So a few days ago i started getting error messages when I tried to upload a sketch. this is the message:
Arduino: 1.8.8 (Mac OS X), Board: "Arduino/Genuino Uno"
Sketch uses 1718 bytes (5%) of program storage space. Maximum is 32256 bytes.
Global variables use 25 bytes (1%) of dynamic memory, leaving 2023 bytes for local variables. Maximum is 2048 bytes.
avrdude: ser_open(): can't open device "/dev/cu.usbmodem14101": Resource busy
Problem uploading to board. See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.
It will still upload occasionally, but it is quite frustrating. I have tried on multiple boards with the same result. Any ideas on what has happened?
It shouldn't. The Arduino IDE automatically closes the Serial Monitor connection when you do an upload. The only exception is when you have two instances of the Arduino IDE running at the same time, Serial Monitor open in one, attempt to upload in the other. I'm not even sure if it's possible to have multiple instances of the IDE open on macOS (I've only tried on Windows).
I updated my computer recently. Then the first time I plugged in the Arduino a message popped up about something needing updating but it disappeared before I could actually read it. Then all the trouble started. I reinstalled IDE and made sure it was the most current version. There is nothing else using the usb port and other than updating the computer, nothing changed.