Failure to Show 6 Display Card in Ubuntu 16.04

I get Ubuntu 16.04 and 6 pieces of Nvidia 1070 display cards.

I have installed the driver for the 6 display cards by referring to https://www.youtube.com/watch?v=PeWTSprpq1M.

With 4 display cards, the software Nvidia X Server Settings can only shows 3 in the Ubuntu OS. With 6 display cards, the software can show 2 only. How can the OS identify all of the 6 display cards?

Use a power supply that can actually support that many gpus.

Also make sure your BIOS is correctly configured for more than 4 GPUs (4G decoding enabled)