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In Ubuntu 12.04 Mono package has been dropped from the official repository, therefore, it is not supported by Ubuntu and users are not able to install it from Ubuntu Software Center or Synaptic by default. In addition, the latest available version on official Mono website is 2.6.0.1 but the current release is 4.0.1. Unfortunately, binary file of version 4.0.1 has bot released yet and if you interested in installing it, you need to compile and install it from source code which could be tedious task. The latest available binary version is 3.0.3.2.
Installing 3.0.3.2 version is quite easy and you can install Mono version 3.0.3.2 easily with just using three following commands.
$ sudo apt-add-repository ppa:directhex/ppa
$ sudo apt-get update
$ sudo apt-get install monodevelop
The installation commands are from izx, user of askubuntu.com. Click here to see original thread.
More information can be found in official site of Mono, Askubuntu.com, Ubuntuforums.org.
