How to handle a modem that stops responding...

Jessy Exum jessy.diamondman at
Thu Oct 29 16:29:49 UTC 2020

Makes sense (origin of the behavior).

I have seen that behavior with opening the serial port (had to get the
modem expert on my team to stop doing that and run commands through mmcli).
I don't think I waited long enough for ten failures.

On Thu, Oct 29, 2020, 1:30 AM Aleksander Morgado <aleksander at>

> Hey,
> >
> > It is good to know that this has been considered in the core design. I
> agree that there should be no modem specific behavior for this.
> >
> The original implementation was done to support RS232 modems, as
> looking at the AT command timeouts was the only way to detect that a
> modem was gone. But it really has shown to be useful also for USB
> modems as the "stale AT port" issue is something we've seen multiple
> times in the past years.
> > I will try to get a device in this failed state and diagnose why it is
> not being released.
> >
> I believe it's easy to "force" this situation; just run a minicom
> session on the TTY you want to break while ModemManager is already
> using the port. Running minicom on a TTY that MM is already using will
> "hijack" all the responses for the commands sent by MM (i.e. MM sends
> command, minicom gets the response), which is kind of similar of what
> would happen if the AT port goes silent by itself.
> --
> Aleksander
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