The following command create a list of installed packages on a machine, and then reinstall the same packages in another machine (or the same).
It seems that the command work fine on Ubunt 32 Desktop , but on Ubuntu amd64 (Desktop) the sudo apt-get dselect-upgrade tell me that he need to uninstall a lot of packages (even unity unity-2d unity-common!! ) even if in the list of packages those packages are present. Even if those command are give in sequence on the same computer, they work fine in a 32 bit environment, and seems to fail in a 64 bit environment. May be i have miss something
sudo dpkg --get-selections > installed-software
sudo dpkg --set-selections < installed-software
sudo apt-get dselect-upgrade