[GLLUG] Reading USB serial port broken

Dimitrios Siganos dimitris at siganos.org
Fri Sep 20 09:04:36 UTC 2019

Have you checked that it is not a baud rate, flow control or other serial
setting issue? You can strace tail to see what it does.

On Fri, 20 Sep 2019, 08:02 Henrik Morsing via GLLUG, <
gllug at mailman.lug.org.uk> wrote:

> Hi,
> I have an Arduino connected via USB to a PC, to read sensors around my
> house. It calls a Python script as a Munin plugin.
> For quite some time now, and I think this possible broke after an upgrade,
> the Python script gets no output from ttyACM0.
> Unless I run a 'tail -f' on the device from the command line! Then it
> works. Otherwise the script just times out getting nothing.
> I'm guessing it's down to a kernel change in how it opens or signals
> through USB serial devices but what? Googling for a year has found nothing
> similar to this problem. I'm not really an expert on serial devices and
> even less on USB serial devices.
> It's getting really frustrating now as the monitoring just never works
> anymore, so any help appreciated.
> Thanks
> Henrik
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