Troubles programming Sparkfun Pro Micro from Ubuntu

It took me a while to figure out what was wrong with my ProMicro…

When trying to program it from Linux/Ubuntu, avrdude was not working, with the following error :

avrdude: ser_open(): can't open device "/dev/ttyACM0": Device or resource busy
Eavrdude: butterfly_recv(): programmer is not responding

The command I was using :

avrdude -v -P /dev/ttyACM0 -c avr109 -p atmega32u4 -U flash:w:program.hex:i

After some trials, I noticed that ModemManager was in fact stealing the access to ttyACM0, briefly when the ProMicro was reset, causing the problem.

The solution : sudo apt-get purge modemmanager