How to find the packages that depend on a certain package in apt?

Question

How can I get, not the dependencies of a package, but the packages that are depending on a certain package?

I'm on debian 6.0 Squeeze-LTS (the first-time extension to squeeze for long term support!) for my web server, and it reports that support has ended for a certain package:

Unfortunately, it has been necessary to limit security support for some
packages.

The following packages found on this system are affected by this:

* Source:libplrpc-perl, ended on 2014-05-31 at version 0.2020-2
  Details: Not supported in squeeze LTS
 Affected binary package:
 - libplrpc-perl (installed version: 0.2020-2)

I don't really want to try to uninstall that binary package without seeing what depends on it, and it's description describes stuff that I've never heard of before:

libplrpc-perl: Perl extensions for writing PlRPC servers and clients

So I'd be fine with just removing the package if possible, but want to determine the things that depend on it before doing so.

Answer 1

Another solution would be to run apt-cache rdepends libplrpc-perl.

Answer 2

• Why it is installed:

  aptitude why libplrpc-perl

• What depends on this package:

  aptitude search '~i~Dlibplrpc-perl'

• What would happen, if libplrpc-perl is removed:

  aptitude -s purge libplrpc-perl

Answer 3

These are called reverse dependencies.

apt-rdepends -r libplrpc-perl | less

should do what you want. This shows the reverse dependencies of the specified package, and then the reverse dependencies of those reverse dependencies, and so on, in recursive fashion. libplrpc-perl doesn't have any reverse dependencies, so perhaps a better choice is

apt-rdepends -r libslang2 | less

Answer 4

Does this do what you want/need?

aptitude -v --show-summary=all-packages why <package>