Lynis is yet another FOSS tool that you can use to scan your systems for vulnerabilities and bad security configurations. It comes as a portable shell script that you can use not only on Linux, but also on a variety of different Unix systems and Unix-like systems. It's a multipurpose tool, which you can use for compliance auditing, vulnerability scanning, or hardening. Unlike most vulnerability scanners, you install and run Lynis on the system that you want to scan. According to the creator of Lynis, this allows for more in-depth scanning.

The Lynis scanning tool is available as a free-of-charge version, but its scanning capabilities are somewhat limited. If you need all that Lynis has to offer, you'll need to purchase an enterprise license.