Update: As Kiran points out in his comment, the initial three apt-get are not required. apt-get mongodb-stable should suffice. Also, no harm is done if you do it exactly the way mentioned below.
First install the dependencies. Helpful if you plan to work on the code or build from source. Helpful otherwise too. So just do it.
$ apt-get -y install tcsh git-core scons g++ $ apt-get -y install libpcre++-dev libboost-dev libreadline-dev xulrunner-1.9.1-dev $ apt-get -y install libboost-program-options-dev libboost-thread-dev libboost-filesystem-dev libboost-date-time-dev Next, import the 10gen signing key (company that makes mongodb) $ apt-key adv --keyserver keyserver.ubuntu.com --recv 7F0CEB10 Then, add the 10gen repo to the apt sources.list $ sudo gedit /etc/apt/sources.list Also, add the following line for ubuntu 9.10 deb http://downloads.mongodb.org/distros/ubuntu 9.10 10gen save and exit. Finally, install mongo-db $ apt-get -y install mongodb-stable You can also get the edge version using $ apt-get -y install mongodb-unstable $ apt-get -y install mongodb-snapshot Then check the installation $ mongo You should be doing fine by now.