How to force screen resolution on CentOS machine

Question

I have CeontOS machines connected to LCD via KVM which causes failure to properly detect screen resolution and I'm stuck with 800x600 until I reset X server with the LCD connected directly to the PC. How can I enforce higher screen resolutions?

Thanks.

EDIT: I followed the advise and left only one resolution in my xorg.conf but it didn't help.

Section "Screen"
    Identifier "Screen0"
    Device     "Videocard0"
    DefaultDepth     16
    SubSection "Display"
            Viewport   0 0
            Depth     16
            Modes    "1440x900" 
    EndSubSection
EndSection

Solution

You could try creating a new resolution mode with xrandr and setting the display output to the new mode. The following example assumes that your external monitor is on HDM1 and you want a 1920x1080 resolution.

cvt 1920 1080 # Get the correct settings for the new mode
              # Output for me:  "1920x1080_60.00"  173.00  1920 2048 2248 2576  1080 1083 1088 1120 -hsync +vsync

xrandr --newmode "1920x1080_60.00"  173.00  1920 2048 2248 2576  1080 1083 1088 1120 -hsync +vsync 
xrandr --addmode HDMI1 1920x1080_60.00 # Change HDMI1 to whatever output you want to use
xrandr --output HDMI1 --mode 1920x1080_60.00

After executing the last command, your display should be using the new resolution.