Install dependencies

apt-get install ocl-icd-libopencl1

Install OpenCL drivers and CPU runtime from https://software.intel.com/en-us/articles/opencl-drivers#latest_CPU_runtime

Clone the hashcat GitHub repo

cd /usr/local/src && git clone https://github.com/hashcat/hashcat.git && cd hashcat && git submodule update --init

Build and install hashcat

make && make install

Verify that the CPU is detected

hashcat -I