External sites

Miscellaneous

https://lzone.de/cheat-sheet/

Networking

Nmap Cheat Sheet

https://hackertarget.com/nmap-cheatsheet-a-quick-reference-guide/

Regex

https://regex101.com/

Shell tricks

http://www.etalabs.net/sh_tricks.html

https://shellmagic.xyz/

Security

https://highon.coffee/blog/security-harden-centos-7/

Unbound DNS checker

https://unboundtest.com/