Adafruit Circuit Playground Express fails to upload When uploading code to the Adafruit Circuit Playground Express, I have found that most of the time it fails to upload saying that the port is busy. There seems to be no logical reason behind this, as it uploads perfectly to an Arduino Uno (Yes, I did switch the board types). What am I doing wrong?
Here is the error: 

processing.app.debug.RunnerException
    at cc.arduino.packages.uploaders.SerialUploader.uploadUsingPreferences(SerialUploader.java:152)
    at cc.arduino.UploaderUtils.upload(UploaderUtils.java:77)
    at processing.app.SketchController.upload(SketchController.java:732)
    at processing.app.SketchController.exportApplet(SketchController.java:703)
    at processing.app.Editor$UploadHandler.run(Editor.java:2075)
    at java.lang.Thread.run(Thread.java:748)
Caused by: processing.app.SerialException: Error touching serial port '/dev/ttyACM1'.
    at processing.app.Serial.touchForCDCReset(Serial.java:107)
    at cc.arduino.packages.uploaders.SerialUploader.uploadUsingPreferences(SerialUploader.java:136)
    ... 5 more
Caused by: jssc.SerialPortException: Port name - /dev/ttyACM1; Method name - openPort(); Exception type - Port busy.
    at jssc.SerialPort.openPort(SerialPort.java:164)
    at processing.app.Serial.touchForCDCReset(Serial.java:101)
    ... 6 more


Operating system: kubuntu linux 64 bit

EDIT: Never mind. In the end I used chmod a-x /usr/sbin/ModemManager to remove execute permissions from every user, and that worked without any noticeable repercussions to my system. For anyone who wants to do the same, make note of the original permissions, so you can change it back if you have to.
The actual error part of that stack trace is:

Port name - /dev/ttyACM1; Method name - openPort(); Exception type - Port busy.


You have something else using /dev/ttyACM1.  If you don't yourself have something open, such as a serial terminal or the Arduino serial monitor, then the most likely culpret is modemmanager.


https://majenko.co.uk/blog/diagnosing-arduino-problems-linux