On Debian at least, there are two major upgrading methods - upgrade, and dist-upgrade. Upgrade (also called safe upgrade) doesn't introduce new invasive dependencies (for example it doesn't remove existing packages). It upgrades the current system to latest packages given those restrictions. dist-upgrade on the other hands brings all existing updates, including removing packages and other new dependencies. Is there a way to tell apper which path to choose? There doesn't seem to be any option for that in the configuration UI.

Another related question - how does apper handle packages which ask questions during installation? So far I didn't encounter such case, but I was wondering what will happen, or it answers yes by default? Is there optionally a way to see a terminal output while it runs?

(Just to note, I use CLI tools like apt-get to upgrade, but I'd like to understand how apper works when I recommend it to users who prefer GUI tools).
Thanks.

first apt-get upgrade is completely different from aptitude safe-upgrade never mix the two, the same is true for apt-get dist-upgrade and aptitude full-upgrade.
aptitude uses a completely different code for resolving dependencies which is not in the apt-pkg library.
About Apper it is just an user interface it doesn't has options to tell the difference about upgrade and dist-upgrade since most users don't know the difference which is pretty much just "Allow packages to be removed". I was careful with this since I'm the author of the UI (Apper) and also the backend (aptcc), so the backend always emit packages that a dist-upgrade would install, that is because if I don't do that people would have blocked updates (those that would remove something) that could never be installed (the original behavior was to use the upgrade and this ended up with messed systems). So since the user can cherry pick packages he can choose to update just a few maybe only those that the upgrade command would install.
Even if the user select all updates I took care enough to show the packages to be removed always and they are
presented to the user first, so he'll always know that the upgrade will remove some packages.

About the questions done in packages, yes it's properly handled it took a while for me to work this out, but after I wrote libdebconf-kde PackageKit has full support for that, so if a package has to ask you something you will just see a native KDE dialog asking you the questions. Even if this fail it won't answer the questions probably showing up again on a next installation.

And last no, there's no way to see a terminal because we don't actually have one, we cared enough to put all possible information on a user-like interface so the "terminal" output is parsed and the progress is properly show on the user interface, even conffile conflicts are properly shown there.

The upcomming release of Apper will even deal with apt-get -f install so your users will never need a terminal (hopefully )

Best

Thanks for the detailed answer!

One of the things that I find quite useful is apt-listbugs tool, which adds bug reports to apt-get, helping to postpone some updates which are potentially broken. Is it possible to add something of that sort to the apper?