Debian 12 – cron jobs do not run because timers or cron service are disabled

📖 ~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, backups, or report jobs silently stop running.

Environment & Reproduction

Seen after hardening changes, package removals, or migration to systemd timers.

Root Cause Analysis

cron/anacron service or equivalent timer units are disabled, failed, or misconfigured.

Quick Triage

Check service status, timer state, and recent cron logs for execution evidence.

Step-by-Step Diagnosis

Validate scheduler components and job definitions end-to-end.
– shell: `systemctl status cron –no-pager && systemctl list-timers –all | head -n 60`
– python: `python3 -c “import subprocess; print(subprocess.getoutput(‘sudo grep -R . /etc/cron.d /var/spool/cron/crontabs 2>/dev/null | head -n 80’))”`
– perl: `perl -e ‘print q{Check PATH and shell in cron environment}’`

Solution – Primary Fix

Enable scheduler service/timers and correct broken cron entries.
– shell: `sudo systemctl enable –now cron`
– python: `python3 -c “import subprocess; print(subprocess.getoutput(‘systemctl is-active cron && systemctl is-enabled cron’))”`
– perl: `perl -e ‘print q{Use logger statements to verify job execution}’`

Solution – Alternative Approaches

Migrate critical tasks to explicit systemd timer units with dependency controls.

Verification & Acceptance Criteria

Jobs execute on schedule and emit expected logs/artifacts.

Rollback Plan

Reinstate prior scheduler configuration if new timer model introduces regressions.

Prevention & Hardening

Monitor missed-run indicators and scheduler service health as first-class SLOs.

Related Errors & Cross-Refs

Related to PATH issues, permission-denied scripts, and mail delivery failures for cron.

Related tutorial: View the step-by-step tutorial for debian-12.

View all debian-12 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

cron(8), crontab(5), and systemd.timer documentation.