Sometimes there is no external network connection on the machine where Mongo needs to be installed. In this case, one way is to use the general linux installation method: http://docs.mongodb.org/manual/tutorial/install-mongodb-on-linux/
Another method is to manually download the installation package and then copy it to the target machine, taking Ubuntu as an example:
1) First download it on a machine with external network, such as:
2) copy to your target machine
3） sudo dpkg -i mongodb-org-server_2.6.4_amd64.deb
it's ok
This only installs mongod. If you want to install mongos or tools, or other versions, you can do the same. All installable deb files are here: http://downloads-distro.mongodb.org/repo/ubuntu-upstart/dists/dist/10gen/binary-amd64/