arduino/Arduino · error · SerialException

Error opening serial port ''{0}''. Try consulting the docume

Error message

Error opening serial port ''{0}''. Try consulting the documentation at http://playground.arduino.cc/Linux/All#Permission

What it means

The Serial constructor throws this SerialException when opening the port fails with TYPE_PERMISSION_DENIED on a /dev* port. The message specifically points Linux users to the Arduino permission documentation because it almost always means the user is not allowed to access the serial device.

Source

Thrown at arduino-core/src/processing/app/Serial.java:150

    if (istopbits == 2) stopbits = SerialPort.STOPBITS_2;

    // This is required for unit-testing
    if (iname.equals("none")) {
      return;
    }

    try {
      port = new SerialPort(iname);
      port.openPort();
      boolean res = port.setParams(irate, idatabits, stopbits, parity, setRTS, setDTR);
      if (!res) {
        System.err.println(format(tr("Error while setting serial port parameters: {0} {1} {2} {3}"),
                                  irate, iparity, idatabits, istopbits));
      }
      port.addEventListener(this);
    } catch (SerialPortException e) {
      if (e.getPortName().startsWith("/dev") && SerialPortException.TYPE_PERMISSION_DENIED.equals(e.getExceptionType())) {
        throw new SerialException(format(tr("Error opening serial port ''{0}''. Try consulting the documentation at http://playground.arduino.cc/Linux/All#Permission"), iname));
      }
      throw new SerialException(format(tr("Error opening serial port ''{0}''."), iname), e);
    }

    if (port == null) {
      throw new SerialNotFoundException(format(tr("Serial port ''{0}'' not found. Did you select the right one from the Tools > Serial Port menu?"), iname));
    }
  }

  public void setup() {
    //parent.registerCall(this, DISPOSE);
  }

  public void dispose() throws IOException {
    if (port != null) {
      try {
        if (port.isOpened()) {
          port.closePort();  // close the port

View on GitHub (pinned to a0df6e0e83)

Solutions

1. Add your user to the dialout group and re-login: sudo usermod -aG dialout $USER (or uucp on Arch), then verify with `groups`
2. Check device permissions (ls -l /dev/ttyACM0) and stop conflicting services: sudo systemctl stop ModemManager brltty
3. Use a udev rule to grant stable access to the device, then replug the board
4. Run once with sudo to confirm it is purely a permission problem, then fix group membership rather than always using sudo

Example fix

// before: permission denied on /dev/ttyACM0
// after (system fix, then restart session)
// sudo usermod -aG dialout $USER && newgrp dialout
Serial serial = new Serial(portName, 9600, 'N', 8, 1);

File dev = new File(portName);
if (!dev.exists()) throw new IllegalStateException("No such port: " + portName);
try (var ch = new java.io.RandomAccessFile(dev, "rw").getChannel()) {
  // opening rw succeeds only with permission
} catch (java.io.IOException e) {
  throw new IllegalStateException("No permission on " + portName + ": add user to dialout");
}

try {
  Serial serial = new Serial(portName, 9600, 'N', 8, 1);
} catch (SerialException e) {
  if (e.getMessage().contains("Permission")) {
    System.err.println("Add yourself to dialout and re-login, then retry.");
  } else throw e;
}

When it happens

Trigger: new Serial(...) calls port.openPort(); jSSC returns SerialPortException with exception type TYPE_PERMISSION_DENIED and port name starting with "/dev" (Linux/macOS), e.g. /dev/ttyUSB0 or /dev/ttyACM0.

Common situations: User not in dialout/uucp group on Linux; modemmanager or brltty grabbing the device; device node with unusual permissions; macOS inaccessible /dev/cu.* device.

Understand the failure class

Background: Permission denied / not authorized / 403 Forbidden: access-control rejections when the caller lacks the required role, grant, or ownership — this error's family across 18 libraries.

Related errors

• Couldn't find a Board on the selected port. Check that you h
• serial.port
• Could not remove old version of {0}
• Error touching serial port ''{0}''.
• Error opening serial port ''{0}''.

AI-assisted analysis of arduino/Arduino@a0df6e0e83 (2026-09-06). Data as JSON: /api/errors/57e61b5910e9108e. Report an issue: GitHub.