ttyACM0 connected but not showing received data

I have a STM32F4 microcontroller, with the USB interface, I connected it to the raspberry pi. When connected, it shows up as /dev/ttyACM0. I send some chars every second from the device. In windows, with putty, all works fine. I receive the chars nicely. On the raspberry pi, if I run the command: >> sudo tail -f /dev/ttyACM0 It does not show anything on the screen. In my debugger, I do see that the device does not "hang", it seems like it is sending properly. If the tail command is not running, the device (with a simple program) does hang, and the watchdog timer does time out. This behavior seems normal, as I have the same symptom in windows when putty is not listing. How to display the sent chars? Is this a problem with rights? Should I use another program? I did try some suggestions from forums: change rules in 99-com.rules, set all rights to /dev/ttyACM0`, but with no luck.