arduino/Arduino · error · SerialException

Error opening serial port ''{0}''.

Error message

Error opening serial port ''{0}''.

What it means

Thrown by the Serial constructor in arduino-core when jSSC fails to open the requested serial port. It wraps the underlying SerialPortException and indicates the OS refused or failed the port open. The message includes the port name; a special variant with a documentation link is used for Linux permission failures.

Source

Thrown at arduino-core/src/processing/app/Serial.java:152

    // 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
        }
      } catch (SerialPortException e) {

View on GitHub (pinned to a0df6e0e83)

Solutions

  1. Close any other program using the port (Serial Monitor, screen, another IDE instance)
  2. Verify the device is connected and the port name matches (Tools > Serial Port)
  3. On Linux add your user to the dialout group or install the udev rules
  4. Reconnect/replug the board and retry
  5. Catch SerialException and show the wrapped cause for diagnosis

Example fix

// before
Serial serial = new Serial();
serial.open("/dev/ttyUSB0");
// after
try {
  Serial serial = new Serial();
  serial.open("/dev/ttyUSB0");
} catch (SerialException e) {
  System.err.println("Port open failed: " + e.getMessage());
}
Defensive patterns

Strategy: try-catch

Validate before calling

boolean canOpen = Arrays.asList(Serial.list()).contains(iname);
if (!canOpen) throw new IllegalStateException("Port not listed: " + iname);

Type guard

static boolean portAvailable(String name) {
  return name != null && !name.isEmpty() && Arrays.asList(Serial.list()).contains(name);
}

Try / catch

try {
  serialPort = new Serial(iname);
} catch (SerialException e) {
  // e.getCause() is the underlying SerialPortException: check its type
  System.err.println("Open failed for " + iname + ": " + e.getCause());
}

Prevention

When it happens

Trigger: Calling new Serial() / Serial.open with a port name that the OS cannot open: port busy (already opened elsewhere), device disconnected, driver missing, or (on Linux, /dev/tty* paths) permission denied handled by the sibling message.

Common situations: Serial Monitor already holding the port; Arduino unplugged or re-enumerated with a different COM number; user not in dialout/uucp group on Linux; bogus or empty port string.

Understand the failure class

Background: "open() failed", "failed to open file", "cannot create file" — what a file open error means and how to fix it — this error's family across 42 libraries.

Related errors

AI-assisted analysis of arduino/Arduino@a0df6e0e83 (2026-09-06). Data as JSON: /api/errors/0baf94be3c4da7bb. Report an issue: GitHub.