Fw: Modem manager trashing serial LCD display

Neil Cooper neilcoo at yahoo.co.uk
Sat Dec 4 21:48:27 UTC 2010

Since upgrading to ubuntu 10.10, the LCD display on my mythtv home server is having garbage sent to it whenever the box boots up, which very annoyingly just so happens to also include a series of bytes that reprograms the display's firmware settings. 

I finally tracked down what was doing it, it turns out to be modem manager.

I presume what modem manager is doing at startup is trying to discover connected modems by sending AT codes down every serial interface it can find.

I can't emphasise enough how bad/rude having a service assume everything connected to a serial must be a modem, and it autmatically has rights to send data to it without any regard to what damage sending incompatible commands to any other type of device could cause. Just FYI I also have a device programmer that uses serial. Imagine the damage modem manager could do to that.

The default behaviour of modemmanager needs to be fixed so it doesn't send garbage on ports it hasn't been given permission to own.

I can't find any documentation online anywhere about how to configure modem manager. I did find plenty of posts from other people experiencing similar problems though. What is the prescribed remedy for stopping it trashing my display until a better mannered version comes out? Is my only option to totally remove the modemmanager package or can it be somehow configured to be more polite?

Neil Cooper.



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