Who is who

• dpkg, “a medium-level package manager for Debian”
• apt, “the main command-line package manager for Debian and its derivatives”
• aptitude, “an Ncurses and command-line based front-end to numerous Apt libraries” or just “TUI for Apt”

Recipies

Reverse dependencies

1. A simple one

   apt rdepends bash

   or more precise

   apt-cache \
       rdepends \
       --no-recommends \
       --no-suggests \
       --no-enhances \
       --recurse \
       --installed \
       perl

2. More complicated and informative

   aptitude why bash

Package the file came from

$ dpkg -S `which bash`

Packages from alternative sources

$ grep Package /var/lib/apt/lists/*amd64_Packages \
    | grep -v ubuntu\.com \
    | grep -v canonical\.com