Installing impact and the Digilent configuration cable drivers are not always a smooth task. The USB-JTAG cable is not supported directly with the driver provided by Xilinx in the Lab Tools, therefore it is necesarry to install external drivers.
In the Xilinx forums it is possible to find a great number of questions regarding the installation of the cable drivers but most of those solutions do not really work. The following is a proven simple set of instructions that will install correctly the drivers.
First you need to download the Lab Tools from the Xilinx website, then:
Install official cable drivers
Install .hex and rules in correct locations
cd /opt/Xilinx/14.7/LabTools/common/bin/lin64 sed xusbdfwu.rules -e 's:TEMPNODE:tempnode:g s:SYSFS:ATTR:g s:BUS:SUBSYSTEM:g ' > /etc/udev/rules.d/xusbdfwu.rules cp xusb*.hex /usr/share udevadm control --reload-rules