Troubleshooting When GPUs Don’t Show Up

I’ve built a few rigs, and seem to run into problems when added fourth, fifith, and sixth GPUs.

Generally speaking there are a few things to try.

  • When building a rig, don’t add all the GPUs at once.  Add them one at a time and make sure they show up incrementally.  It makes troubleshooting much easier.
  • Go into the BIOS and find the PCI area.  See if there is an option talking about multiple GPUs or cryptocurrency mining.
  • Go into the BIOS and see if your motherboard has a section that shows you per PCI slot if a card is detected.
  • Go into the BIOS under PCI area and set PCI speed to “Generation 1.”
  • Others online speak to having to clear the CMOS (BIOS) memory after each GPU add.  This usually involves shorting two jumpers on the motherboard – you will have to read your manual.  You may also have to readjust your boot order.  I tried this once, and Ubuntu complained until I reordered the boot disks.  I consider this effort a last resort.
  • Double check all of your connections and that you are supplying power to the card.  If you are using PCI risers try swapping cables or trying different PCI slots methodically.  This will let you determine if an individual piece is bad, or if you are running into a motherboard limit.
  • See if you can get a clue from the syslog file.  Look to see if the log is being perpetually written to, or something video related you can do more research on.
    $ tail -f var/log/syslog
  • Sometimes getting the manufacturer of the card helps.
    lspci -knn | grep VGA -A1
  • Running lspci gives you a lot of raw information of what is connected to your system. Can be useful in some situations.