I installed RHEL 7.x (GUI) in HP Z400 desktop machine. These machine has two monitors. I want to extend the display so that I can work easily in two monitors in similar way we do in windows by pressing window+p and we choose extend. When I ran following commands it does not show any name.

# xrandr
xrandr: Failed to get size of gamma for output default
Screen 0: minimum 1920 x 1080, current 1920 x 1080, maximum 1920 x 1080
default connected primary 1920x1080+0+0 0mm x 0mm
1920x1080 0.0*

Second monitor is connected via HDMI.

If you have gnome-control-center installed you can use it to make configuration of the displays easier.

Run "gnome-control-center" from a terminal window, select Panel, info to see the current setup, or Panel, display to change the configuration.