If you are a legacy systems administrator, a reverse engineer, or a developer maintaining older Windows applications, you have likely encountered PortMon (PortMonitor). This Sysinternals tool, while retired by Microsoft, remains invaluable for debugging serial and parallel port activity on Windows XP, Vista, and older Server editions.
Start your troubleshooting by verifying the physical or virtual COM port exists and is not locked. If you are on a 64-bit OS or using USB-to-serial adapters, stop immediately and switch to a modern alternative. PortMon was retired for good reason – Error 2 is often the first sign that you have outgrown this legacy tool. Have a legacy system that still needs PortMon? Share your specific error log below – we can help decode the IOCTL stack. portmon error 2
mode com1: baud=9600 parity=n data=8 stop=1 Or use a PowerShell snippet: If you are a legacy systems administrator, a
This post breaks down exactly what this error means, why it happens, and the precise steps to resolve it. PortMon is a kernel-mode driver tool that intercepts and logs all interactions with COM (serial) and LPT (parallel) ports. It hooks into the Windows I/O subsystem to display IRP_MJ_WRITE , IRP_MJ_READ , and IOCTL calls. If you are on a 64-bit OS or
| Tool | Platform | Supports USB? | Free | |------|----------|---------------|------| | (Eltima) | Windows 10/11 (x64) | Yes | No | | Free Serial Port Monitor (HHD Software) | Windows 10/11 | Yes | Yes (limited) | | com0com + Wireshark | Windows (x64) | Yes | Yes | | socat (Linux) + Serial to network | Cross-platform | Yes | Yes | | PySerial + logging wrapper | Any Python | Yes | Yes |