It's a good idea to safe a list of all installed packages for a reinstall
Safe a list of all selected packages
sudo dpkg --get-selections > packages.txt
To restore all the applications from your list, you must follow a three step process very carefully.
sudo dpkg --set-selections < packages.txt sudo apt-get dselect-upgrade
Ref: http://savvyadmin.com/backup-and-restore-package-lists-in-ubuntu/
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