LogMon

📋 LogMon

Simple, automated log file monitoring with email notifications.

Scan your log files for errors, exceptions, and warnings — get instant email alerts when issues are detected.

✨ Features

Feature	Description
🔍 Smart Pattern Detection	Detects errors, exceptions, warnings, timeouts, and more using optimized regex
📧 Email Notifications	Instant HTML email alerts via secure SMTP/SSL
⚡ High Performance	Concurrent scanning with thread pools and compiled regex
⏱️ Incremental Scanning	Per-file byte offset tracking — only scans new lines, handles log rotation
📦 Standalone Executable	No Python required on your servers
🔄 Self-Updating	Automatically updates itself from GitHub Releases (once daily)
🔧 Flexible Configuration	Environment variables or config file

🆕 What’s New in v1.5.2

Offset safety: scan_all_logs now initialises new_offsets from the existing offsets dict, so entries for files not discovered in the current run are preserved rather than wiped
Stat failure: find_errors_in_file now returns the original last_byte/last_line on OSError instead of resetting to 0, preventing duplicate alerts after transient stat failures
State write resilience: _save_file_offsets and set_last_check_time now catch OSError so a full disk cannot silently swallow alerts
Config %: switched to RawConfigParser — passwords or values containing % no longer raise InterpolationSyntaxError
Version compare: pre-release tags (e.g. v1.5.2-rc1) in GitHub Releases no longer crash the update check
PyInstaller state dir: state files (file_offsets, last_check) now resolve relative to sys.executable under PyInstaller rather than the extracted bundle temp dir
Email header injection: From/To MIME headers now reject values containing \r or \n
HTML escaping: line_number and timestamp in email body now go through html.escape() for consistency
Tarfile extraction: unsafe fallback extractall replaced with per-member path validation to prevent path traversal on Python < 3.12

v1.5.1

Fix html.escape crash: Local variable html in _create_html_email was shadowing the html module import, causing 'str' object has no attribute 'escape' on every email send. Renamed local to body.

v1.5.0

Per-file incremental scanning: LogMon now tracks byte offsets per file in .file_offsets, so only new lines are scanned on each run. Previously reported errors are never re-reported. Handles log rotation and truncation automatically.

v1.4.9

Broader exit code matching: Pattern now matches both exit code: 1 (with colon) and exit code 1 (without colon), while still ignoring exit code: 0
HTML-safe email alerts: Log content in alert emails is now HTML-escaped, preventing rendering issues from log lines containing HTML/script tags
install.sh fix: Corrected stale GitHub URLs in installer comments

v1.4.8

Smarter exit code pattern: Now only matches non-zero exit codes (exit code: 1, exit code: 127), ignoring benign exit code: 0 and exit code directory

v1.4.7

Self-scan fix: Multiline _log() messages (containing \n) now prefix every line with [LogMon], preventing false positives when cron redirects output to a log file

v1.4.6

Cleaner --update output: --update no longer dumps full debug info — only shows update status. Use --update --debug for verbose output.

v1.4.5

Branded email footer: Alert emails now include a “Generated by LogMon” footer with version number and link to vgx.digital

v1.4.4

Self-scan fix: LogMon no longer triggers false positives from its own debug output — all output is now prefixed with [LogMon] and skipped during scanning, so genuine errors in log_monitor.log are still caught

v1.4.3

--truncate-logs: New flag to truncate all monitored log files to zero bytes — handy for test environments where logs keep growing

v1.4.2

Self-updating: LogMon auto-updates itself from GitHub Releases (checks once daily)
One-line install: curl -sfL https://raw.githubusercontent.com/VGXDigital/LogMon/main/install.sh | bash
Manual update: ./log_monitor --update
Smart config lookup: finds log_monitor.conf next to the binary or in the current directory
Disable auto-update: set auto_update = false in [Settings]
Fix: Handle quoted values in config file

📦 Installation

Option 1: One-Line Install (Recommended)

curl -sfL https://raw.githubusercontent.com/VGXDigital/LogMon/main/install.sh | bash

Or specify an install directory:

curl -sfL https://raw.githubusercontent.com/VGXDigital/LogMon/main/install.sh | bash -s -- /opt/logmon

Then configure and test:

cp log_monitor.conf.example log_monitor.conf
nano log_monitor.conf
./log_monitor --debug

Option 2: Run with Python

# Clone the repository
git clone https://github.com/VGXDigital/LogMon.git
cd LogMon

# Configure
cp log_monitor.conf.example log_monitor.conf
nano log_monitor.conf

# Run
python3 log_monitor.py --debug

🔧 Configuration

Edit log_monitor.conf with your settings:

[SMTP]
server = smtp.example.com
port = 465
username = your_smtp_username
password = your_smtp_password
from_email = monitoring@example.com
to_email = admin@example.com

[Paths]
log_dir = /var/log/myapp

[Settings]
# Auto-update is on by default. Disable with:
auto_update = false

The config file is looked up in this order:

Current working directory
Same directory as the log_monitor binary

Environment Variables

Environment variables override config file settings. Use the VGX_LM_ prefix:

Variable	Description
`VGX_LM_SMTP_SERVER`	SMTP server hostname
`VGX_LM_SMTP_PORT`	SMTP port (default: 465)
`VGX_LM_SMTP_USERNAME`	SMTP username
`VGX_LM_SMTP_PASSWORD`	SMTP password
`VGX_LM_SMTP_FROM`	From email address
`VGX_LM_SMTP_TO`	Recipient email address
`VGX_LM_LOG_DIR`	Directory to scan for *.log files

🔍 Detected Patterns

LogMon scans for these error indicators:

error, fail, exception, traceback, critical, fatal,
warning, not found, permission denied, connection refused,
timeout, unable to, could not, exit code N (non-zero only),
returned non-zero, aborted, killed

⏰ Automation (Cron)

Add to crontab for automated monitoring:

# Edit crontab
crontab -e

# Run every 15 minutes
*/15 * * * * cd /path/to/logmon && ./log_monitor

# Or with debug logging
*/15 * * * * cd /path/to/logmon && ./log_monitor --debug >> /var/log/logmon.log 2>&1

📖 Usage

# Normal mode (silent unless errors found)
./log_monitor

# Debug mode (detailed output)
./log_monitor --debug

# Truncate all monitored log files (useful in test)
./log_monitor --truncate-logs

# Check for and install latest version
./log_monitor --update

# Show version
./log_monitor --version

📧 Email Alert Example

When errors are detected, you’ll receive an HTML email like:

Log Monitor Alert: 3 error(s) detected

File Line Content Timestamp

/var/log/app/error.log 142 ERROR: Connection timeout 2026-01-22 10:15:32

/var/log/app/app.log 89 Exception in thread main 2026-01-22 10:15:32

File	Line	Content	Timestamp
/var/log/app/error.log	142	`ERROR: Connection timeout`	2026-01-22 10:15:32
/var/log/app/app.log	89	`Exception in thread main`	2026-01-22 10:15:32

🏗️ Building from Source

# Install build dependencies
pip install -r requirements.txt

# Build standalone executable
pyinstaller --onefile --name log_monitor log_monitor.py

# Executable will be at dist/log_monitor

📄 License

Unauthorized copying, modification, distribution, or use of this software is strictly prohibited.

Made with ❤️ by VGX Consulting