Notes about Ubuntu and Lubuntu (a lightweight Ubuntu).
Ubuntu is based on Debian so you may find my Debian notes useful.
Determine Ubuntu version
lsb_release -a
Reference: Checking your Ubuntu Version
Purge an application
sudo apt-get purge [package]
Purge will remove the application and its configuration files.
Add a PPA repository
PPA is a third-party archive of application packages.
sudo apt-add-repository ppa:foo/bar
Remove a PPA repository
sudo apt-add-repository --remove ppa:foo/bar
However, at the time of writing there is a bug that prevents this working properly. See apt-add-repository –remove doesn’t remove deb-src entry .
Until this is fixed you’ll have to remove them manually:
sudo rm /etc/apt/sources.list.d/foo-bar-precise.list
sudo rm /etc/apt/sources.list.d/foo-bar-precise.list.save
Where ‘precise’ is the Ubuntu release.
Reference: How do I remove a PPA added via command-line?.