Ubuntu 18.04 LTS Cron Jobs Stop Running Due to PAM or Permission Changes

📖 ~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 and data pipelines fail silently, causing operational drift.

Environment & Reproduction

Ubuntu 18.04 after PAM updates, file permission changes, or service disablement.

Root Cause Analysis

Cron daemon state, user allow/deny lists, or executable permissions prevent task execution.

Quick Triage

Confirm cron service status and inspect syslog entries around expected run times.

Step-by-Step Diagnosis

Validate crontab syntax, environment variables, PAM auth logs, and script ownership/execute bits.

Solution – Primary Fix

Re-enable cron, repair PAM/permissions, and test tasks with explicit paths and logging.

Solution – Alternative Approaches

Migrate critical jobs to systemd timers for better observability and dependency control.

Verification & Acceptance Criteria

Jobs execute on schedule and produce expected output and logs over multiple intervals.

Rollback Plan

Restore prior cron and PAM configuration backups if changes break authentication flow.

Prevention & Hardening

Monitor job success metrics and enforce script permission checks in change review.

Related Errors & Cross-Refs

Related incidents include missing PATH in cron context and silent script runtime 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

See cron, crontab, and Ubuntu automation reliability guidance.