Ubuntu 18.04 LTS – Common Problem 023 – 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 tasks do not execute, causing missed backups, reports, or maintenance jobs.

Environment & Reproduction

Ubuntu 18.04 using cron with scripts that rely on interactive shell PATH or unset environment variables.

Root Cause Analysis

cron runs with minimal environment; scripts fail due to missing absolute paths, permissions, or shell assumptions.

Quick Triage

Check systemctl status cron and inspect /var/log/syslog for CRON entries and exit codes.

Step-by-Step Diagnosis

Execute the same command with env -i to simulate cron environment and capture missing PATH or locale dependencies.

Solution – Primary Fix

Use absolute paths, define PATH/SHELL in crontab, set executable bits, and redirect output for diagnostics.

Solution – Alternative Approaches

Migrate critical jobs to systemd timers for clearer dependency and logging control.

Verification & Acceptance Criteria

Jobs run on schedule, expected outputs are produced, and failures are observable in logs.

Rollback Plan

Restore previous crontab from backup and disable newly added job entries if side effects occur.

Prevention & Hardening

Standardize script wrappers with explicit environment and centralized logging.

Related Errors & Cross-Refs

command not found in cron, permission denied, and silent task failures.

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

man 5 crontab, man cron, and systemd timer migration notes.