With sincere thanks to the link above, this is how you can adjust the screen resolution under CentOS 6.
Run this command (with the appropriate resolution):
cvt 1920 1080
You’ll get output similar to this:
# 1920x1080 59.96 Hz (CVT 2.07M9) hsync: 67.16 kHz; pclk: 173.00 MHz
Modeline “1920x1080_60.00″ 173.00 1920 2048 2248 2576 1080 1083 1088 1120 -hsync +vsync
Copy the modeline and paste it after –newmode, like so:
xrandr --newmode "1920x1080_60.00" 173.00 1920 2048 2248 2576 1080 1083 1088 1120 -hsync +vsync
Then assign the new mode to the device:
xrandr --addmode VGA-1 "1920x1080_60.00"
This was done on a clean stock CentOS 6.4 installation, no custom drivers.
To get the settings to persist across sessions, I created /etc/gdm/PostLogin/Default
Under the account, I add the Default file:
Be sure to grant execute permissions on both /etc/gdm/PostLogin/Default and $HOME/.gdm/PostLogin/Default.
Adding nVidia drivers didn’t help, adding hplip didn’t help. There is a Tripp-Lite KVM switch. This was the answer.
And, it looks great.