Ubuntu's max resolution is 1024x768 (unknown monitor)

From https://askubuntu.com/questions/139947/why-cant-ubuntu-12-04-detect-my-screen-resolution

Open your terminal and run this:

xrandr --newmode $(cvt 1280 1024 60 | grep Mode | sed -e 's/.*"/1280x1024/')

First type xrandr -q to see your valid screen outputs eg. VGA1/DVI-1 etc...
Then xrandr --addmode DVI-1 1600x1200
Then new option will appear in your Displays configuration
Tested on ubuntu 14.04 and 2 screens ;)
note this change is not persistent after restart. To make it persistent I made shell script which do above mentioned command xrandr --addmode... and then I add line to file /etc/lightdm as follows

[SeatDefaults]
display-setup-script=pathToYourScript

this way new resolution is added before desktop try to set it...

For 1920x1080 res 60 Hz use following:

xrandr --newmode $(cvt 1920 1080 60 | grep Mode | sed -e 's/.*"/1920x1080/')
xrandr --addmode VGA-1 1920x1080

One may encounter different output names: VGA1, VGA-1, etc.

More info HERE.