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Learn DevSecOps

Linux essentials

The starting course for the Linux track, taught on Ubuntu Server 26.04 LTS with notes wherever RHEL 10 differs. You learn how a Linux system is put together, work confidently in the shell, read and set permissions, manage users and sudo, run and debug services with systemd, find what you need in the logs, handle disks and mounts, and troubleshoot networking and name resolution. Every command was run on a real server and the output you see is what it printed. Twenty-nine lessons across seven sections, each with a self-test, and a final exam.

Beginner7 sections · 29 lessons · ~8h total · 54-question self-test

01

Linux, the shell and the filesystem

5 lessonsTest yourself

01How Linux is put togetherKernel, userspace, distributions and the shell.12 min 02The shell: commands, paths and helpCommands, options, paths and getting help.12 min 03The filesystem hierarchyWhat lives in /etc, /usr, /var, /run and /tmp.12 min 04Files, directories and linksCreate, copy, move and delete safely; links and inodes.14 min 05Reading and editing files safelyRead logs, edit config with drop-ins, validate first.14 min

02

Working in the shell

5 lessonsTest yourself

01Pipes, redirection and exit statusstdin, stdout, stderr, pipes and exit codes.14 min 02Finding files and text: find and grepSearch by name, time, owner and content.14 min 03Text processing: answering questions from logssort, uniq, cut, sed and awk on real logs.16 min 04Quoting, wildcards, history and aliasesHow the shell expands what you type.12 min 05Environment variables and PATHVariables, export, PATH lookup and startup files.12 min

03

Permissions and ownership

3 lessonsTest yourself

01Reading and setting permissionsrwx, octal modes, directories and umask.14 min 02Ownership: users and groups on fileschown, chgrp and sharing with groups.12 min 03SUID, SGID and the sticky bitThe special bits, their risks and nosuid.14 min

04

Users and privilege

2 lessonsTest yourself

01Users, groups and the account filespasswd, shadow, group and creating accounts.14 min 02sudo and least privilegesudo-rs on Ubuntu, sudo on RHEL, and the logs.14 min

05

Processes and services

6 lessonsTest yourself

01Processes and /procps, top, states, parents and /proc.14 min 02Signals and job controlkill, TERM vs KILL, jobs, fg, bg and nohup.14 min 03System resources: CPU, memory and loginsLoad, memory, uptime and who is logged in.12 min 04Services with systemdRead state, write a unit, debug a failure.16 min 05Logs: the journal and /var/logjournalctl filters, text logs and rotation.14 min 06Scheduling: cron and systemd timerscrontab, cron environment and timers.14 min

06

Storage and networking

6 lessonsTest yourself

01Disks, filesystems and mountslsblk, findmnt, fstab and full disks.16 min 02Networking basicsAddresses, routes, ports and listeners.14 min 03DNS and name resolutionhosts, resolved, dig and getent.14 min 04Connecting with SSHKeys, known_hosts, config and debugging.14 min 05Archives, downloads and checksumstar, compression, rsync and verifying files.12 min 06Packages and updatesapt, signed repositories and updates.14 min

07

Putting it together

2 lessonsTest yourself

01Troubleshooting a server, step by stepA method, applied to three real failures.18 min 02Where to go nextWhat a fresh install exposes, and what to learn next.10 min

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Quick reference

Linux command cheat sheetCheat sheet Linux interview questionsInterview guide

Final exam

Test yourself on everything

54 questions drawn from all 7 sections — every answer explained as you pick.

Start final exam