Add system unrecognized but monitor supported resolution in X

xrandr.sh

#!/bin/bash

usage() {
    echo "usage:"
    echo "    $0 HResolution VResolution [RefreshRate] [Display]"
}

[[ -z $1 || -z $2 ]] && {
    usage
    exit 1
}

refresh_rate=${3:-60}
default_display=$(xrandr | awk '/ connected / {print $1}')
display=${4:-$default_display}

# First we need to get the modeline string for xrandr
# Luckily, the tool `gtf` will help you calculate it.
# All you have to do is to pass the resolution & the-
# refresh-rate as the command parameters:
#gtf 1920 1080 60

mod_string=$(gtf $1 $2 $refresh_rate | sed -n -e '3{p;q}' | sed -e 's/.*Modeline \(.*\)/\1/')
mod_name=$(echo $mod_string | sed -e 's/\(\".*\"\) .*/\1/')

# In this case, the horizontal resolution is 1920px the
# vertical resolution is 1080px & refresh-rate is 60Hz.
# IMPORTANT: BE SURE THE MONITOR SUPPORTS THE RESOLUTION

# Typically, it outputs a line starting with "Modeline"
# e.g. "1920x1080_60.00"  172.80  1920 2040 2248 2576  1080 1081 1084 1118  -HSync +Vsync
# Copy this entire string (except for the starting "Modeline")

# Now, use `xrandr` to make the system recognize a new
# display mode. Pass the copied string as the parameter
# to the --newmode option:
#xrandr --newmode "1920x1080_60.00"  172.80  1920 2040 2248 2576  1080 1081 1084 1118  -HSync +Vsync

xrandr --newmode $mod_string

# Well, the string within the quotes is the nick/alias
# of the display mode - you can as well pass something
# as "MyAwesomeHDResolution". But, careful! :-|

# Then all you have to do is to add the new mode to the
# display you want to apply, like this:
#xrandr --addmode VGA1 "1920x1080_60.00"

xrandr --addmode $display $mod_name

# VGA1 is the display name, it might differ for you.
# Run `xrandr` without any parameters to be sure.
# The last parameter is the mode-alias/name which
# you've set in the previous command (--newmode)

# It should add the new mode to the display & apply it.
# Usually unlikely, but if it doesn't apply automatically
# then force it with this command:
#xrandr --output VGA1 --mode "1920x1080_60.00"

xrandr --output $display --mode $mod_name

# That's it... Enjoy the new awesome high-res display!