What the kernel does, and what happens from power-on to login.

How the filesystem is laid out, what inodes are, and why FHS matters.

Users, groups, permission bits, setuid/setgid/sticky, and ACLs.

Process lifecycle, signals, job control, and what PID 1 really does.

Unit files, targets, dependencies, and debugging service failures.

apt/dnf internals, repositories, pinning, and building packages.

Interfaces, routing, DNS, sockets, and common troubleshooting tools.

Block devices, LVM, RAID, ext4/xfs/btrfs, and mount options.

grep, sed, awk, jq, and pipelines for log analysis.

Robust scripting: arrays, traps, error handling, and debugging.

CPU, memory, I/O, and network profiling with perf, bpftrace, and eBPF.

journald, rsyslog, structured logging, and correlation IDs.

Capabilities, seccomp, AppArmor/SELinux, and auditd.

cron, systemd timers, at, and idempotent automation.

Namespaces, cgroups, overlayfs, and container runtimes.