Bandwidth Monitor Server Scripts

Shell scripts for bandwidth monitoring on AsusWRT-Merlin routers.

Files

File	Purpose
bwmon.sh	Core monitoring script - uses iptables to count traffic
S80bwmon	Init script - manages cron jobs for scheduled updates
install.sh	Installer - sets up dependencies and copies files
uninstall.sh	Clean removal of all installed files
sample-lighttpd-index.html	Sample landing page for lighttpd

Requirements

• AsusWRT-Merlin router
• Entware package manager
• lighttpd web server (installed automatically)
• bc calculator (installed automatically)

How It Works

Data Collection

1. iptables chain (RRDIPT) counts bytes per IP address
2. Cron job runs every 30 minutes to collect data
3. ARP table (/proc/net/arp) identifies connected devices
4. User resolution maps MAC/IP to usernames via:
   • /etc/hosts.dnsmasq
   • /etc/dnsmasq/hosts/hosts
   • /etc/hosts
   • NVRAM custom_clientlist

Data Flow

Router Traffic
      │
      ▼ (iptables RRDIPT chain)
bwmon.sh update
      │
      ▼ (writes)
usage.db ──► lighttpd ──► React Frontend

Commands

bwmon.sh

bwmon.sh setup <path>    # Create iptables rules
bwmon.sh update <path>   # Collect data and publish
bwmon.sh publish <path>  # Publish without collecting

S80bwmon (Service)

/opt/etc/init.d/S80bwmon start    # Start cron jobs
/opt/etc/init.d/S80bwmon stop     # Stop cron jobs
/opt/etc/init.d/S80bwmon restart  # Restart service
/opt/etc/init.d/S80bwmon check    # List active cron jobs

Cron Schedule

Job	Frequency	Purpose
bwmon_setup	Every 1 minute	Ensure iptables rules exist
bwmon_update	Every 30 minutes	Collect and publish data

Data Format

Input Database (bwmonUsage.db)

YYYY-MM,MAC,IP,USAGE_IN,USAGE_OUT,CREATE_TIME,UPDATE_TIME

Output Database (usage.db)

Served to the React frontend:

YYYY-MM,IP,MAC,USER,USAGE_IN,USAGE_OUT,CREATE_TIME,UPDATE_TIME

• Usage values are in kilobytes
• Times are Unix timestamps

Development Constraints

• POSIX shell only - No bash-isms (runs on router's busybox shell)
• Use bc for math - Shell has no built-in arithmetic for large numbers
• File locking - Uses /tmp/bwmon.lock to prevent concurrent updates
• Flow Cache - Disabled automatically for accurate packet counting

Installation Paths

Source	Destination
bwmon.sh	/opt/share/bwmon/
S80bwmon	/opt/etc/init.d/
react/build/*	/opt/share/www/bwmon/
sample-lighttpd-index.html	/opt/share/www/

Logs

Log file: /opt/var/log/bwmon.log

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For installation instructions, see the main README.md.