The kernel primitives, init systems, and tooling behind the world's most-deployed OS.
The real story behind Linus Torvalds' 1991 Usenet post, what it actually said, and how a self-described hobby project became the kernel running most of the internet.
A complete walkthrough encrypting a disk or partition with LUKS, from initial setup through mounting it automatically (with a key file) at boot.
A complete walkthrough from raw disks to a mounted, resizable logical volume — physical volumes, volume groups, and logical volumes explained as you build them.
A practical toolkit for watching CPU, memory, disk, and network usage live — going beyond top to actually find what's causing a resource problem.
A complete, working nftables ruleset for a typical server — default-deny inbound, stateful connection tracking, and a handful of explicit allowed services.
A complete walkthrough generating an SSH key pair, deploying it correctly, and disabling password authentication safely — without locking yourself out.
A complete walkthrough using strace to see exactly which system calls a misbehaving program is making — often the fastest way to diagnose a problem with no useful log output at all.
A complete, working example converting a nightly backup cron job into a properly supervised systemd timer, with logging and failure visibility cron never gave you.
A minimal but complete walkthrough of writing, building, loading, and communicating with a Linux kernel module.
How SELinux's label-based policy and AppArmor's path-based profiles both extend Linux's discretionary permission model, and how to work with each day to day.