## Overview

This project provides lightweight disk monitoring for a VPS with:

- Daily storage reports
    
- Rapid disk usage change detection
    
- Alerts sent to a Matrix room
    
- Minimal dependencies (Python + SQLite only)
    

It is designed to be:

- Simple
    
- Transparent
    
- Easy to debug
    
- Low overhead
    

---

## Architecture

```
systemd timers
    ↓
Python script (disk_monitor.py)
    ↓
SQLite (local state/history)
    ↓
Matrix API (alerts + reports)
```

---

## Components

### 1. Python Script

**Location:**

```
/opt/diskmon/disk_monitor.py
```

**Responsibilities:**

- Collect disk usage stats
    
- Store historical samples
    
- Detect rapid changes
    
- Format messages
    
- Send messages to Matrix
    

---

### 2. SQLite Database

**Location:**

```
/var/lib/diskmon/diskmon.sqlite3
```

**Purpose:**

- Store disk usage history
    
- Track alert cooldowns
    

---

### 3. Environment Config

**Location:**

```
/etc/diskmon.env
```

**Contents:**

```
MATRIX_HOMESERVER=https://matrix.yourdomain.com
MATRIX_ROOM_ID=!roomid:yourdomain.com
MATRIX_ACCESS_TOKEN=your_token
DISKMON_DB=/var/lib/diskmon/diskmon.sqlite3
DISKMON_MOUNT=/
```

---

### 4. systemd Timers

#### Sample Timer (every 5 min)

```
diskmon-sample.timer
```

#### Report Timer (daily)

```
diskmon-report.timer
```

---

## Data Flow

### Sampling Loop (every 5 minutes)

1. Read disk usage (`shutil.disk_usage`)
    
2. Insert sample into SQLite
    
3. Compare against:
    
    - 10-minute-old sample
        
    - 60-minute-old sample
        
4. Trigger alerts if thresholds exceeded
    
5. Apply cooldown logic
    

---

### Daily Report

1. Read current disk usage
    
2. Format summary
    
3. Send to Matrix
    

---

## Database Schema

### samples

|column|type|description|
|---|---|---|
|id|int|primary key|
|ts|int|unix timestamp|
|mount|text|mount path|
|used_bytes|int|used disk space|
|avail_bytes|int|free space|
|total_bytes|int|total capacity|

---

### alerts

|column|type|description|
|---|---|---|
|key|text|alert identifier|
|last_sent_ts|int|last time alert was triggered|

---

## Alert Logic

### Thresholds

|Condition|Trigger|
|---|---|
|Warning|≥ 1 GiB increase in 10 minutes|
|Critical|≥ 10 GiB increase in 60 minutes|

---

### Cooldowns

|Alert Type|Cooldown|
|---|---|
|Warning|30 minutes|
|Critical|60 minutes|

---

### Why cooldowns exist

Prevents:

- Alert spam
    
- Repeated messages for same event
    
- Noise during sustained writes
    

---

## Message Formats

### Daily Report

```
[VPS Storage Report]
Mount: /
Used: 48.2 GiB
Available: 131.7 GiB
Total: 180.0 GiB
Usage: 26.8%
Timestamp: 2026-04-01 09:00:00 EDT
```

---

### Alert

```
[Storage Alert]
Mount: /
Used space increased by 1.4 GiB in 10 minutes
Previous used: 48.2 GiB
Current used: 49.6 GiB
Timestamp: 2026-04-01 09:40:00 EDT
```

---

## Monitoring the System

### Check timers

```
systemctl list-timers | grep diskmon
```

---

### Check logs

#### Sample job

```
journalctl -u diskmon-sample.service -f
```

#### Report job

```
journalctl -u diskmon-report.service -f
```

---

### Run manually

```
systemctl start diskmon-sample.service
systemctl start diskmon-report.service
```

---

### Check service status

```
systemctl status diskmon-sample.service
systemctl status diskmon-report.service
```

---

## Debugging

### 1. Environment variables not found

**Symptom:**

```
KeyError: MATRIX_HOMESERVER
```

**Fix:**

```
set -a
source /etc/diskmon.env
set +a
```

---

### 2. SQLite errors

**Symptom:**

```
sqlite3.OperationalError
```

**Fix:**

- Check SQL syntax
    
- Delete DB and recreate if needed:
    

```
rm /var/lib/diskmon/diskmon.sqlite3
```

---

### 3. No Matrix messages

Check:

- correct homeserver URL
    
- valid access token
    
- correct room ID
    
- HTTPS used
    

---

### 4. Script not running

```
systemctl status diskmon-sample.timer
```

---

## Testing Alerts

### Trigger disk usage spike

```
fallocate -l 2G /tmp/testfile
```

Wait ~5–10 minutes.

Cleanup:

```
rm /tmp/testfile
```

---

## Maintenance

### View database

```
sqlite3 /var/lib/diskmon/diskmon.sqlite3
```

---

### Clean old data

Handled automatically:

- keeps ~2 days of samples
    

---

## Extending the System

### Possible improvements

- Monitor multiple mounts
    
- Add low disk space alerts (e.g. <20GB)
    
- Send HTML-formatted Matrix messages
    
- Integrate with Uptime Kuma push monitor
    
- Add inode monitoring
    
- Add disk I/O rate tracking
    

---

## Design Philosophy

This system intentionally avoids:

- Prometheus
    
- external monitoring stacks
    
- heavy dependencies
    

Instead it focuses on:

- clarity
    
- reliability
    
- minimalism
    
- full control over alert logic
    

---

## Summary

This setup provides:

- Continuous disk monitoring
    
- Time-window-based change detection
    
- Daily reporting
    
- Matrix integration
    
- Minimal operational overhead
    

All in ~1 script + systemd.

---