Linux Fundamentals & Systems Administration

Kernel Architecture, File Permissions, Process Trees & Systemd

8 modules, 39 lessons: The Kernel, The Distribution, The Filesystem; Users, Groups And Permissions; Processes, Signals And Services; Packages, Disks And Space; Addresses And Routes; Transport, Ports And Sockets; HTTP, TLS And SSH; Serving, Guarding And Diagnosing.

Beginner · 1 hour · 39 lessons · 78 labs

Who it is for

Beginner level.

For anyone starting out with Linux: support and operations staff, new security analysts, testers and developers who want to understand the servers their work runs on.

What you don't need yet:

What helps:

Before you start:

Take next:

Learning paths:

Nobody needs to know everything before they start. Each course builds on the one before, so a learning path takes you there step by step.

Labs

78 labs, 78 of them graded: you write the code, it runs, and graded labs check the result. The outline lists each lesson's labs.

What is free

Start free: First module free with an account. Pro: Every course, lab, handbook, practice exam and certificate.

Course outline

The Kernel, The Distribution, The Filesystem

  1. What A Kernel Does, And What It Refuses To Do (2 labs): Explain how the kernel mediates hardware access without replacing user space
  2. What A Distribution Actually Is (2 labs): Describe how a Linux distribution assembles a kernel, user space, and release policy
  3. The Filesystem Hierarchy (2 labs): Navigate the Linux filesystem hierarchy by purpose rather than by memorized paths
  4. Inodes, Hard Links And What rm Removes (2 labs): Explain how directory names point to inodes and why removing a name does not erase every reference
  5. Everything Is A File: proc, sys And dev (2 labs): Distinguish ordinary files from the kernel-backed interfaces exposed through proc, sys, and dev

Users, Groups And Permissions

  1. Users, UIDs And The Password File (2 labs): Explain how Linux identifies users with UIDs and how account metadata is separated from password hashes
  2. Groups, And How Shared Access Is Granted (2 labs): Use supplementary groups to reason about shared ownership and access without making files world writable
  3. Reading And Setting A File Mode (2 labs): Read a Unix file mode and choose owner, group, and other permissions deliberately
  4. Directories, Umask And The Sticky Bit (2 labs): Predict default permissions for new objects and explain how the sticky bit protects shared directories
  5. Setuid, Setgid, And Root Through sudo (2 labs): Explain how setuid, setgid, and sudo change effective privilege and how to keep those changes narrow

Processes, Signals And Services

  1. What A Process Is (2 labs): Describe a process as a running program with identity, state, resources, and a parent relationship
  2. Signals, And What kill Really Sends (2 labs): Choose an appropriate Unix signal and understand what kill sends to a process
  3. Job Control, And Processes That Outlive You (2 labs): Explain foreground and background jobs and how a process can outlive the shell that started it
  4. Booting: GRUB, The Kernel Command Line And initramfs (2 labs): Trace the main Linux boot stages from firmware through the kernel and initramfs
  5. systemd: Units, Targets And The Boot Graph (2 labs): Read systemd units and targets as a dependency graph rather than a flat startup script
  6. Your Own Unit, And Reading journald (2 labs): Design a small systemd service and read its journal by unit and time

Packages, Disks And Space

  1. What A Package Manager Guarantees (2 labs): Explain how a package manager tracks files, dependencies, versions, and trusted sources
  2. Three Families: apt, dnf And pacman (2 labs): Recognize the apt, dnf, and pacman package families and choose commands from the host distribution
  3. Disks, Filesystems And Mounting (2 labs): Distinguish block devices, filesystems, and mount points when inspecting storage
  4. Running Out Of Space: df, du And Inodes (2 labs): Distinguish block exhaustion from inode exhaustion and use df and du evidence in the right order

Addresses And Routes

  1. The Layer Model, As Far As It Earns Its Place (2 labs): Use a small network layer model to locate where a connection problem begins
  2. IP Addresses, Netmasks And Subnets (2 labs): Calculate a host and network boundary from an IP address and prefix length
  3. Interfaces, Routes And The Default Gateway (2 labs): Read interface state and route selection, including the role of a default gateway
  4. DNS Resolution, End To End (2 labs): Trace a DNS name from an application through a resolver to an authoritative answer
  5. Record Types, Caching And Time To Live (2 labs): Interpret common DNS records and explain how TTL controls cached answer freshness

Transport, Ports And Sockets

  1. TCP Versus UDP (2 labs): Choose between TCP and UDP by comparing connection state, delivery guarantees, and application needs
  2. Ports, Sockets And What Listening Means (2 labs): Distinguish a port, socket, and listening endpoint when inspecting a service
  3. The Handshake, And The States A Socket Passes Through (2 labs): Trace the TCP handshake and use socket states to locate connection progress
  4. Refused, Timed Out, Reset: Reading A Failure (2 labs): Differentiate refused, timed out, and reset connection failures by the evidence they provide

HTTP, TLS And SSH

  1. HTTP Is Text: Requests, Status Codes And Headers (2 labs): Read the main parts of an HTTP request and response and interpret common status classes
  2. What HTTPS Adds, And What It Does Not (2 labs): Explain how HTTPS uses TLS to protect HTTP in transit and where that protection ends
  3. Certificates, Chains And What A Handshake Proves (2 labs): Read certificate identity and chain validation as evidence of a TLS server handshake
  4. SSH: The Protocol, And The Host Key You Accept (2 labs): Explain SSH host key verification and distinguish server identity from user authentication
  5. SSH Keys, The Agent And The Config File (2 labs): Use SSH key, agent, and host configuration concepts without confusing convenience with authorization

Serving, Guarding And Diagnosing

  1. Firewalls: Default Deny, State And Rule Order (2 labs): Reason about firewall defaults, stateful return traffic, and first-match rule order
  2. Forward And Reverse Proxies (2 labs): Distinguish forward and reverse proxy roles and identify where each one terminates a request
  3. Load Balancing: Algorithms, Health Checks And Layers (2 labs): Explain how a load balancer selects backends and why health checks must test the right layer
  4. The Diagnostic Ladder: Is It Up, Is It Named, Is It Routed (2 labs): You can diagnose a service in order by checking process state, name resolution, and the route to its address.
  5. The Diagnostic Ladder: Is It Listening, Answering, Arriving (2 labs): Complete a service diagnostic by checking listeners, application responses, and packet arrival

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