups, reports, or maintenance tasks.

Environment & Reproduction

Ubuntu 20.04 using cron and/or systemd timers with recent script or environment changes.

Root Cause Analysis

Wrong PATH, missing executable bit, invalid crontab syntax, or timer not enabled.

Quick Triage

Check ‘systemctl list-timers –all’, ‘crontab -l’, and ‘/var/log/syslog’ for scheduler entries.

Step-by-Step Diagnosis

Run script manually with minimal env, verify user context, and inspect journalctl for unit/timer failures.

Solution – Primary Fix

Correct schedule syntax, use absolute paths, enable timer/service, and set proper script permissions.

Solution – Alternative Approaches

Migrate critical cron jobs to systemd timers for better logging and dependency handling.

Verification & Acceptance Criteria

Next run executes on schedule and expected output/artifacts are generated.

Rollback Plan

Restore previous crontab/timer units if updated schedule causes duplicate or missed runs.

Prevention & Hardening

Add job heartbeat monitoring and capture stdout/stderr to persistent logs.

Related Errors & Cross-Refs

CRON skipped due to bad minute field, systemd timer inactive, and script not found.

Related tutorial: View the step-by-step tutorial for Ubuntu 20.04 LTS.

View all Ubuntu 20.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

crontab(5), systemd.timer docs, and Ubuntu task scheduling best practices.