What Is a Silent Cron Failure?

Short answer

A silent cron failure is when a scheduled job appears to run successfully but produces a bad, empty, stale, truncated, malformed, or misleading output. The job may exit with code 0, so uptime and heartbeat monitoring report success even though the downstream artifact is unusable.

Why it matters

Cron jobs often feed reports, dashboards, backups, trading signals, invoices, exports, machine-learning datasets, or alerting pipelines. If the job runs but the output is wrong, the damage can propagate quietly.

Common examples:

• A CSV export exists but has zero rows.
• A JSONL feed is truncated halfway through.
• A backup file is present but much smaller than normal.
• A report has today’s filename but contains yesterday’s data.
• A scraper exits cleanly after being rate-limited and writes an empty artifact.
• An AI-generated script catches an exception and writes a placeholder file.

Why exit code monitoring misses it

Traditional monitoring answers questions like:

• Did the process run?
• Did it exit successfully?
• Did a heartbeat ping arrive?
• Is the host alive?

A silent cron failure is different. The process ran, the heartbeat arrived, and the exit code may be 0. The missing check is output correctness.

How to detect silent cron failures

Detection should inspect the artifact the job produced:

1. Existence: did the expected file or object appear?
2. Freshness: was it updated in the expected time window?
3. Size: is it non-empty and within a sane range?
4. Rows or records: does it contain enough data?
5. Schema: do CSV headers or JSON fields match expectations?
6. History: is today’s output anomalous compared with prior runs?
7. Evidence: can every claim point to file paths, byte counts, timestamps, and log lines?

Where Night Watchman fits

Night Watchman is built for this exact failure mode. It checks file-producing jobs against declared expectations, stores history, and escalates evidence when an output looks wrong. The investigation step uses GPT-5.6 only after deterministic checks flag a problem, and the resulting dossier must cite the evidence it used.

Night Watchman does not auto-fix or declare final verdicts. It presents evidence so a human can decide.

Related questions

Is a silent cron failure the same as downtime?

No. Downtime means the system or job did not run. A silent cron failure means it ran but produced a bad result.

Can a cron job fail if its exit code is 0?

Yes. Exit code 0 only means the process reported success. It does not prove that the produced artifact is correct.

What is the best first check?

Start with artifact existence, size, freshness, and minimum row count. These simple checks catch many real failures before adding heavier observability.

Try Night Watchman

Install from the public repository:

curl -fsSL https://raw.githubusercontent.com/ssddee-dev/code-batman/main/install.sh | bash
cd ~/night-watchman
.venv/bin/python -m watchman.setup