Watch each command run in a real-looking terminal, see what every part of it means, then try it yourself with practice tasks. From ls to kubectl.
The first three commands on any server: where am I, what's here, and how full is the disk.
Keys, certificates, brute-force protection, firewalls and auditing.
ssh-keygenCreate and manage SSH keysBeginnerssh-copy-idInstall your public key on a serverBeginneropensslInspect certificates, test TLS and create keys and CSRsIntermediatefail2ban-clientInspect and control fail2ban's brute-force bansIntermediateufwManage the host firewall the simple wayBeginnerauditctlAdd kernel audit rules: who touched what, and whenAdvancedsestatusCheck SELinux status and modeIntermediatelastShow login history, reboots and failed loginsBeginner