Security guides

Links to security hardening guidelines:

https://help.ubuntu.com/community/Security

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/pdf/security_guide/Red_Hat_Enterprise_Linux-7-Security_Guide-en-US.pdf

https://openvas.org/

https://linux-audit.com/find-the-alternatives-cis-cat-auditing-tool/