running more than one linux distribution without rebooting ...

My laptop has reached Nirvana with Debian Squeeze, everything works out of the box, and I very happy with the stability of the system. I don't feel the software is outdated, because I anyway install some applications I need or like directly from source.
However, I still want to be able to run Debian testing, and see how my system evolves. Enter "chroot".

With chroot I can run more that one Linux Distro and more than one X-Server with out the need to stop my work and reboot my laptop. This is just great.

Here is how to do it, assuming you already have a partition with a Debian installed on in do the following (if you don't have a partition with Debian installed, I suggest you take a look at "debootstrap"):

1. First make a location where you will work as the root of the new debian, in my case:

$ su -
# mkdir /debian-sec

2. now mount that partition, in my case /dev/sda5:

mount /dev/sda5 /debian-sec

3. enable important devices so the new Debian will work as expected.

mount -o bind /proc /debian-sec/proc
mount -o bind /dev/ /debian-sec/dev/ 

mount /dev/pts /debian-sec/dev/pts -t devpts 

mount -t sysfs /sysfs/ /debian-sec/sys 

4. finally change the root with chroot:

chroot /debian-sec/ /bin/bash

If you want to run a secondary X-Server, do the following inside the chroot:

chroot # vi /etc/gdm/gdm.conf # do s/vt7/vt9/ in [servers] section
chroot # /etc/init.d/gdm start

this will start another X-Server on vt9, to which you can switch with Alt+Ctrl+F9.

Cheerios, Linux and Debian !

UPDATE: The last section about GDM in chroot seems not to work in gdm3...
with gdm3:

chroot # vim /usr/share/gdm/gdm.schemas

change the following keys:
   <schema>
      <key>daemon/FirstVT</key>
      <signature>i</signature>
      <default>9</default>
    </schema>


What does work ?

Switch to tty1, login as root, and chroot into the chrooted debian.
Then chanage to with "su - "

now start the X server as the following:

startx /usr/bin/fluxbox -- :1&

or

startx /usr/bin/gnome-session -- :1&

or

startx  -- :1&