Napkin expects you to have sleeptracker port at /dev/sleeptracker On linux you'd need to have 'ftdi_sio' kernel module loaded (and usb support, of course) and something along these lines in your udev rules: BUS=="usb", SYSFS{product}=="FT232R USB UART", SYSFS{serial}=="********", SYSFS{manufacturer}=="FTDI", KERNEL=="ttyUSB*", SYMLINK="sleeptracker", MODE="660", GROUP="usb" Note, that the I've wiped out the serial number, so that you don't try to use mine. Perhaps it will differ, although I have only one device. You can also set the other port name using SLEEPTRACKER_PORT environment variable, like env SLEEPTRACKER_PORT=/dev/ttyUSB0 napkin