I'm trying to do a multihead setup and xrandr gives me the following.

xrandr: Failed to get size of gamma for output default
Screen 0: minimum 640 x 480, current 2560 x 1440, maximum 2560 x 1440
default connected 2560x1440+0+0 0mm x 0mm
2560x1440 0.0*
1280x1024 0.0
1024x768 0.0
800x600 0.0
640x480 0.0

I'm pretty confused and don't really know where to go from here.
My monitor is connected through HDMI and Displayport (PC won't output VGA for some reason).
And I haven't set anything up but I get a mirrored screen through both HDMI and Displayport.

The Display app lists my monitor as unknown, and doesn't detect either monitors.
Is there something I'm missing?

I'm using CentOS 6, Intel HD graphics 520 graphics card.

What/which "Display app"?

http://fm.no-ip.com/Share/setup contains hundreds of xrandr commands I've used over time, many of which are for multiple display use, any of which I use several times a month for software and hardware testing. Perusing them might help you understand something you're missing.

Before jumping right into xrandr, did you try arandr, or any of the multiple display utilities built into desktop settings of the various DEs?

Thanks for the reply.
I meant to say the system Display preferences, my bad.
There it says monitor unknown and doesn't detect other monitors.

I'm a novice in terms of linux use, so I have only used what I have found online.
Trying arandr I got command not found.

Which DE or WM is that in? Gnome? XFCE? KDE? Something else?

If CentOS doesn't package it you should be able to install one of the Fedora arandr packages from https://rpmfind.net/linux/rpm2html/s...p?query=arandr or from https://christian.amsuess.com/tools/arandr/ .

If you have a nVidia adapter and driver, nvidia-settings will automatically set up dual-monitors.

Not very helpful to someone with Intel 520 graphics. My guess at the problem is running new hardware with CentOS 6, which is end-of-life. Should update to Fedora to run recent hardware.