# CronSentry (now CronRabbit) - Full Technical Manual

> Complete integration instructions, developer documentation, cron syntax guide, and tool details for CronSentry and CronRabbit.

- [Back to Main Index](https://www.cronsentry.com/llm.txt)

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## 1. Introduction to Cron Job Monitoring

Cron jobs are often silent failures. They run in the background via daemon executors (like `cron` or `systemd-cron`), meaning that when a job fails, hangs, or crashes, it frequently goes unnoticed until it causes downstream data inconsistencies, missed backups, or business process failures.

Common reasons for cron job failures:
1. **Environment Mismatches**: Crontabs run with a restricted shell environment (often `/bin/sh` instead of `/bin/bash`) and minimal `PATH` variables.
2. **Resource Exhaustion**: The script runs out of memory (OOM), disk space, or database connections.
3. **Overlapping Executions**: A previous execution takes longer than the schedule frequency, causing concurrent runs that lock resources or crash.
4. **Network Outages**: External API dependencies are unreachable.

CronSentry (now CronRabbit) solves this using **Heartbeat / Push-based Monitoring**. Instead of checking if a server is online, the job itself pings CronRabbit when it runs successfully. If CronRabbit does not receive a ping within a scheduled window (plus a defined grace period), it immediately alerts the developers.

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## 2. Integration Architectures & Snippets

Integrating CronRabbit into your infrastructure is incredibly easy and requires no persistent agents.

### A. The Simple Append Pattern (stdout / stderr ignoring)
Simply append a command to ping CronRabbit upon successful execution (`&&`) of your task.

```bash
# Ping CronRabbit only if script.sh completes with exit code 0
0 * * * * /path/to/script.sh && curl -s https://endpoint.cronrabbit.com/ping/YOUR-UNIQUE-UUID > /dev/null 2>&1
```

### B. The Exit Status Safe Pattern
To capture both successes and failures, use a conditional block or inline shell logic. This ensures CronRabbit is notified whether the task succeeded or failed, allowing for rich alerting.

```bash
# Capture status and ping appropriate endpoints
0 * * * * /path/to/script.sh; [ $? -eq 0 ] && curl -s https://endpoint.cronrabbit.com/ping/YOUR-UNIQUE-UUID || curl -s https://endpoint.cronrabbit.com/fail/YOUR-UNIQUE-UUID
```

### C. Advanced Shell Wrapper Script
For complex cron jobs, we recommend using a standard wrapper script. This captures the execution duration, standard output (stdout), and standard error (stderr), and posts them to CronRabbit for debugging.

```bash
#!/bin/bash
# cron-wrapper.sh
# Usage: ./cron-wrapper.sh "YOUR-UNIQUE-UUID" /path/to/actual-job.sh arg1 arg2

JOB_ID="$1"
shift
API_URL="https://endpoint.cronrabbit.com/ping/${JOB_ID}"
FAIL_URL="https://endpoint.cronrabbit.com/fail/${JOB_ID}"

start_time=$(date +%s%N)

# Execute the job and capture output
output=$("$@" 2>&1)
exit_code=$?

end_time=$(date +%s%N)
duration_ms=$(( (end_time - start_time) / 1000000 ))

if [ $exit_code -eq 0 ]; then
  # Success: Send duration and standard output
  curl -s -X POST -H "Content-Type: application/json" \
    -d "{\"status\":\"success\", \"duration_ms\": $duration_ms, \"output\": \"$(echo "$output" | tail -c 2000 | jq -sRr @json)\"}" \
    "$API_URL" > /dev/null
else
  # Failure: Send exit code and standard error
  curl -s -X POST -H "Content-Type: application/json" \
    -d "{\"status\":\"fail\", \"exit_code\": $exit_code, \"duration_ms\": $duration_ms, \"output\": \"$(echo "$output" | tail -c 2000 | jq -sRr @json)\"}" \
    "$FAIL_URL" > /dev/null
fi
```

### D. Systemd Service Integration
If you are using systemd timers instead of traditional cron jobs, you can use the `OnFailure` directive in your service unit to trigger notifications, or use `ExecStopPost` to ping CronRabbit on job completion.

```ini
# /etc/systemd/system/backup.service
[Unit]
Description=Daily Database Backup
OnFailure=backup-failure@%n.service

[Service]
Type=oneshot
ExecStart=/usr/local/bin/backup-db.sh
ExecStopPost=/usr/bin/curl -s https://endpoint.cronrabbit.com/ping/YOUR-UNIQUE-UUID
```

---

## 3. Visual Cron Generator Tool Details

CronSentry provides a fully featured, interactive visual **Cron Generator** tool to help developers build and validate cron schedules without having to parse complex syntax in their heads.

### Cron Format Syntax Guide
A standard cron expression consists of 5 fields separated by whitespace:
```
┌───────────── minute (0 - 59)
│ ┌───────────── hour (0 - 23)
│ │ ┌───────────── day of the month (1 - 31)
│ │ │ ┌───────────── month (1 - 12)
│ │ │ │ ┌───────────── day of the week (0 - 6) (Sunday to Saturday; 7 is also Sunday on some systems)
│ │ │ │ │
* * * * *
```

### Supported Special Characters
- `*` (Asterisk): Matches all values in the field. (e.g., `*` in the hour field means "every hour").
- `,` (Comma): Separates a list of values. (e.g., `1,3,5` in the day of week field means "Monday, Wednesday, Friday").
- `-` (Hyphen): Defines a range of values. (e.g., `1-5` in the day of week field means "Monday through Friday").
- `/` (Slash): Specifies step increments. (e.g., `*/5` in the minute field means "every 5 minutes").

### Visual Generator Tool Implementation
Our tool is built using clean static HTML, styled with responsive CSS, and powered by robust libraries loaded via CDN:
1. `cronstrue` - Instantly parses cron expressions and generates human-readable text descriptions (e.g. `*/5 * * * *` -> "Every 5 minutes").
2. `cron-validator` - Fully validates expressions to prevent system configuration crashes before they occur.

You can run, validate, and preview your cron strings interactively at:
`https://www.cronsentry.com/tools/cron-generator/`

---

## 4. Rebranding: From CronSentry to CronRabbit

CronSentry.com is now officially **CronRabbit.com**. The rebranding brings multiple performance, reliability, and security upgrades:
- **Global Edge Routing**: Ultra-low latency ping endpoints powered by Cloudflare edge workers.
- **Deeper Team Collaborations**: Shared access controls, multi-channel alerting profiles, and unified organization dashboards.
- **Robust Integration Ecosystem**: Native integrations with Slack, Microsoft Teams, Discord, Pushover, Opsgenie, and generic custom webhooks.
- **Extended History Retention**: Archive execution logs and analytics up to 90 days.

All legacy CronSentry configurations are fully backward compatible with CronRabbit.