Need to find out about the setup then!
CPU?
USB 3 Risers?
Motherboard?
Number of GPUs?
Type of GPUs?
Ubuntu Version?
Do you have one GPU acting as the display output or are you using onboard graphics?
PCI-E settings?
6600K
MSI Z170 Pro
2x 1060, 2x 1050 Ti (USB3 Risers)
Ubuntu 17.04
onboard output (tried GPU but doesn't work either)
Gen1, 4G decoding