Python Snippets

File Size Monitor Script

This Python snippet monitors the size of a specified file and alerts the user if the file grows beyond a specified threshold. This is useful for logging systems, large data files, or any scenario where unexpected file growth could indicate an issue.

import os
import time

def monitor_file_size(file_path, max_size_mb, check_interval=60):
    """
    Monitor a file's size and alert if it exceeds a threshold.
    
    Args:
        file_path (str): Path to the file to monitor.
        max_size_mb (float): Maximum allowed file size in megabytes.
        check_interval (int): Time between checks in seconds (default: 60).
    """
    max_size_bytes = max_size_mb * 1024 * 1024  # Convert MB to bytes
    
    try:
        while True:
            if not os.path.exists(file_path):
                print(f"Error: File {file_path} does not exist.")
                break
            
            file_size = os.path.getsize(file_path)
            file_size_mb = file_size / (1024 * 1024)
            
            if file_size > max_size_bytes:
                print(f"ALERT: File {file_path} has exceeded {max_size_mb} MB. Current size: {file_size_mb:.2f} MB")
            else:
                print(f"File size OK: {file_size_mb:.2f} MB / {max_size_mb} MB")
            
            time.sleep(check_interval)
    
    except KeyboardInterrupt:
        print("\nMonitoring stopped.")
    except Exception as e:
        print(f"An error occurred: {e}")

# Example usage
if __name__ == "__main__":
    file_to_monitor = "/var/log/syslog"  # Example file (adjust as needed)
    monitor_file_size(file_to_monitor, max_size_mb=10)  # Alert if >10MB

Explanation

What It Does

This script:

1. Continuously checks the size of a specified file at regular intervals.
2. Converts the file size to megabytes (MB) for readability.
3. Alerts the user if the file exceeds a specified threshold size.
4. Gracefully handles interruptions (Ctrl+C) and errors.

Why It’s Useful

• Log Management: Prevents log files from growing uncontrollably.
• Disk Space Monitoring: Helps avoid unexpected disk space issues.
• Customizable: Adjust the threshold (max_size_mb) and check interval (check_interval) as needed.

How to Run It

1. Save the script as file_monitor.py.
2. Modify file_to_monitor and max_size_mb in the example usage.
3. Run with Python:

   python3 file_monitor.py
   

4. Press Ctrl+C to stop monitoring.

For production use, consider extending this script to send email alerts or integrate with logging systems.