This post describes howto reinstall or duplicate a Debian or Debian based distribution like Ubuntu.
First we need to extract the installed packages on the source server and save them in a file

debian:~# dpkg --get-selections >> packages

Now we move to the target server and set the package selections according to the package file we just created on the source machine.

debian:~# dpkg --set-selections < < packages

Now we just need to run this in order to actually install the packages.

debian:~# apt-get -u dselect-upgrade