The Mahout installation manual from Cloudera has the following section:
Mahout prerequisites
Important If you have not already done so, install Cloudera's yum, zypper/YaST or apt repository before using the instructions below to install Mahout. For instructions, see CDH3 Installation.
During the CDH3 Installation Cloudera's package repository http://archive.cloudera.com/debian <RELEASE>-cdh3 contrib
is being configured in your system, so that after following the manual you shall be able to install mahout using apt-get
.