'COM PORT in USE' - What to do?

Well Every now and then during our training classes someone or the other running windows vista / 7 runs into this problem where the arduino ide throws up an error saying 'Com Port in use' and only a restart would fix this. Are there anyways to override this by forcing windows to close the port in question?(i know using linux will be a better solution but a lot of my students work on windows)

Cheers, pracas

Hi! Usually a message 'COM PORT in USE' comes up when the device is incorrectly plugged out or the program is left open. Windows still thinks that the device is connected.

There must be some program you are running which opens the serial port.

Try looking in task manager for anything that might be keeping it open.


well i'm inside the arduino ide and i upload a sketch and then i use the serial monitor, later i close the serial monitor and try to upload the code again and this happens... perhaps a bug in the serial monitor process being terminated? not sure... but it seems to fix itself after some time or restart.

Hmm, I thought you might say it was something like that.


this happens occasionally on vista. restarting the ide is my only resolution.


If you have access to task manager on those computers (not limited network computers), then you will want to look in there to make sure that windows has not still got the IDE open even if you can't see it. Then you can end it through there rather than just restarting.

Logging off and back on should work too.


If this is a specific win7 problem you could try running the arduino software in XP mode. Probably won't change anything but it might be worth a try.

Well it's probably to do with windows 7 not closing the program properly which I doubt could be sorted by running in xp compatibilty.

I have a solution though. Run XP! :) I have windows 7 but i'm not going to use it as it's slow and pointlessly graphical...