🖥️ System Administration & DevOps — Complete Study Notes

A comprehensive, production-grade reference for System Administrators, DevOps Engineers, and Cloud Practitioners.

46 markdown files · 22,825+ lines · Fully cross-linked · Mermaid diagrams throughout

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📖 What Is This?

This repository is a complete, structured knowledge base covering every major topic a modern sysadmin or DevOps engineer needs to know — from Linux fundamentals to Kubernetes, from bash scripting to AWS, from Git basics to ELK Stack.

Every file is:

• Self-contained — can be read independently
• Cross-linked — every file links to related topics
• Practical — real commands, real configs, real examples
• Visual — Mermaid architecture diagrams, flowcharts, sequence diagrams
• Up to date — covers modern tooling (Terraform, K8s, GitHub Actions, Prometheus, etc.)

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🗂️ Topics at a Glance

🖥️ Operating System Fundamentals

#	Topic
01	OS Fundamentals — Linux vs Windows, Kernel, User Space, GUI vs CLI
02	File System Structure and Navigation — FHS, inodes, mounts
03	Linux Command Line Basics — ls, cd, grep, pipes, redirects
04	Windows CMD and PowerShell Basics — dir, tasklist, Get-Process
05	User Permissions and Privilege Management — chmod, sudo, UAC, ACL
06	File Management Concepts — compression, search, checksums, rsync

🌐 Networking

#	Topic
07	Networking Fundamentals — OSI, IP, Subnet, Gateway, DNS, Ports, TCP/UDP
08	Networking Tools — ping, traceroute, netstat, nslookup, curl, nmap
09	Active Directory — Domain, DC, GPO, Kerberos, LDAP, FSMO Roles
10	IIS Web Server Basics — app pools, bindings, web.config
11	Time Synchronization — NTP, chrony, w32tm, stratum hierarchy
12	VPN Basics — IPSec, SSL/TLS, WireGuard, OpenVPN, split tunnel
22	DNS Deep Dive — BIND9, zone files, reverse DNS, SPF/DKIM/DMARC
32	Network Protocols Deep Dive — HTTP/2/3, DHCP, ARP, BGP, OSPF

🔐 Security

#	Topic
13	System Monitoring and Logging — journalctl, Event Viewer, syslog
14	Basic Security Concepts — auth, encryption, firewall, PKI, EDR
26	SSL/TLS & Certificates — Let's Encrypt, certbot, openssl, HTTPS
38	Linux System Hardening — SSH, Fail2Ban, PAM, auditd, sysctl, AppArmor

⚙️ System Management

#	Topic
15	Services and Process Management — systemd, cron, Windows SCM
16	Software Installation Methods — apt, pacman, winget, pip, npm
17	Cloud and Remote Access — SSH, RDP, Docker basics, AWS CLI
18	Troubleshooting Methodology — identify, isolate, fix, verify, document
35	Storage & RAID — LVM, RAID levels, ZFS, SAN/NAS, disk tools
37	Virtualization & Hypervisors — KVM, VMware ESXi, Hyper-V, VirtualBox
39	Windows Server Administration — DHCP, DNS, File Server, Registry, WEF

🔧 Git & Version Control

#	Topic
19	Git Fundamentals — objects, commits, staging, .gitignore
20	Git Commands and Workflow — init, clone, add, commit, push, pull
21	Branching, Merging, Conflicts & Best Practices — rebase, cherry-pick, Helm

🌍 Web Servers & Email

#	Topic
25	Web Servers — Nginx & Apache — vhosts, reverse proxy, PHP-FPM, SSL
34	Load Balancing & Reverse Proxy — HAProxy, Nginx LB, health checks
40	Email & Mail Servers — Postfix, Dovecot, SPF/DKIM/DMARC, SpamAssassin

💻 Scripting & Automation

#	Topic
23	Bash Scripting — variables, loops, functions, error handling, real scripts
31	PowerShell Scripting — objects, remoting, AD automation, modules
33	Regex Fundamentals — syntax, groups, lookaheads, grep/sed/awk/Python
45	Python for Sysadmins — psutil, paramiko, boto3, log parsing, SSH

