Proactive Server Management: A Simple Bash Script for Disk Usage Alerts
Unexpected downtime is a system administrator’s worst nightmare, and one of the most common culprits is a surprisingly simple one: a full disk drive. When a server’s storage reaches capacity, applications can crash, data can become corrupted, and critical services can grind to a halt. Manually checking disk space is inefficient and unreliable. The key to preventing these emergencies is proactive monitoring with automated alerts.
This guide will walk you through creating and deploying a simple yet powerful Bash script to monitor your server’s disk usage and automatically notify you before it becomes a critical issue.
Why Automated Disk Monitoring is Non-Negotiable
Relying on manual checks for disk space is a recipe for disaster. An automated system provides several crucial advantages:
- Prevents Service Downtime: Receive alerts when usage hits a predefined threshold (e.g., 80%), giving you ample time to free up space or provision more storage before applications are affected.
- Protects Data Integrity: A full disk can lead to incomplete writes and data corruption. Automated monitoring helps ensure your systems always have the space they need to operate correctly.
- Enables Proactive Maintenance: Instead of reacting to emergencies, you can perform scheduled cleanups, archive old logs, or expand storage during planned maintenance windows.
- Saves Time and Resources: Automating this fundamental task frees you up to focus on more complex administrative duties, confident that a critical system metric is being watched.
Building Your Disk Monitoring Script
This script uses standard Linux command-line tools, making it highly portable and easy to implement on almost any server. The logic is straightforward: check the disk usage percentage, compare it to a set threshold, and send an email if the usage exceeds that limit.
Here is the complete script. You can save this file as disk_monitor.sh.
#!/bin/bash
# --- Configuration ---
# Set the percentage threshold for the alert.
THRESHOLD=85
# Set the recipient email address for alerts.
ALERT_EMAIL="[email protected]"
# Set the filesystem to monitor (e.g., "/" for the root filesystem).
FILESYSTEM="/"
# --- End Configuration ---
# Get the current disk usage percentage for the specified filesystem.
# The command chain breaks down as follows:
# 1. df -h: Shows disk usage in a human-readable format.
# 2. grep "$FILESYSTEM": Filters the output to only the line for our target filesystem.
# 3. awk '{print $5}': Prints the 5th column, which is the usage percentage.
# 4. sed 's/%//g': Removes the "%" symbol.
CURRENT_USAGE=$(df -h "$FILESYSTEM" | grep "$FILESYSTEM" | awk '{print $5}' | sed 's/%//g')
# Check if the current usage is greater than the defined threshold.
if [ "$CURRENT_USAGE" -gt "$THRESHOLD" ]; then
# Get the server's hostname to include in the alert message.
HOSTNAME=$(hostname)
# Prepare the email subject and body.
SUBJECT="Disk Space Alert on $HOSTNAME: Usage is at ${CURRENT_USAGE}%"
BODY="Critical Warning: Disk usage on server '$HOSTNAME' for filesystem '$FILESYSTEM' has exceeded the threshold of ${THRESHOLD}%. Current usage is ${CURRENT_USAGE}%."
# Send the email alert.
# Ensure your server has a mail transfer agent (like mailutils, sendmail, or postfix) configured.
echo "$BODY" | mail -s "$SUBJECT" "$ALERT_EMAIL"
fi
exit 0
Key components of the script:
- Configuration Variables: At the top, you can easily set the
THRESHOLD, theALERT_EMAIL, and theFILESYSTEMyou want to monitor. This makes the script easy to adapt without changing the core logic. - Checking Usage: The command
df -his used to get disk information. We then usegrep,awk, andsedto isolate the exact numeric percentage for the root filesystem. - Conditional Logic: An
ifstatement compares theCURRENT_USAGEwith yourTHRESHOLD. The alert is only triggered if the usage is higher. - Sending the Alert: If the threshold is breached, the script constructs a clear subject line and body and sends an email using the
mailcommand. You must have a mail transfer agent (MTA) likemailutilsorpostfixinstalled and configured on your server for this to work.
Automating the Script with Cron
A monitoring script is only useful if it runs automatically and consistently. The perfect tool for this job is cron, the built-in Linux task scheduler.
Step 1: Make the Script Executable
First, you need to give the script permission to be executed. Navigate to the directory where you saved the file and run:
chmod +x disk_monitor.sh
Step 2: Add a Cron Job
Next, open your crontab file for editing:
crontab -e
This will open a text editor. Add the following line to the end of the file to schedule the script to run once every hour, at the top of the hour.
0 * * * * /path/to/your/disk_monitor.sh
Make sure to replace /path/to/your/disk_monitor.sh with the actual, absolute path to your script. Save and close the file. The cron daemon will now automatically execute your monitoring script every hour.
Security and Best Practices
- Use Specific Filesystems: While monitoring the root (
/) filesystem is essential, consider creating copies of this script to monitor other critical mount points, like/var(for logs) or/home. - Error Logging: For more robust monitoring, you can redirect the script’s output to a log file to track when it runs and if any errors occur. You can modify the cron job like this:
0 * * * * /path/to/your/disk_monitor.sh >> /var/log/disk_monitor.log 2>&1 - Consider Advanced Alerting: For production environments, you might want to integrate alerts with services like Slack, PagerDuty, or a centralized monitoring platform instead of just email. This can be achieved by replacing the
mailcommand with an API call. - Use a Dedicated User: For enhanced security, avoid running maintenance scripts as the
rootuser whenever possible. Create a dedicated, non-privileged user for running monitoring tasks.
By implementing this simple, automated solution, you can move from a reactive to a proactive server management strategy, ensuring system stability and preventing one of the most common causes of service interruptions.
Source: https://www.tecmint.com/monitor-disk-usage-bash-script/
