There are some issues with the steps listed on the hashcat FAQ found here. This quick tutorial is specifically geared for Ubuntu when you have installed the nvidia packages from the repository. This is what I did to get it to work so hopefully it will be helpful to others.
1. Boot as normal and get to login screen (or desktop if you autologin).
2. Press the key combination Ctrl + Alt + F1 to exit out of the GUI. Authenticate with your username and password.
3. type sudo service lightdm stop and press Enter to stop X11 (desktop GUI).
4. type sudo apt-get remove --purge nvidia* and press Enter to purge all nvidia items.
5. type sudo find / -name libOpenCL\* -print0 | xargs -0 rm -rf to find and puge all libOpenCL files
Boot as normal and get to login screen (or desktop if you autologin).
Press the key combination Ctrl + Alt + F1 to exit out of the GUI.
Authenticate with your username and password.
Don’t follow this command from the hashcat FAQ ==>For Linux only: apt-get -y install ocl-icd-libopencl1 opencl-headers clinfo
Install the latest Nvidia Driver
Visit https://launchpad.net/~graphics-drivers/+archive/ubuntu/ppa to determine the latest Nvidia drivers found in the repository. Also check to ensure your graphics card supports the latest driver (http://www.nvidia.com/object/unix.html).
$sudo apt-get -y install nvidia-384 nvidia-libopencl1-384
For Linux only: rm -rf ~/.hashcat/kernels
Reinstall hashcat, choose:
Stable Version: Download and extract (under Linux, make sure to use: “7z x” to extract) the newest hashcat from https://hashcat.net/
Development Version: git clone https://github.com/hashcat/hashcat
Try to run hashcat –benchmark