Hello Linux Geeksters. The Linux Mint developers have decided to delete the Cinnamon Stable PPA from LaunchPad, so Cinnamon (stable) is not available for Ubuntu 14.04 Trusty Tahr anymore. This decision has been taken due to the fact that the old GNOME packages will be removed from the Ubuntu repositories and so, installing Cinnamon on Ubuntu will be very difficult, if not impossible.
As you may know, Cinnamon is a GNOME Shell fork, created by the Linux Mint, in order to provide an alternative for the good old GNOME2. The latest version is Cinnamon 2.2.0 (used by default on Linux Mint 17 Cinnamon), which brings changes to the previous version. For information about it, see this article.
For now, Cinnamon 2.2.0 can still be installed on Ubuntu 14.04 Trusty Tahr via either the Linux Mint repositories or the Cinnamon Nightly PPA (that contains only under development versions of Cinnamon).
Method 1: How to install Cinnamon 2.2.0 on Ubuntu 14.04, via the Linux Mint repository:
$ sudo sh -c 'echo "deb http://packages.linuxmint.com/ qiana main upstream import" >> /etc/apt/sources.list'
$ sudo apt-get update
$ sudo apt-get install linuxmint-keyring
$ sudo apt-get update
$ sudo apt-get install cinnamon
Reboot the system and choose Cinnamon from the LightDM greeter:
$ sudo reboot
If the first method fails, use the Cinnamon Nightly PPA, but this may break you system, due to the fact that the Cinnamon version there is not stable.
Method 2: How to install Cinnamon 2.2.0 on Ubuntu 14.04, via the Cinnamon Nightly PPA:
$ sudo add-apt-repository ppa:gwendal-lebihan-dev/cinnamon-nightly
$ sudo apt-get update
$ sudo apt-get install cinnamon
Reboot the system and choose Cinnamon from the LightDM greeter:
$ sudo reboot