Thanks for the replies! I have the ttyACM0 device when I connect my Arduino:
$ ls -l /dev/ttyACM*
crw-rw---- 1 root dialout 166, 0 jul 12 10:57 /dev/ttyACM0
$ dmesg
...
[ 2307.912135] usb 5-1: new full-speed USB device number 8 using uhci_hcd
[ 2308.114370] cdc_acm 5-1:1.0: ttyACM0: USB ACM device
$ lsub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 004 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 006 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 007 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 002 Device 003: ID 5986:0102 Acer, Inc Crystal Eye Webcam
Bus 006 Device 003: ID 0458:003a KYE Systems Corp. (Mouse Systems) NetScroll+ Mini Traveler / Genius NetScroll 120
Bus 005 Device 008: ID 2341:0042
The last one is the Arduino, the device with ID 2341:0042. The problem is that is not listed as Acmel right? I've already flashed the firmware so It shouldn't be the problem. Maybe I have some hardware issue?