non so più dove sbattere la testa 
Adesso neanche arduino IDE mi vede più /dev/ACM0
l'output di lsusb è questo:
Bus 007 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 006 Device 003: ID 046d:c316 Logitech, Inc. HID-Compliant Keyboard
Bus 006 Device 002: ID 046d:c018 Logitech, Inc. Optical Wheel Mouse
Bus 006 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 004 Device 003: ID 093a:2468 Pixart Imaging, Inc. SoC PC-Camera
Bus 004 Device 002: ID 2341:0001
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
e quello di dmesg è questo:
[ 29.998434] vboxdrv: Successfully done.
[ 29.998435] vboxdrv: Found 4 processor cores.
[ 29.998514] VBoxDrv: dbg - g_abExecMemory=ffffffffa0decd60
[ 29.998556] vboxdrv: fAsync=0 offMin=0x53a offMax=0x20b8
[ 29.998605] vboxdrv: TSC mode is 'synchronous', kernel timer mode is 'normal'.
[ 29.998606] vboxdrv: Successfully loaded version 3.2.8_OSE (interface 0x00140001).
[ 121.993023] lo: Disabled Privacy Extensions
[ 322.625042] usb 4-1: USB disconnect, address 2
[ 325.960076] usb 4-1: new full speed USB device using ohci_hcd and address 4
[ 326.155040] cdc_acm 4-1:1.0: ttyACM0: USB ACM device
Probabilmente tra i mille tentativi avrò toccato qualcosa che non dovevo... il problema è ricordarsi cosa!