- [A Guide to Securing Red Hat Enterprise Linux 7](https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html-single/security_guide/index)
- [nixCraft - How to set up a firewall using FirewallD on RHEL 8](https://www.cyberciti.biz/faq/configure-set-up-a-firewall-using-firewalld-on-rhel-8/)
- [NSA Harden Network Devices](https://apps.nsa.gov/iaarchive/library/ia-guidance/security-tips/harden-network-devices.cfm) - very short but good summary
- [NIST IR 7966 - Security of Interactive and Automated Access Management Using Secure Shell (SSH)](https://nvlpubs.nist.gov/nistpubs/ir/2015/NIST.IR.7966.pdf)
- [ANSSI - (Open)SSH secure use recommendations](https://www.ssi.gouv.fr/en/guide/openssh-secure-use-recommendations/)
- [Linux Audit - OpenSSH security and hardening](https://linux-audit.com/audit-and-harden-your-ssh-configuration/)
- [LDAP: Hardening Server Security (so administrators can sleep at night)](https://ff1959.wordpress.com/2013/07/31/ldap-hardening-server-security-so-administrators-can-sleep-at-night/)
- [Hardentools](https://github.com/securitywithoutborders/hardentools) - for Windows individual users (not corporate environments) at risk, who might want an extra level of security at the price of some usability.