Debian 9 – cron jobs stop running due to anacron or timer overlap

📖 ~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 automation misses execution windows and downstream jobs produce stale output.

Environment & Reproduction

Frequent where cron, anacron, and systemd timers overlap without ownership clarity.

# Capture baseline
systemctl status cron --no-pager
crontab -l
ls -l /etc/cron.*
systemctl list-timers --all | head -n 40

Root Cause Analysis

Environment differences, overlap suppression, or daemon state issues prevent expected task execution.

Quick Triage

Confirm scheduler service health and recent execution evidence first.

# Quick triage
ps -ef | grep cron
tail -n 100 /var/log/syslog | grep CRON
run-parts --test /etc/cron.daily

Step-by-Step Diagnosis

Validate job syntax, executable permissions, and runtime PATH assumptions.

# Detailed diagnosis
crontab -l | sed -n 1,80p
namei -l /path/to/script
env -i /bin/sh -c /path/to/script

Solution – Primary Fix

Correct schedule definitions, declare full PATH, and restart scheduling services.

# Primary fix
( crontab -l; echo PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin ) | crontab -
sudo systemctl restart cron

Solution – Alternative Approaches

Migrate critical tasks to systemd timers for stronger observability.

# Alternatives
systemctl list-timers --all
sudo systemctl enable --now .timer

Verification & Acceptance Criteria

Jobs execute on schedule and produce expected artifacts without manual retries.

# Verify
grep CRON /var/log/syslog | tail -n 40
ls -l /var/log/.log

Rollback Plan

Restore previous crontab from backup if schedule behavior regresses.

# Rollback
crontab /var/backups/root.crontab 2>/dev/null || true
sudo systemctl restart cron

Prevention & Hardening

Use absolute paths and add monitoring for missed runs and non-zero exits.

# Hardening
crontab -l
systemctl list-timers --all | grep 

Related Errors & Cross-Refs

Related to stale backups, delayed reports, and timer overlap suppression.

Related tutorial: View the step-by-step tutorial for Debian 9.

View all Debian 9 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Debian cron, anacron, and systemd timer operations references.