SELinux AKA Security-Enhanced Linux

• https://en.wikipedia.org/wiki/Security-Enhanced_Linux
• https://learning.oreilly.com/topics/selinux/
• https://learning.oreilly.com/library/view/selinux-system-administration/9781800201477/
• https://learning.oreilly.com/library/view/selinux-cookbook/9781783989669/
• https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/using_selinux/

The first time I now came seriously across it was with Oracle Linux Server. I wasted like hours logging into that OS unsuccessfully supposedly making use of $HOME/.ssh/authorized_keys, misinterpreting the error messages.