I have Ubuntu 22.04 and an NVIDIA Corporation GA102 GeForce RTX 3080 video card. The video card has 3 Displayport outputs and 1 HDMI. I have an ASUS VE278 monitor that has the HDMI plugged in and it works fine. The HDMI is plugged in with an HDMI cable going from the computer to a KVM, and another HDMI cable from the KVM to the ASUS VE278.
I also have an ASUS VE276 that has the Displayport plugged in. This has a Displayport cable going straight from the computer to the VE276.
When the computer is booting, Both screens show the POST, the Ubuntu loading logo, the login screens, etc.
However, when it finally loads into KDE, the Displayport monitor goes black and I get "DisplayPort No Signal" on the screen.
I am using the Nvidia video driver:
lspci | grep VGA
01:00.0 VGA compatible controller: NVIDIA Corporation GA102 [GeForce RTX 3080 12GB] (rev a1)
monitors currently found:
xrandr --listmonitors
Monitors: 1
0: +*HDMI-0 1920/598x1080/336+0+0 HDMI-0
More info:
lspci -k | grep -EA3 'VGA|3D|Display'
01:00.0 VGA compatible controller: NVIDIA Corporation GA102 [GeForce RTX 3080 12GB] (rev a1)
Subsystem: Micro-Star International Co., Ltd. [MSI] Device 389b
Kernel driver in use: nvidia
Kernel modules: nvidiafb, nouveau, nvidia_drm, nvidia
Why would it see the DisplayPort monitor as everything is booting, and then not be able to find it when KDE finally loads?
I noticed the monitor did show up when I ran this command (DP-4):
It turned out there is a dropdown in the Display Settings and I had to enable it there. It's just under the screen and labelled "Device". I just selected the other monitor and checked the enabled box: