Open source IT, Cybersecurity, hacking, networking books?

Web: https://www.reddit.com/r/cybersecurity/comments/xfoebr/open_source_it_cybersecurity_hacking_networking/

Does anyone know of any actually open source (Creative Common License) books for the title's subjects? I'm looking for resources that students can use legally for studying in school and can be tested on.

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I don't know why this was removed initially, but here we go again.

books cybersecurity hacking networking open source