🗄️ Data & Storage

#	Topic
24	Database Basics — MySQL, PostgreSQL, SQLite — CRUD, users, backup
29	Backup and Disaster Recovery — rsync, Restic, 3-2-1 rule, RPO/RTO

🚀 DevOps & Cloud Native

#	Topic
27	CI/CD Fundamentals — GitHub Actions, GitLab CI, Docker pipelines
28	Infrastructure as Code — Terraform & Ansible — HCL, playbooks, roles
30	Docker & Containers — Dockerfile, Compose, networking, volumes
41	Kubernetes Deep Dive — kubectl, Deployments, RBAC, Helm, HPA, Jobs
44	AWS Cloud Deep Dive — VPC, EC2, S3, IAM, RDS, Lambda, CloudWatch

📊 Observability & Monitoring

#	Topic
36	SNMP & Network Monitoring — Nagios, Zabbix, SNMP OIDs, traps
42	Monitoring with Prometheus & Grafana — PromQL, alerting, exporters
43	ELK Stack — Elasticsearch, Logstash, Kibana, Filebeat, ILM

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🚀 Quick Start

Clone and Open

# Clone the repository
git clone https://github.com/YOUR_USERNAME/sysadmin-notes.git
cd sysadmin-notes

# Start at the master index
# Open 00_INDEX.md in your preferred viewer

Recommended Viewers

Viewer	Platform	Notes
Obsidian	Windows / macOS / Linux	Best experience — graph view, backlinks
VS Code + Markdown Preview Enhanced	All	Renders Mermaid diagrams
GitHub	Browser	Renders tables + code blocks
Typora	Windows / macOS / Linux	Clean WYSIWYG editor
Zettlr	All	Academic-style, great for links

⚠️ Keep all .md files in the same folder — cross-links use relative paths.

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✨ Features

Feature	Details
📐 Architecture Diagrams	Mermaid flowcharts, sequence diagrams, state diagrams, gitGraphs
🔗 Cross-linked	Every file links forward and backward to related topics
💻 Dual coverage	Linux AND Windows side-by-side for most topics
📋 Comparison tables	Tools, commands, config options — all tabulated
🛠️ Real commands	Copy-paste ready — no placeholder examples
🗺️ Learning paths	4 structured paths: Linux Sysadmin, Windows Sysadmin, DevOps, Security
📚 4-week schedule	Day-by-day study plan included in index
⚡ Cheat sheets	Quick reference for Linux, Git, Docker, K8s, AWS, Networking

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📊 Repository Stats

Total Files    : 46 (1 index + 45 topic files)
Total Lines    : 22,825+
Largest File   : 43_ELK_Stack.md (870 lines)
Sections       : 10
Learning Paths : 4

Lines per Section

Section	Files	Total Lines
OS Fundamentals	6	~2,313
Networking	8	~3,175
Security	4	~1,557
System Management	7	~2,937
Git & Version Control	3	~1,364
Web Servers & Email	3	~1,718
Scripting & Automation	4	~2,811
Data & Storage	2	~1,067
DevOps & Cloud Native	5	~3,475
Observability & Monitoring	3	~2,163

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📖 Learning Paths

🟢 Linux Sysadmin (Beginner → Intermediate)

01 OS → 02 FileSystem → 03 LinuxCLI → 05 Permissions → 07 Networking →
13 Monitoring → 15 Services → 23 Bash → 25 Nginx → 26 SSL → 22 DNS → 29 Backup

