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🔧 Intermediate Tier

Levels 3–4 · Goal: understanding, then operations · ~8–12 weeks at 45–60 minutes a day

You can use Linux. Now you'll learn how it works: what the kernel does at boot, how processes and memory behave, and how filesystems are built. Then you'll use that understanding to run real servers.

What you'll be able to do

  • Trace the whole path from power-on to login screen, and from a keypress to command output.
  • Read top, free, vmstat, and df correctly, including why "free memory is low" usually isn't a problem.
  • Explain inodes, hard and soft links, mounts, and why df and du disagree.
  • Manage software, services, timers, users, logs, disks (LVM and RAID), and firewalls.
  • Set up hardened SSH, nginx as a reverse proxy, and TLS certificates.
  • Troubleshoot a broken server methodically instead of guessing.

The levels

  • Level 3: How Linux works

    Boot, processes and signals, memory, filesystems and links, devices with /proc and /sys, and package management.

    Start Level 3

  • Level 4: System administration

    systemd, scheduling, networking, firewalls, SSH, disks and backups, troubleshooting, users and PAM, logging, LVM and RAID, and web servers with TLS.

    Start Level 4

Tier checkpoint

You're ready for the Expert tier when you can do all of these without notes:

  • Explain what GRUB, the initramfs, and systemd each do during boot.
  • Explain what a zombie process is and how to get rid of one.
  • Explain the difference between "free" and "available" memory.
  • Write a systemd service and a timer from scratch, and debug them with journalctl.
  • Explain how a DNS lookup works on Ubuntu, from /etc/nsswitch.conf to the stub resolver at 127.0.0.53.
  • Rebuild the Level 4 capstone server in a fresh VM in under an hour.

See the full roadmap for every concept in this tier.