dpkg
PackagesPackage: dpkg
The low-level package manager: installs a .deb, lists what is installed (dpkg -l), says which package a file belongs to (dpkg -S). It does not resolve dependencies — that is apt's job.
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
dpkg -L- Lists every file a package installed. The answer to “where did that thing actually go”.
dpkg -S- The reverse: which package owns this file. A file with no answer was not installed by apt, which is itself worth knowing.
dpkg -l- Lists packages and their state. The first two letters carry it:
iiinstalled and configured,rcremoved but its configuration kept,iUunpacked but not configured. dpkg -V- Compares the installed files against their recorded checksums and prints only those that have changed since. A quick way to see what was hand-edited on a machine.
dpkg --configure- Finishes configuring a package that was unpacked and left unfinished, usually after an interrupted upgrade.
dpkg -a- With
--configure, applies to every pending package:sudo dpkg --configure -ais what unblocks a machine after an interrupted upgrade.