@utu:

As long as you use a persistent image or an HD istall all modifications will be permanent. I think you should make a backup copy of the files you want to modify. /etc/init.d/knoppix-startx is the only file I would change. In this file you can search for the command line which calls startx and alter the command. You have to restart your Xserver after this customisation. Usually you can restart the Xserver from inside the graphical environment by hitting the key combo Ctrl-Alt-Backspace. It is also possible to change the system's runlevel from a virtual terminal:
Code:
init 2
init 5
The first command changes the runlevel to a runlevel without the Xserver. The second command starts runlevel 5 which includes the Xserver. You should close all your applications inside the grahical environment (like Iceweasel or LXTerminals) before you kill the Xserver. The log file will be created and you will able to read it.

If you like to keep your log file during reboots then it must be created in a directory that is permanent. I would use the home diretory /home/knoppix for this purpose.

You don't need vt #6 for logging purposes, but on my system switching over to a virtual terminal is faster than opening an xterm and starting an application to read the log file.