When upgrading to version 15.04 from 14.10 there was a "clean up" time period where I received a query to eliminate 18 unused or unnecessary packages. Can anyone show me where I can make sure that I don't have any superfluous unused packages?
First you should know our systems is not that smart !! A system can't know which package is needed by you or not. Ubuntu can't remove any package that were installed by the user himself, instead it offers you to delete the packages that were downloaded as dependencies for other packages and not used anymore, which means those packages were installed by the system itself and not by the user...
autoremove autoremove is used to remove packages that were automatically installed to satisfy dependencies for other packages and are now no longer needed.
sudo apt-get autoremove will uninstall the unused packages which were used as dependencies for other packages.
A system can show you the Important or required packages so those is not supposed to be removed.
Install aptitude if you don't have it:
sudo apt-get install aptitude
Now you can search for packages considered required:
aptitude search '~prequired'
aptitude search '~pimportant'
How To know The unused packages in Ubuntu
There is a bash script for a tool called unusedpkg, this can test since when you didn't use the packages so you can determine what to delete.
Download the script. Extract the zipped folder then give permission to the script
chmod +x unusedpkg
Now you can run it from dir containing the script
* UnusedPkg 0.6 Find unused packages in your Linux system. WARNING: Idle days may be wrong. Before delete anything, check package timestamps using 'unusedpkg info <package>', or manually with 'ls -alu'. View README for infos. Minimum packages size: 1MB IDLE DAYS SIZE PACKAGE NAME 1 year and 6 months (553 days) 8MB 0ad 1 year and 6 months (553 days) 2MB gnect 1 year and 6 months (553 days) 1MB libgvc5 1 year and 6 months (553 days) 8MB locales
These tips might be helpful to clean up your system and remove unused packages
sudo apt-get autoclean to clean up outdated package deb files
sudo apt-get autoremove to remove any unused dependencies
sudo apt-get clean to clean up apt cache
man apt-get to get more info on apt-get and how to use it.