user-data/synterloper

SYNterloper - First-boot Truncated Rolling PCAP Logger

SYNterloper is a utility for creating a persistent, rolling packet capture for a specific network port (defaulting to TCP/22 for SSH). Its primary purpose is to provide a simple, low-overhead log of connection attempts for troubleshooting, security analysis, and auditing.

The tool is delivered as a single, self-contained script designed for automated deployment on first-boot, making it ideal for cloud environments like AWS, where it can be included in User Data to configure new instances.

Core Functionality

• Self-Contained: A single script handles installation, service creation, and uninstallation. No external dependencies like git are required for deployment.
• System Service: Runs as a standard systemd (Linux) or rc.d (FreeBSD) service.
• Rolling Buffer & Automatic Pruning: Creates hourly log files and prunes logs older than 7 days to manage disk space.
• Efficient Capture: Captures only packet headers to keep logs small and focused.
• Self-Managing: The script copies itself to /usr/local/sbin/synterloper during installation, making it easy to manage or uninstall later.

Automated Deployment (AWS User Data)

To install SYNterloper on a new EC2 instance, paste the entire contents of the synterloper.sh script into the "User Data" field at launch.

Example User Data:

#!/bin/bash
#
# User Data script to install SYNterloper.
# The contents of synterloper.sh are placed directly below.
#

# --- Start of synterloper.sh ---

# PASTE THE ENTIRE CONTENTS OF THE synterloper.sh SCRIPT HERE

# --- End of synterloper.sh ---

When the instance boots, the cloud-init service will execute this script, which will then run the install_synterloper function by default.

Manual Installation

To install on an existing system:

1. Save the script's contents to a file named synterloper.sh.
2. Make it executable: chmod +x synterloper.sh.
3. Run it with root privileges: sudo ./synterloper.sh.

Usage and Verification

Service Management

• Check Status (Linux): systemctl status synterloper.service
• Check Status (FreeBSD): service synterloper status

Reading Capture Files

The raw .pcap files are stored in /var/log/synterloper/.

To read the most recent log file from the command line:

sudo tcpdump -n -r $(ls -t /var/log/synterloper/*.pcap | head -1)

Uninstallation

Because the installation process places a copy of the script in the system's path, you can easily uninstall the tool at any time.

sudo /usr/local/sbin/synterloper uninstall

For non-interactive uninstallation, pipe yes to the command (note: this is not required for the updated script, but is a common pattern).

sudo /usr/local/sbin/synterloper uninstall

This command will stop the service, remove all system files it created (service definitions, cron jobs), delete the log directory, and remove the /usr/local/sbin/synterloper script itself.