Is there a method or command which can tell from which repository a package is coming from?

Commands Needed:

• 
  dpkg -s <package> - allows you to
  find the version of that
  you have installed. (source)


• 
  apt-cache showpkg <package> - will
  show a list of Versions of the
  package available. For each version,
  the source of the package, in the
  form of an index file name, will be
  given.

If you want to find the source of the package that's currently installed, you'll need the output of dpkg -s <package>. Otherwise, you can simply look at the newest version output by apt-cache showpkg <package>.

Example:

$ dpkg -s liferea

Package: liferea

Status: install ok installed

Priority: optional

Section: web

Installed-Size: 760

Maintainer: Ubuntu Developers <ubuntu-devel-discuss@lists.ubuntu.com>

Architecture: i386

Version: 1.6.2-1ubuntu6

...



$ apt-cache showpkg liferea

Package: liferea

Versions: 

1.6.2-1ubuntu6.1 (/var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_lucid-updates_main_binary-i386_Packages)

 Description Language: 

                 File: /var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_lucid-updates_main_binary-i386_Packages

                  MD5: 557b0b803b7ed864e6d14df4b02e3d26



1.6.2-1ubuntu6 (/var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_lucid_main_binary-i386_Packages) (/var/lib/dpkg/status)

 Description Language: 

                 File: /var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_lucid_main_binary-i386_Packages

                  MD5: 557b0b803b7ed864e6d14df4b02e3d26

...

From the first command, I can see that Liferea version 1.6.2-1ubuntu6 is installed. From the second command, I can see that that version is listed in /var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_lucid_main_binary-i386_Packages.

Without too much effort, I can deduce that the source line contains archive.ubuntu.com, ubuntu, lucid, and main.

And, sure enough, my /etc/apt/sources.list contains the following line.

deb http://archive.ubuntu.com/ubuntu lucid main universe restricted multiverse

Use following command. It has better output:

apt-cache policy <Package Name>

For Ubuntu 16.04 and later there is a shorter way to do that:

apt policy <Package Name>

Sadly, this information is not recorded during package installation. You can make a decent guess if the repository is still in the source list and the repository still has the package:

grep -l PKG /var/lib/apt/lists/*

Even synaptic cannot tell if you disable the repository and update.

apt on Ubuntu 16.04+

Beside apt-cache policy, showpkg and show, now we have a more simple, easy to remember subcommands: apt (don't confuse with classic apt-*):

apt policy <package> 

or the alternative with more info apt show <package>, line starting with "APT-Sources:".

Description: This package provides commandline tools for searching and managing as well as querying information about packages as a low-level access to all features of the libapt-pkg library. These include:apt-get, apt-cache, apt-cdrom, apt-config, apt-key.

Basic commands from apt --help

Other also easy to remember subcommands:

• 
  list – list packages based on package names


• 
  search – search in package descriptions


• 
  show – show package details


• 
  update – update list of available packages


• 
  install – install packages


• 
  remove – remove packages


• 
  upgrade – upgrade the system by installing/upgrading packages


• 
  full-upgrade – upgrade the system by removing/installing/upgrading packages


• 
  edit-sources – edit the source information file