リンク
Install MongoDB on Red Hat Enterprise, CentOS, or Fedora — MongoDB Manual 2.4.9
流れ
sudo vi /etc/yum.repo.d/mongodb.repo
[mongodb] name=MongoDB Repository baseurl=http://downloads-distro.mongodb.org/repo/redhat/os/x86_64/ gpgcheck=0 enabled=1
# yum install mongo-10gen mongo-10gen-server
# service mongod start