Arduino Tools > Serial Port greyed out

I am running Debian 7 (Linux Crunchbang) and wanted to use The Arduino IDE to program my Arduino UNO. To do that I installed the package arduino. When I started the Arduino I was asked to add my user to the dialout group. So I did with sudo usermod -a -G dialout <my-username>.

However when I start the Arduino IDE using arduino in the commandline the IDE opens but I am not able to load my program to the Arduino. The error message is "Serial port COM1 not found. Did you select the right one from the Tools > Serial Port menu?" And when I went to select the Serial Port, the option "Tools > Serial Port" is greyed out.

I thought it is because I did not grant read and write permissions on my usb port (ttyACM0). So I did sudo chmod a+rw /dev/ttyACM0 but the option is still greyed out.