write a code to monitor disk space quota in linux

To monitor disk space quota in a Linux system, you can create a simple shell script that checks disk usage and sends an alert when usage exceeds a specified threshold. Below is an example of a script that accomplishes this task.

### Shell Script to Monitor Disk Space Quota

```bash
#!/bin/bash

# Set the threshold percentage (e.g. 80 for 80%)
THRESHOLD=80

# Get the list of mounted file systems
FILE_SYSTEMS=$(df -h --output=pcent,target | tail -n +2)

# Loop through each file system
while read -r line; do
    # Extract the usage percentage and mount point
    USAGE=$(echo "$line" | awk '{print $1}' | tr -d '%')
    MOUNT_POINT=$(echo "$line" | awk '{print $2}')

    # Check if the usage exceeds the threshold
    if [ "$USAGE" -ge "$THRESHOLD" ]; then
        echo "Warning: Disk usage on $MOUNT_POINT is at ${USAGE}%."
    fi
done <<< "$FILE_SYSTEMS"
```

### How to Use the Script

1. **Create the Script File**:
   Open a terminal and create a new script file:
   ```sh
   touch disk_space_monitor.sh
   ```

2. **Edit the Script**:
   Open the script file in a text editor (e.g., `nano` or `vim`):
   ```sh
   nano disk_space_monitor.sh
   ```

   Copy the script above and paste it into the file. Save and exit.

3. **Make the Script Executable**:
   Make the script executable by running:
   ```sh
   chmod +x disk_space_monitor.sh
   ```

4. **Run the Script**:
   You can run the script manually:
   ```sh
   ./disk_space_monitor.sh
   ```

5. **Automate the Monitoring**:
   To check disk space on a regular basis, you can add the script to your cron jobs by running:
   ```sh
   crontab -e
   ```
   Add the following line to run the script every hour (as an example):
   ```sh
   0 * * * * /path/to/disk_space_monitor.sh >> /path/to/disk_space_monitor.log 2>&1
   ```

### Notes
- You may want to change the `THRESHOLD` variable to set the usage percentage that you consider critical.
- This script checks all mounted filesystems and alerts if any of them exceed the specified threshold.
- The output can be redirected to a log file for later review.
- You might consider sending notifications (e.g., email or alerts via monitoring systems) in a production scenario.

### Additional Improvements
Depending on your requirements, you may want to:
- Send email alerts using `mail` command.
- Implement logging with timestamps.
- Check specific file systems instead of all mounted systems.
- Enhance the script with better error handling.