I found the base of the solution here: https://askubuntu.com/questions/186288/how-to-detect-and-configure-an-output-with-xrandr
In modern Linux distributions, including CentOS, the xrandr library is responsible for things such as screen resolution, rotation and so on. Since your system does not autodetect, you have to manually tell it about the mode your monitor is capable of.
I had the same problem with a KVM, and the sample output is from my computer:
Find the name of your port. This will be something like VGA1, HDMI1 or so. You maybe able to find it from /var/log/Xorg.0.log, or you can use the xrandr utility:
Screen 0: minimum 8 x 8, current 1024 x 768, maximum 32767 x 32767
DP1 disconnected (normal left inverted right x axis y axis)
HDMI1 disconnected (normal left inverted right x axis y axis)
VGA1 connected primary 1024x768+0+0 (normal left inverted right x axis y axis) 0mm x 0mm
800x600 60.32 56.25
VIRTUAL1 disconnected (normal left inverted right x axis y axis)
My KVM is connected to the VGA port called VGA1. Because the KVM blocks auto-detection, xrandr only saw the 1024x768 resolution.
Tell xrandr about the new mode. Modes are simply strings that have video display parameters attached to them.
Find the display parameters you need. I wanted 1600x900 @ 60 Hz:
> gtf 1600 900 60 -x
# 1600x900 @ 60.00 Hz (GTF) hsync: 55.92 kHz; pclk: 119.00 MHz
Modeline "1600x900_60.00" 119.00 1600 1696 1864 2128 900 901 904 932 -HSync +Vsync
Create the new mode with xrandr using the values from the gtf command:
> xrandr --newmode "1600x900" 119.00 1600 1696 1864 2128 900 901 904 932 -HSync +Vsync
The first parameter is the name of the new mode - you could actually call it anything you like, just use the same name in the subsequent steps.
Tell xrandr that VGA1 understands the mode called 1600x900:
> xrandr --addmode VGA1 1600x900
Tell xrandr to switch to the new mode.
> xrandr --output VGA1 --mode 1600x900
Note: if you made a mistake and your monitor does not actually understand the new mode, you will get a blank screen!
If you do get a blank screen, you can probably recovery by blindly typing:
> xrandr --output VGA1 --mode 1024x768
Another way around that is to connect from another computer via SSH, and executing this command via SSH instead of on the console.
Create a script that automates the newmode, addmode and output commands, since they will not be preserved during a reboot.