Cron Expression: First 30 Minutes of Every Hour (0-30 * * * *)

The cron expression 0-30 * * * * executes a task every minute during the first 30 minutes of every hour, making it ideal for intensive monitoring, data collection, or tasks that need frequent execution during specific periods of each hour.

Expression Breakdown

0-30 * * * *
│   │ │ │ │
│   │ │ │ └─── Day of week: * (every day)
│   │ │ └───── Month: * (every month)
│   │ └─────── Day of month: * (every day)
│   └───────── Hour: * (every hour)
└───────────── Minute: 0-30 (minutes 0 through 30)

Field Values

Range Syntax

The 0-30 in the minute field is a range that means "every minute from 0 to 30":

• Runs at: :00, :01, :02, ..., :30 of every hour
• Total: 31 executions per hour × 24 hours = 744 executions per day

Execution Time

This expression runs 744 times per day at:

• Every minute from :00 to :30 of every hour (e.g., 00:00-00:30, 01:00-01:30, etc.)

Common Use Cases

1. Intensive Monitoring

0-30 * * * * /usr/local/bin/intensive-monitor.sh

Monitor system health or services intensively during the first half of each hour.

2. Data Collection

0-30 * * * * /usr/bin/python3 /scripts/collect-metrics.py

Collect real-time metrics, logs, or sensor data during specific periods.

3. Queue Processing

0-30 * * * * /usr/bin/node /app/process-queue.js

Process job queues or message queues intensively during the first half of each hour.

4. Cache Warming

0-30 * * * * /usr/bin/python3 /scripts/warm-cache.py

Warm cache or pre-load data during the first half of each hour.

Example Implementations

Intensive Monitor Script

#!/bin/bash
# /usr/local/bin/intensive-monitor.sh

LOG_FILE="/var/log/intensive-monitor.log"
THRESHOLD_CPU=85
THRESHOLD_MEM=90

CPU_USAGE=$(top -bn1 | grep "Cpu(s)" | awk '{print $2}' | cut -d'%' -f1)
MEM_USAGE=$(free | grep Mem | awk '{printf "%.0f", $3/$2 * 100}')

if (( $(echo "$CPU_USAGE > $THRESHOLD_CPU" | bc -l) )); then
    echo "$(date): WARNING - CPU usage at ${CPU_USAGE}%" >> $LOG_FILE
fi

if [ $MEM_USAGE -gt $THRESHOLD_MEM ]; then
    echo "$(date): WARNING - Memory usage at ${MEM_USAGE}%" >> $LOG_FILE
fi

Best Practices

1. Resource Usage: Every-minute execution is resource-intensive; keep tasks lightweight
2. Execution Time: Tasks must complete within 30-40 seconds to avoid overlap
3. Error Handling: Implement comprehensive error handling and logging
4. Idempotency: Ensure tasks can run multiple times safely
5. Monitoring: Track execution time and failures closely

When to Use

✅ Good for:

• Intensive monitoring during specific periods
• Data collection
• Queue processing
• Cache warming
• Tasks needing frequent execution during first half of hour

❌ Avoid for:

• Heavy computations
• Long-running processes
• Tasks requiring more than 30 seconds
• Operations needing full-hour coverage

Related Patterns

Conclusion

The 0-30 * * * * expression is perfect for intensive operations during the first half of each hour. It provides maximum frequency during specific periods while allowing the second half of each hour for other operations or system recovery, making it ideal for intensive monitoring and data collection during peak periods.