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I connect to my Arduino board with the following Python code.

device=glob.glob("/dev/ttyUSB*")[0]
time.sleep(1)
arduino = serial.Serial(device, 115200, timeout=5)

It generally works, but somehow some other process must be accessing the board after reboot giving me the error

serial.serialutil.SerialException: could not open port /dev/ttyUSB0: [Errno 16] Device or resource busy: '/dev/ttyUSB0'

When unplugging and replugging the USB-plug I can execute the Python code normally, without the error occuring. How can I avoid any other process blocking the port? And how do I find out the reason for this error?

MPelletier
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birgit
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3 Answers3

33

You can use

$ fuser /dev/ttyUSB0

to list the PIDs of the processes using the file. Alternatively, if your fuser command supports it you can use the -k option to kill them.

Diego Torres Milano
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    This doesn't always work, for example, if you used GNU screen to access a `ttyUSBx device`, and then quit using `Ctrl-C`, you will get "Device busy" but it will not show up with the above command. – gbmhunter Sep 16 '14 at 23:16
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    How do I fix it then?!?! :D – 0xbaadf00d Oct 03 '14 at 09:34
  • You need to kill the attached screen session. Ideally reattaching via screen and closing it nicely, unideally by killing the screen process that owns the ttyUSB. – timB33 Nov 26 '18 at 11:58
10

In my case

$ fuser /dev/ttyUSB0

was not working (it showed nothing).

What was working, however, was the following:

$ sudo lsof /dev/ttyUSB0

This gave me a list of the processes that were using my serial port and I could simply kill them using the PID (corresponding to the second column in the list).

Alf
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0

Run:

$ ps ax

You will see what process is using serial port. Kill that process. This solved it for me.

Anastasia
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