When I used Windows 7 on the same PC, I didn't have this problem. Now I can't start my server if monitor is not connected. When I turn it on without monitor, I can't hear HDD loading and also can't connect via SSH. I tried to add nomodeset to my /etc/default/grub, and then grub2-mkconfig -o /boot/efi/EFI/centos/grub.cfg, but it doesn't fix anything. Booting with keyboard doesn't work, monitor is a rootcause.

What can I do?

  • What is displayed when you connect the monitor after it has failed to boot? – Fabby Feb 17 at 14:02
  • when i connect monitor after boot, monitor doesn't show anything at all, i thing its a bug of hdmi – stiv Feb 17 at 14:08
  • Try booting it with just a keyboard attached, does it boot? – Michael Prokopec Feb 17 at 14:24
  • Did you update the firmware between upgrading from W7 to CentOS? – Fabby Feb 17 at 14:36
  • no, hardware and bios are the same absolutely – stiv Feb 17 at 14:43

You could try these dummy plugs as options:


  • HW problem, HW solution: +1 although technically off topic. – Fabby Feb 17 at 15:42
  • This is software problem, because Windows7 works correctly on same hardware. – stiv Feb 17 at 16:13
  • Windows talks directly to the BIOS these days and does things to make using it easier, without notifying the user what it did. So there is no telling what it did or is doing. – Michael Prokopec Feb 18 at 4:25

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