how to Configure Additional Repositories


Before you install any additional packages it's best to first install the Synaptic Package Manager since it lets you download multiple packages at a time easily. Open a terminal (Dash > Terminal) and enter
sudo apt-get install synaptic
Some packages like the Adobe Reader are not available in the standard Ubuntu repositories. The easiest way to make such packages available to your system is to add the Medibuntu repository.
Again, open a terminal and edit /etc/apt/sources.list...
sudo gedit /etc/apt/sources.list
... and enable the oneiric partner and Ubuntu Extras repositories (if they are not already enabled):
[...]
## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and
the
## respective vendors as a service to Ubuntu users.
deb http://archive.canonical.com/ubuntu oneiric partner
deb-src http://archive.canonical.com/ubuntu oneiric partner

## This software is not part of Ubuntu, but is offered by third-party
## developers who want to ship their latest software.
deb http://extras.ubuntu.com/ubuntu oneiric main
deb-src http://extras.ubuntu.com/ubuntu oneiric main
[...]

Then save the file.
To enable the Medibuntu repository, please do the following:
Import the repository:
sudo wget http://www.medibuntu.org/sources.list.d/$(lsb_release -cs).list --output-document=/etc/apt/sources.list.d/medibuntu.list
Import the gpg-key and update your package-list:
sudo apt-get update && sudo apt-get install medibuntu-keyring && sudo apt-get update
Then run
sudo update-apt-xapian-index
to make Synaptic display packages from third-party repositories.