remove and reinstall mongodb

sudo apt-get purge mongodb mongodb-clients mongodb-server mongodb-dev
sudo apt-get purge mongodb-10gen
sudo apt-get autoremove

above 3 commands will remove all the installed libs from the ubuntu server. 

Install MongoDB

Configure Package Management System (APT)

The Ubuntu package management tool (i.e. dpkg and apt) ensure package consistency and authenticity by requiring that distributors sign packages with GPG keys. Issue the following command to import the 10gen public GPG Key:

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv 7F0CEB10

Create a /etc/apt/sources.list.d/10gen.list file using the following command.

echo 'deb http://downloads-distro.mongodb.org/repo/ubuntu-upstart dist 10gen' | 

sudo tee /etc/apt/sources.list.d/10gen.list

Now issue the following command to reload your repository:

sudo apt-get update

Install Packages

Issue the following command to install the latest stable version of MongoDB:

sudo apt-get install mongodb-10gen

When this command completes, you have successfully installed MongoDB! Continue for configuration and start-up suggestions.