Prasanta Kumar Behera
Linux — Level by Level
Learning Hub / Linux & Scripting

Linux — Level by Level

Beginner → Advanced19 lessonsAvailable

Linux is the ground every platform stands on: every container, node and cloud VM runs on it. This track starts with the commands you use every day, moves to troubleshooting real broken servers, and ends with the kernel features (cgroups, namespaces, sysctl, eBPF) and security controls that containers and Kubernetes are built from.

You'll meetshellfilesystempermissionssystemdjournaldprocessesnetworkingcgroupsnamespacesSELinuxsysctl
Start lesson 01 →

What you'll be able to do

  • Move around, read, search and edit on any Linux server with confidence
  • Troubleshoot full disks, slow hosts, failed services and network problems methodically
  • Explain how cgroups and namespaces turn processes into containers
  • Tune and harden a host with sysctl, SELinux, SSH and firewall policy

Before you start

None. Access to any Linux machine or VM (a free cloud VM or WSL is fine).

How it works

Each lesson: plain-language idea → how it really works → hands-on. Each section ends with a cheat sheet & self-check.

Curriculum

Lessons marked “Read” are ready; the rest are on the way.

Level 1 — Beginner: everyday commands

  1. 01Your first terminal sessionShell, prompt, man pages, tab completion, historyRead →
  2. 02Files & directoriesls, cd, cp, mv, rm, find and the filesystem treeRead →
  3. 03Reading & searching textcat, less, head, tail, grep, pipes and redirectionRead →
  4. 04Users, groups & permissionschmod, chown, sudo, umask, rwx explainedRead →
  5. 05Processes, services & packagesps, top, kill, systemctl, apt/dnfRead →
  6. 06Checkpoint: a day on a serverFind the logs, fix a permission, restart a serviceRead →
  7. 📋Cheat sheet & self-checkEvery command from this section on one page, then 23 questions to check yourself.Open →

Level 2 — Intermediate: troubleshooting

  1. 07systemd & journald in depthUnits, dependencies, journalctl filters, failed bootsRead →
  2. 08Disks & filesystemsdf vs du, inodes, deleted-but-open files, LVM, mountsRead →
  3. 09Networking from the hostip, ss, dig, curl, tcpdump, routes and firewallsRead →
  4. 10Performance triageUSE method: uptime, vmstat, iostat, free, sar, pidstatRead →
  5. 11SSH, keys & remote workKeys, agents, config, jump hosts, tmuxRead →
  6. 12Checkpoint: five broken serversDiagnose each from symptoms to root causeRead →
  7. 📋Cheat sheet & self-checkEvery command from this section on one page, then 23 questions to check yourself.Open →

Level 3 — Advanced: kernel & security

  1. 13Kernel, modules & sysctlWhat the kernel does, tuning parameters safelyRead →
  2. 14cgroups & namespacesThe building blocks of every containerRead →
  3. 15NUMA, huge pages & CPU pinningPerformance for latency-sensitive workloadsRead →
  4. 16Tracing with perf & eBPFSee inside the kernel without rebootingRead →
  5. 17SELinux & AppArmorMandatory access control without tearsRead →
  6. 18Host hardeningSSH, firewall, auditd, CIS benchmarksRead →
  7. 19Capstone: harden & tune a hostBuild it, measure it, lock it downRead →
  8. 📋Cheat sheet & self-checkEvery command from this section on one page, then 22 questions to check yourself.Open →

Real-world scenarios

Work through each one: symptom → misleading signal → evidence → root cause → prevention.

The disk is full, but du says it isn't

A deleted log file still held open by a process. Find it and free the space without a reboot.

Load average 40 on an idle CPU

Processes stuck in I/O wait (D state). What load average really measures.

SSH works for root but not for the service account

Permissions on ~/.ssh, SELinux contexts, or sshd config?

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