Offloading to GPU for a time study on my new rig - advice
As stated - I have a new system that my wife let me build for Christmas, and I am wanting to do a time study on cracking a cap file using the CPU vs using the GPU.  I'm an engineer on furlough, this is how I am spending my morning.

I have a seemingly-common 15 GB word list, and I purposely set the passcode on my old Lynksys router to a very late word from a dictionary with a trailing question mark (after ensuring the word list is in alphanumeric order) to make certain it would take a fair amount of time.

Aircrack is actually running as I'm writing this; 8 hours to go on a pretty consistent bead of the originally-estimated 12 hours to complete.  I got curious about whether or not I could offload this to my GPU, and looking into that question has led me here.

irst, my system:

OS: Ubuntu 20.04 LTS x86_64 
Kernel: 5.4.0-29-generic
CPU: Intel i9-9900K (16) @ 5.000GHz 
GPU: AMD ATI Radeon R9 285/380
Memory: 32032MiB

My concern is the GPU itself - The default kernel does not play well with the GPU, and requires "radeon.cik_support=0 radeon.si_support=0 amdgpu.cik_support=1 amdgpu.si_support=1" kernel parameters.  I have to admit that the specific reasons for that requirement are at the extreme limit of my Linux knowledge, but the amount of research that it took me to ultimately find that bit of information was a rocky path, and it has left me perhaps a little overly cautious when it comes to messing with such things as offloading processes to the GPU. 

My question is this:  Does this system appear to support hashcat as is, or are there there any pitfalls or horror stories that I should be aware of?  I don't want to spend the rest of my furlough having to relearn 'kernel parameters 101' all over again!

give us an
sudo hashcat -I
for more clarification on your setup. Most likely just a driver issue, being an AMD you will most likely need OpenCL drivers to be installed if they are not already. If they are installed and are POCL drivers you will need to remove them and install ROCM drivers.
Basically what slyexe said. Install rocm and hope your GPU is supported (it might be too old).