Linux¶
Linux administration and internals for DevOps work, organised so one folder serves four uses: learning a topic in depth, revising before an interview, preparing for interview rounds, and day-to-day lookup. Commands are distro-neutral first; where RHEL and Ubuntu differ, both appear side by side.
How the Folder Works¶
| Layer | Where | Use it for |
|---|---|---|
| Learn | Numbered modules below, one focused file per topic | Depth and daily lookup |
| Revise | Each module's Revision Card, and Must-Know Facts | The night before, or a one-hour sweep |
| Interview | Checkpoints at the end of every topic, and Interview | Round-by-round preparation |
| Practice | Labs, and the Roadmap tracker | Hands-on repetition and break-fix |
Every topic file declares a Track (Core, RHCSA, Advanced) and an Interview weight (High, Med, Low). High-weight topics go deep; Low-weight topics stay short. Command output on these pages was captured on real machines (Rocky Linux 10.2 and Ubuntu 24.04 LTS), never written by hand.
Modules¶
| # | Module | Covers |
|---|---|---|
| 00 | Foundations | History, kernel vs distribution, distributions, architecture, system information |
| 01 | Shell and CLI | Shell basics, help, command lookup, environment, quoting, redirection, exit codes, editors, scripting essentials |
| 02 | Files and Filesystem | Hierarchy, file types, file operations, inodes and links, file descriptors, finding files, archives |
| 03 | Text Processing | Viewing, grep, sed, awk, pipeline tools, xargs, JSON and YAML on the command line |
| 04 | Users and Access | Users, groups, passwords, sudo and su, PAM, login records, central identity |
| 05 | Permissions | Modes, umask, special bits, ACLs, attributes |
| 06 | Package Management | rpm/dnf, dpkg/apt, repositories, Flatpak, shared libraries |
| 07 | Processes | Lifecycle, states, signals, job control, priorities, system calls and tracing |
| 08 | Systemd and Services | Targets, systemctl, unit files, writing a service |
| 09 | Logging | Log locations, journalctl, rsyslog, logrotate, log parsing |
| 10 | Scheduling | cron, at, systemd timers |
| 11 | Kernel and Hardware | /proc and /sys, sysctl, modules, devices, kernel messages |
| 12 | Storage | Disks, partitions, filesystems, mounts, swap, LVM, resizing, usage, backup |
| 13 | Networking | Interfaces, configuration, routing, DNS, sockets, testing, capture, time |
| 14 | SSH and Remote Access | Client, tunnels, server, file transfer, troubleshooting |
| 15 | Security | Firewalls, SELinux, AppArmor, capabilities, auditing, GPG, TLS, hardening |
| 16 | Boot and Recovery | Boot sequence, GRUB, recovery, kernel panic, kernel updates |
| 17 | Performance and Troubleshooting | Method, CPU, memory, virtual memory, disk I/O, limits, profiling |
| 18 | Network Storage | NFS, autofs, Samba, iSCSI |
| 19 | Containers | Namespaces, cgroups, overlayfs, containers vs VMs, Podman |
| 20 | Virtualization and Provisioning | KVM and libvirt, VM images, cloud-init and Kickstart |
Modules without a link are planned and appear as they are completed.
Reference¶
Quick-lookup pages for revision and daily work, drawn from every module.
| Page | Use it for |
|---|---|
| Cheatsheet | The commands used most, grouped by task |
| Command Index | A to Z: a command name to its topic page |
| Important Files | Key /etc files: format and the command that manages each |
| Glossary | One-line definitions of the terms used here |
| RHEL vs Ubuntu | Where the two families differ in command and default |
| No-Tools Fallbacks | /proc and built-ins when the usual tools will not run |
| Must-Know Facts | Every topic's facts table on one page |
| Error Messages | Real error text to cause and fix |
| Coverage Map | Certification objectives mapped to files |
Out of Scope¶
- Desktop topics: X11 and Wayland configuration, accessibility, printing.
- Running mail, DNS, DHCP, web, directory and FTP servers (client-side use is covered).
- Kernel compilation.
- Git, Python, Ansible and full shell scripting, which have their own folders in this knowledge base.