/dev/ttyACM busy for the first 15 seconds after plugging [closed]

Question

I have two USB devices which appear as /dev/ttyACMn (a barcode reader and a motor controller). For each of them, when I try to open them in the first 15 seconds after plugging in, I get a "device or resource busy" error. After more than 15 seconds, they open fine. Do you have any idea what's causing it?

I tried using lsof to check if a process is using the device, but it finds no such process (it finds my process after I manage to connect to the device).

I'm currently using Ubuntu 14.04, kernel 3.13.0 64-bit, but I have seen this behavior in earlier Ubuntu versions too.

Thank you very much,

Noam

Answer 1

I think the problem is ModemManager. It scans serial interfaces on startup to see, if they belong to a modem.