I believe that this question gets asked from time to time, but I do not know that a solution has been found.
The question is this; does a utility exist, that can be ran, to produce a list of installed packages, in a way that can be used by a user (system administrator), to perform a system rebuild, so as to, after installing the system again, ensure that all of the optional packages that were previously installed, are again installed in the new system installation?
I am running UbuntuMate 15.10, on a system with other Linux operating system versions (which are inappropriate for the hardware), that are not used, installed, and, with wanting to eliminate them, and, repartition the HDD, for a number of reasons, including occasionally seeing an error message that states that the partitioning is out of alignment, or something (I am not sure of the exact message, or, how to reproduce the error message), I believe that a new installation of the operating system, is needed, but, I want to again, have all of the existing installed optional packages, installed and operable.
So, I figure that, if a utility exists, that can produce a list of the installed optional packages, that could help me to reproduce the system, with its current functionality, in terms of the currently installed, optional packages.