#!/bin/bash
sudo cpufreq-set -r -g performance
DISPLAY=:1.0
xinit /usr/bin/urbanterror $* -- :1
Then if you want to return to your regular desktop without quitting UrT, hit Ctrl+Alt+F7 (assuming you have 6 ttys) and then F8 is UrT. Personally I only use 2 ttys though.
The cpufreq line is for bringing me back up to max speed as I usually have the "conservative" governor in use, and I only get consistent 125 fps at max speed.
I use DWM with a few patches for additional tiling modes, window movement and coloured statusbar.