This article provides step-by-step instructions on installing and using the Nessus vulnerability scanner on Ubuntu Linux. Nessus, an open-source tool for vulnerability assessment and penetration testing, uses the CVE architecture and can be installed on various platforms. The article details the download and install process of Nessus DEB package and how to launch and manage Nessus services. It also gives instructions on setting up the Ubuntu firewall and accessing the Nessus web portal.