Linux Security Books and Resources

Question

linux

Please tell me good resources and tutorials on securing Linux systems.
I am looking for an “advanced” manual, because I am familiar with the basic concepts of security - I read the recommendations of the NSA and partially applied them, I make backups, I use hids and nids, firewalls are configured.
I would like to systematize and deepen my knowledge.
Thank you.

Answer 1

cisecurity.org/

Answer 2

Yes, there are quite a few useful standards on cisecurity. Here are some direct links at once:
RHEL
Solaris
Debian
FreeBSD

Answer 3

Thanks to all who answered)