Eks is out of business.

1. Create/edit /etc/udev/rules.d/10-local.rules
2. Add the line

   KERNEL="hiddev*", NAME="usb/%k", GROUP="plugdev"

3. Make sure your user account is a member of plugdev:

   sudo usermod $USER -a -G plugdev

4. Reload udev:

   sudo /etc/init.d/udev reload

5. Now plug in the controller and start Mixxx.