cron Jobs Not Running on Ubuntu 16.04

📖 ~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 never run, causing missed backups, stale reports, and delayed maintenance actions.

Environment & Reproduction

Ubuntu 16.04 with cron service active but jobs relying on interactive shell environment. Reproduce using relative paths or missing executable bits.

Root Cause Analysis

Cron runs with a minimal environment; scripts fail due to PATH assumptions, permissions, bad shebang, or incorrect crontab syntax.

Quick Triage

Confirm cron service status with systemctl status cron and inspect /var/log/syslog for CRON entries.

Step-by-Step Diagnosis

Run the exact command with /bin/sh in non-interactive mode, verify script permissions, and add explicit PATH and absolute paths in crontab.

Solution – Primary Fix

Correct crontab syntax, ensure scripts are executable with valid shebangs, and set required environment variables directly in crontab.

Solution – Alternative Approaches

Migrate critical recurring jobs to systemd timers for richer logging and dependency controls on Ubuntu 16.04.

Verification & Acceptance Criteria

Cron logs show expected execution at schedule time, and job outputs/artifacts are generated successfully.

Rollback Plan

Restore previous crontab from backup using crontab and disable newly added entries if side effects appear.

Prevention & Hardening

Standardize cron script wrappers, add health checks for job freshness, and centralize scheduling telemetry.

Related Errors & Cross-Refs

Connected to locale warnings, permission denied errors, and missing dependency binaries in restricted PATH.

Related tutorial: View the step-by-step tutorial for Ubuntu 16.04 LTS.

View all Ubuntu 16.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

crontab(5), cron(8), systemd.timer(5), and job reliability engineering practices.