print double side.

lpoptions -p printer_name -l
the above will display all the options for help. And the final command is:
lpoptions -p printer_name -o Duplex=DuplexNoTumble

start GUI windows using root account.

Usually I did is to start a terminal, su to root account and then start the GUI window. Another way to do is:
1. click the K menu.
2. click "run command..."
3. input "kdesu kate" for example, then you will be asked to input root's password.

Change default x window manager.

How to change the default window manager (KDE, Gnome, etc.) in Debian "Sarge":

Symlinks in /etc/alternatives point to various "default" programs (as far as Debian is concerned).

The one you're looking for is /etc/alternatives/x-session-manager

You can also use `/usr/sbin/update-alternatives --config x-session-manager`.

To change the default display manager (the program that presents the login screen) to KDE,
install kdm using `apt-get install kdm` and it should ask you which display manager you want to be the default.

From here


What I did is the following, since I already installed kdm and gdm before. I can not automatically start kdm. So I did the following:
# /usr/sbin/update-alternatives --config x-session-manager

There are 4 alternatives which provide `x-session-manager'.

Selection Alternative
-----------------------------------------------
*+ 1 /usr/bin/gnome-session
2 /usr/bin/startkde
3 /usr/bin/icewm-session
4 /usr/bin/xfce4-session

Press enter to keep the default[*], or type selection number: 2
Using `/usr/bin/startkde' to provide `x-session-manager'.


After this, I still cannot start kdm automatically.

Sysv-rc-conf

From Wiki

[edit]

sysv-rc-conf - Run level configurator (front-end) for init.d scripts (Debian)

apt-get install sysv-rc-conf

To Run, type in:

sysv-rc-conf

A graphical list of all items stored in /etc/init.d/ will be listed. Items placed in this directory must be given a run-level.

I run

sysv-rc-conf

and found that kdm is not run under run level 4 which is the run level I used. So I check kdm up, and try.