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Port Already in Use

Arduino Microcontroller Board

Severity: Moderate

Source: OnlyErrorCodes.com — Every error code. One place.

Arduino Port Already in Use — How to Fix

What Does This Error Mean?

Arduino port already in use means another program has the COM port open and the IDE cannot access it. Close the Arduino Serial Monitor, any other serial terminal, and any IoT apps connected to the board, then try uploading again.

Affected Models

  • Arduino Uno
  • Arduino Nano
  • Arduino Mega 2560
  • Arduino Leonardo
  • Arduino Pro Mini
  • Arduino clones

Common Causes

  • Arduino Serial Monitor is open while attempting to upload
  • Another serial terminal (PuTTY, CoolTerm, Termite) has the port open
  • An IoT platform or dashboard app connected to the board
  • Previous upload crashed leaving the port handle open
  • Another Arduino IDE instance has the port locked

How to Fix It