🔵 Windows Sysadmin

01 OS → 04 WinCLI → 05 Permissions → 09 AD → 10 IIS →
11 NTP → 31 PowerShell → 39 WinServer

🟡 DevOps Engineer

19 Git → 20 GitCmds → 21 Branching → 23 Bash → 27 CICD →
30 Docker → 28 IaC → 41 Kubernetes → 42 Prometheus → 44 AWS

🔴 Security Engineer

05 Permissions → 14 Security → 26 SSL → 38 Hardening →
12 VPN → 22 DNS → 09 AD → 13 Monitoring → 43 ELK

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🗓️ 4-Week Study Schedule

Week	Days	Topics
Week 1 — Foundation	Day 1–2	01, 02, 03 — OS + Linux CLI
	Day 3–4	05, 06, 07 — Permissions + Networking
	Day 5–7	19, 20, 21 — Git complete
Week 2 — Sysadmin	Day 1–2	15, 16, 18 — Services + Troubleshooting
	Day 3–4	13, 14 — Monitoring + Security
	Day 5–7	23, 33 — Bash + Regex
Week 3 — Web & Network	Day 1–2	22, 08 — DNS + Networking Tools
	Day 3–4	25, 26 — Nginx + SSL/TLS
	Day 5–7	09, 40, 38 — AD + Email + Hardening
Week 4 — DevOps	Day 1–2	30, 27 — Docker + CI/CD
	Day 3–4	28, 41 — IaC + Kubernetes
	Day 5–7	42, 43, 44 — Prometheus + ELK + AWS

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⚡ Quick Reference

Linux One-Liners

# Find large files
find / -xdev -size +100M -exec ls -lh {} \; 2>/dev/null | sort -k5 -rh | head -20

# Top 10 CPU processes
ps aux --sort=-%cpu | head -11

# Check all service statuses
systemctl list-units --type=service --state=failed

# Disk usage sorted
du -sh /* 2>/dev/null | sort -rh | head -20

# Watch logs in real time
journalctl -f --since today

# Active network connections
ss -tulpn | grep LISTEN

Git One-Liners

# Undo last commit (keep changes staged)
git reset --soft HEAD~1

# Delete all local branches that are merged
git branch --merged | grep -v '\*\|main\|master' | xargs git branch -d

# Search all commits for a string
git log -S "function_name" --oneline

# Show what changed in last commit
git show --stat HEAD

# Clean untracked files (dry run first!)
git clean -nd && git clean -fd

Docker One-Liners

# Remove all stopped containers + unused images
docker system prune -af

# Shell into running container
docker exec -it $(docker ps -qf "name=myapp") bash

# Show logs since 1 hour ago
docker logs --since=1h myapp

# Resource usage live
docker stats --format "table {{.Name}}\t{{.CPUPerc}}\t{{.MemUsage}}"

Kubernetes One-Liners

# Get all resources in namespace
kubectl get all -n production

# Watch pod restarts
kubectl get pods -w --all-namespaces | grep -v Running

# Debug with temporary pod
kubectl run -it --rm debug --image=busybox --restart=Never -- sh

# Get events sorted by time
kubectl get events --sort-by='.lastTimestamp' -A

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🤝 Contributing

Contributions are welcome! Please:

1. Fork the repository
2. Create a feature branch: git switch -c add/topic-name
3. Follow the existing file format and cross-linking style
4. Include at least one Mermaid diagram for architecture topics
5. Add the new file to 00_INDEX.md
6. Submit a Pull Request with a clear description

File Naming Convention

NN_Topic_Name.md    e.g. 46_Git_Advanced.md

File Template

# NN — Topic Name

> **[← Index](00_INDEX.md)** | **Related: [File A](XX_File_A.md) · [File B](XX_File_B.md)**

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## Section 1

Content...

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## Related Topics
- [Related Topic ←](XX_Related.md)

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> [Index](00_INDEX.md)

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📄 License

This project is licensed under the MIT License — see the LICENSE file for details.

You are free to:

• ✅ Use for personal study and reference
• ✅ Share with colleagues and students
• ✅ Fork and extend for your own needs
• ✅ Use in commercial training material (with attribution)

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🙏 Acknowledgements

These notes draw on knowledge from:

• Official documentation: Linux man pages, Microsoft Docs, AWS Docs, Kubernetes Docs
• Tools: Nginx, Postfix, Elasticsearch, Prometheus, Terraform, Ansible
• Standards: RFC documents, CIS Benchmarks, OWASP, FHS

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