removing software that wasn't installed with apt
 

I want to uninstall some software, but for some reason (I suppose because it's third-party software that I didn't use apt to install?), apt doesn't seem to know the software (Virtualbox) is installed. (I used the Virtualbox shell script to install it.) Apt and dpkg are generally the only tools I fully know how to use to install or remove software; in some cases (such as with the shell script) I know how to install without apt, but I don't think I know how to cleanly uninstall anything.

See section 2.3.3.4 in the User Manual -->http://download.virtualbox.org/virtu...UserManual.pdf

Thank you. And what about software in general that apt didn't install and doesn't recognize?

The reason you usually see things like " Use the package manager for your distro " is so you don't have this problem. You will have to investigate each piece of software you install through other means. There is no set answer here that will work in all cases.

I try to avoid adding software from other sources. The exceptions for me are Virtual Box and nVidia drivers. Both provide a path to remove, and upgrade. Oh yes, plugins for Firefox are often 3rd party as well. The best advice I can give you is to look at the doc for the software, if it doesn't clearly tell you how to uninstall it, or upgrade, don't install it.

if you built the source
( and KEPT IT )

just run ( as root) in the build folder
most ( but NOT all ) make files have a "make uninstall" section

if it is a .bin( AKA .run) installer
rerun the installer with the option " --uninstall"
see the "help" section in that installed
for example the nvidia.run driver